BLVM 
 ENTH 
 
 EX A I LIB 
 88 /\ ^ R1S 
 
 A
 
 A TREATISE 
 
 ON 
 
 SHOEING AND UNDEKPINNING.
 
 TEEATISE 
 
 ON 
 
 SHOEING AND UNDERPINNING, 
 
 AND GENERALLY DEALING WITH 
 
 RUINOUS AND DANGEROUS STRUCTURES. 
 
 BY 
 
 CECIL HADEN STOCK, 
 
 ARCHITECT AND SURVEYOR. 
 
 WITH ILLUSTRATIONS. 
 
 LONDON: 
 B. T. BATSFOKD, 52 HIGH HOLBOBN. 
 
 1882.
 
 TO THE MEMORY 
 OF 
 
 THE LATE GEOBGE EDMUND STEEET, R.A., 
 
 IS MOST RESPECTFULLY DEDICATED 
 BY 
 
 ONE WHO HAS EXPERIENCED THE VALUE OF HIS INSTRUCTION 
 AT THE ROYAL ACADEMY OF ARTS. 
 
 OF CAtlF. LIBRARY.
 
 PREFACE. 
 
 THE object which the author of the following treatise has in 
 view is, as far as he can, to supply a want which has for some 
 time been felt among the younger members of the architectural 
 profession. It has been impossible hitherto, from the author's 
 own experience, to get up the subject of shoring and under- 
 pinning, whether as a necessary part of the education of an 
 architect, or for an examination, without a wearisome search 
 in different libraries for the scraps of information on the sub- 
 ject, scattered about among the works of various authorities ; 
 and the difficulty of obtaining information in this way has also 
 been considerably enhanced by the fact that two of the best 
 authorities on the subject write in a foreign language. Con- 
 sequently the student has been obliged, at a great sacrifice of 
 time, to fall back upon the expedient of sketching and measuring 
 existing cases ; an admirable method in its way, but which 
 would be more interesting and instructive (especially as what 
 one most wishes to know is very often hidden out of sight) 
 if some previous knowledge of the subject had been acquired. 
 Accordingly the following pages comprise a careful collection 
 of all the authorities, together with a few additional notes and 
 sketches made from actual experience with the work. 
 
 The shoring and underpinning of the towers, columns, and 
 arches of mediaeval churches or other old buildings, which have 
 succumbed after having served their purpose well for many 
 years, is a subject too wide and complicated to be thoroughly 
 investigated in a text book such as this ; a few examples how- 
 ever are given in Chapter VI., and methods are described in 
 which some one or two suppositional cases should be treated. 
 Instances of this class are, however, comparatively rare, and so
 
 Till PBEFACE. 
 
 varied in their character, that each requires to be treated in 
 its own peculiar way; and it is impossible to lay down any 
 fixed rules, or to prescribe any definite methods by which 
 shoring and underpinning may be successfully carried out in 
 every case. But in the more general cases of shoring, such, 
 for instance, as are met with every day in London or other 
 large towns, where one house is so much like another in its 
 purpose and construction, it is possible, more or less, to prescribe 
 methods which will answer as well in one case as in another ; 
 and it is more the purpose of this book to explain these methods, 
 and the rules involved in them, as they are more useful to the 
 student, and come into the every-day practice of the majority 
 of architects. 
 
 Shoring and underpinning, and dealing with ruinous and 
 dangerous structures, is one of the subjects of which a know- 
 ledge is required in the new examination for admission into the 
 Koyal Institute of British Architects ; and the author has con- 
 sequently been careful to compile this treatise with a view, as 
 far as possible, to enable a student to answer any question that 
 may be set on this subject. 
 
 CECIL HADEN STOCK. 
 
 PARLIAMENT MANSIONS, 
 
 VICTORIA STREET, WESTMINSTER.
 
 CONTENTS. 
 
 CHAPTER PAGE 
 
 I. INTRODUCTORY .. 1 
 
 II. ON RAKING SHORES 
 
 III. ON A FEW ADDITIONAL PRINCIPLES, VARIETIES, AND 
 
 USES OF THE RAKING SHORE 11 
 
 IV. ON HORIZONTAL OR FLYING SHORES 14 
 
 V. ON NEEDLE SHORING, AND UNDERPINNING 18 
 
 VI. ON THE SHORING AND UNDERPINNING OF MEDIEVAL 
 
 BUILDINGS 32 
 
 VII. ON THE MECHANICS OF RAKING SHORES.. 48
 
 LIST OF WORKS CONSULTED, 
 
 AND FROM WHICH LITERAL EXTRACTS HAVE IN SOME 
 CASES BEEN MADE. 
 
 ' Builder,' March 15th, 1861. 
 1 Building News/ February 7th, 1873. 
 ' Building News,' August 24th, 1877. 
 ' Building News,' September 14th, 1877. 
 Burnell, on Limes, Cements, and Mortars. 
 
 Burnell, on the Operations carried out at Chicb ester and Bayeux Cathe- 
 drals. Trans. R.I.B.A. 1860-1862. 
 
 Dion et Lasvignes, Cathedrale de Bayeux. 
 
 Dobson, on Foundations. 
 
 Nash, on Failures in Construction. Trans. R.I.B.A., vol. 14. 
 
 Scott, on the Shoring of the Tower of St. Mary's, Stafford. Trans. R.I.B.A., 
 1860-1862. 
 
 Seddon, on the Shoring of Grosmont Church Tower. Trans. R.I.B.A., 
 vol. 14. 
 
 Tredgold : Barlow's edition. 
 
 Tredgold : Hurst's edition. 
 
 Viollet-le-Duc : ' Dictionnaire de 1'Architecture,' tome 5. 
 
 The author has also been greatly assisted by the kind co-opera- 
 tion of Messrs. J. and J. Greenwood, the contractors for the 
 shoring executed by the Metropolitan Board of Works.
 
 A TREATISE 
 
 ON 
 
 SHORING AND UNDERPINNING. 
 
 CHAPTEE I. 
 
 INTRODUCTORY . 
 
 THERE is, perhaps, no place where the principles of Shoring 
 and Underpinning ought more fully to be understood than 
 poor London, founded upon treacherous clay, built of bricks, 
 and abounding in ruinous buildings, where everything is done 
 in such a desperate hurry that anything that comes to hand 
 seems to be used as a building material by so many of our 
 builders, with, no doubt, the reflection on their part, " At all 
 events it will last our time." The delinquencies of the builder 
 and the treachery of the soil are, however, evils which are 
 common to most places ; and the student in the art of shoring 
 can hardly complain of a scarcity of examples to examine. In 
 London, at all events, he has only to turn sharply round the 
 corner of a street and he will run against a huge obstruction in 
 the middle of the footpath, the feet and sole-piece of a system 
 of raking shores. He will, doubtless, at once take out his note- 
 book and rule, and jot down the scantlings and the position of 
 the separate struts; but when he comes to examine how the 
 whole system is wedged up, he finds that he is baffled by the 
 sole-piece being so buried in clay and dirt that he can elicit no 
 definite information from it. This is nearly always the case 
 when work is examined without any previous acquaintance 
 with its principles ; and it is the desire of the author to instil 
 into the mind of the reader a sufficient acquaintance with the 
 principles and the terms used in shoring and underpinning, 
 that he may afterwards with confidence perfect himself in the 
 practical knowledge of the subject by sketching and measuring, 
 and by questioning foremen engaged upon the work. 
 
 It is always necessary, in attempting to obtain information 
 from a workman, to go well armed with terms ; for as a rule he 
 takes it for granted that you understand the phrases he uses, 
 and vouchsafes no explanation concerning them. However, 
 this is always the best way to gain practical knowledge upon 
 anything : see the work begun and carried out to the end, go 
 into its object, criticise it if possible, and consider whether,
 
 2 A TREATISE ON 
 
 from your knowledge of the subject, it could not have been done 
 better some other way. No student should be content with the 
 knowledge he had gained simply by reading a book. 
 
 The mathematical investigation of the nature of the forces 
 brought into play in the case of raking shores, though it can 
 hardly be said to be absolutely necessary, is still well worth 
 the attention of the reader; for it gives him an altogether 
 superior grasp of the subject, and makes him feel competent to 
 undertake the most difficult problem it can afford. The in- 
 vestigation of the nature of strains comes, of course, into many 
 other of the studies of an architect, and the time spent in con- 
 sidering the proof of formulae employed can never be said to be 
 spent in vain. But, for the convenience of those who may not 
 be acquainted with the science of trigonometry or statics, the 
 theoretical has not been allowed to interfere too much with the 
 practical side of the subject ; and the mechanics of raking shores 
 have been banished to a chapter by themselves at the end of the 
 book, so that those who do not understand them need not trouble 
 themselves to read them at all. 
 
 As there are now so many and varied subjects connected with 
 our profession, making it almost an impossibility to gain a 
 sufficient practical knowledge of all of them, there is every 
 reason to believe that there will be in the future a demand for 
 specialists : that is to say, an architect having on hand some 
 work which has not before come much within the range of his 
 practice, might be glad to consult with some other member of 
 his profession who had made a special study of that 'one par- 
 ticular subject. And so, if any of the readers of this book feel 
 that they have any inclination to make a special study of shoring 
 and underpinning, and generally dealing with ruinous and 
 dangerous structures, they will find it a pleasing and interest- 
 ing pursuit, having an element of danger and excitement about 
 it sometimes which gives it a superior charm over many other 
 of the architect's duties. 
 
 When once the study and practice of shoring has been 
 acquired, there will always be found, especially in London, 
 ample scope for the specialist in this branch of the profession 
 to exercise his ingenuity; for there is scarcely ever a house 
 cleared away for the erection of a new building without its being 
 necessary to shore up its neighbours on either side. And so this 
 subject cannot be too well understood by all architects, for many 
 accidents occur from the shoring being left to the rule-of-thumb 
 of the foreman employed on the works, without any supervision 
 by some more responsible person. 
 
 We shall now proceed to describe the different methods used 
 in shoring and underpinning, taking first into our consideration 
 the ordinary every-day cases to be met with in London and 
 other brick-built towns.
 
 SHOEING AND UNDERPINNING. 
 
 CHAPTER II. 
 
 ON RAKING SHORES. 
 
 WE shall describe in this chapter only the ordinary use of 
 raking shores, reserving the different varieties of this method 
 to be considered by themselves in another chapter. 
 
 In Plate I., Fig. 1, there is depicted an example of the 
 raking shore in its most simple form, i. e. with only one 
 principal strut. Let us suppose it to be supporting a brick- 
 wall, 9 inches thick and 20 feet high from the ground, A C ; 
 then A B is the principal strut, called a shore. E is a deal, 
 called the wall-piece, 9 inches wide and 3 inches thick, and 
 long enough to take the foot of the secondary strut G. In 
 this wall-piece, about 2 feet from one end, a rectangular hole 
 is cut and a small piece of wood D, called a needle, or by 
 some workmen a tos.4e, or joggle, is inserted, projecting about 
 4 inches on either side of the deal. A half header is taken 
 out of the wall near the top and the wall-piece placed in 
 position, the needle fitting into the hole thus prepared. The 
 other end of the needle, projecting beyond the face of the 
 wall-piece, serves as an abutment to the head of the shore 
 at B. For additional security a wedge-shaped piece of wood, 
 C, called a cleat, is nailed on to the wall-piece just above the 
 needle, and prevents it from being forced out of its place by 
 the upward pressure .of the shore AB. F is a balk of timber, 
 called the footing block, or sole-piece, let into the ground, or 
 if the ground be soft, laid upon a small platform of timber. 
 A cleat is nailed upon the upper side of the sole-piece at A 
 to prevent the foot of the shore from slipping. All these 
 parts in connection with the shore will be taken more in detail 
 further on in this chapter ; at present let it suffice only to 
 name them and describe their functions. 
 
 Now, the object of this shore is to prevent the wall from 
 being turned over by the thrust caused by a house leaning 
 against it. In considering the resistance to be offered to this 
 thrust, though it may but seldom be the case, yet we must 
 always be prepared for it at its greatest magnitude, and that 
 will be when it is great enough to upset the wall. The 
 direction of this thrust will of course be at right angles to 
 the wall, and it will act at a point near the top, i. e. where 
 the head of the shore presses against the wall, as shown by 
 the line Q in the figure. Now, the most convenient way to 
 
 B 2
 
 4 A TBEATISE ON 
 
 overcome such a thrust, would be, of course, to place a strut 
 at right angles to the wall, or in other words, in a line with 
 the direction of this thrust Q (as in the case of a flying 
 shore). But when this cannot be done a raking shore is 
 necessary, and it is easy to see that as soon as the position of 
 the strut is altered from a horizontal to an inclined position, 
 a certain percentage of force is wasted in an endeavour to 
 thrust up the wall ; so, taking into consideration the fact that 
 action and reaction are the same, there may be said to be two 
 forces brought into play in the case of a raking shore, one the 
 thrust (Q) of the wall, and the other a force, P, exercised ver- 
 tically by the weight of the wall above D upon the head of 
 the shore, tending to keep it down, in which the weight of 
 the shore itself must be taken into account. These two forces, 
 acting at right angles to each other at the point B, must have 
 by the law of forces an equivalent single force acting in some 
 direction between the angle of the directions of these two 
 forces ; and this force is called the resultant. Now, this resultant 
 does not act down the direction of the shore itself, but in 
 some direction which varies as there is more or less thrust, 
 Q ; and this direction is found by mathematics to be always 
 outside the angle which the shore makes with the horizon, as 
 the line p A ; consequently the balk or sole-piece must not be put 
 at right angles to the direction of the shore, but at an angle, as 
 near as can be judged, at right angles to a mean of all the 
 directions the resultant may take ; and this will be, as near as 
 possible, at right angles to the line p A. 
 
 Now in practice this truth is of the greatest convenience, 
 for the foot of the shore, being gently levered along the sole- 
 piece, is compressed tighter and tighter, and so the necessity 
 of wedges is dispensed with entirely. In order to facilitate 
 this operation of levering the shore into its place, a groove or 
 slot is cut in the underside of the foot of the shore, large 
 enough only for the carpenter to insert the end of a crowbar 
 as a lever. (See Plate II., Fig. 6.) This is the method employed 
 in most of the shoring executed for the Metropolitan Board of 
 Works, and it may be considered the best ; for, in dealing with 
 structures that are really in danger of falling, the greatest care 
 must be taken to avoid all blows with a hammer or mallet, 
 such as are necessitated by the use of wedges at the foot of the 
 shore. 
 
 From what has been said about the tendency of the shore 
 to lift the wall, and the consequent reactionary force P, which 
 keeps the head of the shore down, it is obvious that the needle 
 must not be placed too near the top of the wall ; for, unless 
 there is sufficient weight upon its head, the shore will rise and 
 burst up the courses above it. 
 
 There is yet another force brought to bear upon a raking
 
 SHORING AND UNDERPINNING. 5 
 
 shore which we must not forget to mention, and that is a 
 cross strain, S, acting at right angles to the shore and tending 
 to bend it inwards, the truth of which may be investigated in 
 the chapter on the Mechanics of Baking Shores, at the end of 
 the book. It is to counteract this cross strain that the 
 secondary strut G is necessary, and in cases where three or 
 four shores are combined in one system, as in Figs. 2 and 3, 
 this strut answers the double purpose of counteracting the 
 cross strain and binding the shores together. 
 
 Having now considered briefly the nature of the forces 
 brought into play in the case of this single raking shore, 
 and the practical lessons that they teach, it only remains to be 
 said that where there are any number of shores in a system, 
 each separate shore in that system is subjected to the same 
 forces or strains as have been described in the case of Fig. 1. 
 In fact, this figure may be considered as the outer shore in a 
 system of two or more shores. It has been used here more for 
 convenience of description than as a method to be adopted. As 
 a general rule, two or more shores should be used in a system. 
 
 With regard to the scantlings of the timbers used in raking 
 shores, as they are for the most part but temporary erections, 
 builders generally use such timbers as they may have by them, 
 which are too rough for better work. But in order to be quite 
 sure that the timbers are strong enough to resist the utmost 
 strain that can be put upon them, it is always as well to use 
 the formulae, which are appended, with an example, at the end 
 of this chapter. 
 
