. Official proceedings . Works,California, 26860 feet long, was driven 466 feet in granite in Oc-tober, 1908. The heading I2xi2 was driven with a model 6-Awater Leyner drill, the mucking being done by hand and thetramming by electric motors. Cost per foot, $ An excellent record in driving a railroad tunnel was madein 1908 on the Bitter Root Tunnel of the Chicago, Milwaukee &St. Paul Railroad, through the Bitter Root IMountains, tunnel was driven by the regular top heading method andwas advanced feet in May of 1908, the average advancefor the three months of March, April
. Official proceedings . Works,California, 26860 feet long, was driven 466 feet in granite in Oc-tober, 1908. The heading I2xi2 was driven with a model 6-Awater Leyner drill, the mucking being done by hand and thetramming by electric motors. Cost per foot, $ An excellent record in driving a railroad tunnel was madein 1908 on the Bitter Root Tunnel of the Chicago, Milwaukee &St. Paul Railroad, through the Bitter Root IMountains, tunnel was driven by the regular top heading method andwas advanced feet in May of 1908, the average advancefor the three months of March, April and May being rock is a quartzite somewhat laminated and the heading isthe full roof arched section for a double track tunnel. The new Croton Aqueduct has a length of miles, ofwhich miles is in tunnel, being horseshoe in form, high and feet wide and carrying an estimated capacityof 318,000,000 gallons of water per day. This is the longest tun- a«H5 600 ft. apart Tifp Hem^hg. Loefschberg Tunnel MethodsFisfure 2. 66 Proceedinos Railway Club of Pittsburi^rh. fe nel in the world. It was driven from shafts about a mile and aquarter apart along the length of the line, and the best record inany one heading was 550 feet per month. This was in hard rockin an unsually large heading and the ordinary progress was about175 feet per month. Fig. 2 shows the method of attack and the sequence of oper-ation in driving the south heading of the Loetschberg Tunnel,which is being built in Switzerland on the line of the railway toconnect Berne with the Simplon Tunnel route to Italy. Thistunnel when completed will be about 8^ miles long. The bot-tom heading 6 6 high by 10 feet wide is driven by machine drillsmounted on drill carriages, and the rock encountered varies fromgranite to gneiss and is hard drilling. Compressed air is fur-nished by two electrically driven Ingersoll Rand compressors ofthe cross compound two stage type. The record in this tunnel is37
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