MKTHODS OF HAULING IN TUNNELS 61 



preferable hoisting device where the quantity of material to be 

 handled is large, where the shafts are deep, and where the work 

 will extend over a long period of time ; but when the contrary 

 conditions are the case, direct hoisting of the skips is generally 

 the cheaper. The engineer has to integrate the various factors 

 in each individual case, and 

 determine which method will 

 best fulfill his purpose, which 

 is to handle the material at 

 the least cost within the 

 given time and conditions. 

 The construction of ele- 

 vators for tunnel work is 

 simple. The elevator car 

 consists usually of an open 

 framework box of timber and 

 iron, having a plank floor on 

 which car tracks are laid, 

 and its roof arranged for 

 connecting the hoisting cable 

 (Fig. 38*). Rigid construc- 

 tion is necessary to resist the 

 hoisting strains. The sides 

 of the car are usually de- 

 signed to slide against tim- 

 ber guides on the shaft walls. 



Pio. 38. Bcnftor Ow for Tunnel Shaft*. 



Some form of safety device, 



of which there are several kinds, should be employed to pre- 

 vent the fall of the elevator, in case the hoisting ro(>e breaks, 

 or some mishap occurs to the hoisting machinery, which en- 

 dangers the fall of the car. Shaking tulws and electric-bell 

 signals should also l>e provided to secure communication be- 

 tween th<- toj) and bottom of the shaft. 



Reproduced from the catalogue of the Ledgvrw<NMl Manufacturing Company, New 



York. 



