196 TUNNELING 



laid in one conduit, except across Manhattan St. and beyond 

 190th St., where it will be carried on an elevated structure. 

 The East Side Line will consist of a double-track tunnel driven 

 from 102d St., and the boulevard under Central Park to 

 110th St. and Lenox Ave., and two parallel circular tun- 

 nels excavated under the Harlem River, the other portions 

 of the road being double-track, subway and elevated structure. 

 The subway, both for four and two tracks, may be built by 

 open excavation, cut-and-cover methods. 



For the main line the Slice method, so successfully em- 

 ployed in the Boston Subway, will be adopted as the most 

 convenient in a case where the width of the excavation is 

 great and the traffic enormous, as is the case especially below 

 43d St. and along the boulevard. For the double-track sub- 

 way, the method of the wide trench will perhaps be adopted 

 on account of it being the least expensive ; and since the 

 streets where such a trench will be opened are very wide, with 

 only a light traffic. 



Lining. The lining of the subway is of concrete, carried 

 by a framework of steel. The floor consists of a foundation 

 layer of concrete at least eight inches thick on good founda- 

 tion, but thicker, according to conditions, where the founda- 

 tion is bad. On top of this is placed another layer of concrete, 

 with a layer of waterproofing between the two. In this top 

 layer are set the stone pedestals for the steel columns, and the 

 members making up the tracks. 



In the four-track subway, the steel framework consists of 

 transverse bents of columns, and I-beams spaced about five feet 

 apart along the tunnel. The three interior columns of each 

 bent are built up bulb angle and plate columns of H-section. 

 The wall columns are I-beams, as are also the roof beams ; 

 between the I-beams, wall columns, and roof beams there is a 

 concrete filling. So that the roof of the subway will be made 

 up of concrete arches resting on the flanges of the I-beams of 

 the roof. The concrete to be used is of one part Portland 