 We will now go on to consider Fig. 2 in Plate I. This is the 
 raking shore most commonly seen ; it is simply a triple arrange- 
 ment of that described in Fig. 1. The wall-piece is made much 
 longer in consequence, and has three holes cut in it, and three 
 needles inserted with their cleats nailed above each. The outer 
 shore is called the top raker, the middle shore the middle raker, 
 and the lowest is called the bottom shore. As the top raker of 
 this system is a much longer shore than that shown in Fig. 1, 
 it will be necessary to strengthen it with more than one 
 secondary strut. This is done by nailing pieces of timber about 
 1 inch thick and from 6 inches to 9 inches wide on either side 
 of the shores, as shown at G in Figs. 2 and 3. These braces are 
 brought home against the wall and nailed to the sides of the 
 wall-piece (which, if wider than the shores, is best notched out 
 to receive them), and their position is generally just below the 
 points where the needles enter the wall. As the bottom shore 
 cannot conveniently have a secondary strut, it is generally tied 
 up by a brace similar to those at G ; this brace is also useful to 
 bind the three shores together as they approach each other at 
 their feet, and helps to render the whole a homogeneous system, 
 incapable of turning about or warping when tried by the thrust
 
 6 A TBEATISE ON 
 
 of the wall. Hoop iron is also nailed round and round the feet 
 of the shores, to prevent any possibility of their separating. 
 
 In Plate I. Fig. 3, we have a much larger and more com- 
 plicated system of shores. It differs from the other in this 
 respect, that the top raker or rider shore, as it is called in this 
 case, instead of coming down to the ground as before, is made 
 to spring from the back of the shore immediately below it. 
 This is, of course, done because it would be impossible, except 
 at considerable expense, to obtain so long a piece as would 
 otherwise be required. In some cases the foot of this rider 
 shore is made to rest upon a large cleat, nailed to the back of 
 the shore below, but the best method is to let it rest upon 
 another piece of timber of the same scantling, which, secured to 
 the back of the shore below, goes down to the sole-piece, as 
 shown in the Fig. 3. This rider shore may be of a smaller 
 scantling than the others. 
 
 Now this plan, though it answers very well in a case like 
 Fig. 3, should not be allowed in the case of Fig. 2 (unless there 
 was great difficulty in obtaining a piece long enough for the 
 top raker), for this reason, that the power of wood to resist 
 compression is very much impaired by any cross strain that may 
 be put upon it. But still, if in the case of Fig. 2 the house was 
 really in imminent danger of falling, or was very much out of 
 the perpendicular, it would not only be advisable, but even 
 absolutely necessary, to keep the top raker in two pieces, and 
 fix it as in Fig. 3, because the disturbance and blows upon the 
 wall, which would be caused by the moving about and fixing 
 so large and heavy a piece of timber, might result in bringing 
 about what it is the object of the shores to prevent, viz. 
 the total wreck of the house. But whenever the method 
 of a rider shore is adopted, the shore below it must be 
 made proportionately stronger, to enable it to resist the cross 
 strain. 
 
 In these two cases Figs. 2 and 3 the method described for 
 Fig. 1 of levering the shores into their positions on the sole- 
 piece is used; but if it is found impracticable to compress 
 sufficiently the two middle rakers in this way, oak wedges 
 can be used, care being taken to drive them home gently, the 
 object being to support the wall, not to thrust it over. The 
 rider shore, Fig. 3 r is compressed by two oak wedges, gently 
 driven home on either side of the foot where it meets the 
 timber secured to the shore below, as shown in Plate II., Fig. 1. 
 The system of shores which has only two struts is a very 
 common one, its principles and construction being in every way 
 similar to what we have already described. 
 
 The following paragraph may be taken, as a general rule, 
 for the number of shores to be employed in each system and the 
 scantlings that should be given to each :
 
 PLATE, II. 
 
 Fitf 6. 
 
 C.HcUUn Stock In* el Del. 
 
 '. Akerman Photo -l;lh.Londor..WC
 
 SHORING AND UNDERPINNING. 7 
 
 For walls from 15 ft. to 30 ft. high, two shores are necessary in each system. 
 Ditto 30 ft. to 40 ft. three ditto. 
 
 Ditto 40 ft. and upwards, four ditto. 
 
 Taking the angle of the shore at 60 to 75, 
 
 For walls from 15 ft. to 20 ft. high, 4 in. x 4 in., or 5 in. x 5 in., may be the 
 
 scantling for each shore. 
 
 Ditto 20 ft. to 30 ft. 9 in. x 4 in. or 6 in. x 6 in. ditto. 
 Ditto 30 ft. to 35 ft. 7 in. X 7 in. ditto. 
 
 Ditto 35 ft. to 40 ft. 6 in. x 12 in., or 8 in. x 8 in. ditto. 
 Ditto 40 ft. to 50 ft 9 in. X 9 in. ditto. 
 
 Ditto 50 ft. and upwards, 12 in. x 9 in. ditto. 
 
 The systems of shores should not if possible be more than from 
 12 feet to 15 feet apart; but if they are placed nearer to each 
 other than this the scantlings may be made lighter, which will 
 be of great advantage in the case of a really dangerous struc- 
 ture for the reasons mentioned above. 
 
 The general arrangement and construction of the raking 
 shores which are most commonly used having been explained, 
 it now remains only to say a few words with regard to their 
 details. As these can best be explained by the figures on Plate II., 
 it will be sufficient merely to refer to them, pointing out their 
 uses. 
 
 The meaning of Fig. 1 has already been explained ; the oak 
 wedges, which compress the rider shore, have been driven 
 home, and sawn to a neat appearance. Fig. 2 is the needle 
 which in good shoring is made out of a piece of wood about 
 4 inches square and 1 foot long, cut down at one end to the 
 size required to fit the hole made in the wall ; a shoulder is 
 thus formed to butt against the wall-piece, and a good strong 
 abutment is afforded for the head of the shore. Fig. o is 
 a sketch showing the needle in position in the wall-piece, with 
 the cleat above it, and the manner in which the head of the 
 shore is notched to fit the under side of the needle. This is a 
 very necessary expedient ; for the author has known an instance 
 of the top raker in a system of shores, a long and heavy piece 
 of timber, having been blown down by a sudden gust of wind 
 seriously injuring two workmen who were underneath it at 
 the time from the neglect to notch the head of the shore, or 
 otherwise secure it in case of its becoming loose. Iron braces, 
 as Fig. 3, called iron dogs, are sometimes used for this purpose, 
 as also for securing the feet of the shores to the sole-piece, and 
 the foot of the rider shore to the shore below it. It will be 
 noticed that, in the sketch Fig. 5, the wall-piece is secured to 
 the wall with iron hooks, a detail of which is shown in Fig. 4 ; 
 these are convenient to hold it in position during the insertion 
 of the needles and fixing of the shores. Fig. 6 shows the 
 method of levering the feet of the shores along the sole-piece. 
 A cleat should be nailed to the sole-piece against the foot of
 
 8 A TREATISE ON 
 
 the outer shore, and the spaces between the shores, if they do 
 not quite touch, should be filled in with a bit of stuff. 
 
 The greatest care must be taken that the sole-piece rests upon 
 a firm foundation of solid ground, for the efficacy of the shore 
 depends so much upon an unyielding base. It should first be 
 ascertained that there are no cellars or vaults under the spot 
 that the sole-piece is to occupy, and all made ground, soft clay, 
 &c., should be avoided if possible ; but if, as often happens, it is 
 impossible to obtain a firm foundation without going to a con- 
 siderable depth, the sole-piece must rest upon a carefully made 
 platform of timbers, laid across each other, which will press 
 equally upon the ground all over. This platform may be laid 
 level, and the sole-piece raised to the required inclination by 
 wedge-shaped pieces of oak fixed upon it ; or it may be laid at 
 once to the inclination of the sole-piece. In some cases, where 
 great pressure is likely to come upon the shore, a good bed of 
 concrete is prepared, and the platform which takes the sole- 
 piece laid upon it. 
 
 When a space has been cleared away, and raking shores 
 are erected to support the surrounding buildings, they must not 
 be put up indiscriminately, without reference to the plans and 
 sections of the new building which is to occupy the space ; but 
 care must be taken that they shall interfere with the building 
 operations as little as possible. As the new building rises to 
 the under side of the bottom shores, they are taken down, the 
 middle and top rakes being left in position till they are reached 
 in their turn. The foundation of the shores should be left 
 untouched until all are taken down. 
 
 It is obvious that the more inclined the shore is with the 
 horizon, the greater is the lateral thrust it will exert. An 
 angle of 40 is considered to be the best inclination for raking 
 shores ; but there is very seldom room for so great a spread at 
 the foot as this requires, and they are more often raised to an 
 angle of 60 or 70. But it should always be borne in mind 
 that the more the shores are brought in at the feet, the less will 
 be the lateral thrust they will exert against the wall. 
 
 Formulae, for determining the pressure brought to bear upon a raking 
 shore by the house which it supports. 
 
 Referring back to the example (Plate I., Fig. 1), we have seen 
 that there are two principal forces, P and Q, brought to bear 
 upon the shore. Before we can determine what effect these two 
 forces have in compressing the shore, we must first discover the 
 magnitude of each of them separately. 
 
 To find the maximum horizontal thrust Q exercised upon the 
 wall (Q being in cwts.), we must use the following formula : 
 
 WX *
 
 SHORING AND UNDERPINNING. 9 
 
 Where W is the weight of the wall in cwts., t is the thickness 
 of the wall at the ground line in feet or parts of a foot, and B 
 is the distance of the head of the shore from the ground, also in 
 feet. 
 
 To find the vertical force P, to be expressed in cwts. : 
 
 P = Q tan. 6* - ,.-.. II. 
 
 A 
 
 Where 6 is the angle the shore makes with the horizon, and w 
 is the weight of the shore itself in cwts. 
 
 Having found by the above formulae the values of Q and P, 
 we can now find the compression F down the shore which they 
 produce, by the formula 
 
 F = P sin. -f Q cos. 0, .... III. 
 
 where F is in cwts. and is the angle the shore makes with the 
 horizon. 
 
 Now, taking the example in Plate I. Fig. 1, a wall 20 feet 
 high, with a frontage of 10 feet, is supported by a raking shore 
 of fir, 4 inches by 4 inches, the head of which B is 16 feet from 
 the ground A C. The angle 6, or B A C, is 70, and by referring 
 to a table of natural sines, &c., we find that sin. is '93969, 
 cos. 6 is -34202, and tan. is 2-7474. Taking the wall at 
 1 cwt. per cubic foot, its weight W will be 150 cwt., and its 
 thickness t is 9 inches, or f of a foot. The weight w of the 
 shore itself is f cwt. 
 
 The value of Q is obtained from I. 
 
 ~ W x t 150 X | 112 
 
 Q = -jj-gQ- = 32 = ~W = * ' a PP roximatelv > 
 
 i. e. the maximum horizontal thrust is 3^ cwt. 
 The vertical pressure P is obtained from II. 
 
 P = Qtan.0 - ^ = 8^ x 2-7474 - & = 9| cwt. 
 J 
 
 The compression F down the shore is found from III. 
 F *.- Psin.0 + Qcos.0 = 9 x 93969 + 3 x '34202 = 9|cwt. 
 approximately. 
 
 i. e the shore as a post has to resist a pressure of 9| cwt. 
 
 * The reader, even if he has never before been acquainted with the trigo- 
 nometrical symbols, sin., cos., tan., &c., need not be at all alarmed at their 
 appearance here ; for if we know how many degrees there are in the angle Q, 
 we have only to refer to some table of natural sines, cosines, tangents, &c.,and 
 we shall find that the expression tan. 6 is transformed into a convenient decimal. 
 For instance, the shore A B in PI. I. fig. 1 makes an angle of 70 with the 
 horizon, A C. We look, say in Molesworth'a ' Pocket-book of Engineering For- 
 mulae,' for the tables of natural sines, &c., and we see that tan. 70 is 2*7474.
 
 10 A TREATISE ON 
 
 To find whether the shore is strong enough to resist this 
 pressure, we must use the formula for a long, square post, 
 
 d* 
 L = a x ja 
 
 where a is 15 '5 for fir, d is the width in inches, and I is the 
 length in feet ; L being the safe load in cwts. that may be put 
 upon it. 
 
 Very often, however, the breadth of a shore is double its 
 width, i.e. the sides of the section bear a proportion to one 
 another of ; consequently, as we get twice the resistance, we 
 multiply L as found by the above formula (in which d in this 
 case is the lesser side) by 2 for the safe load required. 
 
 When the section is 6 inches by 4 inches, for instance, the 
 sides bear a proportion to one another of or f, consequently 
 we multiply L as found by the above formula (in which d is the 
 lesser side) by f for the safe load required ; and so for all scant- 
 lings. 
 
 It has, however, been found by experience to be always best 
 to make shores of square timber. The shores erected by the 
 Metropolitan Board of Works are generally of a square section, 
 and timber of this kind can easily be obtained from 4 inches by 
 4 inches to 13 inches by 13 inches. 
 
 In the example before us the shore has a square section; 
 then, 
 
 L= 15-5 X Iff = 13f cwt. 
 
 i. e. the safe load which the shore will carry is slightly in excess 
 of the compression F, to which it is actually subjected. 
 
 In this manner the top raker in a system of shores can be 
 tested. 
 
 The compression down the middle raker and bottom shores 
 can also be determined in the same way, a separate value of Q 
 being worked out for each. It will be found that this com- 
 pression increases as the shores are placed lower down the wall ; 
 but as the power of resistance in the lower shores is also con- 
 siderably increased from their being so much shorter than the 
 top raker, they will be quite strong enough if made of the same 
 scantling.
 
 PLATE, III. 
 
 Firf: 3 
 
 C.HvuLen. Sr^ijt Del 
 
 J Akerrmm Photo -lith Lonaon,W. C .
 
 SHORINa AND UNDERPINNING. 11 
 
 CHAPTEE III. 
 
 ON A FEW ADDITIONAL PRINCIPLES, VARIETIES, AND USES OF THE 
 RAKING SHORE. 
 
 THOUGH we but seldom see any other modifications of the 
 raking shore than those which have already been described, 
 yet there are certain cases which call for special adaptations of 
 this system ; and it is for the carpenter to prescribe that method 
 in each case, which his skill suggests or his experience dictates. 
 It would, of course, be needless to describe every variety and 
 use of the raking shore ; but the few additional remarks (for 
 which, with the diagrams, the author is indebted to M. Viollet- 
 le-Duc's article on Shoring), may possibly be useful. 
 
 It is usual in most cases, where more than one shore is 
 used in a system, to spread them out at the top and bring them 
 together at the foot ; but this should not be done if there is a 
 sharp bend in the wall, as at C in Plate III. Fig. 1, but the shores 
 should be placed as is indicated in the figure, i. e. they should 
 be farther apart at their feet than at their head. For (as it is 
 necessary, in all cases where there is a prominent bend or 
 rupture in a wall, that the head of the outer shore should rest 
 exactly above the point where this bend or rupture occurs), 
 if the usual method be adopted the head of the lower shore will 
 act at the point E ; but it will be dangerous to exert a hori- 
 zontal pressure upon the wall at this point, for it will only tend 
 to aggravate the rupture below the bend at C. But when a 
 wall is bent in a uniform manner as in Fig. 2, the shores are 
 best placed in the usual way, approaching together at the foot ; 
 for while the upper shore A B takes the load, the lower shore 
 E B can exercise a more effectual resistance to the bend of the 
 wall. Thus it is always best to employ more than one shore in 
 a system. 
 
 Fig. 3 shows the way in which the head of a raking shore 
 may be fixed in a masonry wall. A hard header of stone is 
 built into a bole made in the wall, projecting beyond the face 
 of the old work, and a piece of heart of oak is placed underneath 
 it as a seating for the head of the shore. 
 
 When two or more shores are employed in a system they 
 should never be parallel, but (to quote M. Viollet-le-Duc), " they 
 should always form a triangle or a portion of a triangle, for 
 this reason, that a triangle can never be thrown out of shape ; 
 when braced, shores which are not parallel present an entirely
 
 12 A TEEATISE ON 
 
 homogeneous resistance ; whereas if they are parallel they will 
 become bent however well braced they may be." 
 
 This truth may be extended further ; and when two systems 
 are combined in one, as is sometimes done when great strength 
 is required, they should not be placed parallel to each other, 
 but they should form a triangle on plan, as is shown in Fig. 4 
 in perspective. This kind of shore, if it is well braced, is ex- 
 ceedingly strong, and suitable to prevent the pressure of the 
 earth from overturning a terrace wall. 
 
