182 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



Travelling-cranes placed at the sides of the trenches raised 

 the excavated material to a high-level tramway extending the 

 whole length of the dock. The skips used for lifting the 

 excavated material were formed of the upper part of the tipping 

 waggons, and were lowered into the trench by the travelling- 

 cranes, the waggon bed remaining on the tramway. When 

 loaded, the waggons were run along the tramway and tipped 

 into barges lying outside the clam. 



The gravel in the bottom of the trenches was excavated down 

 to the clay, turned over and mixed with one-sixth part of lias lime, 

 thus making a solid concrete foundation of great depth resting 

 on the clay. 



The side walls were then built of lias lime and 7-to-l 

 Portland-cement concrete, faced with granite ashlar in 8 -inch 

 courses. 



After the side walls were built, the centre portion was 

 excavated, and the gravel in the bottom turned over and made 

 into 6-to-l lias concrete. On the top of the lias concrete, a layer 

 of Portland -cement concrete 15 inches thick was added; upon 

 this 6 and 9-inch granite pitchers or paving setts were bedded in 

 Portland cement, forming the finished bottom of the dock, and 

 having the appearance of a well-dressed street crossing. 



On each side of the dock, at the top, there are three shoring- 

 altars, each 18 inches in width by 2 feet 6 inches deep; the 

 remainder of the depth having simply a batter of 1 in 12. 



Access to the dock bottom is obtained by means of a 

 combined stair and timber slide at the break in the east-side 

 wall, and by a timber stair or brow in the west-side wall, near 

 the head of the dock, and also by ladders formed of the vertical 

 fenders attached to the side walls. 



The foundations of the entrance were formed of Portland- 

 cement concrete, carried down to the clay, and across the longi- 

 tudinal walls of brickwork, on which are built the invert floor 

 of caisson berth, and inner apron and sides of the entrance. 



The pockets between the brickwork walls are filled with 9- 

 to-1 Portland-cement concrete. The invert is of brickwork in 

 Portland cement, faced with granite. 



The caisson stop-quoins are granite, having a raised meeting- 

 face of f inch projection and 12 inches in width, against which 

 the caisson abuts. 



The drainage of the dock is effected at the centre of the 



