ST. GOTHAED RAILWAY AND TUNNEL. 



821 



diameter, into the rock. This tool makes only 

 three or four turns a minute in the rock, and 

 is worked without the noise, without the loss 

 of force at every blow, and without the act- 

 ive movement of air and spontaneous venti- 

 lation that accompany the use of the com- 

 pressed-air drill. In the Brandt system, the 

 supporting apparatus is as ingenious as the 

 machine itself, and is so disposed against the 

 face of the rock as to present a solid and effi- 

 cient resistance to the strong pressures that 

 are brought to bear upon it. Several perfora- 

 tors may be mounted upon the same support- 

 ing apparatus. The Brandt engine has given 

 satisfactory service, but the employment of 

 compressed air seems at present to be regarded 

 with more favor than that of compressed water. 

 The compressed-air engine was used in the 

 construction of the St. Gothard Tunnel for the 

 three purposes of driving the drilling-machines, 

 of securing a full ventilation of the chambers, 

 and of propelling the locomotive-engines that 

 were employed to carry away the broken rocks 

 and rubbish. Steam could not be used in the 

 tunnel, for the smoke and vapor would have 

 added to the noxious properties of an atmos- 

 phere that was already hardly supportable. 

 At first, special compressed-air engines were 

 built to draw the construction-trains. A sim- 

 ple arrangement was afterward adopted, by 

 which the machinery of ordinary locomotives 

 was fitted to receive and be moved by com- 

 pressed air while within the tunnel, and changed 

 so as to take on steam immediately on reaching 

 the outside. 



The power by which air was compressed 

 and the force necessary to move the machines 

 was transmitted to them was obtained from 

 the natural sources of the streams near either 

 end of the tunnel. The river Reuss afforded 

 an abundant supply with a strong fall at the 

 Goeschenen end ; at the Airolo end the main 

 supply, drawn from the brook Tremola, was 

 supplemented by a more regular but less pow- 

 erful current drawn from the river Ticino. 

 The force of the stream was applied to turn 

 four turbine-wheels which made three hundred 

 revolutions in a minute, and exerted a force of 

 about two hundred horse-power. These wheels 

 were made to turn a horizontal axis with cranks 

 revolving eighty-five times a minute, which 

 kept the compressors in .operation. The air, 

 which was subjected to a compression of from 

 four to eight atmospheres, became very hot, 

 and had to be cooled by special applications of 

 water kept circulating in cold currents around 

 the pumps and in the pistons and piston-rods, 

 and by injections of fine spray. After being 

 further cooled and freed from water in suspen- 

 sion by passing it through reservoirs, the com- 

 pressed air was conducted into the tunnel by 

 tubes which were of considerable size at the be- 

 ginning of the course, but were diminished to 

 correspond with the diminishing supply of air 

 as the work was advanced. The capacity of 

 the compressors may be measured by the fact 



that about eighty thousand cubic metres of air 

 were introduced into the chambers at either 

 end of the tunnel every day. The provisions 

 for supplying the compressed air to the cham- 

 bers, requiring a system of pipes five thousand 

 metres or more than sixteen thousand feet 

 long for each gallery, gave an opportunity for 

 the institution of some interesting experiments 

 relative to the flow of compressed air through 

 long metallic pipes. The loss of the charge in 

 the pipes was a factor of great importance. 

 The absolute pressure of the air, which was 

 equivalent to six and a half atmospheres at the 

 mouth of the tunnel at Goeschenen, diminished 

 as the conduits were carried along during the 

 progress of the work, till finally it was no more 

 than one atmosphere and an eighth at the end 

 of the excavation. At Airolo it was necessary, 

 in order to counteract the waste, to enlarge 

 the diameter of the perforators, and to expend 

 a considerably larger volume of air to perform 

 the same work. The boring of the tunnel was 

 begun at Airolo on the 13th of September, 

 and at Goeschenen on the 9th of December, 

 1872, and was continued uninterruptedly till 

 the 29th of February, 1880, when a junction 

 of the two galleries was effected at a point only 

 two hundred and eighty-nine metres south of 

 the center of the work. The extreme errors in 

 the direction of the two galleries amounted to 

 not more than eight inches lateral and four 

 inches vertical. The borings were carried on 

 by first cutting a chamber, or advance-gallery, 

 about eight feet square, at the top of the in- 

 tended excavation. This chamber was then 

 enlarged on the right and left, after which the 

 arches of the roof were built, and a trench 

 nearly ten feet wide was dug to the level of 

 the base of the tunnel. This was called the 

 " Cunette de Strosse." All the matter that re- 



STBTEM OF EXCAVATION : 1, advance gallery ; 2, side- 

 workings ; 3,4, "Cunette Ue Strosse" ; 5, "Strosse.' 



mained to the right and the left of the intended 

 excavation, called the "Strosse," was next re- 

 moved. Thus most of the digging was done 

 downward, and under conditions that presented 

 superior advantages. The blasting was done 

 chiefly with dynamite, and it has been calcu- 

 lated that, taking the work all through, each 



