Seismic Site Response of A Large Deep-seated Rock Slope Revealed by Field Monitoring and Geophysical Methods

Abstract

Shidaguan Slope (hereinafter short for SDG Slope) is an unstable rock slope with an area of 30.78×104 m2 and a deformation depth of 30-70 m in Maoxian County, Sichuan Province, China. Three seismometers (P2-P4) with high sensitivity were installed at different locations on the unstable part of the slope. P2 and P3 were almost at the same elevation (2221 m and 2247 m), while P4 was the lowest (at 2140 m). Another seismometer (P1) sat in a stable location at a higher elevation (2373 m). 99 shallow earthquakes were analyzed. According to the peak acceleration ratios of three seismometers (P2-P4) on the unstable part and another seismometer (P1) on the stable part, the points at lower elevations showed greater seismic amplification (with the amplification coefficient of 2.64-3.51) than one at a higher elevation. And points at relatively thinner part (23 m thick) of unstable slope showed greater seismic amplification than ones at thick part (60-75 m thick). The same rule was also found in studying the site-epicenter azimuth and earthquake magnitude data. Based on the relationship between amplification coefficient and resistivity and rock core, the seismic response amplification was affected by the lithofacies difference. The lithofacies with resistivity values of 50-100 Ohm.m and RQD values of 0-50 % incurred seismic response amplification, which was restrained by the below lithofacies with resistivity values of 10-50 Ohm.m and ROD values of 0 %. When building on slope areas, the lithofacies difference should be taken into full consideration.