Graveholz Tunnel.
—The Graveholz tunnel on the Bergen Railway in Norway is notable as being the longest tunnel in northern Europe, and also as being built for a single-track narrow-gauge railway. This tunnel is 17,400 feet long, and is located at an elevation of 2900 feet above sea-level. Only about 3% of the length of the tunnel is lined. The mechanical installation consists of a turbine plant operating the various machines. There are two turbines of 100 H. P. and 120 H. P. taking water from a reservoir on the mountain slope, and furnishing 220 H. P., which is distributed about as follows: Boring-machines, 60 H. P.; ventilation, 30 to 40 H. P.; electric locomotives, 15 H. P.; machine shop, 15 H. P.; electric-lighting dynamo, 25 H. P.; electric drills, the surplus, or some 40 H. P. The boring-machines and electric drills will be operated by the smaller 100 H. P. turbine.
Sonnstein Tunnel.
—The Sonnstein tunnel in Germany is particularly interesting because of the exclusive use of Brandt rotary drills. The tunnel was driven through dolomite and hard limestone by means of a drift and two side galleries. The dimensions of the drift were 71⁄2 × 71⁄2 ft. The power plant consisted of two steam pressure pumps, one accumulator, and four drills. The steam-boiler plant, in addition to operating the pumps, also supplied power for operating a rotary pump for drainage and a blower for ventilation. The hydraulic pressure required was 75 atmospheres in the dolomite, and from 85 to 100 atmospheres in the limestone. The drift was excavated with five 31⁄2 in. holes, one being placed at the center and driven parallel to the axis of the tunnel, and four being placed at the corners of a rectangle corresponding to the sides of the drift, and driven at an angle diverging from the center hole. The average depths of the holes were 4.3 ft., and the efficiency of the drills was 1 in. per minute. One drill was employed at each front, and was operated by a machinist and two helpers, who worked eight-hour shifts, with a blast between shifts at first, and later twelve-hour shifts, with a blast between shifts. The 24 hours of the two shifts were divided as follows: boring the holes, 10.7 hours; charging the holes, 1.1 hours; removing the spoil, 11.7 hours; changing shifts, 0.5 hour. The average progress per day for each machine was 6.7 ft. The total cost of the plant was $17,450.
St. Clair River Tunnel.
—The submarine double-track railway tunnel under the St. Clair River for the Grand Trunk Ry. is 8500 ft. long, and was driven through clay by means of a shield, as described in the [succeeding chapter] on the shield system of tunneling. The mechanical plant installed for prosecuting the work was very complete. To furnish steam to the air compressors, pumps, electric-light engines, hoisting-engines, etc., a steam-plant was provided on each side of the river, consisting of three 70 H. P. and four 80 H. P. Scotch portable boilers. The air-compressor plant at each end consisted of two 20 × 24 in. Ingersoll air compressors. To furnish light to the workings, two 100 candle-power Edison dynamos were installed on the American side, and two Ball dynamos of the same size were installed on the Canadian side. The dynamos on both sides were driven by Armington & Sims engines. These dynamos furnished light to the tunnel workings and to the machine-shops and power-plant at each end. Root blowers of 10,000 cu. ft. per minute capacity provided ventilation. The pumping plant consisted of one set of pumps installed for permanent drainage, and another set installed for drainage during construction, and also to remain in place as a part of the permanent plant. The latter set consisted of two 500 gallon Worthington duplex pumps set first outside of each air lock, closing the ends of the river portion of the tunnel. For permanent drainage, a drainage shaft was sunk on the Canadian side of the river, and connected with a pump at the bottom of the open-cut approach. In this shaft were placed a vertical, direct-acting, compound-condensing pumping engine with two 191⁄2 in. high-pressure and two 333⁄8 in. low-pressure cylinders of 24 in. stroke, connected to double-acting pumps with a capacity of 3000 gallons per minute, and also two duplex pumps of 500 gallons capacity per minute. For permanent drainage on the American side, four Worthington pumps of 3000 gallons’ capacity were installed in a pump-house set back into the slope of the open-cut approach. For the permanent drainage of the tunnel proper two 400 gallon pumps were placed at the lowest point of the tunnel grade. Spoil coming from the tunnel proper was hoisted to the top of the open cut by derricks operated by two 50 H. P. Lidgerwood hoisting-engines. The pressure pumping plant for supplying water to the hydraulic shield-jacks at each end of the tunnel consisted of duplex direct-acting engines with 12 in. steam cylinders and 1 in. water cylinders, supplying water at a pressure of 2000 lbs. per sq. in.