Polytechnic Association Proceedings. §75 



moderately easy, these columns can be driven from ten to twenty 

 feet per day. When boulders, logs, etc., are encountered, they 

 can be cut through by the workmen, from the inside of the column, 

 "vv^ith much less delay than would be expected by those not familiar 

 with the operation. 



One of the columns at Harlem was driven twenty-seven feet, 

 through a constant succession of hard boulders, in as many days; 

 and another eight feet, through a sunken vessel, with a delay of 

 only two days. 



When a stratum of clay or other tight material was met with, 

 which prevented the water from passing out at the bottom, a syphon 

 pipe was used, leading up through the column and out at the top, 

 through which it was discharged. 



These columns can be driven at any season, in the winter months 

 as well as in the summer. The compression of the air raises its 

 temperature ten or fifteen degrees, but when the workmen com- 

 plained of cold, this was increased to any desired extent by the 

 use of a heater through which the exhaust steam was piissed, which 

 heated the air that was forced into the column, to any desired 

 extent. 



In the intensely hot weather of summer, a simple process of 

 evaporation from water spray will cool the atmosphere within the 

 column, ten or fifteen degrees. 



In conducting some other works of which I have descriptions, the 

 labor had to be suspended, from these expedients not havmg been 

 used. 



One of the most important modern improvements in this system 

 of foundations, is what I have termed " the expansion of the base," 

 by means of which the supporting power of the pile or column is 

 vastly increased at a trifling cost. 



This was first developed at Harlem, when we trebled the base 

 support, at a cost of less than a hundred dollars, by extending the 

 concrete filling to a distance of three feet beyond the exterior of 

 the columns, and to a depth of four feet below them, and this 

 may be generally carried to a still greater extent. 



The value of this improvement will be appreciated, when it is 

 stated that the supporting power of the Harlem columns, from 

 their exterior frictional surface, was about two hundi'ed tons, and 

 from their base support, unexpanded, a little less than three hun- 

 dred tons, while the expansion of the base added eight hundred 



