116 



TUNNELING 



front of this platform carries a hinged leaf which may be raised 

 and lowered, and which forms a sort of gang-plank reaching to 

 the floor of the heading. By running the heading cars out on to 

 this traveling platform, they can be dumped into the cars below 

 entirely clear of the work in progress on the bench front. 



For the purpose of illustrating the two methods of driving 

 tunnels by a heading, which have been briefly described, the St. 

 Gothard and the Busk tunnels have been selected. The St. 

 Gothard tunnel is selected, as being the longest tunnel in the 

 world, and because it was excavated by a number of small parts ; 

 and the Busk tunnel, as being a single-track tunnel, driven by 

 a heading, and bench, and having a timber lining. 



St. Gothard Tunnel The St. Gothard tunnel penetrates the 

 Alps between Italy and France, and is 9^ miles long. It was 

 constructed in 1872-82. 



Material Penetrated. The St. Gothard tunnel was excavated 

 through rock, consisting chiefly of gneiss, mica-schist, serpen- 

 tine, and hornblend, the strata having an inclination of from 

 45 to 90. At many points the rock was fissured, and disin- 

 tegrated easily, and water was en- 

 countered in large quantities, caus- 

 ing much trouble. 



Excavation. The sequence of 

 excavation is shown by Fig. 15, 

 p. 32. First the top center head- 

 ing, No. 1, whose dimensions varied 

 from 8.25 x 8.6 ft. to 8.5 x 9 ft., 

 according to the quality of the rock, 

 was driven never less than 1,000 ft. 

 and sometimes over 3,000 ft. in 

 advance of parts No. 2. The exca- 

 vation of parts No. 2 opened up the full top section, and parts 

 Nos. 3, 4, 5, 6, and 7, were removed in the order numbered. 



Strutting. Where regular strutting was required, the con- 

 struction shown in Fig. 59 was adopted. 



FIG. 58. Diagram Showing Se- 

 quence of Excavation in Heading 

 Method of Tunneling Rock. 