 It is often possible to make use of a raking shore, not only as 
 a support, but also as a means whereby a wall may be pushed 
 back again from a leaning to an upright position. An instance 
 of this has come under the author's notice in the case of one 
 of the walls of a large warehouse, which had gradually been 
 pushed out of the perpendicular. The foundations were ex- 
 amined and found to be in a comparatively good condition, and 
 the face of the wall, though out of the perpendicular, presented 
 a uniform appearance, i. e. there were no serious bulges or cracks 
 perceptible on its face ; and consequently the idea of restoring 
 its perpendicularity seemed possible to be put into execution, 
 without any danger to the wall itself. Accordingly, raking 
 shores were placed at intervals along the wall, and a powerful 
 screw jack fitted under the sole-piece of each system ; the con- 
 nections of the quoins with the return walls were then cut 
 away, and the roof and floors of the buildings, having first been 
 propped up with posts and struts from the basement to the 
 topmost story, were also cut off from all connection with the 
 wall. A wedge-shaped fissure was next cut in the brickwork, 
 at a point near the base of the wall on the internal face, and 
 the space thus cut out was filled up with sand. The screw 
 jacks were turned evenly and gently, and the wall, squeezing 
 the sand out of the fissure, was gradually pushed back by the 
 shores into its original position. The roof and floors were 
 again firmly connected with the brickwork, the posts and 
 shores taken down, and the whole then presented an appearance 
 as strong and satisfactory as when it was first erected. 
 
 Another method used for bringing back into the perpendicular 
 the two opposite walls of a building, which have been thrust 
 outwards by a roof or vault, though it is perhaps hardly a 
 propos here, may as well be mentioned. It consists in fixing 
 bars of wrought iron across the building from one wall to the 
 other, which pass through to the outside, and are then screwed 
 to large nuts, or washers, placed against the external face of 
 the walls. Fires are lighted under these bars, and as the metal 
 expands the washers are screwed up as tightly as possible. The 
 fires are then extinguished, and when the bars begin to cool, 
 the force of their contraction gradually draws the walls 
 together.
 
 SHORING AND UNDERPINNING. 13 
 
 But to return to the raking shore, another of its many uses 
 is to steady a wall whilst it is in process of being underpinned ; 
 these raking shores should be left in position for some time 
 after the works have been carried out, so as to enable the wall 
 to take its bearing upon the new work without danger of dis- 
 ruption. 
 
 The best wood in which all shores should be made is un- 
 doubtedly the fir, because its grain is always straight, and it 
 can be obtained in long pieces. It is difficult to make good 
 shores of oak, as it is generally of a middling length, has a 
 twisted grain, and is heavy and more troublesome to lift in 
 consequence. Oak ought to be used, however, in preference to 
 all other woods for the wedges, seatings, &c., and even for the 
 sole-piece (though this is seldom done), because its texture does 
 not crush under the load like that of fir. 
 
 Care should be taken that the shore is thoroughly well put 
 together, that all the joints are made to fit exactly, and that 
 the foot of each strut has a perfect bearing upon the sole-piece. 
 Nothing is more satisfactory than to see a shore well made, and 
 those who design and construct in this art cannot help feeling, 
 in such a case, a pang of regret when their handiwork is cleared 
 away.
 
 14 A TREATISE ON 
 
 CHAPTER IV. 
 
 ON HORIZONTAL OR FLYING SHORES. 
 
 WHEN a house is taken down in a street, and the party walls of 
 its neighbours on either side require supporting, if the space 
 between the two is not greater than about 32 feet or 33 feet, 
 horizontal struts, reaching from one wall to the other, are 
 employed ; these are called flying shores. 
 
 In Plate IV., Fig. 1 is depicted the usual method of con- 
 structing these shores. Two wall-pieces E are provided and a 
 rectangular hole cut in the centre of each for the insertion of 
 the needles D, which rest in holes cut in the walls, just as has 
 been described in the case of raking shores, a cleat C being 
 nailed below them for additional security. The horizontal 
 strut A B is compressed by oak wedges driven together above 
 the needles D, and it is stiffened by the raking struts G, which 
 butt against cleats C on the wall-pieces, and against straining 
 pieces F, securely nailed to the top and under side of the 
 horizontal strut A B. 
 
 It will be easy to see that by this method a very effectual 
 resistance is offered to any inclination of the houses to fall in 
 upon each other ; but it will also be necessary, in most cases 
 where flying shores are employed, to support the angles of the 
 walls towards the street with raking shores, as shown at H in 
 Fig. 1. Of the two houses, however, here represented, the one 
 on the left hand is secure, and needs no shoring at all, having 
 been built independently of the house that has been cleared 
 away, or in other words, the return wall belongs to it ex- 
 clusively, and has not been shared as a party wall by the 
 house adjoining ; consequently the flying shore has to resist the 
 thrusts of the opposite house only. But when both are party 
 walls it will be best to allow sufficient strength in the shore to 
 resist the thrust of both the houses together ; and it will also be 
 necessary to support the angles of both the walls, both in the 
 front and at the back, with raking shores. 
 
 The thrust exercised by the wall of the house on the right 
 hand side in Fig. 1 may be found at any point in its height by 
 the useful formula, 
 
 ~ 2BC' 
 
 where Q is the thrust in cwts., W is the weight of the wall in 
 cwts., t is the thickness of the wall at the ground in feet or
 
 PLATE , IV. 
 
 -h 
 
 Scale of hill I 1 
 
 C.Haslrr, SteekJrar.ttDd
 
 SHORING AND UNDERPINNING. 15 
 
 parts of a foot, and B C is the distance, in feet, from the ground 
 to the point at which it is desired to ascertain the thrust. 
 
 It is obvious from the laws of leverage, that the best position 
 for the shore to occupy is near the top of the wall, as shown in 
 the figure ; and by working out examples by the above formula, 
 which is framed on the supposition that the wall is just falling, 
 it will be found that the thrust will increase considerably as we 
 come lower down the wall. Consequently, if from some in- 
 convenience, the shore cannot be placed near the top of the 
 wall, it must be made proportionately stronger the lower it is 
 brought down. It is a common and a good practice to place 
 two or more flying shores one above the other, in the same 
 perpendicular plane, thus holding up the wall at every point in 
 its height. In this case it is best if possible to have the wall- 
 pieces in one length from the top to the bottom of the system. 
 If the wall bulges at certain points, as in the figure, or if any 
 projections occur upon its face, the wall-piece must be packed 
 up behind with firring pieces, and so made to press equally 
 against the wall at every point in its length. 
 
 The reason why the span of a flying shore was limited, 
 apparently so dogmatically, at the commencement of this 
 chapter, to 32 feet or 33 feet, is because ordinary Dantzic fir 
 cannot easily be obtained in pieces of a greater length than 
 this. Scarfing or joining two lengths into one is not a wise 
 practice in shoring ; for unless the scarf is executed with greater 
 care than is warranted by the temporary character of the work, 
 it is worse than useless. For it cannot be guaranteed that the 
 horizontal strut will only be compressed in the direction of its 
 axis, but the wall, if it leans forward uniformly, will make its 
 thrust first felt down the upper raking struts, and so produce a 
 cross strain upon the principal strut ; and the power of the 
 principal strut to resist this cross strain, even though it is 
 stiffened by the lower raking struts, would be very much 
 diminished by a scarf, especially if the span is considerable, as 
 of course it would be if a scarf was necessary. Thus it is 
 always best to use only one whole piece of timber for the 
 principal strut ; and if this cannot be obtained long enough in 
 Dantzic fir pitch pine must be used, which can be procured in 
 pieces, if necessary, 66 feet long. But unless the houses to be 
 shored are a great height, say from 70 feet to 80 feet high, it 
 would be more economical to make use of raking shores. 
 
 With regard to the scantling that should be given to the 
 timbers of a flying shore, the following may be taken as a 
 general rule : 
 
 For spans not exceeding 15 feet, the scantling for the prin- 
 cipal strut may be 6 inches by 4 inches, and for the raking 
 struts, 4 inches by 4 inches. 
 
 For spans from 15 feet to 33 feet, the scantling for the
 
 16 A TKEATI9E ON 
 
 principal strut may be from 6 inches by 6 inches to 9 inches by 
 9 inches, and for the raking struts from 6 inches by 4 inches to 
 9 inches by 4^ inches. 
 
 In both cases the straining pieces must be stout enough to 
 give a good bearing to the ends of the raking struts. 
 
 The scantlings given above are for shores which occupy a 
 position at about three-fourths of the distance from the ground 
 line to the top of the wall, and which are placed at intervals of 
 not more than 10 feet to 15 feet from each other. 
 
 It may sometimes happen that when it would be more con- 
 venient and economical to support a house with flying shores, 
 an objection is raised by the owner of the house which it is 
 proposed to use as an abutment, either because he is afraid of 
 his wall being pushed in by the presstire brought to bear upon 
 it, or because the unsightly appearance of the shores may be 
 prejudicial to his premises. This objection he has a perfect 
 right to make, and he can compel his neighbours of course at 
 his own risk to tie in the wall from the back, or, if there is 
 room on their property for the erection of raking shores, to 
 adopt this method of supporting the wall. There is an instance 
 of a case of this kind on the Thames Embankment, opposite the 
 Temple Station of the District Railway, where, although the 
 wall of the house which requires support is over 60 feet high, 
 and there is an admirable abutment for flying shores close at 
 hand, yet the more expensive method of raking shores has 
 been adopted, no doubt because the adjoining owner has 
 objected to have his premises disfigured, as they certainly 
 would be by flying shores butting against them. The raking 
 shores used in this case are, by the way, excellent examples of 
 their kind ; and if they are still in position when this book is 
 published, the London reader cannot do better than pay them a 
 visit ; for, although they are not accessible to the two-foot rule, 
 yet it is possible to get near enough to them to examine them 
 satisfactorily. It will be found that they are of a lighter 
 scantling than that laid down in the general rule in Chapter II., 
 but this is accounted for by the interval between them being 
 not more than about 7 feet. 
 
 Apologising for this digression, we will go back to consider 
 Plate IV., Fig. 2. This is a contrivance which must be employed 
 if the house to be supported is higher than the house which is 
 used as an abutment. It is more convenient, more economical, 
 and more effectual than a raking shore springing from the 
 ground would be, especially if the height of the building is 
 considerable. In fact, in all cases where the span is not more 
 than about 33 feet, and there is no difficulty in obtaining a good 
 abutment, it is always best to employ flying shores in preference 
 to raking shores ; for, apart from the consideration of economy, 
 they present a more direct resistance to the thrust, are well
 
 SHOEING AND UNDERPINNING. 17 
 
 out of the way of any building operations that may be carried 
 on below them, and can remain in position without danger of 
 being disturbed ; whereas the feet of raking shores are always 
 in the way, and the excavating and pumping which is so often 
 carried on around them, unless great care is taken, is almost 
 sure to loosen their foundations, and so to render them useless.
 
 18 A TREATISE ON 
 
 CHAPTER V. 
 
 ON NEEDLE SHORING AND UNDERPINNING. 
 
 WE have hitherto been dealing only with those methods of 
 shoring which are used more particularly when some pre- 
 cautionary measures must be taken to arrest a dangerous 
 movement in the wall of a building, but which may be said only 
 to assist the foundation in the real task of supporting the wall. 
 We now come to consider the case when the support of the 
 foundation is no longer to be relied upon, and the wall is to be 
 gripped and held suspended in the air by the shores alone, 
 while its lower portion is cleared away entirely, either to be 
 replaced by new work or to remain open for a doorway or 
 shop front. The method employed to support the wall in such 
 a case is called needle shoring : in principle it is the most 
 simple of any, and needs but little explanation ; but in practice 
 it requires the greatest care. 
 
 It consists merely in cutting holes about 14 inches square 
 through the wall of a building, at intervals of from 5 feet to 
 7 feet from each other, and inserting through these holes short 
 balks of timber called needles, which are propped up at either 
 end by stout posts, resting upon sole-pieces laid upon timber 
 platforms on the ground. Oak wedges are driven together at 
 the feet of these posts, or the sole-pieces are laid at a slight 
 inclination, and the posts are levered into position in the same 
 way as the feet of raking shores. The needle is thus pressed 
 tightly against the under side of the brickwork, and after 
 raking shores have been fixed as an additional security in 
 supporting the wall, the lower portion can be taken down with- 
 out fear ; the whole weight of the wall and floors being carried 
 by the needles, and transmitted through the posts to the ground. 
 The wall is supported on the principle of a corbel springing 
 from either side of the needle, and finding its way through the 
 perpendicular joints, until it is met by the line of the corbel 
 springing from the neighbouring needle. It might be supposed 
 from this that the triangular space between the corbels, having 
 nothing to support it, would fall out ; but this is not the case in 
 practice, for the adhesion of the mortar is sufficient to hold all 
 the bricks together if the distance from one needle to the other 
 is not greater than about 6 feet or 7 feet. However, if there is 
 any tendency on the part of the bricks in this space to fall, they 
 must be temporarily strutted up from below. In this kind of
 
 SHOEING AND UNDERPINNING. 19 
 
 shoring there is nothing to be gained and everything to be lost 
 by using timber of a small scantling. For the needles, and for 
 the posts as well (unless they are very securely braced to each 
 other), whole timbers (i. e. about 13 inches by 13 inches) should 
 be used. 
 
 The above brief description brings us to an end of the three 
 methods of shoring usually employed to support a building ; but 
 before we give a practical example of this last method, it may 
 be as well to say a few words here upon the general subject of 
 ruinous and dangerous structures.* 
 
 The first thing of course to be done when a structure is found 
 to be unsafe is to shore it up at once on all sides, either with 
 raking or flying shores, as may be most convenient ; but, before 
 we can determine how it can best be restored to a sound con- 
 dition, a careful survey must be made of all the walls, so that 
 we may find out from the nature of the cracks and bends, and 
 other guiding marks, what is the cause of the failure, and in 
 what direction the fault lies ; for in this way only can we know 
 with certainty how and where to apply a remedy. There are, 
 of course, many causes to which the failure may be attributed, 
 all of which should be considered when the building is 
 examined, such, for instance, as the use of bad mortar, the 
 overloading of the wall, the thrust of a vault, or, more com- 
 monly, some defect in the foundations.! But as it would be an 
 impossible and useless task for us to go into all the cases of 
 failure that are likely to occur, and to prescribe here what 
 should be done in the way of remedy in every instance, we 
 must content ourselves with the investigation of one example 
 only, and let it suggest in principle at least what should be done 
 in many other cases. 
 
 The failure of the foundations is, as we have said above, the 
 most common cause of ruin in a building, and the method of 
 restoration known as underpinning which is employed in such a 
 case is of every-day occurrence ; consequently we cannot do 
 better than select this subject in considering the treatment of 
 ruinous structures. 
 
 If, after a thorough examination has been made of a dangerous 
 building, and from the nature of the cracks and bends and 
 other evidences of failure in the walls, it is proved beyond doubt 
 that the fault is not to be found in the superstructure, then 
 inspection trenches should be cut, and the foundations examined. 
 At one time it may be discovered that the footings have been 
 built with bricks or stones which are both bad in themselves 
 
 * For the convenience of the London reader, the law concerning dangerous 
 structures in the metropolis is appended at the end of this Chapter. 
 
 t The reader is referred to an excellent paper, by Mr. Edwin Nash, on 
 " Failures in Construction," recorded iu the ' Transactions of the Koyal 
 Institute of British Architects,' 1867, vol. xiv. 
 
 C 2
 
 20 A TREATISE ON 
 
 and improperly bonded in the work ; for this is, unfortunately, 
 a very common practice with some builders, to get rid of all 
 their bad bricks, or odd bits of stuff, in the work below the 
 ground. Nothing leads to more disastrous results ; for it should 
 be remembered that the lower a stone or brick is placed in a 
 wall the greater is the weight it has to carry, and consequently 
 the very best materials should be used in the foundations of a 
 building. At another time it may be found that the footings 
 have buckled up at either side into the shape of the letter V> 
 from the offsets being too great, or from the fact that back joints 
 have been allowed beyond the face of the upper work. Only 
 heading courses should be allowed in footings, stretching courses 
 should only be used when the footing courses are doubled, and 
 then the stretching course should occupy a position under the 
 heading course. It may often happen that the concrete or the 
 mortar used for the brickwork below the ground, if the situation 
 is a very damp one, has never properly set from the want of 
 hydraulic properties in the lime used ; or the concrete and 
 foundation generally may have been dislocated by the expansion 
 and contraction of the clay on which it rests. Again, the 
 failure may be caused by some defect in the design of the wall 
 below the ground, such for instance as piers standing upon 
 inverted arches which have not sufficient abutment ; or if the 
 building be an old one, the materials of which the foundation is 
 composed may have decayed so much in process of time as to be 
 no longer strong enough to carry the superincumbent weight. 
 
