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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fAuGUST, 



capable of excludinir from tlie inside the sand which was so lial)le 

 to replace wliat wari roinoved from the interior. For tlie excava- 

 tion ot'tlie rock, on tlie other hand, it was necessary that the dam 

 ihiiiild he water-tifiht. and suitable for takinjj out all the ])arti- 

 tions ; anil botli situations required piles for fittinp^ close to the 

 irreijular bottom, and those piles needed some support other than 

 the soil into which they were to be driven. 



To effect such objects, it was clear that the means to be adopted 

 m!ist be at once easily manafied and efficient. For although, 

 where there is time for their emjiloyment, many complicated and 

 troublesome refinements of construction are forced to answer 

 purposes which misht have been attained by simpler means, or by 

 less cumbrous arranfjements, yet 1 was well aware that in the 

 hurry and bustle attendins^ tidal operations and nif>;ht-work, nothiiifi- 

 can be tolerated but what is in every respect easily managed and 

 truly efficient. 



In the accompanying diagrams, A G represents a frame of 

 double waling-[)ieces connected at the angles by the uprights 

 I I, and bound together by the long bolts L, with forelocks 





and washers, while E F shows similar double-framed walings for 

 the inside of the dam, and of smaller dimensions, with their up- 

 rights U, and connecting bolts K. These frames being jdaced in 

 the required ]iosition, the one frame inside of the other, the piles 

 C, are driven down between them with heavy malls. 



The dam was V-i feet long by lu feet broad inside, so that five 

 men were able to work in the interior." If it was to be fixed 

 within low-water mark, the two fi-ames being placed in the water, 

 were guided to the sjiot by the men in charge, and whenever they 

 were in the desired position, the men at once moored or fixed the 

 frames to the bottom, by driving down a pile at each corner. After 

 this was done, all the jiiles were placed between the frames and 

 driven down, anil keyed up by the small piles called " closers." 

 Four iron jumpers J, were then driven down to their ]iroper places 

 outside of the frames, and edge ])lanks for retaining the clay were 

 slipped down ujion the jumpers through iron staples, which were 

 fixed to the planks. After this, good clay (which should have some 

 gravel mixed with it, to protect it from the wash of the sea) was 

 piiiuied hard between the planks and the coft'erdam, after which the 

 mast N was erected, and the water taken out by means of the iron 

 scoop shown in the drawing, which not only was used in taking 

 out the stuff, but proved far more efficacious than any pump we 

 ever had. Indeed, to get the dam pumped dry was for long the 

 greatest difficulty we had to contend with. But Mr. AVilliam 

 Downie, to whom I gave the charge, soon removed this difficulty, 

 by using the scoop instead of a pump. The capacity of the scoop 

 was about 37 gallons, and they generally made nine deliveries a 

 minute, so that we found this method greatly more expeditious 

 than any other. 



As the excavation proceeded, the piles were from time to time 

 driven down ; and when the rising tide began to come over the 

 pile-heads, or to rise above the clay, the men, before lea\ing their 

 work, placed the flooring or "rfec/f,"as it was called, within the 

 piling, with the ends of the planks resting upon the top of the 

 inner frame. On this deck, ballast (consisting of stones of a con- 

 venient size) was deposited to prevent the whole frame from being 

 floated up, — the quantity so dei)osited varying with the height of 

 tide, or appearance of the weather. As each compartment of the 

 excavation was completed, and before the dam was removed, the 

 rock below the two rows of piles which adjoined the next cuttings 

 was completely taken out, and the piles driven down to the bottom 

 of the excavated pit, ami left standing.t \V'hen the dam was 

 taken up, the frames were, for the next compartment of cutting, 

 again sujierimposed upon one of the rows which iiad been left 

 standing in the last pit. In this way no rock could possibly escape 

 being removed ; and when the frames were to be put down anew, 

 there was no difficulty (although the pit was entirely co\ered with 

 sand) in knowing exactly the position which they were to occupy, 

 as the piles which had been left standing were an infallible guide. 



The advantages peculiar to this description of dam are its cheap- 

 ness, — its portability, — its ready adaptation to a slojjing-, or even to 

 a very irregular bottom, — the ease and certainty with which the 

 partitions between the different pits are removed, — and the double- 

 fiamed walings that supjiort and direct the driving of the piles. 

 Wherever excavations require to be made in a rocky beach, covered 

 by a stratimi of sand, however thin, there need not be any hesita- 

 tion in adopting this form of dam, as there is no kind of lateral 

 support, such as stays or shores wanted, the structure containing 

 within itself the elements necessary for its stability. It possesses, 

 indeed, all the properties of a caisson, and has the further advantage 

 of accommodating itself to an irregular bottom. J 



I may observe, in conclusion, that although this form of con- 

 struction is specially adapted to marine works, in the execution of 

 which it has proved a most valuable auxiliary, the same principle 

 might also be carried to a greater extent, and be rendered fit, with 

 little trouble, to answer for a variety of works, — such asunder- 

 footing quay walls, founding bridges, and in removing fords or 

 other obstructions from the beds of rivers. The application of a 

 double-framed waling I have also found in itself a very useful ap- 

 plication in several situations, and for a variety of purposes. 



* Since this pap-r was printeii, a fotf<T(lain on the same principle and thirty-five 

 feet square, lias been made fur the Fortli Navigation vvorlfs, Stirliiiij, where, in the 

 removal of tile '* fords," no ier my directio'i, nmcft ditficulty has hitherto been experi- 

 enced, from the coiistani ti jw of the river. 



t Before lidiiig the cutferdam, the pit was tilled with sand, to support the piles that 

 were to remain, which, when the works vveie done, was cleired out by means of a wate.'- 

 sconr, provided for the purpuse of keeuing permanently open the navigable tract. 



J lu siluaiiotis also, where there is a considerable depth of water, and where, conse- 

 qaently, the frames must l»e made so as ti stand high above the ground, it will be found 

 of great advantage to plank the outside of the frames between A and G. Th's will not 

 onlj make the dam uiore wat«r-tlght, but have the elfect of binding and strengthening 

 the framework. 



