82 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



might be caused by the pressure from the coffer-dam at high 

 water. That this was not the case was shown by the change 

 in the width of the crack. At high water the crack was 

 scarcely visible, whilst during low water, when the pressure from 

 the dam was least, it increased to the extent of 1 inch in width. 

 As any further settlement in this wall might have endangered 

 the safety of the dam, the two portions into which the wall 

 was divided by the fissure were connected by four wrought- 

 iron tie-rods 2 inches in diameter, which were secured to the 

 finished portion of the wall adjoining the Railway Creek by 

 lewis bolts and passed through baulks placed across the 

 unfinished end of the wall. No further change occurred in 

 this wall during the progress of the work. 



For the further protection of this side of the lock a dam 

 (X, Y, Fig. 58) was driven from the north basin wall eastwards 



IO CHAINS 



FIG 58. 



parallel to the Railway Creek. The dam consisted for the first 

 80 feet west of the return wall of 2 rows of sawn piles 13 

 inches square and 5 feet apart, and for the remaining distance 

 of about 300 feet of a single row of sawn piles averaging 47 

 feet long, and extending to a depth of 55 feet below coping 

 level. It was constructed throughout its whole length with 

 the whaifing of the Railway Creek by iron tie-bars from 1J 

 to 2 inches diameter, carried through the bank at a depth 

 of 2 or 3 feet below the surface and at distances of about 

 30 feet apart. A single row of piles was also driven across 

 the angle formed by the large semicircular dam and the 

 return wall. 



