Can tilt tests provide correct insight regarding frictional behavior of sliding rock block under seismic excitation?

Earthquake induced dip-slope sliding or rock-block sliding is usually analyzed using friction angles or friction coefficients measured at the sliding interface. A tilt test is a convenient test for measuring the required friction angle. However, a tilt test is a test under static conditions, and the applicability of measured friction parameters to analyze slopes under dynamic excitation requires further discussion.This study conducts a static tilt test and a dynamic shaking table test to simulate block sliding with base excitation, compares differences in measured sliding thresholds, and discusses the cause of these differences. Tests on three different materials (aluminum, sandstone, and synthetic sandstone) show that friction coefficients measured by tilt tests are always larger than the ones derived by shaking table tests. Moreover, high frequency tests yield larger friction coefficients, suggesting the sliding threshold is non-constant under excitation. In addition, tests with varying normal stresses on the sliding block show that with increasing contact stresses, sliding thresholds decrease, implying that sliding threshold varies with normal stress.Instantaneous friction coefficients, μi(t), during sliding are also studied in this work. It has been found that frictional behavior of synthetic sandstone deviates from the idealized Coulomb friction model. The instantaneous friction coefficient varies with relative displacement and relative velocity during sliding. Finally, reasons for differences between a static tilt test and a dynamic shaking table test are discussed. This study preliminarily identifies the limitations of the tilt test when applied to dynamic problems, and concludes that realistic sliding thresholds can only be obtained using dynamic tests such as shaking table tests.

Research Highlights
► The applicability of tilt test under excitation condition is discussed here.
► We discuss it by comparing the sliding thresholds obtained from different tests.
► Using μt in sliding block dynamic analyses leads to overestimate friction resistance.
► The inertial forces of sliding block cause reductions to friction coefficients.