Foundation Investigations of Concrete Dams

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


This paper discusses a series of foundation investigations conducted on concrete dams by Pacific Gas and Electric Company. The paper focuses on investigative techniques, equipment, appropriate material property tests and lessons learned. Four specific investigations will be discussed. Dams investigated include three concrete gravity dams and an arch dam. Drilling equipment used includes high speed, low torque pneumatic drills; low speed, high torque hydraulic drills; and double and triple core barrels of various lengths and sizes. Drilling conditions at dams are often quite difficult due to poor access and limited drilling space. Great care must be taken during the coring operations to insure the minimum of mechanical breakages in both the concrete and the foundation material and particularly at the interface of the two. Inspection of the completed boreholes and all available foundation drains by borehole cameras has provided invaluable information on the condition of the concrete, interface and foundation material(s). Appropriate material property tests of both the concrete and foundation materials include measuring the unit weights, unconfined compression tests with measurement of the modulus of elasticity, direct shear testing of joints and fractures, triaxial tests of both intact and fractured specimens, direct tensile tests and splitting tensile tests. Intact interface samples may be tested by direct tensile tests, triaxial compression tests and direct shear tests. Mechanically broken or unbonded interface samples may be tested by triaxial and direct shear tests.

Subject Headings: Triaxial tests | Compression tests | Arch dams | Gravity dams | Dam foundations | Concrete dams | Material tests | Shear tests

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