Analysis of Seismic Stability of an Obsequent Rock Slope Using Time-Frequency Method

Obsequent rock slopes are often thought to be more stable than consequent slopes and passive sliding is unlikely to occur under earthquake loading. However, failures in obsequent rock slopes were indeed observed in recent large earthquakes. This paper presents a time-frequency solution to the seismic stability of obsequent rock slopes fully considering the time-frequency characteristics of earthquake waves. Large-scale shaking table tests were conducted to illustrate the application of the time-frequency method to an obsequent rock slope containing multiple weak layers with a small dip angle. The seismic stability of the obsequent rock slope is analyzed combining the time-frequency method, outcomes from the shaking table test, and conventional pseudo-static and dynamic numerical analyses. The results show that passive sliding can develop in the obsequent rock slope when taking the time-frequency components of the earthquake waves and the vertical seismic force into account. The middle-upper part of the obsequent rock slope is more vulnerable to seismic damage. The slope bulges under the earthquake loading; the maximum permanent surface displacement occurs at the middle-upper part of the slope, rather than the slope crest. Additionally, the response of seismic safety factor lags behind the responses of acceleration and surface displacement.