The study concerns the analysis of a retaining structure composed by a couple of r.c. diaphragm walls propped at the crest in loose and medium-dense, variably saturated sand under seismic conditions. Fully coupled dynamic equilibrium conditions and pore water flow in the porous soil have been taken into account, in order to assess the effects that the development and subsequent dissipation of excess pore water pressures can have on the performance of such structures under seismic conditions. To this end, a series of simulations in which the saturated soil permeability is varied of about two orders of magnitude has been carried out, in order to consider different evolution rates for the dynamic consolidation process. The von Wolffersdorff hypoplastic model and the van Genuchten water retention equation have been used to describe the mechanical and hydraulic behavior of the sand. The results obtained in a large series of finite element simulations show a significant dependence of the seismic performance of the structure evaluated in terms of permanent rotations and structural loads, in view of the modern performance-based design criteria on the excess pore pressures buildup during the seismic shaking and on its dissipation with time. For the particular seismic input considered, neither fully drained nor fully undrained conditions can be considered applicable in most of the cases considered. In such conditions, the quantitative assessment of wall and soil displacements, pore water pressures and effective stress distributions within the soil requires necessarily the solution of a fully coupled, nonlinear dynamic consolidation problem.

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The study concerns the analysis of the behaviour of two propped reinforced-concrete diaphragm walls in coarse sand under seismic conditions. Fully-coupled dynamic equilibrium and pore water flow under unsaturated conditions for the soil have been taken into account, in order to assess the effects that the development of excess pore water pressures can have on the performance of such structures when dynamic conditions occur. The von Wolffersdorff hypoplastic model and the van Genuchten soil-water retention model have been used to describe the mechanical and retention behaviour of the sand. The Finite Element predictions of the soil and retaining structure behaviour show a significant dependence of the seismic performance of the structure – evaluated in terms of permanent displacements and structural loads, in view of the modern performance-based design criteria – on the excess pore pressures developed in the soil during the seismic shaking, even when dynamic liquefaction does not occur.