This study verified a slip safety factor evaluation method, as developed subsequent to equivalent linear analysis, for the existing rock slope subject to earthquake ground motion records of the 2011 Tohoku earthquake off the Pacific coast of Japan. Results demonstrated that, although a large deformation was not confirmed via slope measurements taken after the earthquake, the minimum slip safety factor was determined to be lower than 1.0. Therefore, it was found that a certain margin is included in the slip safety factor evaluation method. Next, for the purpose of developing a more practical seismic stability evaluation method, the slip safety factor was calculated based on seismic response analysis in the time domain while taking into account the stress redistribution. The analysis revealed the results to be consistent with the existing rock slope.

1 Introduction

Since the great earthquake of 2011 struck the north-eastern part of Japan, evaluation of the stability and safety of slopes situated in the vicinity of important structures when a large-scale earthquake strikes have been called for all the more fervently.

The stability evaluation of a rock slope against potential sliding failure during earthquakes, typically conducted as an evaluation of its safety factor against slipping (hereinafter, "slip safety factor"), has been carried out through examination of stresses in the slope based on seismic response analysis in the frequency domain using the equivalent linearization method (hereinafter, "equivalent linear analysis") (Nuclear Standards Committee of Japan Electric Association, 2015) (Nuclear Power & Civil Engineering Committee of Japan Society of Civil Engineers, 1985). However, since only the equilibrium between forces is considered in the evaluation of a slip safety factor, it has usually been the case that a slope is judged to be subject to failure if its safety factor is evaluated to be below 1.0 due to the fact that the equilibrium has broken down at that time momentarily. However, it cannot be said that a slope is likely to fail only because the equilibrium condition is not satisfied momentarily. Conventional slip safety factor evaluations, it has to be said, tend to be very conservative in nature.

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