402 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



of a cylinder whose diameter would be equal to that of the 

 smaller face of the frustum. 



Streams of water through two 1J inch iron pipes were led 

 directly upon the screw, and the hitherto great resistance to 

 screwing down the piles at once ceased. 



A subsequent determination of the resistance to screwing 

 down the piles developed the fact that nine-tenths of the resist- 

 ance disappeared upon the proper application of the water-jet 

 to the upper surface of the screws. 



Through the aid of the water-jet, it became possible to settle 

 the screw-piles as deeply as was deemed necessary in a bottom 

 where, without the jet, the strongest iron screws were broken 

 as though they had been made of glass, when main force alone 

 was used in the unsuccessful effort to sink them more than 

 4 feet. 



When it became necessary to remove some of these piles, 

 the application of the water-jet to the upper face of the screw 

 rendered the operation quite easy, when previous efforts, by 

 backing the screw, or to raise the pile bodily, had proved un- 

 successful 1 



At the Queen's Dock, Glasgow, in sinking some foundation 

 cylinders constructed of concrete, 30 feet long and 12 feet 

 diameter, by the aid of the water-jet, the presence of large 

 boulders caused considerable difficulty, which was met by forcing 

 the water-jet pipes some feet below the obstruction, and washing 

 out the sand from beneath and round it. By this means the 

 boulders were either lowered vertically or sideways so as to 

 clear the cylinder edge. 2 



The general principle upon which the efficiency of the water- 

 jet depends is the increased fluidity of the material ; hence the 

 efficiency is greatest in clean sand, mud, or very soft clay 

 or marl. 



In gravel, or in sand containing a large percentage of grnvd, 

 the jet is almost useless, except under a volume and pressure 

 sufficient to force the stones from under the piles. 



In applying the water-jet, it is better to deliver large 

 quantities at a moderate pressure rather than a small quantity 



1 Mr. L. T. Schermerthorn's paper on "The Water-jet as an Aid to KM MH-M rinrr 

 Construction," from which the above is taken, gives an interesting and valu:il>l 

 rfford of the application of the water-jet under varying conditions. " Aim ric.ni 

 Knginerring and Building Record for 1889," pp. 117-131. 



1 Engineering, vol. xlviii. p. 55. 



