-0/7- 



the caisson above before the next 

 section was excavated. 



This is probably the first time 

 that a pneumatic caisson has been 

 undermined. 



All of the columns are seated on 

 rectangular or circular concrete piers 

 with their footings carried down by 

 wooden pneumatic caissons through 

 quicksand and hard pan to solid 

 rock about 90 feet below the level 

 of the Broadway curb. The piers 



were built as shafts constructed above the surface of the ground and 

 afterwards sunk to bed rock by men working in the interior chambers. 



Ten of the piers were provided with vertical steel anchorages extending 

 nearly to the bottom and built into the concrete. These were made in such 

 a manner as to utilize the full weight of the pier, estimated at 1,150,000 

 pounds in a maximum case, besides the very large indeterminate friction 

 between the sides of the pier and the earth, which is not counted on, to 

 resist the upward reaction of 925,000 pounds. 



The adhesion of the pier concrete to the steel anchor rods, assumed at 50 

 pounds per square inch, was utilized in designing the anchorages. So secure- 

 ly is the Tower anchored that it would be necessary to exert a force sufficient 

 to pull the caissons out of the ground before the stability of the building would 

 be endangered, and as the cutting edge of the caisson was stopped near the 

 top of the hard pan and the excavation then carried through the hard pan 

 from 20 to 30 feet to 

 rock and the whole 

 space then filled with 

 the best Portland ce- 

 ment concrete, it can be 

 realized that before the 

 caisson could be lifted 

 the concrete would have 

 to be broken in two 

 or else the hard pan 

 would have to come up, 

 too. This would prac- 

 tically mean lifting all 

 the hard pan off of the 

 rock and all the quick- 

 sand and water on top 

 of the hard pan re- 

 sults which could occur 

 only in the wildest 

 imagination. 



The total weight 

 of the Singer Building, 

 including the Tower, 

 is figured in the vi- 

 cinity of 165,000,000 



[15] 



