COST OF EXCAVATION AND TIME RFXJFTRED 301 



excavation. To estimate the cost of excavation involves the 

 consideration of three general items, viz., the excavation proper, 

 the strutting of the walls of the excavation, and the hauling of 

 the excavated materials and the materials of construction. 



The cost of excavating the preliminary headings or drifts is 

 greater per unit of material removed than that of excavating 

 the enlargement of the section. The cost of bottom drifts is 

 also always greater than that of top headings, the material pene- 

 trated remaining the same. Mr. Rziha gives the comparative 

 unit costs of excavating drifts, headings, and enlargement of 

 the profile as follows : 



Bottom drifts $9.20 per cu. yd. 



Top headings 4.80 " " 



Enlargement of profile 2.84 " " " 



The cost of hauling increases with the length of the tunnel. 

 This fact and amount of this increase are indicated by the 

 following actual prices for the Arlberg tunnel: 



Top heading 96.76 per en. yd., increasing 37 cts. per mile 



Bottom drift 7.40 " " " " 20 " " " 



Enlargement of profile ... 2 70 " " " " 10 " " 



In all the prices given above, the cost of strutting and haul- 

 ing is included in the cost of excavation. 



The cost of excavation is not always the same for the same 

 character of materials in different tunnels. The following 

 figures si low the prices paid for the excavation of calcareous 

 rock in four different German tunnels: 



Berliner Nordhausen Wetzler R.R $1.24 per cu. yd. 



Ofen l.-TO " " " 



Stafflach 2.76 " 



Ories 1.02 " * " 



The method of tunneling has little influence upon the cost 

 of the work, as shown by the following figures from tunnel** 

 excavated through calcareous rock by different methods: 



