H K I D O E. 





tiee. the sides were to be raised it was only Decenary in 

 /"" unscrew tlic nuts. Across the top of the i 



there \ve>v seven tics of timber, each \'Z nichei by (>. 



In some cases, in very deep water, where tli 

 of the river, though soft, is nearly level, or can be 

 made so, a very strong grated frame of timber, much 

 larger than the foundation of the masonry, may be 

 let down by placing great weights around the edges 

 of it, and having piles driven to keep it in its place, a 

 caisson may be sunk upon it. This, when once settled 

 by the weight of the pier, stands as well as if piles 

 were driven under the bottom of the caisson. Some- 

 times pile-planks should be driven round the frame. 



We learn from the work of L. A. Cessart, that 

 the mode of laying foundations in deep water, by 

 mean* of caissons, was not practised in France till 

 the year 17.57, when M. de Voglio and himself (en- 

 couraged by Perronet) introduced it with success at 

 the bridge of Saumur, after the manner of Labelye. 



Having detailed the different modes which have 

 been practised by eminent engineers upon large ri- 

 vers, it may be useful to young artists to mention, 

 ti at in smaller rivers, where the foundations are to 

 be laid on firm gravel, mud, or quicksand, it is 

 frequently necessary to drive a row of dovetailed 

 three -inch pile-planks around the pier or abutment, 

 from five to ten feet in length, according to the na- 

 ture of the ground, and lay some clay round the 

 outside of them; then to excavate the foundation 

 about two feet below the level of the bed of the ri- 

 ver, and lay down sills nine inches by six longitudi- 

 nally, at the distance of about tour feet from each 

 other, filling up the spaces between them with rub- 

 ble masonry ; upon this to lay two thicknesses of 

 three-inch planking crossing each other, and pinned 

 with oak trenails ; around the outer edge of these, 

 and immediately without the first coarse of masonry, 

 to fix a curbing six inches by four, to which, after 

 the masonry has been built up to the level of low 

 water, and the clay removed from them, the pile- 

 planking should be fixed by spike nails, and cut 

 down to nearly that level. If the ground is very 

 soft and loose, it is also necessary to drive piles 

 under the platforms. In some instances, besides the 

 platforms under the piers and abutments, gratings 

 filled with masonry, and covered with planking, have 

 been carried quite across the bed of the river. M. 

 Blondel performed this in the bridge of Xaintes upon 

 the Charante. In a bridge over the Liffy, in Dublin, 

 Mr George Semple carried a solid mass of masonry 

 across the bed ot the river, between the piers. In- 

 verted arches have also been made between the piers, 

 and more especially between the abutments, in the 

 . case of having one arch only across the stream. 



Excavations for the foundations and gratings in 

 deep rivers can now be much more expeditiously 

 performed by the improved dredging machines, work- 

 ed either by horses or steam engines. 



Having completed the cofferdams and caissons, it 

 is, in large works, an important consideration to 

 have a perfect command of the water which may rise 

 within them. The modes formerly employed were 

 hand buckets, or pumps worked by men or horses, 

 also water-wheels; but of late, in England, recourse 

 has been had to steam-engines. These can now be 



suited to any exertion required, and are the most !' 

 powerful and certain means yet devi.scd. '1 he gang- ' " ' t " "- 

 ways and scaffolding must be regulated hy local < 

 ciini'itances, no general rules being applicable. \V ' 

 shall, therefore, only noiico, that tin: labour in re- 

 moving l-rge stones, may frequently be much a- 

 In idged by laying down cast-iron railways ; and that 

 much aid is to be derived from the use of properly 

 4 nictcd cranes. The form and properties of these 

 will be explained under their respective heads. 



To lay the foundations of piers in deep water, Cofferdam 

 upon rock, and in the tideway, being a difficult for found- 

 operation, it becomes of serious importance to ex- j"f . ''" ! " 

 plain how it has been performed upon a large scale. ^ *| 

 We do not recollect of this having been done in a trj ,, ce / 

 satisfactory manner in any former publication, and the C'aledo- 

 thercfore trust the following narrative will prove in- nian Canal, 

 teresting to those who may be connected with similar l* L r* 

 works. It affords a minute detail of every operation f .^ ,, ' 

 in the construction of a cofferdam upon rock, in deep 

 water, and in the tide-way. It has been practised 

 with perfect success at the western termination of 

 the Caledonian canal, for the tide-lock built there 

 by Messrs Simpson and Wilson, and is equally appli- 

 cable to the abutments or piers of bridges. 



The entrance from the canal into the tide-way 

 having been fixed on the north-west side of a rock 

 which projects into the sea about 100 yards from 

 high-water mark, and which was covered at three- 

 quarters flood, it became necessary to discover in 

 what direction, and at what depth it lay below the silt 

 or mud which composed the beach at that place. By 

 boring with augers, it was found, at the distance ot 

 21 yards from low- water mark at the lowest spring 

 ebbs, that the rock, in the middle of the entrance, 

 was 21 feet below high-water neap-tides, which af- 

 fording the desired depth, was fixed upon as the ex- 

 tremity of the space to be enclosed by a cofferdam 

 for the sea-lock. 



In the spring and summer of 1807, the earthen- 

 bank was carried forward to near the end of the 

 timber work for the coffer-dam. The first leading 

 frame was begun in August, and put together on 

 the beach, near high water-mark, that it might be 

 floated off to its situation. The first leading frame 

 was begun by fishing together end to end, two beams 

 13 inches square, by pieces 20 feet long, 13 inches 

 broad, and 6 inches thick, laid on opposite sides of 

 the beams across the joints, and fastened by four 

 screw bolts, which passed through the whole. The 

 length of these beams, when joined, was 95 feet. 

 In order to form the sides of the leading frames, 

 from the ends of these last-mentioned beams, two 

 others, each 63 feet in length, were laid with an in- 

 clination to each other, that left their inner ends 65 

 feet apart. They were fastened to the ends of the 

 long beam by half chucking or gaining, and two 

 screw bolts through each corner. There was a 

 beam 38 feet long laid across each angle, and fasten- 

 ed down to the front and side leading beams by 

 screw bolts. At the height of the springs this first 

 leading frame was floated off, and at low water ad- 

 justed in its precise situation, and sunk to the bot- 

 tom by means of a number of large stones being 

 placed upon it. A considerable degree of attention 



