PARAMETRIC ANALYSIS OF HORIZONTAL ACCELERATION RESPONSE OF ROCK SLOPE TO SEISMIC WAVES IN A SHAKING TABLE TEST

Abstract

Studies on landslides triggered by the 2008 Wenchuan earthquake show that topography, geology and seismic source are of great importance in amplifying seismic waves and in determining spatial concentration of slope failures. A shaking table test on two rock slopes was carried out in the present study. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Based on the measurements from accelerometers installed on free surface of the model slopes, horizontal acceleration responses were analyzed. It is found that the amplification factor of peak horizontal acceleration, RPHA, increases with elevation of each model slope, though the upper and lower halves of the slope exhibit different increasing patterns. Comparing the responses considering different lithology, excitation direction, intensity and frequency, the results show that: (1) the model slope with materials of low strength (HS model) produces horizontal responses over 2.5 times stronger than the model slope with materials of high strength (HH model) at the crest; (2) both PHA (Peak Horizontal Acceleration) and RPHA show general increase with the excitation intensity, indicating that the horizontal acceleration response of slopes gets strengthened before the slope deformation enters nonlinear phase; (3) the HS model presents frequency-dependent amplification at lower frequency than the HH model; and (4) the coupling effect of horizontal and vertical (XZ) direction shakings not only produces larger PHA amplification than the horizontal (X) direction shakings, but also a larger spectral amplification at high frequencies. The coupling effect indicates the non-ignorable role of vertical motions in response of a slope to an earthquake and should be considered in engineering design.