Tl'NNKLS HlKitK.ll I1AKD ItOCK 



101 



the tool and a second 

 striking ; measure- 

 ments of exeavation 

 are taken every 2 or 

 3 yds., a pluml>-line is 

 suspended from the 

 center of the roof, and 

 at every half-meter 

 (20 ins.) of height 

 horizontal measure- 

 ments are taken to 

 each side. 



At the Brigue end 

 a softer rock is en- 

 countered, necessitatr 

 ing at times heavy 

 timbering in the head- 

 ing, and especially in 

 the final excavation 

 to full si/.e, Fig. 56. 

 The bottom heading, 

 6 ft. 6 in. high, is 

 driven in the center, 

 and the heading is 

 then widened to the 

 full extent and tim- 

 bered ; the concrete 

 forming the water 

 channel and the foun- 

 dation for one side 

 wall is put in ; the 



side walls are built to a height of 6 ft. 6 ins., and the tunnel 

 is fully excavated to a further height of 6 ft. 6 ins. from the 

 first st;r_rni'_;. Tii-- side Vffclll |M fcaMB MUtfaNiad ':; fol tfci 

 second 6 ft 6 ins., and froi.i the second floor a third height of 



Fio. Bfl. RkctchM Showing StfMMt of Work la 

 Excaratlng and Lining luo Hlui|>ln Tunnel. 



