46 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



of close, compact sand containing fragments of shells which 

 rested on coarse open gravel. Beneath the gravel and resting 

 on the clay, was a layer of septaria, which presented a serious 

 obstruction to the passage of the piles; once through this 

 stratum, and into the clay, the driving became comparatively 

 easy. 



The width of the dam was 25 feet in the clear, with a space 

 of 6 feet between the piles for puddle. The piles were of whole 

 timbers in lengths of from 40 to 48 feet, and from 12 to 14 

 inches square. They were shod with shoes weighing 70 Ibs. 

 each, and were driven 4 feet into the clay. Shoes having cast- 

 iron bases and wrought-iron straps were used in preference to 

 shoes made wholly of wrought-iron, as giving at an equal cost 

 a much larger base for the timber, a matter of considerable 

 importance where the driving is difficult. 



The piles were secured by three rows of walings of whole 

 timbers 13 to 14 inches square, through which, and passing 

 through the puddled space, were tie-bolts 2J inches in diameter 

 in the lower walings, and 2 inches diameter in the middle and 

 upper walings. These bolts were placed at an average distance 

 of 6 feet 6 inches apart in each waling. Their heads and nuts 

 pressed against cast-iron washers 8 inches square and 2J inches 

 thick with splayed edges. The washers were afterwards made 

 circular, 9 inches in diameter and 2f inches thick, and it was 

 frequently found that the pressure of the puddle had forced 

 them into the walings to the full extent of their thickness. 



To avoid the difficulty of procuring long timbers, the heads 

 of the piles were driven below the level of the top of the dam, 

 which was finished to 4 feet above high- water mark. Lengthen- 

 ing pieces were half-lapped to the heads of the piles at short 

 intervals, and were bolted to each other across the puddled space 

 by bolts 1 inch in diameter; between these lengthening pieces 

 deals were fitted in, longitudinally, up to the level of the top of 

 the puddle. 



Temporary walings, of half timbers, to guide the piles in 

 driving, were fixed to the inner faces of the gauge-piles by bolts 

 \\ inch in diameter, and were removed before the puddle was 

 deposited. 



The 6-feet space between the piles was dredged to the level 

 of the clay by means of a bag and spoon, and the puddle filled 

 in. Before the puddle was raised above the level of low- water 



