58 TUNNELING 



is generally employed in short tunnels and in the advance 

 headings and galleries. In long tunnels, or where the exca- 

 vated material has to be transported some distance away from 

 the tunnel, mechanical power is preferable, for obvious reasons. 

 The motors most used are small steam locomotives, special 

 compressed-air locomotives, and electric motors. Compressed 

 air and electric locomotives are built in various forms, and are 

 particularly well adapted for tunnel work because of their 

 small dimensions, and freedom from smoke and heat. 



Hauling by Way of Shafts. \Yhen the excavated material 

 and materials of construction are handled through shafts, the 

 operation of hauling may be divided into three processes : 

 the transportation of the materials along the floor of the 

 tunnel, the hoisting of them through the shaft, and the sur- 

 face transportation from and to the mouth of the shaft. These 

 three operations should be arranged to work in harmony with 

 each other, so as to avoid waste of time and unnecessary han- 

 dling of the materials. An endeavor should be made to avoid, 

 if possible, breaking or trans-shipping the load from the time 

 it starts at the heading until it is dumped at the spoil bank. 

 This can be accomplished in two ways. One way is to hoist 

 the boxes of the cars from their trucks at the bottom of the 

 shaft, and place them on similar trucks running on the surface 

 tracks. The other way is to run the loaded cars on to the ele- 

 vator platform at the bottom, hoist them, and then run them 

 on to the surface tracks. If the first method is employed, the 

 car box is usually made of metal, and is provided at its top 

 edges with hooks or ears to which to attach the hoisting cables. 

 When the second method is used, the elevator platform has 

 tracks laid on it which connect with the tracks on the tunnel 

 floor, and also with those on the surface. 



Hoisting Machinery. The machines most commonly em- 

 ployed for hoisting purposes in tunnel shafts are steam hoisting 

 engines, horse gins, and windlasses operated by hand. Wind- 

 lasses and horse gins are rather crude machines for hoisting 



