IIIK.'M.H tMJKT UKUt'ND 



CHAI'TKU XIII. 



EXCAVATING TUNNELS THROUGH SOFT 



GROUND; GENERAL DISCUSSION; THE 



BELGIAN METHOD. 



GENERAL DISCUSSION. 



IT may be set down as a general truth that the excavation 

 of tunnels through soft ground is the most difficult tusk which 

 confronts the tunnel engineer. 1'nder the general term of soft 

 Around, however, a great variety of materials is included, be- 

 ginning with stratified soft rock and the most stable sands and 

 clays, and ending with laminated day of the worst character. 

 From this it is evident that certain kinds of soft-ground 

 tunneling may IN- less difficult titan tin- tunneling of rock, 

 and that other kinds may present almost insurmountable dif- 

 ficulties. Classing lx)th the easy and the difficult materials 

 together, however, the accuracy of the statement first made 

 holds good in a genenil way. Whatever the opinion may I* 

 in regard to this jMunt, however, there is no chance for dispute 

 in the statement that the difficulty of tunneling the softer and 

 more treacherous clays, peats, and sands is greater than that 

 of tunneling firm soils and rock; and if we describe the methods 

 which an- used successfully ill tunneling very unstable material*, 

 no difficulty need lie experienced in modifying them to handle 

 stable materials. 



Characteristic* of Soft-Ground Tunneling. The principal char- 

 acteristics which distinguish soft-ground tunneling arc, first, 

 that tin- material is excavated without the use of cxplogives, 

 and second, that the excavation has to be strutted practically 



