WALL SECTIONS ON BLOCK FOUNDATIONS. 121 



Care was taken that the quantity of water pumped out should 

 be equal to that forced in, so that the level of the sand and water 

 within the cube should be always maintained somewhat below the 

 ordinary level at which the water stood in the surrounding sand. 

 As the blocks were lowered, two spirit-levels were laid upon 

 the upper surface, and from these it was easy to see if the blocks 

 were going down perpendicularly; if not, their descent was 



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SECTION ON A B FIG. 84. 



FIG. 86. 



Plate 



FIG. 87. 



regulated by shutting off one or more of the nozzles on the side 

 which was going down too quickly. 



When a curb had reached its ultimate level, the sand in it 



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SECTION ON o D> FIG. 84. 



FIG. 88. 



FIG. 89. 



was allowed to settle, and the opening was then rilled in with 

 hydraulic concrete ; the coned form of the aperture serving 

 to keep the whole together and to prevent any leakage between 

 the filling and the curb. In this way the apertures were filled 

 nearly to the top of the curb (Figs. 80, 81), when the masonry of 

 the wall was commenced. 



The plan of operations adopted was as follows : The positions 

 of all the blocks were carefully set out on a plan, and laid 



