Earthquake Design Pressures from Soil Interaction on Building Basement Walls

Abstract

Free-standing retaining walls are usually designed for earthquake loads using the Mononobe-Okabe method and assuming cohesionless soil backfill. The method assumes active pressure develops as a consequence of a failure wedge in the backfill soil. Building basement walls are usually relatively stiff or restrained from relative displacement so the active pressure state is unlikely to develop. 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. There is no established design method that considers both of these components. A number of recent centrifuge and analytical studies consider the loading from the wave generated soil deformations. Previous analytical studies consider buildings founded on rock or very stiff soil but these are not typical foundations of many buildings with basements that are founded on piles or a raft foundation. The paper reviews published information on earthquake pressures on basement walls. Results are presented from elastic FEA undertaken as part of the present study and calibrated against the experimental centrifuge results. Because of the wide range of building geometries and foundation types it is not possible to develop a simple empirical method that is widely applicable. Instead, it is concluded that simplified elastic FEA should be part of the design process to estimate the earthquake induced pressures.