GENERAL METHODS OF EXCAVATION 



41 



Submarine Tunnels. The mode of procedure followed in 

 excavating submarine tunnels depends upon whether the mate- 

 rial penetrated is pervious or impervious to water. In imper- 

 vious material any of the ordinary methods of tunneling found 

 suitable may K; employed. In pervious material the exi-ava- 

 tion may be accomplished either by means of compressed air 

 to keep the water out of the excavation, or by means of a 

 shield closing the front of the excavation, or by a combination 

 of these two methods. Tunnels on the river bed are built by 

 means of coffer dams which inclose alternate portions of the 

 \\ork, or by sinking a continuous series of pneumatic caissons 

 and opening communication between them. 



Ml 1 I|0|'- Ml' 



K\- \VATIS<J 

 Ti nraij 



In loose soil. 



!>!/ >(]>]>er half: 



the arch is built be- > Belgian method. 



fore the side walls. J 

 By the perimeter: ~\ 



excavated and lined 



before the central > German method. 



nucleus is battered 



down. J 



By whole section : 



thelinin,' Ue-ii 



the whole suction is 



excavated. 

 By halves: 



the lower half is ex- 

 cavated, lined, and 



.... , . > Italian inetliou. 



tilled in au'am. ful- 



lowed by the work of 

 the upper half. 



Kn-lish method. 

 Austrian method. 



In ifuicksand. 



Open-cut 

 tunnels. 



Submarine 

 tunnels. 



In resistant soils. 



In loose soils. 

 Hnilt up. 



At L.'ieat depths under 

 the river bed. 



At small depths 



under the river bed. 



On the river bed. 



ilSy two lateral nar- 

 i-i i \v trenches, 

 i Hy one very large 

 / trench. 

 Hy slices. 



' Hy any method. 



Hy shit-Id. 



Hy i-oinjirpHWHl air. 



By shield and com- 

 pressed air. 



By coffer dams. 



Hy pneumatic cais- 

 KMU 



