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Show 1960 Projects completed during the period were: 1) Mammoth Pool Tunnel Crews of Utah Construction & Mining Co. set a new record for hard rock tunnels by driving 390 ft. of tunnel in the 6-day week ending on January 31, 1959. This was accomplished at the outlet heading of the tunnel which Utah drove to carry the San Joaquin River from the Mammoth Pool Dam 8 miles through the Sierra to the Mammoth Pool Powerhouse. The Southern California Edison Company's Mammoth Pool Project, estimated at $50,000,000, was a part of the Big Creek development, 80 miles east of Fresno, California. The project con- sisted of a 440 ft. high rolled earthfill dam, the 8 mile, 20 ft. diameter horse-shoe-shaped power tunnel, and a two-unit powerhouse with a nameplate capacity of 126,000 kw. Work on the project commenced in January 1958 and was completed in 1960. Utah drove the tunnel from five headings, and driving was approxi- mately 50 per cent complete when the record was set. The crew at the tunnel outlet, under the supervision of Paddy O'Dowd, consistently made the best footage, and had had their eyes on the record for some time. Drilling Gantry jumbos were used in all headings except one, where a main line jumbo was used. The main line had eleven Gardner-Denver No. 93 drifters on tripod jib booms. The gantry jumbos mounted ten No. 93 drifters and one No. 123 drifter machine. Compressed air was furnished by a total of eight 1,800 cfm. Joy Sullivan compressors located in three separate compressor houses. Bits in use were Brunner & Lay carbide insert "Rok Bits." All drill steel was prepared and reconditioned in a fully equipped blacksmith shop located near the Rock Creek adit. Blasting Considerable attention had been given to developing the most economical and satisfactory blasting pattern. Most of these experiments were carried out under the supervision of Utah's explosive expert, R. L. "Moon" Mullen. The pattern which gave the best results had about 85 holes 1-5/8 in. in diameter spread around the 3-in. burn pattern. Atlas powder with Hercules primers were used at all headings. The delay pattern developed gave reasonably consistent breakage with the use of a combination of milli-second delays and regular delay caps. |
