SEISMIC BEHAVIOUR OF FLEXIBLE RETAINING STRUCTURES: NUMERICAL MODELLING VS. SIMPLIFIED APPROACHES

The seismic response of a retaining wall is undoubtedly a complex issue that involves the dynamic interaction between the wall and the retained soil. The problem becomes more complicated if the wall is flexible, especially when constrained by anchors or tiebacks, and in the presence of significant porepressure increase. However, most of the modern seismic norms cope with the design of flexible retaining walls in a rather simplistic way, based mainly on limit-equilibrium methods. The present study tries to shed some light on this important issue. Our aim is the realistic numerical calculation of the earth pressures and of the seismic distress developed along the structure, especially in terms of displacements. Regarding numerical modeling, a finite-difference based computer code has been considered, while as far as the soil behavior is concerned, linear and nonlinear analyses are conducted. The role of parameters, like the wall flexibility, the compliance of the foundation soil, the type of anchoring, and the characteristics of the seismic excitation is examined thoroughly. Based on the results of the numerical dynamic analyses, we have also checked several simplified approaches for dealing with the problem at hand, stemming from the available analytical solutions in the linear case, pseudo-static approaches based on limit-equilibrium considerations, and simplified dynamic approaches based on suitable modifications of the Newmark method, in order to provide guidelines in a format useful for seismic norms.