 Instances such as these may be enumerated by the score, and 
 the time spent in their investigation can never be considered as 
 wasted, for they teach us what to guard against in the future ; 
 and in examining a dangerous structure the knowledge of 
 defects in other cases often helps us in finding out the reasons 
 of failure in the case before us. 
 
 If a wall whose foundations have thus been discovered to be 
 at fault is in all other respects in a comparatively sound and 
 homogeneous condition, i. e. if there are no very serious cracks 
 or sharp bulges perceptible on its face, or if it is only a few 
 inches out of the perpendicular, it can be restored to a perfectly 
 sound and healthy condition by removing the bad foundations 
 and replacing them, either wholly or in part, with good and 
 reliable new work. This operation is called underpinning. 
 
 It is carried out in the following manner : Raking shores 
 are first erected to assist in supporting the wall, and the ground 
 on either side of it is then dug out at one point only, generally 
 at the centre ; and it will depend upon the condition of the 
 brickwork or the masonry of which the wall is composed as to 
 how many feet along the wall this excavation may extend. 
 Good brickwork will carry itself over a span of 6 feet or even 
 7 feet, and the same may also be said of most kinds of
 
 SHOEING AND UNDERPINNING. 21 
 
 dressed masonry; but when the foundations of a wall have 
 failed the homogeneity of the material of which it is composed 
 is partially destroyed, and it will not "be safe to underpin, on an 
 average, more than 4 feet or 5 feet at a time. All the founda- 
 tion comprised within this dimension, whether it be brick, stone, 
 concrete, wood, or iron, is removed entirely, and a new founda- 
 tion is commenced upon the solid ground, and built up within 
 the cleared space to the under side of the old work. 
 
 Before, however, this new work is commenced the ground on 
 which it is to be built must be thoroughly examined, and if 
 necessary inspection shafts should be dug for this purpose ; for 
 the neglect to examine the ground may have been the original 
 cause of the failure. After it has been proved satisfactorily 
 that the ground is fit to be built upon, a good bed of Portland 
 cement concrete should" be carefully laid in a trench cut to 
 receive it. It should not be allowed to be thrown in from the 
 ground level as is so often done, for in that case all the larger 
 stones fall first ; but it should be let down in buckets and 
 quietly deposited, and, after it has been well rammed, the 
 cement on the top should be flushed off to a level surface. If 
 brickwork is to be built upon this concrete, slabs of York stone 
 are often laid over it to receive the footings. A good workman 
 will measure the distance from the surface of this stone to the 
 under side of the wall above, and will so arrange his courses 
 that they will fit into the space exactly, allowing for the 
 breadth of the joints ; but if, when the work has been carried up, 
 it is found that the last course does not quite reach to the 
 under side of the old work, a carefully laid course of pamment 
 tiles or slates must be pinned into the space, and well grouted 
 with liquid cement. The whole of the new work throughout 
 must be built in cement ; for cement possesses the quality, 
 invaluable in this case, of expanding as it sets, and consequently 
 it causes the whole of the new work to rise slightly and press 
 against the under side of the old work. 
 
 When this new pier, as we may call it, has been finished, 
 and the cement has set hard, similar spaces may be cleared 
 away and new work built and bonded into it on either side ; and 
 so we can proceed until the whole of the old foundations have 
 been removed and replaced by new work, which will carry the 
 superstructure with perfect safety for all time to come. 
 
 We have stated above that in all underpinning operations 
 the new work throughout should be built in cement ; this is 
 certainly correct for all brickwork or masonry, but an exception 
 may be made to this rule as far as concrete is concerned. All 
 concretes, whether lime or cement, will expand when they set. 
 The ordinary lime concrete used in and about London, composed 
 of six parts of ballast to one part of greystone lime, will expand 
 as much as three-eighths of an inch to every foot in height, and
 
 22 A TREATISE ON 
 
 the size thus gained the concrete never loses. Consequently, if 
 the underpinning is all under the ground, lime concrete, which 
 is infinitely cheaper than brickwork or masonry in cement, 
 may be the sole material employed ; but, and this is important, 
 some artificial means must be employed to force it up against 
 the under side of the old work. 
 
 A very successful example of underpinning in lime con- 
 crete only, is thus described by Lieut.-Colonel Sir William 
 Denison, E.E., in Mr. Burnell's work on ' Limes, Cements, and 
 Mortars ' : 
 
 " One of the large storehouses in Chatham Dockyard having 
 for some time exhibited serious defects in its walls, the attention 
 of the Admiralty was directed to it in the year 1834, and 
 Mr. Taylor, the Civil Engineer and Architect, was directed to 
 report on the best mode of obviating the evil. 
 
 " Upon investigation, the foundation of the storehouse (a 
 building 540 feet in length and 50 feet in breadth) was found 
 to be in a very bad state ; the front wall, nearest the river, had 
 orginally been built upon piles, while the rear wall was laid 
 upon an upper stratum of 5 or 6-inch planking, supported by 
 two rows of transverse and longitudinal oak sleepers lying on 
 the surface of the ground, which in this case was of a variable 
 consistence, containing flints bedded in a sort of clay, quite 
 pervious to the water, which at high tide rose some height upon 
 the foundation. The sleepers and heads of the piles at the 
 front of the building, thus exposed to alternate moisture and 
 dryness, were in a state of rapid decay ; in some places they 
 were even reduced to a powder, and it was possible for a man 
 to move under the walls in the space previously occupied by the 
 timber. In the rear, the case was pretty much the same ; the 
 sleepers were universally in a state of decay, but in some places 
 were much further advanced towards decomposition than in 
 others. 
 
 " The state of the storehouse requiring immediate attention, 
 it was resolved to attempt to underpin the walls. This the 
 patentee for the new description of concrete, or artificial stone, 
 undertook to do, having adopted a plan proposed by Mr. Taylor, 
 for forcing the soft concrete against the under part of the wall ; 
 and he proceeded to execute this contract in the following 
 manner. 
 
 " I must premise that the storehouse was vaulted underneath, 
 and that the piers, or cross walls, required as much under- 
 pinning as any other part of the building. 
 
 " The walls were laid open to their bottom, both inside and 
 outside the building ; in the front, the heads of the piles and 
 the sleepers were removed for a depth of about 4 feet below the 
 bottom of the wall, and for lengths of about 5 feet at one 
 time. In the rear, all the planks and sleepers were removed for
 
 SHORING AND UNDERPINNING. 23 
 
 the same distance. A mass of concrete, composed of one-eighth 
 of Hailing lime (reduced to a powder by grinding, and in a 
 perfectly caustic state) and seven-eighths of Thames ballast, 
 mixed up with so much boiling water as to reduce the whole to 
 a pasty consistence, was then thrown from a height of about 
 15 feet underneath the wall : it was allowed to project about a 
 foot on each side, where it was confined by planks, and after 
 being roughly levelled, it was well rammed, to give it as much 
 consistence as possible. This mass was raised about 3 feet, or 
 to within 1 foot of the bottom of the wall ; it was then carefully 
 levelled, and covered with ^-inch slates. A kind of framework 
 was then placed on the slates, consisting of two cross-plates of 
 iron, placed perpendicularly to the direction of the wall, about 
 1 foot wide, and long enough to project about 1 foot on each 
 side of the wall. 
 
 " To these were fixed two frames parallel to the wall, about 
 4 feet long, each carrying two sockets for screws. Within these 
 frames were placed two movable planks, long enough to pass 
 just free between the cross-plates, and wide enough to fit nearly 
 the space between the slates and the bottom of the wall. Upon 
 these planks were sockets for the heads of the two screws, by 
 which the planks were pushed forward or withdrawn at 
 pleasure. 
 
 " When the apparatus was fixed, and the movable planks ready 
 on both sides of the wall, about two barrowfuls of concrete, 
 mixed as stated, were thrown in from above; the workmen 
 below then commenced turning the screws on each side simulta- 
 neously, moving the two planks towards the centre of the wall, 
 and forcing the concrete before them into all the vacant spaces, 
 and against the bottom of the wall. When the plank was forced 
 forward as far as it would go, by the strength of two men to 
 each screw, the concrete was allowed to rest for about five or 
 ten minutes, by which time it had set hard enough to stand by 
 itself, and its expansion in the act of setting completed what 
 the pressure of the screws might have left undone. The planks 
 were then withdrawn, another charge thrown in on each side, 
 and compressed as before, and this was continued till the whole 
 space between the frames was filled with concrete. The screws 
 were then removed, the boards and frames unbolted and taken 
 out, and lastly, the side-plates were withdrawn, leaving an in- 
 terval of about f of an inch between each mass of concrete, 
 which space was afterwards filled in with grout. 
 
 " The above description is given from notes taken at the time. 
 The proportion of lime to gravel is as 1 to 6 ; and such is the 
 efficiency of the concrete in the mode in which it was applied, 
 that no settlement has taken place since the work was com- 
 pleted." 
 
 The majority of underpinning operations are carried out by
 
 iM A TREATISE ON 
 
 some such methods as these that have now been described ; but 
 this way of dealing with a ruinous structure may be considered 
 rather in the light of a prevention than a cure, for unless a 
 building is thus treated at once when its foundations first show 
 signs of giving way, the evil will gradually increase, and 
 render it imperative not only that the foundations should be 
 renewed, but also that a considerable portion of the wall above 
 the ground should be taken down and rebuilt. 
 
 If we look, for instance, at the wall of the house depicted on 
 Plate V., Figs. 1 and 2, we shall see that it is ruined for several 
 feet above the foundations. This might, perhaps, have been 
 prevented if it had been underpinned at once, when the failure 
 first showed itself; but no such steps having been taken, it has 
 cracked badly in many places, bulged forward, and dragged the 
 return walls out of the perpendicular. 
 
 The reason why the foundations have so signally failed in 
 this case to carry the superstructure, is because the house has 
 been made to encroach upon the site of an old pit or trench, 
 shown by the dotted line in the section, Fig. 2, which has been 
 filled up for many years, so that its existence has perhaps never 
 been suspected ; and as the foundations do not go down to any 
 great depth, it is quite possible that it may not have been 
 noticed when the wall was built, or the contractor may have 
 chosen rather to risk a settlement than go to the extra expense 
 of excavating the made ground and building up from the virgin 
 soil. 
 
 It is now too late to underpin this wall in the ordinary way 
 that we have just described, for the evil has spread so far that 
 it would still be unsafe, even though its foundations were re- 
 newed ; but after it has been well shored up with raking shores, 
 the method of needle shoring must be employed to support the 
 upper portion (which, though it has been squeezed in a little 
 towards the centre, is otherwise comparatively sound and homo- 
 geneous), and the whole of the lower portion of the wall for a 
 distance of about 12 feet from the ground must be removed 
 entirely. Accordingly four needles, which it is best to make 
 whole timbers, i. e. about 13 inches by 13 inches, are inserted 
 through holes cut in the wall well out of reach of the cracks, 
 and above the point where the bulge is most pronounced, and 
 these are supported by eight posts of the same scantling. In 
 consequence of the peculiar nature of the case, the posts must 
 be placed upon two continuous sole-pieces, laid on either side of 
 the wall, and stretching well across the treacherous ground. 
 On the exterior of the wall, the sole-piece must rest upon a 
 carefully laid platform of stout planks, laid in such a way that 
 the bearing of the two central posts may be spread over so much 
 of the surface that it will be impossible for them to sink when 
 the weight comes upon them. On the inside, the sole-piece
 
 PLATI-:, v. 
 
 Fig. 2. Section. 
 
 Fig: 5. 
 C Hcuduen. Stock Inv ut. DtL 
 
 J.Akermnji ?ha:o-lii,LoBlon,W C
 
 SHOEING AND UNDERPINNING. 25 
 
 may rest upon the concrete under the floor, if it is in a good 
 condition ; but if not, it must rest upon a similar platform of 
 timber to that on the outside of the building. Great care must 
 be taken in arranging these platforms, that there may be no 
 possibility of their being disturbed when the ground is exca- 
 vated for the new foundations. 
 
 It will be noticed in the section, Fig. 2, that the needles pass 
 through the wall just above one of the floors. This is the best 
 and most usual position for the needles to occupy ; for the brick- 
 work at this point, and for some way above it, is perfectly 
 sound, and has not been cut into for the insertion of plates and 
 joists. This floor must, of course, be strutted up independently 
 of the wall, and a hole cut through it and the ground floor to 
 allow the posts which carry the needles to pass freely to the 
 ground. If, however, this cutting through of the floors would 
 be a very costly and troublesome business, platforms of timber 
 may be placed upon the floor and on the under side of the ceiling, 
 spreading the weight over as many joists as possible, and the 
 posts set up in different pieces. 
 
 The needles having been wedged up tightly against the 
 under side of the old work, the whole of the brickwork below 
 the needles must be taken down, the made ground under the 
 wall dug out, and a good trench cut in the virgin soil to receive 
 the bed of new concrete. The rest of the work may then be 
 built up again in cement to meet the wall above, in the same 
 way as has been described already. 
 
 It should always be borne in mind, that even after this new 
 work has been finished and the cement has set, it is still the 
 needles and posts which do the real work of carrying the wall ; 
 and the greatest care must be exercised in removing them, that 
 the weight is transferred gradually, and not all at once, upon 
 the new work. The needles should first be eased a little by 
 knocking out the wedges at the foot of the posts a few inches, 
 and then, after a day or two has elapsed, the wedges may be 
 withdrawn entirely and the needles taken out ; but the raking 
 shores should remain in position for about a week after the wall 
 has settled down upon its new bearings. 
 
 With regard to the responsibilities incurred in case of the 
 failure of underpinning operations, Mr. Edwin Nash, in his 
 paper on " Failures in Construction," * makes the following 
 remarks : " When we see that accidents under this head may 
 cause verdicts of manslaughter to be recorded against architects, 
 as was the case against Mr. Abraham, after the noted fall of a 
 house in the Strand in 1853, we must be awakened to the neces- 
 sity of so arranging the business part of such operations that 
 the architect shall not be made responsible for details he cannot 
 control. It is often a sort of work that requires intelligent 
 * 'Transactions, R.I.B.A.' 1876, vol. xiv.
 
 26 A TREATISE ON 
 
 watching during every moment of its progress, and this is not 
 the architect's business j and if this view be not recognised by 
 courts of law, it behoves us to define the responsibility in a 
 written document between architect and builder before com- 
 mencing the work." 
 
 It is not, however, in connection with ruinous structures that 
 we must look for the most general use of needle shoring, for 
 walls are, as a rule, underpinned at once, without its aid, when 
 the foundations first show signs of giving way ; but it is much 
 more commonly employed in cases where some alteration is to 
 be made in a building which is perfectly sound such, for in- 
 stance, as the addition of a new basement, or the insertion of 
 a shop-front. As an example of the former case, the Gaiety 
 Eestaurant in the Strand may be cited. It was necessary, in 
 order to obtain the space now occupied by the magnificent Grill 
 Eoom, that the walls should be taken down to a greater depth 
 than was previously the case ; accordingly needle shoring was 
 employed, and the whole building stood for many weeks as it 
 were upon crutches, while the new foundations were being 
 built. In consequence of the weight of the walls, and to 
 obviate some difficulty in supporting the floors, the needles were 
 doubled, i. e. placed one above another in the manner shown in 
 the sketch, Plate V., Fig. 5. 
 
 An example where needle shoring is required to support a 
 wall during the insertion of a breastsummer and shop-front is 
 illustrated in Plate V., Figs. 8 and 4. The needles in this case 
 must be made longer than usual to span the vaults under the 
 pavement ; consequently it will be as well to strut them as 
 shown in the section, Fig. 4. Eaking shores need not be used 
 unless the wall is of a great height, or in a bad condition ; but 
 the window openings, immediately above the needles, must in 
 any case be well strutted, as shown in the elevation, Fig. 3, or 
 they will be squeezed in, and the frames, as well as the glass, 
 will be broken. 
 
 When the opening has been made in the wall, and substantial 
 piers have been built at either end of it, the girder or breast- 
 summer is fixed in position, and a plate fitted to its lower flange 
 to take the joists of the first floor. A 3-inch York stone template 
 is then bedded on the top of the girder, and a course or two of 
 brickwork built up in cement to meet the under side of the old 
 work. 
 
 It will now be unnecessary to give any further illustrated 
 examples of this simple method of needle shoring ; but before 
 we go on to consider its use in cases of a more complicated 
 character in the next chapter, there are one or two further points 
 to which it may be as well to draw the reader's attention. 
 
