Till: 1 I I.I. SK< TIMS METHOD 161 



Hauling. To haul away the material and take in supplies, 

 tracks are laid on the invert masonry. Generally the perma- 

 nent tracks are laid as fast as the lining is completed. A short 

 section of temporary track is used to extend this permanent 

 track close to the work of the advanced drift. 



Advantages and Disadvantages. The great advantage of the 

 English method of tunneling is that the masonry lining is 

 built in one piece from the foundations to the crown, making 

 possible a strong, homogeneous construction. It also pos- 

 sesses a decided advantage because of the simple methods of 

 hauling which are possible : there being no differences of level 

 to surmount, no hoisting of cars nor trans-shipments of loads 

 are necessary. The chief disadvantage of the method is that 

 the excavators and masons work alternately, thus making the 

 progress of the work slower perhaps than in any other method 

 of tunneling commonly employed under similar conditions. 

 This disad vantage is overcome to a considerable extent when 

 the tunnel is excavated by shafts, and the work at the different 

 headings is so arranged that the masons or excavators when 

 freed from duty at one heading may be transferred to another 

 where excavation or lining is to be done as the case may be. 

 Another disadvantage of the English method arises from the 

 excavation of the full section at once, which in unstable soils 

 necessitates strong and careful strutting, and increases the 

 danger of caving. The fact also that the arch ring has to 

 carry the weight of the crown bars, and their loading at one 

 end while the masonry is green, increases the chances of the 

 arch iM-ing distorted. 



Conclusion. - The English method of tunneling in its entirety 

 is confined in actual practice pretty closely to the country from 

 which it receives its name. A possible extension of its use 

 more generally is considered by many as likely to follow the 

 development of a successful excavating machine for soft 

 material. The space afforded by the opening of the full sec- 

 tion at once, especially adapts the method to the use of exca- 



