Soil Rocking and Seismic Design Implications for Retaining Walls: Numerical Modeling Considerations from Analyzing a Centrifuge Test

Current design codes for the dynamic design of retaining walls have been criticized for being both over-conservative and under-conservative. However, much of the uncertainty in these cases comes from the dynamic earth pressure coefficients assumed. Recent research has suggested that the limiting dynamic horizontal effective stresses can be more straightforwardly predicted using static earth pressure coefficients once it is recognized that, in some cases, horizontal shaking can induce significant dynamic vertical effective stresses. In this research, results from a dynamic centrifuge test, conducted using the University of Colorado Boulder’s 400 g ton centrifuge, are used to demonstrate the occurrence of soil rocking and to inform finite element modeling of the problem. Dynamic analyses are conducted to investigate the rocking soil response, and the results are validated by comparing the system mechanics and the cyclic shear stress-strain loops mobilized. In this study, particular attention is paid to the numerical modeling of the boundary conditions with a discussion of rigid versus absorbing boundary conditions used to idealize the centrifuge test’s absorbing duct seal boundaries. Overall, the results evidence the occurrence of soil rocking under horizontal shaking and motivate a move away from traditionally used dynamic earth pressure coefficients.