OF THE CITY ENGINEER, QUEBEC, ON THE PROPOSED DRY DOCK IN THE MOUTH OF THE RIVEE ST. CHAKLES. \0KA/f^, JAN S 1915 ^ j .. f^* ^^^^'■'j'^ 3^_ lES lE^ C^ 3^. "OP OF THE CITY ENGINEER, QUEBEC, ON THE PROPOSED DRY DOCK IN THE MOIDTH OF THE RIVER ST. CHARLES. City Hall, Quebec, April 2l8t, 1876. The Mayor and City Council of the Corporation qf Quebec. Gbntleuin,— As joint engineer, on part ol the City, of the proposed doclis and liarbocr improvements in the mouth of the Hirer 8t. Charles, I beg to submit tbe folloviiag infor- mation which Mr. Steckel as resident engi- neer has also reported to O. F. Baillairge, Esq., Assistant Chief Engineer of the Depart- ment of Public Works at Ottawa. Nearly 400 soundings have already been taken at distances apart varying from 250 to 500 feet. Tbe borings, some 20 in number t^) date, fTAach to depths varying from 22 to 7i feet below mean low water mark. Clay and hard pan have been reached at a moderate depth inside the ballast wharf, and clay at a few feet below low water level outside of La- rocho's wharf, one of the proposed Eitcs for the graving dock, as already reported by Mr. Morris. There can therefore, in my opinion, be no further doubt as to the possibility of building the dock at this point, and in the ordinary way, with coffer-dam and from a solid bottom. Tbe borings proceed simultaneously at two different points two Hheils or bouses having been erected for tbe purpose and each of them supplied with a double set of boring tools, which are now worked day and night, as the operation of boring is long and tedious. Much trouble and delay was at first expe- rienced in removing the material from inside the boring pipes, the inside diameter of which is but 2^ inches, until Mr. Steckel and my- self devised a mode of so doing by using an inner tube and pump by which water is forced down the annular space between the two pipes and brings up the sand, clay and peb- bles with it through the inner pipe. Boring artesian or other wells on terra-firmcL is as nothing to the trouble experiened on a y rises and falls to levels con- 6 ot the moon ; .fj the whole ice apparently im- sheet of ice which cc " with every succeeding ? stautly varying with eac to say nothing of the fac , (ioe, however compact anc movable to the eye, is as constHntly shifting its position by such a number of inches as to necessitate the displacement of the boring house and apparatus at each flow and ebb of the tide to bring the ram to its required posi- tion over the boring tube. The accompanying photographs will afford some idea of the structures, tools and pump- — 2 — ing apparatus just alladed to. At the inner •ogle of the ballast wharf Ib another ebed or house answering as » shelter to the man whose duty it is to cote the height of tide at ict^rvals of ten (10) minutes during the day and who is relieved by another party who continues the observaticns during the night. The necessity for these tide gaugings has already been made manifest from the fact that whereas the greatest range of high and low water level wap supposed by many to be but eighteen to twenty feet, it has already been found to extend to t' 'inty.five feet and may possibly go beyond that figure with the bieh waters of the following month. But apart from this alU'mportant information as relating intimately to the proposed levels of the sill and upper surface of the dock, it must be apparent that it is only by comparison of the precise moment >. time at which tbe gauge was read and any depth of boring reached below the floating ice, that such bor- ing and all other borings and soundings can be reduced to one uniform datum level. Mr. Stfcckel's report to head quarters, of course, goes no further for the present than a mere recital of what has been done and how done, with the cost of the sr. ey to date which, I believe, ia some $3,500 00, though much of the apparatus may be again utilized by the Government in similar operations elsewhere ; but it behoves me, I think, at this juncture to set aside all doubts and fears as to the possibility of building the proposed graving dock at the mouth of the St. Charles and at the very point where I have located it on the plan which I lately had the honor of submitting to the Council and of which cop- ies have since been forwarded with the Mayor's compliments to the Governor Gener- al and to the Honorable Mr. Mackenzie at Ottawa, as also to the Quebec Board of Har- bor Commissioners. It is a grievouB error to suppose, as some do, that such a structure as a grc 'ng