Adapting Tunneling to Rocks of the Sierra Nevada

by G. Dan Johnson, Ebasco Services Inc, Placerville, CA, USA,
Steve Sert, Ebasco Services Inc, Placerville, CA, USA,

Document Type: Proceeding Paper

Part of: Water Power '87


Exploration programs were completed to select the most economical tunnel routes which are not only the shortest but are those which can be excavated by tunnel boring machines with the least requirements for supports, lining or the handling of major groundwater inflows. Exploration tools included air photo and topographic analysis, geologic mapping, seismic refraction surveys, laboratory and field testing of rock and subsurface exploration including core and percussion borings, groundwater monitoring and downhole geophysical surveys. Results of exploration showed that excavation of the tunnels and shaft will be through a variety of rock types, typical of the Sierra Nevada. These rocks, as grouped by origin, include alluvium, volcanic rocks, granitic rocks and metamorphic rocks. The tunneling properties of each of these rock units has also been affected by the degree of weathering, discontinuities, rock stresses and groundwater.

Subject Headings: Rocks | Rock properties | Tunneling | Rock mechanics | Tunnels | Excavation | Geological surveys | Groundwater | Nevada | United States

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