OPEN-CUT Tt NNKI.ING METHODS 



189 



over with a timber platform flush with the street surface. 

 Under these platforms the excavation was completed and the 

 lining built As each trench or " slice " was completed, the 

 street above it was restored and the platform reconstructed 



Fio. 111. Pour Track Rectangular Section, Boston Subway. 



over the succeeding trench or slice. During the construction 

 of each slice the street traffic, including the street cars, was 

 carried by the timber platform. 



In the parallel trench method, short parallel trenches were 

 dug for the opposite side walls, and also for the intermediate 



S...-H..H Knowing Slice Mnthod of Conntrii'-tion. Il<wton Subway. 



columns, and completely roofed over during the night I'mler 

 this roofing the masonry of the side walls and column founda- 

 tions and the columns themselves were erected. Wlun the 

 side walls and columns had been erected, the surface of the 

 street between them was removed, the roof beams laid, and a 



