ENCLOSING DAMS. 71 



At every high tide there was trouble with leakage at the 

 through-bolts, owing to the settlement of the puddle. This 

 leakage tended to disturb the mud and peat under the inside 

 artificial bank of sand. To remedy this as much as possible, 

 every conceivable expedient was resorted to ; could through- 

 bolts have been dispensed with, and the puddle reduced in 

 thickness, fewer difficulties would probably have been en- 

 countered. 



PORTSMOUTH DOCKYARD EXTENSION Temporary Dams. 1 

 The general arrangement of the dams used on these works is 

 shown by Fig. 23. 



The Shallow, or inner dam (Fig. 50), consisted of a single 



H.W.O.S.T 



SCALE 



20 



FIG. 50. 



row of whole-timber piles averaging about 30 feet long. No 

 shoes were used, as they had only to penetrate soft mud. The 

 heads of the piles were on an average 10 feet above the surface 

 of the mud, or about 2 feefc above high- water level. On the 

 inside, close down to the mud, a half-timber waling was fixed. 

 Similar half-timber walings were fixed on both sides about 2 

 feet below the heads of the piles. Shoring-piles of whole timber, 

 sufficiently long to penetrate the mud and be firmly driven into 

 the hard soil below, were driven at a distance of 20 feet from 

 the dam piles, spaced 9 feet from centre to centre. The shoring 

 consisted of one horizontal and one inclined half-timber, secured 

 to the back shoring-pile and to the upper and lower walings. 

 The horizontal shore was secured with 1 J-inch strap bolts, whilst 

 1 M.P.I.C.E., vol. Jxiv. p. 177. 



