Polytechnic Association Proceedings. , 377 



places along its sides, controllable water-jets, which will allow the 

 water from the inside to pass outward at many points under pres- 

 sure, and so soften and lubricate the material as to lessen the 

 resistance and destroy a portion of the friction. 



When the material to be penetrated is sufficiently close to pre- 

 vent the entrance of the water at the bottom, the top may be left 

 open, and the water removed in the ordinary way of pumping, and 

 the excavation performed, either by hand or by machinery. 



For the latter, the ordinary mill-bucket elevator is probably the 

 best machinery that can be used. 



A patent has been taken out by Gen. W. S. Smith, for removing 

 soft excavation, by means of a syphon steam-jet. 



With the hydrostatic process, piles as small as seven inches out- 

 side diameter, have been driven into firm sand at a cost of nine 

 cents, gold, per foot for the driving. 



In regard to size and form, this system has been extended to 

 cover the shape and size of the entire pier, embracing forms which 

 were cylindrical, elliptical, triangular and rectangular. In these 

 cases, the shell was usually of wrought-iron and removable, and the 

 support obtained by filling them with masonry. 



When of large size, and the pneumatic process used, they are 

 usually called inverted caissons. 



A pier was built by Brunei, at Saltath, by this method, with a 

 caisson thirty-seven feet in diameter, and to a depth of ninety-eight 

 below the water; the lower fifteen feet being an inverted caisson, 

 where the pneumatic process was used and connected with the 

 upper portion, which was direct and removable. 



It may be interesting to add here, that the pier was carried up 

 one hundred feet still higher, by means of iron columns. 



In many cases the entire pier and its foundations may be made 

 of these columns, which can be constructed of ample strength to 

 support the heaviest loads, and to resist the most severe impacts to 

 which they will be sul^jected. 



In exceedingly difficult places, iron piles or piers can be built 

 much cheaper than stone piers on wooden piles. In many places, 

 with no more expense, and in others, they ofi'er to the engineer the 

 only foundation that he can rely upon. 



American engineers have generally looked upon this system of 

 foundations unfavorably, from the unnecessarily expensive exam- 

 ples in this country, and the costly methods which prevail in other 

 countries, but chiefly from not understanding the modifications 



