Dynamic frictional behaviour of synthetic sandstone under low normal stress and seismic excitation

SUMMARY Both New Zealand and Taiwan are located in the Pacific ring of fire, the most active seismic zone in the world, and therefore slope failures triggered by seismic excitation are frequent and they sometimes could cost severe damage to life and property. Earthquake induced slope failure, especially rock-block sliding failure, is usually analysed using friction coefficient measured at the sliding-interface. A tilt test is a convenient test for measuring the required values under static condition, but the applicability of measured results to analyse block sliding under dynamic condition requires further investigation. In this paper, a series of static tilt test and dynamic shaking table test were performed to simulate block sliding with base excitation. The results were compared in terms of measured sliding thresholds, and the causes of the differences were discussed. Tests on synthetic sandstone showed that friction coefficients measured by tilt tests were always larger than the ones derived by shaking table tests. Furthermore, sliding thresholds increased with increasing shaking frequency, suggesting that the sliding threshold is non-constant under excitation. In addition, the sliding threshold is lower at higher contact stresses on the sliding surface, showing that the sliding threshold varies with normal stress. This study identified the limitations of the tilt test when applied to dynamic problems, and recommended that realistic sliding threshold can only be obtained using dynamic tests, such as shaking table tests.