Earthquake design pressures from soil interaction on building basement walls

Free-standing retaining walls supporting a cohesionless soil backfill are usually designed for earthquake induced soil pressures using the Mononobe-Okabe limit state analysis (Mononobe and Matsuo [1]). This method assumes the development of a failure wedge in the backfill soil leading to active soil pressures on the wall. Building basement walls are usually relatively stiff or restrained from relative displacement so the active pressure state is unlikely to arise. In addition, two components of dynamic pressure that develop on the wall need to be considered. The first of these is due the shear deformations in the soil generated by the earthquake waves. The second results from the inertia forces of the building above ground level generating movements of the wall against the soil. Two-dimensional elastic finite element analyses were undertaken in the present study to determine the earthquake induced pressure force and its distribution on simplified basement wall structures. The parameters investigated included the width and stiffness of the basement, the depth of the soil layer and the distribution of the soil shear modulus with depth. Because of the wide range of basement geometries and foundation types it is not possible to develop a simple empirical method that is widely applicable. However, the elastic finite element analyses identified the influence of the most important parameters and the results can be used to decide whether more detailed analyses are necessary for large buildings.