Seismic active earth pressure on bilinear retaining walls using a modified pseudo-dynamic method

Abstract

Background: Proper understanding of seismic behavior of retaining structures is crucial during a strong earthquake event. In particular, response of retaining walls with bilinear backface, where a sudden change in the inclination along its depth make the problem more complex. This study focuses on estimating the seismic earth pressure coefficients of a retaining wall with bilinear backface using a modified pseudo-dynamic method. Methods: In this method, the backfill soil is modeled as a visco-elastic Kelvin–Voigt material. A frequency-dependant amplification function is derived for the waves traveling along the backfill using well-established one-dimensional ground response analysis theory. A rigorous parametric study has been carried out to understand the effect of various parameters such as amplitude of base acceleration, direction of vertical acceleration, soil shear resistance angle, soil-wall friction angle, wall inclination, frequency ratio, and damping ratio on the seismic active earth pressure. Results: It has been observed that the damping ratio of the backfill soil plays an important role, particularly when the frequency of wave is close to the natural frequency of the backfill. Further, the seismic active thrust is found to increase in both upper and lower segments of the wall when the frequency of the primary wave is greater than that of the shear wave. Comparison of results with the previous studies indicates that the conventional pseudo-dynamic methods significantly underestimate the seismic coefficients and seismic pressures, particularly for the high-intensity motions. Conclusions: The results of the study show that the natural frequency and damping of the backfill soil have significant effect on the seismic active earth pressure coefficients. Comparison with conventional pseudo-static and pseudo-dynamic methods indicates that the previous methods largely underestimate seismic coefficients and seismic pressures (as much as 48%). This under-estimation is more prominent for higher-intensity motions and less-damped soil, where the soil amplification effects pose most importance. This modified pseudo-dynamic approach can further be used for design of bilinear retaining structures.