Seismic Evaluation of Historic Searsville Dam, California


Searsville Dam is a 68-foot high curved concrete gravity dam with a central overflow section. Located in San Mateo County, California, the dam impounds San Francisquito Creek by forming a 952 acre-feet reservoir. Built of interlocking cast-in-place concrete blocks in 1890, the dam survived the 1906 San Francisco Earthquake which occurred on the San Andreas fault located only 3,000 feet west of the dam.

Three-dimensional linear and nonlinear finite-element analyses were performed to assess safety of the dam. The seismic inputs included two sets of three-component acceleration time histories associated with a maximum credible earthquake magnitude of 7.8 occurring on the San Andreas Fault.

Initially linear-elastic analyses were carried out to compute vibration properties, perform sensitivity analyses to assess the influence of the foundation modulus on the dam response, and to obtain a preliminary estimate of seismic stresses. The linear-elastic analyses were conducted using GDAP program.

The seismic evlautation required a nonlinear numerical model to account for the effects of potential opening of existing cracks, vertical joints within the dam, and the dam-foundation contact surface. These were conducted using QDAP. The 3D nonlinear finite-element analyses of Searsville Dam were performed for both static and seismic loads. The nonlinear analyses were carried out by assuming zero tensile strength for the vertical cracks and the crown joint and a nominal tensile strength for the dam-foundation joints. In addition to the stress analysis, structural stability of the dam against sliding along the dam-foundation contact surface was also evaluated and factors of safety were determined. This work was done in association with Dames and Moore of San Francisco, as the prime contractor.




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