An Alternative Approach to Dynamic Earth Pressure Coefficients to Improve the Seismic Limit State Design of Earth-Retaining Structures

Abstract

Dynamic earth pressure coefficients are widely used in the seismic engineering design of earth-retaining structures. Nevertheless, there remains confusion about their validity, with past studies conflictingly arguing the same estimates can be either conservative or unconservative. This study aims to address past uncertainty surrounding the limiting dynamic stress state in retained soil. Dynamic centrifuge testing and complementary numerical analyses are used to support a simpler, more fundamental interpretation of the dynamic limiting stress state of retained soil. The case of a dry, cohesionless, and level soil bed retained by smooth walls experiencing seismic loading is used to clarify the underlying mechanics that are relevant for a broad range of engineering problems with retained soil. Ultimately, the findings can promote a move away from previous methods to estimate dynamic earth pressure coefficients. Instead, it is shown that Rankine earth pressure coefficients can be combined with the newly discovered dynamic normal vertical effective stresses to better define the limiting stress state of soils under seismic loading. These vertical dynamic variations are attributed to soil rocking that is a function of the wall-soil interface properties and system dynamics and can be induced by purely horizontal shaking. Finally, simplified analytical methods to estimate the distribution and time histories of dynamic normal vertical effective stresses are proposed. Validation of these against the numerical predictions illustrates a more theoretically sound path forward to estimate the limiting horizontal stresses, and thus forces, for the improved seismic limit state design of earth-retaining structures.