60 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



structed across the Victoria Dock so that the business of the 

 dock might be carried on during the time an extension to the 

 basin was in progress ; it was therefore subject to a constant 

 instead of a tidal head of water. 



The dam was the segment of a circle, the radius being 1500 

 feet, and 470 feet long, the versed line 20 feet, and consisted 

 of two rows of whole-timber piles, each 40 feet long by 13 inches 

 square, driven as close-sheeting about 10 feet into the ground 

 and 6 feet apart between the inner surfaces. It was tied 

 together with two sets of walings 13 inches square, one set at 

 the level of high water in the dock, and the other at 6 feet 

 below high- water level ; through each of these a 2-inch tie-rod 

 passed, and was screwed up on timber chocks and washers on 

 the outside of the walings. The deposit of mud 7 feet in depth 

 between the two rows of piles was cleared out with a bag- 

 and-spoon dredger before the puddle was filled in. 



The water remained at nearly the same level on both sides 

 of the dam during the excavation of the soil in the extension of 

 the dock. When the works had been so far completed that 

 nothing remained but an embankment 40 feet wide parallel 

 with the dam, the water on the extension side was lowered. 

 After the water had been thus lowered 6 feet, the dam showed 

 signs of yielding ; shoring struts 14 inches square were therefore 

 placed against the walings and pitching of the slopes, and the 

 water further run off. The pressure then showed itself greatest 

 near the level of the accumulated mud, and it was found neces- 

 sary to drive stay piles in the slopes 8 feet apart, from which 

 struts were placed resting against an extra waling 13 inches 

 square, fastened to the dam at the level of the mud ; it was also 

 considered prudent to fill the extension works with water to a 

 depth of 13 feet. The pressure from the dam was so great that 

 many of the stay piles were pressed 1 foot into the solid bank. 

 As soon as the great bulk of the pitching on the bank had been 

 removed, the water was permitted to rise in the extension to the 

 same height as in the dock, thereby averting all further risk to 

 the shipping lying therein. 



This dam caused a great deal of anxiety during the time the 

 dock work was in progress, and if it had failed the result would 

 have been disastrous; fortunately it stood, and the reason 

 assigned for its doing so was that it had been constructed of 

 a circular form, according to Sir John Hawkshaw's design, and 



