TUNNELS THROUGH HAUD ROCK 111 



At Brigue the installations are, as far as jxissible, identical. 

 The Rhone water, however, before reaching the water-house, is 

 carried from the filter basins, a distance of 2 miles, in an 

 arm >red canal built upon the Hennebique system,* the walls 

 and supporting beams, of cement concrete, being strengthened 

 by internal tie-bars of steel. The concrete struts, resembling 

 balks of timl>er at a distance, are occasionally 35 ft high and 

 1 ft. 7i ins. square. The metallic conduit is 5 ft, in diameter, 

 with a minimum flow of 170 cu. ft per second and a total fall 

 of 185 ft. In case water-power should be unavailable, three 

 semi-portable steam engines, two of 80 H.P. and one of 60 H.I'., 

 are always kept in readiness at each end of the tunnel, and am 

 geared by belts to the turbine shaft. 



Ventilation. In tunneling, one of the most import a ni prol>- 

 lems to be solved is that of ventilation, and it is for this i> 

 that the Simplon tunnel consists of two parallel headings with 

 crosscuts at intervals of 2*20 yds. At Brigue, a shaft 1JJ ft. 

 deep was sunk through the overlying rock until the "gallery of 

 direction " was encountered. Up this chimney the foul air is 

 drawn by wood fires, the fresh air a volume of llUXMijMH) 

 cu. ft per day, or 13,200 cu. ft per minute entering by 

 heading No. 2, penetrating up to the last cross gallon-, and 

 returning by tunnel No. 1. The entrances of No. 1 and th 

 44 gallery of direction," besides those of all the intermediate 

 cross galleries, are closed by doors. By this arrangement, how- 

 ever, fresh air does not reach the working faces; therefore a 

 pipe, 8 ins. in diameter, is led from the fresh air in No. - to 

 within 15 yds. of the face of each heading, and up this pipe a 

 draft of air is induced by means of a jet of water, the volume 

 to each face l>eing 800 cu. ft. per minute. One single jet of 

 water from the high-pressure mains, with a diameter of ,', in., 

 is capable of supplying over 1,000 cu. ft of air per minute at 

 the end of 160 yds. of pipe, and during the attack the men at 

 the drills are in a constant breeze with the thermometer stand- 



Network u( iel rwl>eoibktod la eooento. 



