Proceedings : 1974 Rapid Excavation and Tunneling Conference, San Francisco, California, June 24-27, 1974 - Rapid Excavation and Tunneling Conference; Pattison, Harry C.; D'Appolonia, Elio; American Society of Civil Engineers; American Institute of Mining, Metallurgical, and Petroleum Engineers; Canadian Institute of Mining and Metallurgy; Engineering Institute of Canada (Society of Mining Engineers of the American Institute of Mining, Metallurgical, and Petroleum Engineers, 1974)