Soil Nails as Temporary Powerhouse Support

by Russell Jernigan, Pacific Gas and Electric Co, San Francisco, United States,

Document Type: Proceeding Paper

Part of: Waterpower '91: A New View of Hydro Resources


Newcastle Powerhouse was constructed as an underground structure with its top deck at the finished ground surface. The powerhouse is three-quarter circular and one-quarter square in plan. The 39 feet (11.9 m) deep excavation for the powerhouse was constructed in decomposed granitic rock, weathered to the strength of a strong soil. A vertical excavation was chosen to conserve construction space. Construction support alternatives included steel sets, soldier piles with sheet lagging and soil nails (untensioned lengths of rebar grouted in place). Soil nails were selected due to the irregular configuration of the excavation walls. Design methodology included determination of the pull-out capacity of individual nails by field tests, potential active failure surfaces, required embedment lengths, the allowable working stress in the individual nails and the required nail pattern.

Subject Headings: Soil nailing | Power plants | Underground structures | Soil strength | Steel construction | Steel piles | Field tests | Hydro power

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