124 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



JO 



FIG. 91. 



removed and another layer added. Before commencing the 

 following layer, the surface of the previous one was thoroughly 

 cleaned and watered, and all vertical joints roughed with the pick. 



In order to allow for 

 expansion and contraction, 

 and to avoid unsightly 

 cracks, straight joints 

 reaching from the low- 

 water mark to coping level, 

 and extending 7 feet back 

 into the work, were formed 

 in the wall at 100-feet 

 intervals, by means of iron 

 plates ^Q to inch thick, 

 4 feet deep by 3 feet G 

 inches wide, placed edge to edge. These plates were embedded 

 in the concrete, and drawn up as it set. 



After a sufficient time had elapsed to allow the concrete to 

 thoroughly set, the vertical joints were pointed up on the face 

 and grouted. 



For draining the back of the walls, the following course was 

 adopted. Where water was met with, a column of dry brick 

 rubbish 3 feet square was built up at the rear, and from the 

 base of this column a 10-inch pipe was carried through the 

 wall to the front. Smaller pipes, 3 inches and 6 inches diameter, 

 were also built through the walls at a level of 19 feet below 

 coping at 80 feet distances, and again at 34 feet below coping 

 level at intervals of 50 feet. 



All backing behind the walls was thoroughly chopped and 

 punned in 9-inch layers. When any slips occurred, they were 

 removed to solid ground, and any mud left in the excavation 

 behind the walls was removed to 100 feet back from the face 

 line. The slope of the original soil was benched out in steps of 

 3 to 4 feet, from top to bottom. 



Wharf Wall, River Front, New York. 1 In improving the 

 river front of New York, Mr. G. G. Green, the engineer-in-chief 

 of the Department of Docks, adopted a method of construction 

 combining in a suitable measure the necessary elements of 

 strength, endurance, and stability, not difficult of execution, 



1 Scientific American, " Commissioners' Report to Dept. of Docks," Now York. 

 December, 1881. 



