276 TI'NNKL1N(J 



porary communication had been opened on the western track of 

 the tunnel, the remainder of the fallen earth was removed and 

 the excavation strutted. The new masonry lining was then 

 built 



To remove permanently the cause of the cave-in, which was 

 the percolation of water from a close-by stream, this stream was 

 diverted to a new channel constructed with a concrete bed and 

 side walls. 



The failure of the original lining occurred by cracks develop- 

 ing at the crown, haunches, and springing lines. The new lining 

 was made considerably thicker than the original lining, and at 

 the points where failure had first occurred in the original arch 

 cut-stone vousaoirs were inserted in the brickwork of the new 

 arch as described in Chapter XIII. 



Chattanooga Tunnel. The Western & Atlantic Ry. passes 

 through the Chattanooga mountains by means of a single-track 

 tunnel 1,477 ft. long, constructed in 1848-49. The lining con- 

 sisted of a brickwork roof arch and stone masonry side walls. 

 After the tunnel had been opened to traffic, this lining bulged 

 inward at places, contracting the tunnel section to such an ex- 

 tent that it was decided to reconstruct the distorted portions. 

 After careful surveys and calculations had been made, it was 

 decided to take down and reconstruct about 170 ft. of the 

 lining. 



Owing to contracted space in the tunnel, it was necessary 

 to remove all men, tools, and material, whenever trains were 

 to pass through ; and in order to do this a work-train of 

 three cars was fitted up with necessary scaffolds, and supplied 

 with gasoline torches for lighting purposes. Mortar was mixed 

 on the cars, and all material remained on them until used. 

 Debris torn out of the old wall was loaded on the cars, and 

 hauled to the waste dump. A siding was built near the West 

 end of the tunnel for the use of this train, and a telephone sys- 

 tem was installed between the entrances and the working-train. 

 On account of the contracted working-space and the greater 



