WATER JET. 



399 



This injector, as anticipated, did not deliver a sufficient 

 quantity of water when the pile was sinking. Nevertheless, 

 the pile was got down to a depth of 12 feet below the surface 

 of the bank. 



A more powerful pump was then applied. A new bottom 

 length of pile was also used, provided with a disc point (Fig. 351), 

 on the under side of which, and at right angles to each other, 

 were four ribs with serrated edges. With these appliances, a 

 pile was got down 18 feet into the ground in two hours, including 

 the time taken up in arranging the guides, pipes, and other 

 incidental matters. 



The water washed away the sand all round the pile, making 

 a large hole, at the bottom of which all the stones collected. 

 The point of the pile rested on these stones, and did not move, 

 however long the pumping was continued. The pile was then 

 twisted, so that the serrated edges of the ribs might work through 

 the stones. 



By combining this action of twisting with pumping, the pile 

 was got down 2 feet further, or 20 feet into the ground. 



Ordinarily the pressure in the delivery pipe was main- 

 tained at 20 Ibs. per square inch, 

 which was increased at the 

 point of the pile to 35 Ibs., 

 owing to the difference of level 

 between the top of the work- 

 ing-stage and the sand-bank. 



With regard to the raking 

 piles, it was considered that if 

 the discs were placed at right 

 angles to the axis of the piles, the water would not drive the 

 sand out equally all round the pile, and that in consequence 

 they would have a tendency to move outwards and be difficult 

 to guide. The discs were, therefore, placed horizontally (Fig. 

 352), by which arrangement the raking piles were got down as 

 easily as the vertical piles. After the piles were down, they 

 were filled with fine Portland-cement concrete. 



Subsequent tests with hydraulic jacks fitted with gauges 

 showed that the piles which went down easily required 8 or 

 10 tons to depress them, while those which had taken the stones 

 down with them required a force of 14 to 15 tons. In nearly all 

 cases, on the pressure being removed, the piles rose about one- 



FIG. 352. 