 If it should be required, for instance, to clear away the lower 
 portion of a party-wall, so as to throw the premises on the
 
 SHORING AND UNDERPINNING. 27 
 
 ground floor into one large shop or office, before the needles, 
 which will carry the wall during this operation, are inserted, 
 the following points should be considered : 
 
 1st. If there are any chimney breasts in the wall, they should 
 be well supported ; two or even three needles, if the width of 
 the breast is considerable, should be inserted under them, with 
 as good a bearing as possible. 
 
 2nd. If there are any piers or corbels in the wall, a needle 
 should be inserted under each. 
 
 3rd. If the upper floors are double, or framed floors, the 
 needles should be inserted in the same perpendicular plane with 
 the binding joists or girders. 
 
 4th. Care should be taken in arranging the position of the 
 posts which are to carry the needles, that they shall not inter- 
 fere with the proper adjustment of the girders and stanchions 
 which are eventually to carry the wall. 
 
 The needles must be inserted above the first floor for the 
 reasons mentioned above, and also to allow of the girders being 
 fixed on a level with this floor. In the case of a warehouse, if 
 the structure is in a bad condition, it will be as well to remove 
 all goods which are stored upon the floors above the needles, or 
 at all events to shift them, so that their weight is carried by the 
 story posts or by another wall. But if this could not be done 
 except at great inconvenience to the proprietors, the floors must 
 be strutted up from the ground, and so made altogether in- 
 dependent of the support of the party-wall. 
 
 In the example we have given above of the underpinning of 
 the storehouses at Chatham, it was not deemed necessaiy to 
 move the goods at all during the operations, though they were 
 very heavy, comprising all sorts of ships' tackling, such as 
 cables, blocks, ropes, spars, &c. ; but it will be recollected that 
 in that case the walls were not needled, and only underpinned 
 in short lengths at a time. However, all such considerations as 
 these depend upon so many things, that they can only be left to 
 the judgment of the architect in each particular case. 
 
 At the commencement of this chapter it was laid down as a 
 general rule that whole timbers should be used in cases of 
 needle shoring, and for this reason, that although the scantling 
 of whole timber may be found by the usual formula to be larger 
 than that required to carry the weight with safety, yet it should 
 be borne in mind that all beams of timber will deflect a little 
 when a weight comes upon them, and it is important in the case 
 of a needle that this deflection should be reduced to a minimum. 
 Again, there is always the possibility of there being some un- 
 foreseen defect in the timber, and the greatest care should be 
 taken, even when a needle is made of whole timber, that it is 
 perfectly sound throughout : the same may also be said of the 
 posts which carry the needles. If, however, economy or space
 
 28 A TREATISE ON 
 
 should require that smaller timbers should be used, we must 
 employ the following formulae, from ' Tredgold's Carpentry,' for 
 the scantling of beams supported at both ends and loaded in the 
 centre, and posts compressed in the direction of their axis : 
 
 To find the scantling for a rectangular piece of timber that 
 will sustain a given weight in the centre, when supported at 
 the ends in a horizontal position. 
 
 When the breadth is known or settled, 
 
 'L 8 x W x a> 
 
 When the depth is known or settled, 
 L 2 X W x a 
 ~TT~ 
 
 where L = length of bearing in feet ; 
 
 W = weight to be carried in pounds ; 
 a = -01 for fir, and '013 for oak; 
 B = breadth in inches ; and 
 D = depth in inches. 
 
 To find the scantling of a rectangular post capable of sustain- 
 ing a given pressure in the direction of its length : 
 
 where L = length in feet ; 
 
 W = the weight to be sustained in pounds ; 
 a = 0-00133 for fir, and 0-0015 for oak ; 
 B = breadth in inches ; and 
 D = thickness required in inches. 
 
 Part II. of the Metropolitan Building Act, 1855 [18 & 19 Viet, 
 c. 122], relating to Dangerous Structures. 
 
 Survey to be Sect. LXIX. Whenever it is made known to the Commis- 
 dangerous sioners hereinafter named that any structure (including in such 
 structures, expression any building, wall or other structure) is in a dan- 
 gerous state, such Commissioners shall require a survey of such 
 structure to be made by the District Surveyor, or by some other 
 competent surveyor, and it shall also be the duty of the district 
 surveyor to make known to the said Commissioner any inform- 
 ation he may receive with respect to any structure being in 
 such state as aforesaid. 
 
 Definition of LXX. In cases where any such structure is situate within 
 
 rioners!" 8 " the City of London or the Liberties thereof, hereinafter included 
 
 under the expression " the City of London" the expression " the 
 
 Commissioners " shall mean " the Commissioners of Sewers of
 
 SHORING AND UNDERPINNING. 29 
 
 the City of London " ; but when such structure is situate else- 
 where it shall mean " the Commissioners of Police of the Metropolis" 
 or such one of them as may be authorised by one of Her Majesty's 
 Principal Secretaries of State to act in the matter of this Act* 
 
 LXXI. Upon the completion of his survey, the surveyor Surveyor, on 
 employed shall certify to the said Commissioners his opinion as ^ u p r vey, n to 
 to the state of any such structure as aforesaid. give certm- 
 
 LXXIL If such certificate is to the effect that such structure ca 
 is not in a dangerous state, no further procesdings shall be had ^btftaken 8 
 in respect thereof ; but if it is to the effect that the same is in a j r r t jg pe j ' of 
 dangerous state, the Commissioners shall cause the same to be 
 shored up, or otherwise secured, and a proper board or fence to 
 be put up for the protection of passengers, and shall cause 
 notice in writing to be given to the owner or occupier of such 
 structure requiring him forthwith to take down, secure, or 
 repair the same, as the case requires. 
 
 LXXIII. If the owner or occupier to whom notice is given as on non-com- 
 last aforesaid fails to comply, as speedily as the nature of the j^^ 6 with 
 case permits, with the requisition of such notice, the said Com- Justice to 
 missioners may make complaint thereof before a Justice of the owner, &c 
 Peace ; and it shall be lawful for such Justice to order the and raake ' 
 owner, or on his default the occupier, of any such structure to pi/with*" 1 
 take down, repair, or otherwise secure, to the satisfaction of the re q ul:iitlOQ ' 
 surveyor who made such survey as aforesaid, or of such other 
 surveyor as the said Commissioners may appoint, such structure 
 or such part thereof as appears to him to be in a dangerous 
 state, within a time to be fixed by such Justice ; and in case 
 the same is not taken down, repaired, or otherwise secured 
 within the time so limited, the said Commissioners may with 
 all convenient speed cause all or so much of such structure as is 
 in a dangerous condition to be taken down, repaired, or other- 
 wise secured, in such manner as may be requisite; and all 
 expenses incurred by the said Commissioners in respect of any 
 dangerous structure by virtue of the second part of this Act . 
 shall be paid by the owner of such structure, but without 
 prejudice to his right to recover the same from any lessee or 
 other person liable to the expenses of repairs. 
 
 LXXIV. If such owner cannot be found, or if, on demand, he if owner 
 refuses or neglects to pay the aforesaid expenses, the said Com- found* c?m- 
 missioners, after giving three months' notice of their intention missioners 
 to do so, by posting a printed or written notice in a conspicuous Sructure, 
 place on the structure in respect of which or of part of which s ivin s l ^ e 
 
 IT. i- j -i/u i j -U -j. j surplus to 
 
 they have incurred expenses, or on the land whereon it stands, owner, &c. 
 may sell such structure ; and they shall, after deducting from the 
 
 * This last clause, printed in italics, has since been repealed (32 and 33 
 Viet. cap. 82), and jurisdiction is now given to the Metropolitan Board of 
 Works, instead of the Commissioners of Police of the Metropolis, in respect 
 of dangerous structures not in the City.
 
 30 A TREATISE ON 
 
 proceeds of such sale the amount of all expenses incurred by 
 them, restore the surplus (if any) to the owner. 
 
 [The following amendment of the above section has since 
 been passed in the Metropolis Management and Building Acts 
 Amendment Act, 1878 (41 & 42 Viet. c. 32)] : Where under the 
 provisions of the Metropolitan Building Act, 1855, and the 
 Acts amending the same, with respect to dangerous structures, 
 any structure is sold for payment of the expenses incurred in 
 respect thereof by the Board in manner prescribed by section 
 seventy-four of the said Act, the person to whom the same is 
 sold (hereinafter referred to as " the purchaser "), his agents and 
 servants, may enter upon the land whereon such structure is 
 standing for the purpose of taking down the same and of 
 removing the materials of which the same is constructed ; and 
 any person who refuses to admit the purchaser, his agents or 
 servants, upon such land, or impedes him in removing such 
 materials, shall be liable on conviction to a penalty not exceed- 
 ing ten pounds, and to a further penalty of five pounds for 
 every day after the first day during which such refusal con- 
 tinues. 
 
 When the proceeds of the sale of any such structure under 
 the said seventy-fourth section are insufficient to repay the 
 Board the amount of the expenses incurred by them in respect 
 of such structure, no part of the land whereon such structure 
 stands or stood shall be built upon until after the balance due 
 to the Board in respect of such structure shall have been paid 
 to the Board. 
 
 [This amendment does not apply to dangerous structures in 
 the City.] 
 
 Payments by LXXV. All payments hereby directed to be made by or to 
 Commit the Commissioners shall in the cases of payments in respect of 
 sioners, how any structure situate within the City of London be made by or 
 to the Chamberlain of the City out of or to the Consolidated 
 Eate made by the Commissioners of Sewers, and in the cases of 
 payments in respect of any structure situate elsewhere within 
 the limits of this Act be made by or to the Keceiver of Metro- 
 politan Police, in the same manner in which payments are made 
 by or to such Chamberlain and Receiver respectively in the 
 ordinary course of their business; but no Commissioner or 
 other officer shall be liable in respect of any loss that may be 
 sustained by any person in consequence of the exercise by the 
 said Commissioners of the powers hereby given them, unless 
 such loss happens through the wilful default of such Commis- 
 sioner or other officer. 
 Surplus, how LXXVI. In cases where any surplus is hereby made payable 
 
 to be applied -r-j TI-J.I 11 
 
 if no demand to any owner, if no demand tor the same is made by any person 
 
 made for it. en titled thereto within one year, then the same shall be paid 
 
 into the Bank of England in the name and with the privity of
 
 SHORING AND UNDERPINNING. 31 
 
 the Accountant-General of the Court of Chancery, to be placed 
 to his account there to the credit of the owner (describing him 
 so far as the Commissioners can) subject to the control of the 
 court, and to be paid out to the owner on his applying by 
 petition, and proving his title thereto. 
 
 LXXVII. There shall be paid to the District Surveyor, or to Fees to Dis- 
 such other surveyor as aforesaid, in respect of his services trict Sur ' 
 under the second part of this Act, such fees, not exceeding the Vey r 
 amounts specified in the second part of the second schedule 
 hereto, as may from time to time be directed by the said Metro- 
 politan Board. 
 
 LXXVIII. If any special service is required to be performed Metropolitan 
 by the District Surveyor, or by such other surveyor as aforesaid, Boar i 1 ma y 
 under the second part of this Act, for which no fee is specified special fees 
 in the said schedule, the said Metropolitan Board may order jj^rovkied 
 such fee to be paid for such service as they think fit. for. pn 
 
 LXXIX. All fees paid to the District Surveyor, or to such Fees to be 
 other surveyor as aforesaid, by virtue of the second part of this ^ e eA P* 1 " 1 
 Act, shall be deemed to be expenses incurred by the said Com- 
 missioners in the matter of the dangerous structure in respect 
 of which such fees are paid, and shall be recoverable by them 
 from the owner accordingly. 
 
 LXXX. In cases where a structure has been certified by a justice of 
 District Surveyor, or such other surveyor as aforesaid, to be Peace . m ay 
 dangerous to its inmates, a Justice of the Peace may, if satisfied to be r"- ma 
 of the correctness of such certificate, upon the application of the ? oved from 
 
 . , ~ . . -i 1- i j -i . dangerous 
 
 said Commissioners, by order under nis hand, direct any inmates structures. 
 of such structure to be removed therefrom by a constable or 
 other peace officer ; and if they have no other abode he may 
 require them to be received into the workhouse established for 
 the reception of the poor of the place in which such structure is 
 situate. 
 
 LXXXI. Subject to the approval of one of Her Majesty's Powers of 
 principal Secretaries of State, the said Commissioners may ^o^to 
 appoint such persons at such salaries, and make such regulations, appoint 
 as they think fit for carrying into execution the second part of ot 
 this Act ; and all expenses incurred by them not hereby other- 
 wise provided for shall, in the case of expenses incurred by the 
 said Commissioners of Police, be deemed to be expenses incurred 
 by them in respect of the police force of which they are Com- 
 missioners, and be payable accordingly ; and all expenses in- 
 curred by the said Commissioners of Sewers shall be paid out of 
 the said Consolidated Kate.
 
 32 A TREATISE ON 
 
 CHAPTER VI. 
 
 ON THE SHORING AND UNDERPINNING OF MEDIEVAL BUILDINGS. 
 
 THE practice of the art of shoring and underpinning does 
 not always confine itself to the meaner buildings in a crowded 
 town, but the sphere of its greatest usefulness and fullest 
 development is to be found in the restoration of our venerable 
 churches and cathedrals, many of which, but for its timely aid, 
 would long before this have fallen victims to the ravages of 
 decay. Every architect who loves his art must be glad to be 
 the means of saving from destruction even one stone of those 
 wonderful and beautiful works executed by the masons of the 
 Middle Ages ; and there have been many instances in which 
 the ponderous towers and steeples of cathedrals have been saved 
 from impending ruin by an opportune application of this useful 
 science. Such were the works of Eondelet at the Church of St. 
 Genevieve at Paris, of Flachat at the cathedral at Bayeux, and 
 in our own country of Cottingham at Hereford ; and had it not 
 been for the interference of the elements, the underpinning at 
 Chichester would no doubt have been successfully carried out, 
 and the original tower and spire of the cathedral might still 
 have been standing. 
 
 The gigantic shores and centres used in cases such as these 
 require, however, a fuller description than can be given in this 
 treatise ; and the reader is referred for an example to the excellent 
 description and drawings of the shoring of the central tower 
 and lantern of the cathedral at Bayeux by MM. Dion and Las- 
 vignes. But instances of shoring on so vast a scale are rare, 
 and more the work of engineers than architects ; and it will be 
 better to describe here a more humble example, and one which 
 is more likely to be of service to us in ordinary practice. 
 
 At a meeting of the Eoyal Institute of British Architects, held 
 on Monday, 3rd February, 1873, an excellent paper was read by 
 Mr. J. P. Seddon, F.R.I.B.A., on the shoring, &c., of the tower and 
 spire of the parish church of Grosmont in Monmouthshire. We 
 cannot do better than quote here Mr. Seddon's own remarks 
 upon that building, describing the state of decay in which he 
 found it, and the subsequent measures which were employed in 
 its restoration. The diagrams on Plates VI. and VII. are 
 copied from the drawings made by Mr. William Ed. Martin to 
 illustrate Mr. Seddon's paper, and which afterwards appeared in 
 the Building News of February 7th, 1873.
 
 -
 
 SHORING AND UNDERPINNING. 33 
 
 " The parish church of Grosmont, dedicated to St. Nicholas, 
 in the diocese of Llandaif, is situated in Monmouthshire, near to 
 where the border of that county joins those of Herefordshire and 
 Breconshire a very beautiful and retired part of the country. 
 
 " The structure is one which by its historical interest and 
 architectural value justifies the pride taken in it by the inha- 
 bitants of the surrounding district ; but it has even wider 
 claims for consideration, and particularly in connection with 
 this metropolis, distant though it may seem to be. 
 
 " It owes, if not its origin, at least its enlargement and 
 embellishment, to the same munificent patronage which directed 
 those on a grander scale at the Abbey of Westminster; and 
 though Grosmont Church is, as befits its position, a compara- 
 tively humble structure in point of style, it may claim some 
 resemblance to its nobler contemporary. Had the same caution 
 been exercised in its case as in that of the Abbey, and had only 
 a modest lantern surmounted its crux, I should not have the 
 following chronicle of disaster to bring before you. But the 
 substructure was in all probability never intended to support 
 the ambitious though elegant central octagon tower and spire 
 which at a later period were piled upon it, exemplifying a 
 temerity of which mediaeval architects were often guilty, and 
 which brought ruin in the case of Chichester and serious danger 
 in that of Salisbury. 
 
