REL1NINU TIMBER-LINED TUNNELS WITH MASONRY 



by Fig. 148, it will be seen that two side trestles were built to 

 carry an adjustable centering for the roof arch. Two sections 

 (>t these trestles and centerings were used alternately, one being 

 carried ahead and set up to remove the timbering while the 

 masons were at work on the other. The manner of setting up 

 and adjusting the trestles and centerings is shown by Fig. 148 

 and also by Fig. 149, which is an enlarged detail drawing of 

 the set screw and rollers for the centering ribs. The following 

 is the bill of material required for one set of trestles and one 

 center : 



Trestles : 



Caps and sills 8 pieces 8 x 8 ins. x 20 ft. 



Posts 18 " 8 x 8 " x 11 " 



Braces 16 " 6 x 4 " x 7 " 



Centerings : 



Ribs 27 " 2 x 18 " x 7 " 



Bracing t ... 12 " 2 x 8 " x 7 " 



Support to crown lagging 2 " 6 x 6 " x 10 " 



Crown lagging 20 " 8 X " x 2" 



Side lagging 80 " 8 x 6 " x 10 " 



Side strips 2 " 2 x 12 ' x 9 " 



Blocking for rollers 1 " 6 x 8 x 12 " 



6 screw and roller castings complete with bolts and lever; 114 

 bolts i-ins. in diameter ; 7; U. II. hexagonalnut and 2 cast washers 

 each. 



With this arrangement the progress made per day varied 

 fmin -2 lin. ft. to 3 lin. ft. of lining complete. Hy work com- 

 plete is meant the entire lining, including stone packing between 

 the brirk\v..rk and the rock. On Feb. 23, 1900, 363 ft. of lin- 

 ing had been completed, at a cost of #33..">0 p-r lin. ft. This 

 r..st includes the cost of removing the old timl)er, the loose rock 

 above it, and all other work whatsoever. 



