32 



TUNNELING 



CHAPTER IV. 



GENERAL METHODS OF EXCAVATION: SHAFTS: 

 CLASSIFICATION OF TUNNELS. 



A NUMBER of different modes of procedure are followed in 

 excavating tunnels, and each of the more important of these 

 will be considered in a separate chapter. There are, however, 

 certain characteristics common to all of these methods, and 

 these will be noted briefly here. 



Division of Section. It may be asserted at the outset that 

 the whole area of the tunnel section is not ordinarily excavated 

 at one time, but that it is removed in sections, and as each 



section is excavated it is thoroughly 

 timbered or strutted. The order in 

 which these different sections are 

 excavated varies with the method of 

 excavation, and it is clearly shown 

 for each method in succeeding chap- 

 ters. As a single example to illus- 

 trate the proposition just made, the 

 division of the section and the se- 

 quence of excavation adopted at the 



OI./^AI_ J i i LJ^T?- 



ot Gothard tunnel is selected (*ig. 



15). The different parts of the 

 section were excavated in the order numbered ; the names given 

 to each part, and the number of holes employed in breaking it 

 down, are given by the table on page 30. Whatever method is 

 employed, the work always begins by driving a heading, which 

 is the most difficult and expensive part of the excavation. All 

 the other operations required in breaking down the remainder 



Fi<;. 15. Diagram Showing Sequence 



of Excavation for st. Gothard 



