72 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



the whole of the other fastenings consisted of -inch round iron 

 bolts. 



On the outside, at a distance of 3 feet from the face of the 

 whole-timber piles, a continuous row of sheet-piling was driven, 

 consisting of 4-inch fir planks 1C feet long driven until the tops 

 were about 1 foot above the mud level on the outside ; a half- 

 timber waling was fixed and connected with the dam by 1 J-inch 

 bolts at 9 feet distances, with 6-inch cast-iron washers under 

 heads and nuts. The mud was removed from the enclosed space 

 to a depth of 4 feet. The main piles were carefully caulked 

 from the heads to the bottom of the trench, which was then 

 filled in with puddled clay to a height of 1 foot above the 

 original mud level at the sheeting-piles, and slightly higher next 

 the main piles. 



This dam was not intended to resist under ordinary circum- 

 stances more than 7 feet depth of water ; this was, however, 

 exceeded on many occasions by about 1 foot, and in one instance 

 by 3 feet. In consequence of the softness of the mud, the dam 

 did not maintain its original straightness, a very slight difference 

 in the head of water being sufficient to produce a very perceptible 

 effect. 



The Outer Dam 1 (Fig. 51) was very similar to the shallow 

 dam in design, but more substantial. It consisted of two rows 

 of whole-timber piles ; in the outer row, the piles were from 20 

 to 30 feet long, and were driven down to about 2 feet above the 

 ordinary level of the mud ; in the inner row, the piles were from 

 46 to 55 feet long, and stood from 12 to 15 feet above the mud 

 level. Whole- timber walings were fixed on both sides of the 

 piles immediately above the mud level, and connected together 

 by IJ-inch bolts spaced 9 feet apart. The mud was removed 

 from between the piles to a depth of from 4 to 5 feet. The 

 inner or main piles were then carefully caulked from the heads 

 down to the bottom of the trench, which was then filled in with 

 puddled clay to the top of the outer row of piles, thus covering 

 the tie-bolts from 1 foot to 1 foot 6 inches. Along the top of 

 the main row of piles whole-timber walings were fixed at about 

 4 feet below the pile heads. Shoring-piles were driven at a 

 distance of 20 feet in the rear of the main piles and spaced 

 9 feet apart centre to centre. Whole - timber shores, one 

 horizontal and one inclined, were fixed to each back pile. The 

 1 MP.I.C.E., vol. Ixiv. p. 179. 



