TiMi:K!:-LiNED TUNNELS WITH MASONRY 28o 



of masonry lining adopted. The side walls are of concrete and 

 the arch of brick. Tbis new masonry, of course, required tbe 

 removal of all tbe original timbering. The manner of doing 

 tliis work is as follows: A 7-ft section, A B, Fig, 146, was first 

 prepared by removing one post and supporting the arch by 

 st ruts, S S. After clearing away any backing, and excavating for 

 the foundation of the side wall, two temporary posts, F F, we re 

 set up, and fastened by hook bolts, Fig. 140, L, and a lagging 

 was built to form a mold for the concrete. Several of these 

 7-ft. sections were prepared at a tin.e, cadi two being sepa- 

 rated by a 5-ft. section of timbering. 



With Wall Plate. w.thout Wail Plate. 



Section ,wWi Concrete Car. Long'rtvdlrtal Section. 



Pio. 146. Conntniction of Centering Mullan Tunnel. 



The mortar car was then nin along, and enough mortar 

 (1 cement to 3 sand) was run by the chute into each section 

 to make an 8-in. layer of concrete. As the car passed along 

 to each section, broken stone was shoveled into the last preced- 

 ing section until all the mortar was taken up. The walls were 

 thus built up in 8-in. layers, and became hard enough to sup- 

 port the arches in about 10 to 14 days. The arches were then 

 allowed to rest on the wall, and the posts of the remaining 5-ft. 

 sections were removed, and the concrete wall built up in the 

 same way as before. 