dock most necessarily be built from and re^l npon a foundation of rock or even clay. We have such massive blocks as the Marine Hospital, here, with nothing but a sub-soil of sand for its support ; tbe Parish Church of l^otre Dame in Montreal with it^ towers 215 feet high rests upon the sand ridge which di- vides Craig street from the St Lawrence. There is hardly a dock in England built on anything more solid than clay and sand. 1 have seen more than thirty feet depth of sand and pebbles below the stateliest and heaviest piles of New York City. Benaud's new block and our Custom Hoase are not oa rock. The very ballast wharf itself rests on a shelving bank of sand and yet it holds its own against wind, weather, and wavee^ against ice and current, and is likely to do so for all time. It is plain that if an attempt were made to erect a structure of any kind on a mere bank of sand which stood above the level of the adjoining soil and not confined in any way to prevent it from spreading, such structure must sink and settle down, as a vessel on a wave will do in mid ocean till it reach's the level of the surrounding water; but confine that sand between four impermeable walls, and, as a wave of water within the precincts ofacanailock is incompressible and will suppoit the mightiest vessel afloat with its burden of 10,000 tons or more, so will the sand, and a fortiori, remain motionless and incompressible beneath the heaviest structure ever dreamed of. This truth is of too elementary a nature to require proof or further explanation, and I must be pardoned if I have thought it ne- cessary to allude to it in any way, except that it behoves me to make the matter clear to the general public as well as to tbeir more enlightened representatives in the City Council. What I am about to propose will now be fully and easily undorstcod, nor is it any- thing new (thousands of struotures the world over are founded in this way) excepting, may be, in point of size, and this t sry element of — 3 — size ia what will make assurance doubly sure; for, as a matter of coarse, the broader the foundation, the more stable the structure. The depth aud nature of the soil ever the proposed site of dock precludes the possibili- ty of anything liko an ordinary coffer-dam, and even if this could be secured the cost ot going ta such a depth would render the an- dertaking fir beyond the means at oar dispo- sal. This is not like the pier of a bridge where an immense weight of masonry rests apOQ a comparatively small surface, and iLUBt therefore be sunk to a more solid bot- tom to prevent settlement, as at New York, to 86 feet, and at St. Louis to 110 iecu below the river. On the coatrary, the difficulty is rather to make the dock heavy tuouE;h to prevent the water from floating it when once it reaches bottom. I avoid the necessity of a dam by building r caisson wherein to construct the dock and sink it gradually as it progresses to such a depth only, previously dredged out and levelled, as may be necessary ta secure the desired depth of 7 feet at low water over the sill or bottom of the dock ; but pre- viously to doing this 1 dredge to a depth of say 25 feet below low water level, ;ind of sufficient breadth, a trench or channel-like space wherein to sink a wharf or wall of tim- ber and stone filling, around the site ta be covered by the dock and caisson, and at a hundred 'feet or more therefrom. This wharf or wall, its outer face close jointed, and sheathed if need be to make it doubly sure against filtration of either sand or water, will confine the soil on which the dock and cais- son rests in such a way as to preclude the possibility of settlement of any kind. Nor need it be apprehended that any action of the water on the soil beneath the surround- ing wall or wharf can prove injurious, as the only effect could be to cause a subsidence of the wharf itself without the possibility of af- fecting the level of the soil within the enclo- sure. No such wash however is likely to occur, lor as I said before, I sink the wharf to 25 feet or more below low water level, and as this wharf itself is further protected by the pre* sent ballast whnrf which lies ontsidu of it, and by another section of breakw iter, 600 feet or mora to the north east of th^ proposed dock, which is part of my scheme fur harbour improven^.ents; fir from there being any wash or deepening of the bottom of the tidal basin within the breakwater, the effect is much more likely to be in the future as in the past, a gradual filling np or shallowing