SUBMARINE TUNNELING 



245 



frames, and it shows quite clearly the complicated details of 

 the shield construction. Two features which are to be particu- 

 larly noted are the suspended staging and centering for con- 



Fin. 122.-Ix>nKltn.1liiiil s,-,-tlon of BrimHV Slil.-M, FlrM Tlmnii* Tqnnel. 



structing the roof ;m-li. and tin- top plate of the shield extending 

 Kirk and overlapping tin- r<...f masonry so as to close completely 

 the roof of the excavation and prevent it falling. Notwithstand- 

 ing its complicated construction and unwieldy weight of 120 



