MKTHUD8 OF LINING TUNNELS 75 



Side Tunnels. When tunnels are excavated by shafts located 

 at one side of the center line, short side tunnels or galleries are 

 built to connect the bottoms of the shafts with the tunnel 

 proper. These side tunnels are usually from 30. ft to 40 ft 

 long, and are generally made from 12 ft. to 14 ft. high, and 

 about 10 ft. wide. The excavation, strutting, and lining of 

 these side tunnels are carried on exactly as they are in the 

 main tunnel, with such exceptions as these short lengths 

 make possible. Table III. gives the thickness of lining used 

 for side tunnels, the figures being taken from European 

 practice. 



Flos. 46 and 47. Trannverne Soctlona of Tunnel* Showing Methods of Increasing th 

 ThickniwH of the Lining at IMii.-r.-nt r<>int*. 



Culverts. Tin- purpose of culverts in tunnels is to collect 

 the water which seeps into the tunnel from the walls and shafts. 

 The culvert is usually located along the center line of the 

 tunnel at the bottom. In soft-ground tunnels it is built of 

 masonry, and forms a part of the invert, but in rock tunnels it 

 is the common practice to cut a channel in the rock floor of the 

 excavation. Both lx>x and arch sections are employed for 

 culverts. The dimensions of the section vary, of course, with 

 the amount of water which has to l>e carried away. The fol- 

 lowing are the dimensions commonly employed: 



