Development of DDBD method for retaining walls subjected to seismic loads

The paper focuses on the development of Displacement Based-Design (DBD) methods in the a-seismic design of earth retaining structures. Previous research has dealt with the application of DBD to cantilever and anchored walls embedded in coarse-grained soils. Comparison of the design seismic thrusts obtained through DBD calculation and more traditional design approaches have suggested that the former approach is realistic and in good agreement with common pseudo-static analyses, despite of its immediateness and simplicity. The main difficulty concerning the application of the method lies in the substitution of the soil/structure system into a simple single-degree-of-freedom system. In fact, the definition of the soil masses interacting with the wall during the seismic motion, as well as the evaluation of the damping ratio of the whole system, are considered a very intriguing matter; in addition, they sensibly affect the results of the proposed DBD approach. For this reason, in this work attention is paid to the effects of a proper choice of participating masses (active and passive soil wedges) and seismic demand, with the aim of simplifying the DBD design process. To this aim, non-dimensional charts and equations for the seismic thrust are provided, allowing the designer to skip the mass discretization and the associated displacement profile, and to use simple (non-dimensional) “reduction factors” of the seismic thrust, as a function of the design displacement.