t.l.KMAN MKTHOD 



145 



CHAPTER XIV. 



THE GERMAN METHOD OF EXCAVATING 



TUNNELS THROUGH SOFT GROUND; 



BALTIMORE BELT LINE TUNNEL. 



THE German method of tunneling was first used in 1803 

 in constructing the St. Quentin Canal. In 1837 the Konigs- 

 dorf tunnel of the Cologne and Aix la Chapelle R.K. was 

 excavated by the same method. The success of the method in 

 these two difficult pieces of soft-ground tunneling led to its 

 extensive adoption throughout Germany, and for this reason 

 it gradually came to be designated as the German method. 

 Briefly explained the method consists in excavating first an 

 annular gallery in which the side walls and roof arch are l>nilt 

 complete before taking out the center core and building the 

 invert. 



Excavation. The excavation of tunnels by the German 

 method is l>egun either by driving two bottom side drifts or 

 by driving a center top heading. Fig. 73 shows the mode of 



PlOB. 72 and 73. Diagram* Showing Sequence of Rxcarattan In Oormmn Method 

 of Tunneling. 



procedure when bottom side drifts are used to start the work. 

 The two side drifts No. 1 are made from 7 ft. to 8 ft. wide, 

 and about one-third the total height of the full section ; the 



