BRIDGE. 



cticr. teney bridge, in the city of Bath. The operations 

 here were rendered peculiarly difficult, by several pre- 

 vious ineffectual attempts ; they were at last IUCCCRS- 

 fully accomplished by Messrs Simpson and Cargill, 

 employed for that purpose by Mr Telfonl. 'i'hi : 

 work much exceeded in difficulty those in Langue- 

 doc, so minutely described by M. Gautier, the French 

 engineer, as very extraordinary efforts of art. 



3. A still simpler mode of constructing cofferdams 

 has been practised in Britain : that is, by driving 

 guaging piles, about 12 inches square, at the distance 

 of about 10 feet from each other, and about 5 feet 

 from the edge of the intended platform. They are 

 driven from 5 to 7 feet into the bed of the river, so 

 as to be about 3 or 4 feet below the level of the plat- 

 form, and rise about 5 feet above low water. They 

 are grooved to receive the pile planks, and a leading 

 beam, 6 inches by 9 inches, is fixed about a foot below 

 their top on thejiiside. These beams are notched on 

 the guaging piles, so that their outer edge is in a line 

 with the inside of the groove for the pile planks. 

 The whole of the pile planks, which fill a space be- 

 tween the guaging piles, are entered together, and 

 the middle pile has a wedge-form narrowest at the bot- 

 tom. The pile planks receive a few strokes alter- 

 nately, so as all to be driven nearly together, while 

 the middle one wedges the whole, and makes the 

 joints water tight. They are driven about three feet 

 below the platform, and the whole properly braced. 

 The water being pumped out, and the ground cleared, 

 piles are driven about two feet and a half distant from 

 centre to centre, over the whole foundation ; those 

 near the middle being driven 7 feet 6 inches below 

 the platform, and 8 inches diameter ; those next the 

 outside 9 feet long, and 10 inches diameter. Imme- 

 diately under the outer edge of the platform, grooved 

 guaging piles are driven about nine feet distant from 

 centre to centre, and nine feet in depth. Nearly in the 

 same range with these, common round piles are also 

 driven. Upon the latter, a leading beam, 12 by 8 

 inches, is fixed, which also embraces the guaging piles, 

 and guides the pile planks which were driven around 

 the platform. The bearing piles may be considered 

 as sufficiently driven, when by 30 blows of a proper 

 ram they are not driven one inch, and -10 blows for 

 driving the sheeting piles the same distance. See Plate 

 II. XCVII. Fig. 1. Along the top of each second row 

 of piles, under the body of the pier, a beam, 12 by 6 

 inches, is laid, reaching quite across, and dovetailed 

 into the beams which surround the platform. The 

 spaces between the beams are filled up with masonry. 

 Upon this platform the regular courses of masonry 

 are laid. 



In whatever manner the cofferdams are construct- 

 ed, there should be means provided to discharge the 

 water near the level of low water of the river, instead 

 ef raising it always over the top of the cofferdam ; 

 and there should also be a sluice near the level of the 

 bed of the river, to fill the cofferdam in case of any 

 defect appearing in the dam, or any risk of a flood 

 rushing in too hastily. 



OF CAISSONS. 

 Mn. Wittf regard to laying foundations by means of 



caissons, this mode was first practised in England I 1 ' 

 by that able engineer Mr Labelye, at Wettminster v 

 bridge. In the sequel of a brief report relative to thil 

 wort, (edition 1751,) he announced an intention of 

 publishing I larger report, with plans and designs, cal- 

 culations and detail). This, hnwever, never appear- 

 ed ; but most of the essential materials have been pre- 

 served by Mr Thomas Gayferc, a venerable old gen- 

 tleman, aged 90, now living in Abingdon-strcet, Weit- 

 minster. He was senior apprentice to Mr Jelf, the 

 mason first employed on Westminster bridge, and wat 

 specially appointed to make working plans and mo- 

 dels, and to be attendant on Mr Labelye's own di- 

 rections; and when Mr Tufnell succeeded Mr Jelf, 

 Mr Gayfere was continued in the same capacity till 

 the bridge was finished. From his manuscript narra- 

 tive and drawings, which he has allowed to be in 

 part copied tor this work, will be seen the injustice 

 to which engineers subject themselves, by not pub- 

 lishing their designs, most of Labelye's inventions 

 having been copied, without acknowledgment, by 

 others, who have since constructed large bridges, and 

 to whom they have rendered similar operations a com- 

 paratively easy task. 



By this valuable manuscript we are informed, that 

 at the situation fixed for the bridge, in the ebb chan- 

 nel on the Surrey side, there was 6 feet at low wa- 

 ter ; in the flood channel on the Westminster side, 5 

 feet 9 inches, and on a shoal between them, 4 feet ; 

 also that the rise of tides at extra springs, with land 

 freshes, was 15 feet ; neaps 7 feet ; and at a mean tide 

 10 or 11 feet ; that the velocity of the surface was 

 something greater with the tide of flood than that of 

 ebb ; that with the former it was about 3 feet per se- 

 cond, with the latter 2 feet ; and that the piers were 

 laid about 5 feet below the bed of the river. About 

 the middle, and at 5 feet under the bed of the river, 

 the gravel is 14 feet deep : this continued from the 

 Westminster side ^ the width of the river. The other 

 fourth part, next the Surrey shore, is a loose sand 

 and mud. 



They commenced the operations by driving fender 

 piles to keep off the barges. These were 34 feet 

 long, 13 or 14 inches square, and driven 13 or 14 

 feet into the bed of the river. They were placed 30 

 feet from the pier, and 7 feet asunder, and were con- 

 nected by floating beams. For the first large pier 

 there were 34 of these piles, for the others 26. They 

 were driven by an engine constructed by M. Vauloue, 

 a watchmaker. The weight of the ram was I7001bs. 

 After the engine had worked for some time, it was 

 found, that by three horses walking at an ordinary 

 pace, when the ram was raised only 8 or 10 feet, 5 

 strokes were made in two minutes. f 



The foundation was formed, by scooping the mud 

 in the usual way of raising ballast in the Thames at . 

 that time. When they came to the gravel, it was ra- 

 ked level. The guage for pioving tlie foundations, 

 was a stone 15 inches square, and three inches thick, 

 fixed to a graduated rod 18 feet in length. The rod 

 was painted red, and the figures white. 



In order to prevent the current from washing the 

 sand into the pit, short grooved piles were driven be- 

 fore the two -ends and part of the sides, not above 4 

 feet higher than low water mark, and about 15 feet 