of the space surrounding the graving dock. This filling np however of the space just alluded to, after it has once been dredged out as proposed to secure a deptli of 25 feet for vessels to lie in at low water, need not be apprehended. True, it has gone on rapidly within the present break- water or ballast wharf since its construction some fifteen years ago ; but this is due to the silt and sediment brougbb down by the St. Charles River and when once cut off as it will be most thoroughly and effectually by the proposed jetty from the Palais, the filling in will not in all probability be more than to require dredging out the tidal dock once in fifty or a hundred years. Einipple & Morris in estimating, as they do, the additional cost of building the grav- ing dock in the mouth of the St. Charles as compared with the rock site at Levis, at some 50 to 60 per cent, had not coaceivea the idea of a caisson and naturally enoagu, as in ii^ngland where timber is scarce and costly, such a gigantic structure of wood, would not likely occur to any one. Their mode of construction, see page 9 of their "He- port on sites for a graving dock in the har- bour of Quebec" Sept. 1^74, consists in dredging out the sand to a depth,of 10 or 12 feet below 'he bottom of the dock and filling in this sr^ce with liquid Portland cement. "It is possible," they sa^, «'to dredge out an area ii the form of a dock, und deposit con- crete over this space for 10 to 12 feet in thickness and to bring up roughly the sides to low water mark. By continuing the sides up to coping level, a shell of great strength — 4 — could be formed out of which water would be pumped, and the whole of the bottom and aides liued with masonry, together with the entraDce works in the usual way ; this me- thod of constructing a dock would avoid the use of a cofier-dam and if properly done would give a water tight dock, and sufficient weight to resist any pressure that could pos. sibly be brought to bear upon its outer sur- face. " "A dock of this description," they go on to say, "could be formed on any doubtful foun- dation, even tnough it were covered by many feet of water at low water." Kinipple and Morris therefore conclude that a dock may be made in the mouth of the St. Charles or, even as they have it, "on any doubtful foundation," and this without any protection wharf around it to prevent the washing away of the sand or soil from be- neath the concrete and the possible settling down and breaking of s portion of the dock when left unsupported from beneath, while my plan of surrenndiog the dock site by a wharf renders it certain that no such wasb can occur, and as I have said before render assurance lonbly sure. But this concrete caisson of theirs, it I may so call it, would cost of itself about $264,000 while the one I propose, inclu- sive of the concrete within it to cause it to become heavy eaougb with the mason- ry to withstand any pressure from without, would not cost more than $126,000. The coffer-dam at Levis, the rock ex- cavation and the guide pier would equal in cost the last mentioned sum, if, in- deed, it did not greatly exceed it ; so that, in reality, by carrying out the project as pro- posed by me, the graving dock in the St. Charles would cost no more, if even as much as it would if built at Levis; and it it did, the city is already pledged to pay the differ* ence ; so that if it be not built in the St. Charlef, reasons other than those of ^, and in much less time ; for the surrounding or protaction wbarf or wharves form part of my scheme of harbor improvements or wet docks, and are charge- able to another fund. Of thiF, however, mora ht reaf ter. I have the honor to be, Mr. Mayor and Gentlement, Your obedient servant, j Chas. Baillairok, I Joint Engineer on Dock and I Harbor Improvements. ' P. 8. — I have just recei'ed a letter from j General W. H. Newton, of the United States, I in answer to my enquiry in relation to the probable cost of dredging in the St. Charles, and I am happy to state that, as already in- ferred by me, this dredging, which has usually cost from 20 to 40 cents a yard when done with the usual dipper dredge, as on Lake St. Peter and elsewhere, is not likely to cost more than 5 cents a yard if done by the new process of pumping up the material, as now carried on by General Newton under his con- tract with the United States Government, and as is also now being done in the harbors of Dunkirk, in France, in Californis, and else- where. C. B. Q^M -it'. -.' ^" ■:*.--/. g- .J. >i,J"J^E* 1