(,I:M:I:AL MKTHODS OF EXCAVATION 37 



have to be hoisted out, and also for the construction tools and 

 matt-rials which have to be lowered down them. They must 

 also afford a passageway for workmen, dnift animals, and for 

 pipes- for ventilation, water, compressed air, etc. The character 

 of this traffic indicates the dimensions required, hut these de- 

 pend also up >:i the method of hoisting employed. Thus, when 

 a windlass or horse gin is used, and the materials are hoisted 

 in buckets of small dimensions, the dimensions of the shaft may 

 also IK? small; but when steam elevators are employed, and the 

 material is carried on cars run on to the platform of the elevator, 

 large dimensions must be given to the shaft. Generally the 

 parts of the shaft used for different purposes are separated by 

 partitions. The elevator for workmen and the various pipes 

 are placed in one compartment, while the elevator for hoisting 

 t'.ie excavated material and lowering construction material is 

 placed i:i another. 



Shaft-; nny be either temporary or permanent. They are 

 temporary when they are filled in after the tunnel is completed, 

 and permanent \\heit they are left open to supply ventilation 

 to the tunnel. lYrmancnt shafts are usually made circular, and 

 lined with brick, unless excavated in very hard and durable 

 rock. \Vhe:i sunk for temporary use only, shafts are usually 

 m.ide rectangular with the greater dimension transverse to the 

 t innel. They are strutted with timber. A pump is generally 

 located at the bottom of the shaft to collect the water \\hich 

 in from the sides of the shaft and from the tunnel 

 excavation. The dimensions of this pump will of course vary 

 with the amount of water encountered, as will also the capacity 

 of the pump for forcing it up and out of the shaft, which has 

 always to be kept dr\ . 



The maj .lily of engineers prefer to sink shrifts directly 

 over the center line of the tunnel. Side shafts are employed 

 chiefly by I-Yeiich engineers. The chief advantage of the 

 former method is the givat facility which it affords for hoisting 

 out the materials, while in favor of the latter method is the 