 " The church, the plan of which is a Latin cross, consists of a 
 nave 67 feet by 18 feet 6 inches, and aisles 9 feet 6 inches wide, 
 separated by arcades of five bays (with responds deeper than 
 ordinary, obviously to give more abutment to the crux arches), 
 central tower and spire, transepts with aisles on the western 
 sides, of the same width as those to nave ; chancel and chapel 
 south of same. There is also a porch on the north side opposite 
 the central bay of the main arcades. The crux arches and 
 transept are the earliest portion, being in the style of the 
 Transition between Norman and Lancet. The chancel is fully 
 developed Lancet. 
 
 " It is now many years since I was first called in to examine 
 this church, and then it was in a condition which cannot be 
 described as other than tottering from old age. In this part of 
 the country it must always have been a difficulty to obtain 
 proper building sand, and the loamy sand at hand would soon 
 destroy the value of any amount of lime mixed with it. From 
 this cause the mortar of the walling throughout had become 
 little better than earth, and the whole of the external walls 
 exposed to the weather were grievously dilapidated. 
 
 " Under the great weight of the tower and spire which were 
 added, the earlier crux, piers, and arches have been crushed and 
 twisted out of shape, and this pressure has been transmitted in 
 the directions of north, south, and west, by the several arches, 
 
 D
 
 34 A TREATISE ON 
 
 which had themselves become distorted so as actually to thrust 
 outwards the end walls of nave and transepts. The more solid 
 walls of the eastern side of transepts and of the chancel had 
 yielded less, yet still in some degree. 
 
 " The whole eastern limb, viz. chancel and Eleanor Chapel, 
 by far the richest architecturally, was in the worst condition, 
 and imperatively needed rebuilding. Under the circumstances 
 described, however, it seemed a perilous operation to undertake, 
 as even the temporary removal of such support as they gave the 
 central tower might accelerate the ruin of the rest of the fabric. 
 Funds adequate for this work only having with difficulty been 
 collected, this was effected with great care. The chancel and 
 Eleanor Chapel were in 1869-70 almost entirely taken down 
 and rebuilt under my directions. 
 
 " Careful examination was made before and after the execution 
 of this work of the state of the crux, piers, and arches, and 
 marks set to show whether these yielded at all by reason of 
 settlement in the new masonry. This, which was mostly to be 
 feared at the north-east angle pier, does not seem to have taken 
 place to any great extent. But still I received reports from time 
 to time that the original mischief was proceeding, and I caused 
 a close examination to be made, from which it appeared that the 
 cracks were surely though slowly extending, particularly in the 
 north-west pier. In consequence of this, I reported that it was, 
 in my opinion, essentially necessary that the tower and spire 
 should be so shored up and supported by centres as to be inde- 
 pendent of the piers, which then, as funds were procured, could 
 be made good; after which the restoration of the arches and 
 superstructure could at any time be taken in hand. 
 
 " I estimated the cost of this preliminary work of supporting 
 the failing arches at about 400Z., and received instructions from 
 the vicar, the Eev. W. H. Twyning, to direct it to be done at 
 once. 
 
 " The failure of the substructure of the tower is primarily 
 traceable to two causes. First, errors in design ; and, secondly, 
 errors in construction. The design is in fault from the weight 
 of the tower being carried upon insufficiently abutted arches > 
 and the construction, from the imperfect execution of the dressed 
 stone- work and the masonry of the walling. 
 
 " From the first cause (imperfect design) four distinct classes 
 of failure are to be traced : (1) Spreading of arches at their 
 springing ; (2) flattening of the arch curves, thus neutralising 
 the keying, and rendering the arch insecure by the liability of 
 voussoirs to fall out ; (3) thrusting of the vertical supporting 
 piers under the tower arches out of the perpendicular ; and (4) 
 transmission of the thrusting force to all adjoining piers, 
 arches, and walls, throwing them out of the normal stable con- 
 dition verticality.
 
 SHORING AND UNDERPINNING. 35 
 
 " From the second cause (imperfect construction) three classes 
 of failure may be traced: (1) The crushing of the wrought 
 stone facings which form the casing of the piers ; (2) the 
 bursting asunder or drawing of the bonders, of the various 
 members of which the piers are composed; and (3) rents or 
 fissures of the walling generally. 
 
 " The most prolific causes of failure in building are generally 
 two, viz. : unequally yielding of foundation trenches, and un- 
 compensated thrusts, whether from roofs or arches. The case 
 now under consideration is a signal example of failure from 
 the latter cause an equally unyielding foundation having con- 
 tributed in some degree to intensify this failure. 
 
 " Writers of books on building generally assume it as a fact 
 not to be questioned that a solid rock foundation, roughly 
 levelled or stepped where necessary, is the foundation most to 
 be desired ; but an attentive consideration of the present case 
 would lead to the belief that such a foundation, if not absolutely 
 dangerous as a base for a building erected in the ordinary way, 
 is at least very undesirable unless extraordinary precautions are 
 used in the selection of the materials for the walls, in the bond- 
 ing, and in the elimination of all unequal settlement from a 
 greater number of mortar joints in any one portion of the 
 walling, than in another on the same level. In this case the 
 functions of the tower piers were to transmit the weight of 
 the tower to the foundations ; the latter being rock and incom- 
 pressible, the piers became crushed between two unyielding 
 forces, which would not have been the case had the foundation 
 been of a partially yielding nature, such as a stiff clay or 
 gravel. 
 
 " Taking the various classes of failure enumerated in detail : 
 (1) The spreading of the tower arches at the springing. The 
 four arches carrying the tower spread as follows : North arch, 
 
 584 feet (7 inches) ; east arch, 375 feet (4^ inches) ; south arch, 
 
 75 feet (9 inches) ; west arch, 625 feet (7^ inches). This 
 spreading has not taken place equally at both sides of the 
 original central line of each arch ; the abutments to some of 
 the arches, being more solid and stable than others, remain 
 almost in their original positions, whilst the spreading has 
 taken place on that side of the centre line towards the weakest 
 abutment. 
 
 " Spreading of the arches leads naturally to the second class 
 of failure, viz. : flattening of the arch curves. This flattening 
 has not taken place regularly ; the arches preserve in some parts 
 their original curves, whilst in other places the curves have 
 been forced into straight lines. The general outlines now 
 assumed by the soffits of the arches are irregular lines not 
 amenable to any known mathematical curve. 
 
 " Spreading of the arches also involves the third class of 
 
 D 2
 
 36 A TREATISE ON 
 
 failure, viz. thrusting the piers supporting them out of the 
 perpendicular. It is evident that the piers could not have 
 remained upright when the arches spread, except on the sup- 
 position that the springers of the arches slipped back on the 
 abaci of the caps ; but this would have been impossible, for the 
 vast weight of the superstructure augmented the friction between 
 the two stone surfaces to such an extent as to make the last 
 stone of the cap and first stone of the arch practically one 
 stone. Hence the number of inches by which the faces of two 
 opposite piers are out of plumb becomes a correct measure of 
 the spread of the superincumbent arch. 
 
 " The fourth class of failure noticed is the transmission of the 
 thrusts of the tower arches to the extremities of the building 
 in all directions. It will be well to remember that those forces 
 commenced and continued to act whilst the walling generally 
 was green, and the mortar in a soft condition, thus facilitating 
 to some extent the accommodation of the surrounding abut- 
 ments to the thrusting forces, without involving any sudden 
 violent or dangerous fractures ; while the gradual subsequent 
 piling on weight when the tower and spire were added con- 
 tinued to increase the distortion. 
 
 " The forces generated by the thrusting of the north and 
 south tower arches are in the directions of the nave arcades to 
 the westward, and the chancel flank walls to the eastward; 
 the latter being comparatively solid walls on account of the 
 narrowness of the lancet window openings have sustained the 
 thrusts in a fairly efficient manner ; but on account of the large 
 openings and small piers in the nave arcades they formed but 
 an indifferent abutment ; hence every pier and arch is thrust 
 westward, the west gable itself being thrust out of the per- 
 pendicular, overhanging its base 5| inches. The east and west 
 tower arches, acting through the transept flank walls which 
 are their abutments, have thrust out of the perpendicular the 
 north and south transept and walls the former 4f inches, and 
 the latter 8^ inches. 
 
 " An inspection of the ground plan of the building will 
 show the north-west and south-west piers to be those most 
 deficient in abutment, and in reality it is found that these two 
 piers are those that have suffered most, and are in the most 
 dangerous condition. The south-west pier had to be cased 
 some forty years since with carefully coursed wrought masonry, 
 increasing the area of the pier by about 10 feet superficial ; and 
 the present extremely dangerous condition of the north-west 
 pier compels its reconstruction before any other portion of the 
 building. 
 
 " The first class of failure arising from the second cause is 
 the crushing of the dressed stonework in the pier facings. 
 This has taken place from the undue concentration of the
 
 SHORING AND UNDERPINNING. 37 
 
 weight on this facing ; the backing being composed of rubble 
 walling, with a greater number of mortar joints than in the 
 facing, has settled down, leaving the casing to do the work of 
 carrying the tower, and thus reducing the working area of each 
 pier from 18 feet to 8 '34 feet. 
 
 " The second class of failure under this head is the drawing 
 of the bond stones or bursting asunder of the piers. This is a 
 very unusual mode of failure ; and is due in this case to im- 
 perfect footings under some members composing the piers. The 
 footings were crushed or squeezed away from this particular 
 part of the foundations ; hence the bursting or drawing of the 
 bonders or headers in the quoins immediately over this defective 
 work. 
 
 " The last class of failure to be noted is that most commonly 
 found in nearly every building, ancient or modern, viz. splitting 
 of the walling in a direction at right angles or inclined to the 
 beds, commonly called settlements. 
 
 " Settlements result from the non-elastic nature of the 
 materials composing a wall ; no one part of the walling being 
 free to sink, or settle down, or change its position, vertically or 
 horizontally, without fracturing or splitting the stones, bricks 
 or mortar joints in a greater or less degree ; always in propor- 
 tion to the depth of settlement. From the description already 
 given of the movements of the arches and piers with their 
 abutments, it will be no matter of surprise to find the masonry 
 of the walls generally, in contact with the tower, fractured, 
 and thrust and crushed in every direction, horizontally as well 
 as vertically. The entire subject affords an interesting and 
 instructive example of the effect produced by a weight of 
 600 tons acting upon four pointed arches for a space of 500 
 years, and serves to demonstrate conclusively the necessity of 
 neutralising thrusts effectively, whether such thrusts be created 
 by the exigencies of style or design. 
 
 " The state of the tower, piers, and arches, was, as may be 
 imagined, the subject of much talk in the village of Grosmont. 
 The oldest inhabitant recollected the structure to have been in 
 exactly the same state ever since he first saw it, and by some 
 extraordinarily subtle process of reasoning deduced this valu- 
 able conclusion, viz. that as the tower had never fallen in his 
 time, it was never going to fall. Almost every village in this 
 part of the world contains at least half-a-dozen of such old 
 inhabitants, whose inexorable logical deductions are supposed 
 to silence most effectually the objections of any unfortunate 
 professional man who happens to disagree with them. 
 
 "It having been decided in the autumn of the year 1869 to 
 restore the chancel of Crosmont Church, the opportunity of 
 seeking to determine if the failure of the tower substructure 
 was at all progressive was seized. With this object all the
 
 38 A TREATISE ON 
 
 fissures in the stonework were filled with cement, and the 
 extent of the fissures lineally determined by drawing lines 
 across the end of them in transverse directions. The structure 
 thus prepared was left, after the chancel had been rebuilt, up 
 to the end of November, 1872 (about two years), when a careful 
 inspection of the parts so prepared revealed the following 
 startling facts : first, that all the fissures which had been 
 sealed up with cement were open again; and, secondly, that 
 the transverse terminal lines of the fissures of 1870 were left 
 2 inches or 3 inches, in some cases as much as 6 inches, behind 
 by the extension of the fissures up to 1872. This discovery 
 compelled immediate attention to the dangerous condition of 
 the tower, and notwithstanding the renewed protests of the 
 oldest inhabitants, I did not hesitate to recommend the taking 
 of immediate steps to restore the four disabled tower piers and 
 arches, and in the event of the necessary funds not being 
 available to effect this restoration, at least to shore up three of 
 the arches, thus relieving the piers, and to needle the fourth 
 arch, leaving a clear space under it for its restoration should 
 the funds obtainable be sufficient to cover the expense. 
 
 " An idea suggested itself that the piers and arches might be 
 restored by taking out a damaged stone here and there, and 
 replacing the stones so removed with other sound stones, thus 
 effecting the restoration with comparative safety and by slow 
 degrees ; but on consideration this plan was abandoned, because 
 some parts of the piers should of necessity be entirely recased 
 or rebuilt, of course vertically. This would have the effect of 
 reducing the width between the piers to something about 
 9 inches less than the width of the arch at the springing, 
 which would be a reversal of the proper way of treating the 
 arches, viz., by having them, as originally constructed, 2 inches 
 narrower at the springing than the space between the piers 
 supporting them. It was therefore decided that the piers and 
 arches should be entirely removed and rebuilt, using in all 
 the old stone not damaged, and that this should be first tried 
 upon the arch and piers on the north side, the arch proposed 
 to be needled, this being in the most unsafe condition of the 
 four. 
 
 " As in constructing an effective system of supports to the 
 tower arches, a safe unyielding bottom was a primary con- 
 sideration, it was determined in this case to clear away the 
 entire space immediately under the tower, tower arches, and 
 for a space of 3 feet all round outside or beyond the tower 
 piers, right down to the solid rock, and to refill the space so 
 cleared with carefully made cement concrete well rammed. 
 The site to be thus operated upon was encumbered with old 
 seats, fittings, and wood floors, all of which having been cleared 
 away, the excavating commenced, planTced runs having been laid
 
 SHOEING AND UNDERPINNING. 39 
 
 down through the church and across the churchyard to pits or 
 graves dug to receive the human remains disinterred ; the soil 
 itself being spread over the surface of the churchyard at some 
 distance from the building. 
 
 " On removing the soil immediately under the floors it was 
 found that the bodies had been at some time interred with not 
 more than four inches of soil over the coffins, which accounted 
 for a hitherto ' unaccountable smell ' that had frequently 
 sickened some members of the congregation during their at- 
 tendance at Divine Service. 
 
 " Lower down, at about two feet under the floor level, five 
 distinct springs made their appearance, evidently the drainage 
 from the hill at the north side of the building. These springs 
 flooded the space already excavated, preventing further pro- 
 gress. A drain six feet deep was cut through the south 
 transept and discharged through the south transept wall into 
 the churchyard, which is lower at that side. This drain kept 
 the working from being submerged, and discharged during 
 the heavy rains 60 gallons of water per minute. 
 
 " The excavations were continued until solid rock was reached 
 at an average depth of 5 feet from the floor level. The entire 
 soil removed was of a very dark colour, light in weight, and 
 spongy in texture, containing human remains in various stages 
 of decay ; in fact the whole mass had apparently been used over 
 and over again for burials, the most recent having been ap- 
 parently thirty-one years ago. This appeared from the coffin 
 breastplate, which, with its gilded lettering, was as fresh as 
 the day it was put in, although there was no trace whatever of 
 the coffin, which was stated to have been of oak by a party who 
 recollected seeing it lowered into the grave. 
 
 " Some graves were hollowed out of the solid rock below the 
 tower foundations, others with steined half brick sides, covered 
 with stone slabs ; the latter were found to be filled with a 
 black fluid, emitting a stench so horrible as to be perceived 
 even in the most remote parts of the building. All human 
 remains disturbed were reverently cared for and interred in the 
 churchyard. The entire space dug out was now filled up with 
 cement concrete well rammed ; 135 tons of concrete having 
 been consumed in this operation. A drain was laid on the 
 rock bottom under the concrete to drain the springs which 
 continued to flow in from the north side of the building. A 
 finer concrete was spread upon the surface between the piers 
 under the tower arches, and upon this a bed of cement 18 
 inches wide was floated off to a level to take the centerings. 
 
 " The shorings to each arch are constructed in two separate 
 portions, the lower portion on ' tressel ' and the upper portion 
 on centre proper. This system has been adopted to facilitate 
 ' wedging up ' or ' striking ' the centres when and where
 
 40 A TREATISE ON 
 
 required. The exact outline of each arch was obtained by 
 'scribing' the soffit of the inner member of the arch to 
 which the centre was to fit, on a skeleton template of f-inch 
 boarding, sufficiently wide to include the whole curve of the- 
 arch, which template was securely fixed against the sides of the 
 arch during the scribing. This template was shaped by the 
 line so scribed, and the permanent framing worked to it ; thus 
 the centres when fixed fitted accurately all the irregularities of 
 the arches. The timber used in the shoring generally is from 
 10 inches to 12 inches square, some having been selected 
 14 inches wide to allow of getting out the curved backs 
 without reducing the working section of the timber below 
 10 inches by 10 inches. 
 
