Abstract:

The seismic response analysis is typically carried out to evaluate the seismic resistance of the civil engineering structure including the surrounding bedrock related to nuclear power facilities. The bedrock is conservatively assumed to be a linear material in the seismic response analysis. It is confirmed that the stress ratios (= stress/failure strength) occurring in the bedrock are within 0.5 from result of the seismic response analysis. Therefore, the multi-stage cyclic compression test of the rock was performed in order to confirm whether the bedrock is generally elastic against the stress ratio. As a result, it was confirmed that the stress-strain relation of the rock specimens were almost linear until the loading stage just before the failure and the elastic wave velocities of the rocks were not generally nearly decreased. Therefore, they has been shown it is reasonable evaluation method to assume the bedrock as a linear material.

1 Introduction

In Japan, the seismic response analysis is typically carried out to evaluate the seismic resistance of civil engineering structure including the surrounding bedrock related to nuclear power facilities. Stress-strain relation of bedrock is conservatively assumed to be a liner elastic material in the seismic response analysis and Young's modulus are calculated from elastic wave velocity, because the stress ratio (= stress/failure strength = reciprocal of local safety factor) is basically used as an evaluation index in the seismic response analysis.

On the other hand, a condition of bedrock is not clear while the stress is increasing in case that bedrock is received by cyclic loading like seismic wave. Stress-strain relation of bedrock is assumed to keep elastic condition on small stress range, but become a plastic state little by little as the stress increases. Regarding the surrounding bedrock of civil engineering structure in Takahama Nuclear Power Plant (operated by Kansai Electric Power Co., Ltd), it is confirmed that the stress ratios occurring in the bedrock is smaller than about 0.5 from the result of seismic response analysis. The bedrock consists of rock and discontinuity and it is assumed that the rocks bear external shear force like seismic wave. If the rock keeps elastic condition while stress ratios are within 0.5, it is appropriated that the bedrock is assumed to be a liner material in the seismic response analysis. Therefore, elastic region of the surrounding bedrock shall be indirectly evaluated by tests which uses the rocks as specimens in this paper.

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