Discrete element method analysis of seismic response of gravity retaining walls

Behavior of retaining structures under seismic loading is a complex soil-structure interaction problem. Since the actual wall movements and pressures depend on many different factors, numerous simplified approaches have been developed throughout the years and adopted by the geotechnical engineering industry. Most commonly used methods are Mononobe-Okabe method that provides useful means of estimating earthquake induced loads and Richards-Elms method for estimation of seismic displacements of retaining walls.;In this study, the analysis of the seismic response of soil-retaining wall system is done based on a three-dimensional microscale framework utilizing the discrete element method. The proposed method is employed to investigate the response of retaining walls with three degrees of freedom under different conditions of ground acceleration. In the simulation, the granular soil deposit is idealized as a collection of spherical soil particles; the retaining wall is simulated as a rigid block composed of clumped particles to yield the physical characteristics of a real-life retaining wall. The model is processed under the gravitational acceleration of 50g to reduce the total duration of the simulation and dimensions of the model. The model accounts for the effects of nonlinear soil behavior, possible separation between the retaining wall and soil deposit, and possible failure of the wall by overturning or sliding. The impact of amplitude and frequency of input dynamic excitation on the response of the wall is analyzed under different input motion conditions.;Effects of seismic loading on the soil-retaining wall system are presented in this study through time histories of magnitude and location of resultant soil thrust, pressure distribution on sides of retaining wall at different time instances, and displacement time histories of the wall. Comparison is made to simplified methods used in geotechnical engineering practice. Development of shear strain within the soil deposit is discussed and presented through strain "maps" at different time instances throughout simulations.;The proposed computational approach is able to capture essential dynamic response patterns such as the effect of resonance on amplifying the response of the soil-retaining wall system and the failure of the wall as it underwent excessive rotation and displacement due to increased earth pressure and inertia forces. The microscale analysis has allowed to capture the formation of soil failure wedge. The proposed approach has been able to overcome the separation between the wall and retained soil in the simulation that resulted in a complete failure of the system which signifies the powerful nature of the discrete element method for analysis of granular material.