 " All the joints in the frames are tenoned (see Plate VI.), the 
 tenons being 2 inches thick in the centre of each piece, and from 
 2^ inches to 3 inches deep ; the joints are all shown on the 
 drawings precisely as they were executed. The framework was 
 fitted together on the nave floor first, and having been num- 
 bered at the joints was knocked to pieces to facilitate the removal 
 and re-erection under the tower. Each tressel was afterwards 
 built up in its proper place, and when the three tressels were 
 securely fixed in their respective archways, a temporary scaf- 
 folding was erected on them to make a platform for the putting 
 together and hoisting of the centres. The springing piece of 
 each arch was laid down on its side in that arch, and the centre 
 framed to it and secured together with |^-inch wrought-iron 
 dogs ; a tackle was then rigged up to the bell beams with a fall 
 to the floor, and each centre was thus hoisted to its proper 
 position under the various arches, and securely wedged up to 
 the soffit with oak wedges. 
 
 " In ordering the first lot of timber for this framing it was 
 assumed that timber in the log, with one side only sawn, would 
 answer every purpose required as well as timber sawn all 
 round ; but this proved to be a mistake, as it was found to be 
 an impossibility to square to the tenons, mortices, shoulders, 
 and bearings, without having at least three sides of every piece 
 sawn die square. There being no sawpits near the building, 
 this timber was squared with adzes and planes where required, 
 causing some loss of time ; but the next consignment of timber, 
 having three sides sawn square, much facilitated the work 
 of fitting together and makes much better work in every 
 way. 
 
 "Three arches having been shored up with centering, as 
 described, the fourth arch was treated as follows : a hole about 
 18 inches square was knocked through the tower wall over the 
 apex of the arch, and about 2 feet above it, to allow sufficient 
 head room for the introduction of a hammered stone discharging 
 arch over the wrought stone arch. Two more holes were
 
 SHORING AND UNDERPINNING. 41 
 
 knocked through the wall of the same size, about 2 feet lower 
 down on either side,* about half-way between the centre of the 
 arch and the transept flank walls. Three holes were thus made 
 to take needles at distances of about 4^ feet apart. 
 
 " Needles 12 inches by 12 inches were inserted through these 
 holes and supported by uprights inclining inwards at the top, 
 and stiffened at the height of every 5 feet by means of straining 
 pieces secured with dog irons. The walling over the needles 
 was pinned up, and wedged in every case with flat stones 
 bedded in cement ; and when the cement had set, a temporary 
 centre was fixed under the arch, the key removed, and all the 
 arch stones safely taken down one by one ; one-half the piers 
 on either side were also removed, and the entire space occupied 
 by the arch and piers cleared away to allow of the erection of 
 the new work." f 
 
 The three remaining arches were afterwards similarly 
 restored, and the tower and spire now stand upon a base which 
 will remain immovable for all future time. 
 
 * The arrangement in the drawing on PI. VII., which shows lintels inserted 
 over the needles, and the needles themselves all on the same level, is con- 
 sidered by Mr. Seddon to be better than that actually executed and here 
 described. The framing also is shown as fitted to a restored arch, it having 
 been found impracticable to delineate the actual distortion of the piers and 
 arches. 
 
 t The following details of the weight thus carried, with the calculations as 
 to the manner in which it was distributed, and the breaking weights of the 
 several portions of the timber framings employed, are appended by Mr. 
 Seddon at the end of his paper : 
 
 By actual experiment, ashlar in spire is found to weigh 1 527 cwt. per 
 
 cub. ft. 
 
 rubble masonry in tower weighs 1'33 cwt. per 
 
 cub. ft. 
 
 There are in spire 2,534 cub. ft., weight (at 1 527 cwt. per cub. ft.) = 3869 '418 
 cwt. = 193 -47 tons. 
 
 There are in tower 9-016 cub. ft., weight (at 1'33 cwt. per cub. ft.)= 
 11991-28 cwt. = 599-564 tons. 
 
 There are six bells, framing and floor, weighing about 5 tons. 
 
 Total weight at arch springings = 798-034 tons. 
 
 There is no discharging arch over tower arches. Actual working sectional 
 area of each arch, 3 45 ft. super. Many stones fractured. 
 
 Sectional area of each pier, wrought facing, 8 '34 ft. super.; rubble core, 
 9 '66 ft. super. : total area, 18 ft. super. 
 
 Weight on each pier, 199-5 tons = 11 '08 tons to theft, super. On failure 
 of the rubble coring, the ashlar facing doing duty for the whole pier carried 
 23 92 tons, and was crushed. 
 
 Actual total weight per ft. square on foundation, 11 '71 tons. 
 
 Breaking weight of the three needles, 216 tons ; weight of one sule of tower 
 at level of needles, 170 tons ; estimated actual weight of the needling, 70 to 
 75 tons. (The corbelling to octagon, with arching over, throws from 40 to 50 
 tons on each quoin N.W. and N.E. These quoins rest on the parts of the 
 piers allowed to stand.) The load on the needling being only temporary, a 
 co-efBcient of safety of only 3 was adopted. 
 
 Actual breaking weight of each warped-up centre, 1050 tons ; weight on each, 
 199'5 tons; safe working permanent load, 210 tons; co-efficient of safety, 5.
 
 42 A TREATISE ON 
 
 The most important lesson to be learnt from this example is 
 the same as that taught us by the memorable fall of the tower 
 and spire of Chichester in February, 1861, viz., that when a 
 heavy load is to be placed upon piers and arches, it is madness 
 to build the piers in rubble masonry with ashlar work only as 
 a casing. The piers which are to carry such a load should be 
 built in ashlar or dressed stone-work throughout their entire 
 thickness, as was done by Mr. Scott (afterwards Sir Gilbert) in 
 the rebuilding of the piers at Chichester. If such a method is 
 found to be impracticable on account of its cost, the core of 
 rubble masonry must at all events be built in cement, so that 
 there can be no possibility of its settling down and leaving the 
 weight to be carried by the casing only. 
 
 The method of restoration adopted at Grosmont may be 
 briefly recapitulated as follows : All the four arches and piers 
 being unsafe it was determined to restore them, i. e. replace 
 them in new work ; there being only funds enough to admit of 
 the restoration of one arch, it was decided to restore that arch 
 which, with its piers, was found to be in the most dangerous 
 condition, consequently the wall above this arch (the north 
 arch) was needled, and the other three arches were temporarily 
 centred to prevent their falling before they could be attended 
 to in their turn. The arch under the needles was then taken 
 down and half the piers on either side, to be replaced in new 
 work set in cement. Now it must be remembered that although 
 the north wall of the tower was carried on the needles and the 
 east and west arches had centres under them which would only 
 break under a load of 1050 tons, yet the north-east and north- 
 west quoins of the tower (which were estimated by Mr. Seddon 
 to weigh 50 tons each) had nothing to carry them but the 
 portions of the piers which were allowed to remain standing ; 
 these must in this case have been strong enough to carry 
 this weight ; but the reader's attention is drawn to this point, 
 because in many instances of similar restoration, the core of 
 rubble work may be so decayed as to be utterly incapable of 
 bearing the quoins, even for so short a time as would be neces- 
 sary ; in such a case the quoins themselves, and all the four 
 walls round the tower, must be shored with needles and posts, 
 so as to take as much of the superincumbent weight off the 
 piers as possible : it is a mistake to suppose that centering 
 under the arches entirely relieves the piers of their load. 
 
 The reader will have noticed in Mr. Seddon's paper that the 
 idea suggested itself of restoring the crushed piers and arches 
 of the tower at Grosmont by taking out a damaged stone here 
 and there, and replacing the stones so removed with other 
 sound stones ; this method, though found to be impracticable 
 in this case because of the piers being so much out of the 
 perpendicular, has still been carried out with complete success
 
 SHORING AND UNDERPINNING. 43 
 
 in many other cases. But when such a method is adopted, the 
 greatest care must be taken that the piers to be recased are 
 first almost entirely relieved of their load by shores and centres, 
 and that only small portions are renewed at a time. 
 
 These old Gothic buildings require the most gentle handling ; 
 for if they have once been damaged by fire or storm, or if at 
 any previous time they have sunk down or become distorted, it 
 takes very little to upset the state of equilibrium into which 
 they have settled, though they may have remained in that 
 state for hundreds of years. The fall of the tower at Chichester, 
 though hastened by the storm of wind which raged during the 
 night before the catastrophe, was no doubt originally brought 
 about by the disturbance caused to the equilibrium of the piers 
 by the removal of the organ screen, which spanned the nave at 
 their feet, and also by the manner in which it was attempted 
 to recase the piers after their dangerous condition had been 
 discovered. So, whenever it is necessary to make any alteration 
 or to underpin a building, every possible precaution must be 
 taken that the equilibrium is not upset or the building shaken. 
 In a speech delivered at the Institute of British Architects, and 
 recorded in their ' Transactions ' at the time of the Chichester 
 disaster, Sir Gilbert Scott thus describes the work that was 
 carried out under his supervision at the Church of St. Mary at 
 Stafford, which is an example of the stone-by-stone method of 
 restoration: 
 
 " The first operation," he says, " was to bind the tower 
 round (internally) with very strong iron bars, with right and 
 left screws, which were screwed up as tight as possible. This 
 was done at two different levels. We then dug round the 
 base of the tower as low, at least, as the bottom of the founda- 
 tions, removed the remains from all surrounding graves (which 
 had, as is too often the case, done very great mischief, being 
 much deeper than the foundations), and filled up the whole space 
 with a solid mass of concrete. Having shored the arches and 
 the piers, so as to carry as much as possible of the superincum- 
 bent weight, we began gradually to remove the loose stone- 
 work and to put in new (or rather additional) foundations, 
 spreading out upon the new concrete. This operation requires 
 a system of movable shoring quite distinct from the more 
 permanent shoring already mentioned. This secondary shoring 
 is continually being moved upwards as the work proceeds, no 
 part of the old work being taken out at one time beyond what 
 is necessary to give room for the insertion of the new portions 
 actually in hand at the time. In each course, or at short inter- 
 vals in the height, we inserted chain bars (which are best of 
 copper) in short lengths, but so constructed as eventually to 
 form continuous ties all round the pier. In effecting these 
 operations, I was brought to the conclusion that it is impossible
 
 44 A TREATISE ON 
 
 to exaggerate the danger and the difficulty that exists in pro- 
 viding shoring of sufficient strength ; for in this,, as in every 
 work of the kind in which I have been engaged, I found that 
 all the shoring that I could by any possibility get in was only 
 barely sufficient for the purpose. I have seen enormous timbers 
 bend under the pressure to which they have been subjected, and 
 I wish to offer my most decided opinion that in most cases it is 
 absolutely necessary, before a single stone is removed, to insert 
 all the shorings which can be brought to bear within the space 
 to be operated upon. I would also advise that in no case should 
 the shores be half timbers, or timbers of an oblong section, but 
 that they should be of square or round timbers, so as to have no 
 tendency to bend in one direction more than in another (in 
 large works, indeed, the shores must be larger than single 
 timbers). In one case (a minor work) which I had in hand, I had 
 expressly provided for the use of whole timbers in the specifica- 
 tions ; but the clerk of the works had permitted half-timbers to 
 be used, and the consequence was that the shoring gave way 
 very perceptibly, much to the detriment of the work. Another 
 precaution I would recommend is the use of the hardest stones 
 which can be procured, for if this be neglected, the new work 
 is almost sure, when the shoring is removed, and the weight 
 brought to bear upon it, to split ; and it is needless to say that 
 cracks in such supplemented masonry are far more dangerous 
 than in a new structure, for by throwing the weight upon the 
 old core (if any remains), or upon piers not yet repaired, or upon 
 other old work, such partial failure of the new stonework may 
 lead to the most serious consequences. Under no circumstances, 
 therefore, should anything approaching a soft stone be made use 
 of, whatever may be the materials of the old pier. The next 
 thing I would urge is the avoiding of ordinary lime mortar, and 
 the use of cement. Besides setting the new work and pinning it 
 in cement, it has been my practice to run the core behind 
 with liquid .cement, first pouring in water and then the cement 
 grout, which, when thus used, I have found in some cases to 
 penetrate the interstices to a depth of 9 to 10 feet below the 
 level at which it was poured in, as if it were so much quick- 
 silver. While engaged upon these works on one occasion a loud 
 report was heard by the workmen, like the report of a gun, and 
 it was found that one of the pillars of the chancel (quite uncon- 
 nected with the tower) had split almost from bottom to top, 
 owing to some indirect pressure brought upon it by the opera- 
 tions going on at the tower, which shows that the shoring 
 should not be limited to the tower itself, but should in some 
 degree be extended to adjoining parts. The shoring should 
 have in all cases a special foundation provided for it. The floor 
 of the church is wholly insufficient for the purpose, and it would 
 be a fatal error to trust to it."
 
 PLATE, VIII. 
 
 J.AkermaTi Photo-lith London.W.C.
 
 SHORING AND UNDERPINNING. 45 
 
 The reparation of the tower of Hereford Cathedral by the 
 late Mr. Cottingham, though on a much larger scale, was in all 
 other respects nearly identical with Sir Gilbert Scott's work at 
 Stafford, which has just been described. In all these examples, 
 a good foundation of concrete for the shores was of paramount 
 importance. M. Flachat, before he erected the mammoth shoring 
 which held up the tower and lantern over the crossing at Bayeux 
 Cathedral, sank around the feet of the four piers to a hard 
 stratum no less than twenty wrought-iron tubes of 4 feet 
 diameter internally, which he filled up with concrete ; and upon 
 these tubes, and between the foundations of the piers, he laid a 
 bed of concrete 9 feet thick, the top of the tubes entering 3 feet 
 into this concrete. The weight of the shores and the tower 
 which they had to carry was of course very considerable, and 
 fully justified the extreme caution taken with these foundations. 
 
 A brief description of this work is thus given by Mr. Burnell 
 in a paper published in the ' Transactions of the Eoyal Institute 
 of British Architects ' : " Upon the concrete bed," described 
 above, " M. Flachat erected a double set of frames of whole 
 timbers on either side of the centres originally placed to support 
 the arch (before M. Flachat was called in), for the purpose 
 of forming a seating for a set of needles carried upon a series of 
 screw-jacks, and made to support the masonry of the square 
 part of the tower, a little above the vaulting of the nave and 
 transept. The tower was carefully hooped with iron bars keyed 
 up whilst they were still hot, so that their shrinkage actually 
 closed the masonry which had previously been fissured over the 
 openings ; and before altering the centres to the form M. Flachat 
 thought requisite, he also surrounded the springings of the 
 arches of the nave with a strong wrought-iron cradle, intended 
 to resist the lateral thrust. The centres were then strengthened 
 and modified so as to allow the easy underpinning of the piers ; 
 and the lateral arches of the nave, choir, and transepts, which 
 had participated in the movements of the piers of the tower, 
 were carefully shored up. Every precaution was taken to 
 protect the original mouldings of the vaulting, and the sculp- 
 ture of the capitals, columns, and bases, by enclosing them with 
 rubble masonry, against which the shores were made to act 
 directly." (It should be mentioned that the four quoins of the 
 tower were needled by a system of needle shoring, totally in- 
 dependent of that already described on each side of the centres 
 of the great arches. The needles carrying the quoins were each 
 made of three wrought-iron girders bolted together with four 
 timber flitches, forming one exceedingly strong beam ; four of 
 these needles lying across each other, and forming a square on 
 plan, were inserted just under the neckings of the caps, at the 
 top of each of the four piers, and were carried by sixteen massive 
 posts, each made of nine whole timbers strongly bolted together,
 
 46 A TREATISE ON 
 
 in the same manner in which the masts of a ship are constructed. 
 These posts were each 16 metres high (52-59 feet), and con- 
 ducted the weight of the quoins straight down to the bed of 
 concrete on the ground.) " It is to be observed that the needling 
 was totally independent of the centres of the great arches, and 
 was designed solely to support the weight of the tower and 
 octagon above the line of the vaulting; the arches and the 
 spandril fillings were all that bore directly upon the centres 
 themselves." 
 
 When all this shoring was erected (and it completely filled 
 up the crossing, being braced across and across the space), the 
 piers were entirely removed from under the tower, and rebuilt 
 from their foundations, and the arches were restored by the 
 stone-by-stone method. 
 
