THE TOWER FOUNDATION, OCTOBER 18, 1906 



only 75 feet on one of the busiest thoroughfares in 

 the world, through which all material and excavated 

 soil had to be handled, it will be seen that even the 

 preliminary problems were ones not easy to solve. 

 No sooner were these problems successfully solved 

 than others equally perplexing presented themselves. 

 Concrete had to be prepared, and the machines by 

 which this is done require much space for their op- 

 eration; the hoisting and delivery into the air locks 

 of the caissons had to be done, and the platforms and 

 framing so designed as to admit this being performed 

 without interfering with other work simultaneously 

 in progress. 



In addition to all this, there was the necessity for 

 needling up the walls of the original Singer Building, 

 a heavy and ornate structure, at that time more than 

 1.50 feet high. The needling and mats for its sup- 

 port had to be accommodated, still further reducing 

 the available working space. 



During the progress of this work a daring and 

 unusual feat in building was successfully performed. 

 It was at first intended to stop the caissons at hard 

 pan, about 20 feet above bed rock, but when it was 



CONTRACTORS 

 EXECUTE 

 DARING PIECE 

 OF WORK 



decided to go to bed rock, one of the caissons had 

 already been completed 7 feet below the top of 



the hard pan, its air lock and shaft 



removed and the crib filled with 



concrete. 



How to extend this caisson to 



bed rock was the question which 

 was solved by tunneling through the intervening 

 space from the nearest caisson, excavating the hard 

 pan and underlying stratum beneath the 50 feet of 

 caisson overhanging and filling the cavity below the 

 caisson as well as the tunnel with concrete taken 

 through the tunnel from the adjoining caisson, which, 

 of course, required time and care, for if the entire 

 caisson had been undermined at one time there might 

 have been danger of the great weight of the 50 feet 

 of caisson above breaking loose. 



This feat was successfully accomplished by 

 running a small drift tunnel, 5 feet high by 4 

 feet wide to the farthest end of the caisson above 

 and then excavating vertically downward to bed 

 rock, 15 feet farther, one section at a time and filling 

 each section with concrete from the bed rock up to 



13] 