 The cost of this work was 32,220Z. M. Viollet-le-Duc, whose 
 opinion was consulted before it was decided how the tower 
 should be treated, gave it as his opinion that the simplest and 
 cheapest plan was to pull it down altogether and rebuild it 
 from its foundation, and he estimated the cost of this at a sum 
 considerably smaller than 32,220Z. But even if M. Viollet-le-Duc 
 was right, there will always be a satisfaction to archaeologists, at 
 least, that the original tower was preserved intact. On the 
 top of the Gothic lantern there was an Italian Eenaissance 
 dome, which was removed before the tower was underpinned. 
 
 The success of this operation is, however, considerably marred 
 when it is compared with the stone-by-stone underpinning of 
 the tower of Hereford Cathedral by Mr. Cottingham, where 
 although the weight underpinned was double that at Bayeux, 
 the money expended was less than one-fourth. The weight of 
 the spire at Chichester was also nearly double the weight of 
 the tower at Bayeux, and as it would have been necessary to 
 employ the same method to restore it satisfactorily as was used 
 at Bayeux, on account of the rottenness of the piers, it is 
 perhaps as well from an economical point of view that it fell 
 down, especially as not a life was lost nor a limb broken. 
 
 The cost of rebuilding it was in round numbers 50,OOOZ., and 
 had it been underpinned as the Bayeux tower, the operation 
 would probably have cost much more than this. 
 
 We will now go on to consider the suppositional cases of 
 underpinning, depicted on Plates VIII. and IX., which are 
 copied from M. Viollet-le-Duc's dictionary under the word 
 " IHai." The following is a synopsis of the treatment of these 
 cases described in that work. 
 
 Taking the first case on Plate VIII., the cylindrical column A, 
 which carries vaulting ribs in all directions, and one or two 
 stages of similar columns above, has become crushed under the 
 load, as shown in the sketch. In order to enable the damaged 
 stones to be removed we nrust construct a square frame of oak,
 
 PLATE, IX. 
 
 Elevaii 
 
 Plan. 
 
 C.Hcuden. Stock Del. 

 
 SHORING AND UNDERPINNING. 47 
 
 as indicated in the sketch, B in perspective, and in B' in plan, 
 with sides tenoned into gaping mortices, into which wedges are 
 driven at C, which with the bolts b insure the frames being 
 fitted tightly against the face of the cylinder. This frame is 
 fitted (as at C, in the sketch D) under the necking of the 
 capital, and is carried by eight stout posts G, inclined suffi- 
 ciently to allow the new stones which replace the old at KH to 
 pass in freely. Should there be any sound stones below the 
 necking, four wrought-iron straps must be screwed, as shown in 
 the sketch F, to the sides of the frame, and their feet L inserted 
 in the joint, to catch the under side of the last sound stone ; the 
 rest of the column can then be removed and replaced in new 
 work. 
 
 If the whole of this lower column is crushed, together with 
 the springing stones of the vault, the vaulting ribs must be 
 centred, and the column above must be treated in the way we 
 have just described for the lower column, the eight posts passing 
 through the vaulting panels to the ground below. 
 
 The second case depicted on Plate IX. is a neat application of 
 the principle of needle shoring. A pier E which carries two 
 main arches A', two diagonal arches B', and one transverse 
 arch C', as well as the weight of the upper vault, has become 
 crushed under the load. In this case, where it will be necessary 
 to use so many timbers in so small a space, we must take care 
 to arrange them so that they will not interfere with the building 
 of the new work. " To shore is nothing, but to shore in such a 
 way that one can build between the shores is often a difficult 
 problem to solve." The transverse and diagonal arches having 
 been centred, the two main arches should be supported as 
 shown at A in the elevation, and the springing stones of the 
 arches from I to K, which have shared in the ruin of the pier, 
 can then be taken out and notches cut to receive the needles at 
 L L. The needles, in order to occupy as small a space as 
 possible, are each made of four strong pieces of wrought iron, 
 bound together with hoops as shown at M ; they are made to 
 rest upon strong pieces of oak at O in the elevation and 0' on 
 the plan, and are carried by the four stout posts N and N'. It 
 will also be necessary to support the wall above the needles 
 with raking shores at H and H'. 
 
 When the old work has been removed and the new work 
 finished, the posts and needles should be taken down first, then 
 the centres under the arches, and last of all the raking shores 
 at H and H'.
 
 48 A TREATISE ON 
 
 CHAPTER VII. 
 
 ON THE MECHANICS OF RAKING SHORES.* 
 
 WE will suppose C B (Plate X.) to represent the section of a wall 
 that requires to be supported by the raking shore A B, resting 
 on the ground at A ; AC being the ground line. Let there be 
 a horizontal force T near the top of the wall at d, tending to 
 overturn it about its bottom edge C ; the moment of this force, 
 which measures its tendency to overturn the wall is 
 
 T x Cd. 
 
 This is resisted by the weight of the wall (W) acting vertically 
 at its centre, and having a moment about C of 
 
 W X Ce, 
 
 where C e is generally half the thickness (t) of the wall. When 
 these forces just balance, the wall will be about to fall over, and 
 the two moments will be equal ; therefore 
 
 TxCd = WxCe. 
 
 Now, in order to restore the wall to its original condition 
 before the force T acted upon it, we must find some means of 
 completely balancing this force, and this can be done by placing 
 the shore AB against the wall at B, where it is firmly fixed 
 against a plank or walling piece by means of a needle driven 
 through both the plank and the wall ; then by wedging up the 
 base A, a horizontal pressure (Q) is produced against the wall, 
 such that the moment of Q about C balances that of T, or 
 
 = T X Cd 
 
 = W X C e 
 
 ' " 2BC ' 
 
 In this formula, B C and t should be expressed in feet, W and 
 Q in cwts. If the shore presses against B with a horizontal 
 force Q, there must also be a reaction of the wall against the 
 shore equal and opposite to Q, so that Q represents a horizontal 
 pressure against the head of the shore. 
 
 In order that the raking shore may have its full effect in 
 counteracting the outward thrust or reaction Q, it is essential 
 that it should be prevented from sliding upwards by having a 
 
 * Copied from an article in the Building News, Sept. 14, 1877.
 
 SHORING AND UNDERPINNING. 49 
 
 sufficient weight of wall above B, so that when the pressure Q 
 comes upon it, the head of the needle may be kept immovable 
 by means of the superincumbent load. If, therefore, the top of 
 the shore is put very high up against the wall, it will be of 
 little service in preventing it from being overturned. Let P be 
 the vertical pressure necessary to resist a horizontal thrust out- 
 wards, equal to Q at B, and w the weight of the shore itself, 
 acting at its centre g. Then the sum of the moments of P and 
 w, about A, the base of the shore, must balance the moment of 
 Q about that point ; therefore, we have 
 
 Bg being a horizontal line meeting a vertical from A at g. 
 This equation may be put into the form 
 
 Q sin. 9 = ( P + 5 ) cos. 0. 
 
 being the angle BAG which the shore makes with the hori- 
 zontal ; and from this we obtain 
 
 P = Qtan.0-| ---- (II.) 
 
 So that when Q and w are known, and also the angle of inclina- 
 tion of the shore, we can find from this equation what vertical 
 pressure (P) must be brought to bear on the head of the shore, in 
 order to keep it in its place when the force Q tends to thrust it 
 out. If the value of P is known beforehand, we can also find 
 what amount of horizontal force (Q) it will be able to counter- 
 act; for 
 
 - 2tan.0 ' 
 
 The horizontal and vertical forces at B being thus determined, 
 we can find the compression (F) down the shore by resolving P 
 and Q, in the direction of A B, and adding their resolved parts 
 together ; therefore, we have 
 
 F = P sin. -f Q cos. 9 . . . . (IV.) 
 
 In order to find whether the shore is strong enough to resist 
 this compression, we must use the formula for a long pillar, 
 namely 
 
 Where a = 15-5 for fir, d is the diameter or width in inches, 
 and I the length in feet; L being the safe load in cwt. that 
 may be put on the pillar. As, however, the depth of a shore is
 
 50 A TREATISE ON 
 
 usually double its width, we shall get twice the resistance, as 
 obtained by the above formula, or F should not exceed 
 
 Safe load B 81 X . . . . (V.) 
 
 I 
 
 There will also be produced a cross-strain S, acting at right 
 angles to the shore, and tending to bend it inwards, which is 
 equal to the resolved parts of P, Q, and to namely, 
 
 P cos. 0, Q sin. 0, w cos. 0. 
 
 And since these strains are uniformly distributed over the entire 
 length of A B, the total amount of cross-strain at the centre is 
 equal to half their sum, or 
 
 S = { Q sin. + (P + w) cos. 6 } . 
 If we substitute for P its value as found from (II.), we have 
 
 S = Qsin.0 + cos.0 .... (VI.) 
 
 To find the deflection (D) in the middle which the cross-strain 
 S will produce on a beam of fir, we use the formula 
 
 The dimensions, D, 6, and d, being in inches, and Z in feet ; S is 
 to be expressed in cwt. If the value of D thus obtained is an 
 appreciable quantity, it will be advisable to counteract the cross- 
 strain by a strut g Ji, so as to prevent the resisting power of the 
 shore from being impaired ; and the force S will represent the 
 compression down this strut. If we wish to find what ratio S 
 bears to the breaking-weight of the shore, we can use the 
 formula 
 
 Breaking-weight = 3-2 x ^^ .... (VIII.) 
 
 I 
 
 b and d being in inches, and Z in feet ; the breaking weight is 
 found in cwt. The strain S must not exceed one-sixth of the 
 breaking weight thus obtained. 
 
 We can now determine the magnitude and direction of the 
 resultant (E) of all the forces, its point of action being at the 
 base A of the shore. Suppose this resultant to make the angle < 
 with the horizontal A C, then by the rules of mechanics we have 
 
 E . cos. < = Q 
 
 E . sin. <f) = P -f- w 
 
 from (II.) = Q.tan.0 + ^. 
 
 a 
 
 But, E = EVsin. 2 0-|-cos. 2 
 , .-. E=
 
 SHOEING AND UNDERPINNING. 51 
 
 from which we obtain the magnitude of the resultant K. To 
 find the direction of R or the value of the angle <, we have 
 
 E . sin. <f> P -}- w 
 
 This last formula shows us that the greater we make the 
 horizontal force Q, the more nearly will the angles $ and 
 approach to equality, or the direction of E get nearer and 
 
 nearer to that of the shore, for the quantity ^-~- diminishes with 
 
 tty 
 
 the increase of Q. The minimum value that Q can have is when 
 P is nothing, or the head of the shore merely rests against the 
 wall, and is not pressed upon by any vertical force, in which 
 case we find from (III.) that the value of Q is 
 
 Q = 2tan.0' 
 
 and substituting this value for Q in (X.) we obtain 
 tan. = 2 tan. 0, 
 
 In this case, therefore, the direction of the resultant becomes 
 that of the line A E. We see, then, that the resultant force E 
 may have any direction between A E and A B, according to the 
 amount of the pressure Q ; but it will generally lie nearer to 
 A B than to A E, and consequently it is advisable to have the 
 abutment at A very nearly at right angles to the shore A B, in 
 order that any horizontal thrust at A may be counteracted by 
 the resistance of the earth. 
 
 Example. We will now show the practical application of 
 these ten formulae, by taking the case of a brick-and-a-half wall, 
 40 feet high and 10 feet frontage, supported by a raking shore 
 of fir 12 inches by 6 inches, the top of which is 30 feet above the 
 base of the wall, and its spread at the foot 6 feet. The angle 0, or 
 BAG, will be 78 41', tan. = 5, cos. & = 19623, sin. 6 = 98056, 
 and the weight w of the shore is 4*5 cwt. Taking the wall at 
 1 cwt. per cubic foot, its weight W will be 467 cwt. ; its thick- 
 ness t being of a foot. 
 
 We first find the maximum horizontal thrust Q from (I.) 
 _ W.* 467 x 
 
 2BC O 
 
 The vertical pressure P, which Q. produces, is obtained from 
 
 = 9 X 5 2 = 43 cwt., nearly. 
 
 E 2
 
 52 A TBEATISE ON 
 
 This is the least value of the pressure upon the top of the shore 
 that will counteract the outward thrust Q ; but, as in this case, 
 the actual weight of wall above B is 117 cwt., or nearly three 
 times as much as the above value of P, we see that there is but 
 little danger of the shore being pushed out by Q, provided it is 
 tightly wedged up at A and B, as the shore cannot be turned 
 about the base A without its head being lifted up, which would 
 cause the needle to rise, and also the wall above it. For, if we 
 put P' = 117, we find from (III.) the value of Q' necessary to 
 make the shore lift this load, 
 
 2P + w 238-5 __ 
 
 Q - ni = -10- 
 
 which is more than 2^ times the maximum value of Q as given 
 above. 
 
 The horizontal and vertical forces (P, Q) being known, we 
 can find the compression F which they produce on the shore in 
 the direction of its length from (IV.), 
 
 F = P . sin. x Q . cos. 
 = 43 x -98056 X 9 x '19623 
 = 44 cwt. 
 
 From (V.) we can ascertain what is the safe load that such a 
 pillar will sustain, the length being 30 6 feet, and the diameter 
 6 inches ; 
 
 Safe load = 31 x * 
 
 which agrees very nearly with the value of F obtained above. 
 
 The cross-strain S produced at the middle of the shore, and 
 acting at right angles to its depth, is found from (VI.) 
 
 S = Q . sin. + 2 cos. 
 
 = 9 x -98056 + 1-12 X -19623 
 = 9 cwt 
 
 From (VII.) we can find the deflection which this strain of 
 9 cwt. will cause at the middle of the beam, 
 
 S I 3 
 D = ;r= X 
 
 27 ~ b . d 3 
 9 (30-ey 
 ~ 27 6 x 12 3
 
 PLATE X. 
 
 J AJwrmaji Photo-KtKLondonW C
 
 SHORING AND UNDERPINNING. 53 
 
 In this case, as there is a deflection of nearly 1 inch at the 
 middle of the shore, it will be advisable to introduce a strut g h, 
 otherwise its resisting power as a pillar will be impaired. The 
 compression down the strut will be the above value of S, or 
 9 cwt. 
 
 The breaking- weight at the middle of the shore may be found 
 from (VIII.) 
 
 6 d 2 
 Breaking- weight = 3'2 x -7- 
 
 I 
 
 6 y 144 
 
 which is ten times the strain S, which we have just obtained. 
 
 The pressure which the resultant force R exerts on the base 
 A can be calculated from (IX.) 
 
 R = 
 
 = <v/9 2 + (45 + 2-25)' 
 = 48 cwt. 
 
 The direction in which this force R acts at A, or the angle 0, 
 which it makes with A 0, is found from (X.) 
 
 w 
 tan. = tan. 6 -j- ^ 
 
 2. \cf, 
 
 = 5 + ^ = 5.25. 
 
 By referring to a table of natural tangents, we find that 5 25 
 is the tangent of 79 13', so that the direction of R makes an 
 angle of only half a degree with the shore itself, when Q presses 
 with its maximum force against the head of the shore. 
 
 When P is nothing, the direction of the resultant is A E, and 
 tan. = 2 tan. 6 = 10, in which case the angle E A =84 18' ; 
 the value of the angle 0, therefore, will in any case lie between 
 79 and 84, according to the amount of the reaction (Q) at B. 
 
 The above example, it should be borne in mind, is taken for 
 the case of one shore only in a system of raking shores ; but 
 when two or more shores are erected against a wall in the same 
 perpendicular plane, each shore must be considered as resisting 
 the outward thrust of its own portion of the wall only, and a 
 separate value of Q must be found for each of them. 
 
 It is perhaps needless to say that in practice it would not be 
 necessary to make use of all the formulae which have been 
 proved and demonstrated in this chapter, but for the sake of 
 those who are fond of mathematical investigation the whole
 
 54 SHOEING AND UNDERPINNING. 
 
 science has been laid down in its completeness. An example 
 which shows the application of the more useful of these formulas 
 has already been quoted at the end of the chapter on raking 
 shores, and it will be found that the rules there given will be 
 all that are really necessary in actual practice. 
 
 In conclusion, I must apologize to my readers for the some- 
 what condensed form in which the proofs of the several formulas 
 are worked out; but as I had previously stated that this 
 chapter is only intended for those who are well acquainted 
 with the science of Trigonometry and Statics, I concluded that 
 any more elaborate explanation of the way of arriving at the 
 different steps in the proofs would be unnecessary. 
 
 THE END. 
 
 LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, STAMFORD STREET 
 AND CHARING CROSS.