Effect of layered liquefiable deposits on the seismic response of soil-foundations-structure systems

Abstract

The soil liquefaction is a major cause of damage in structures during earthquakes. This damage varies from small settlements to complete failure due to the loss of bearing capacity. To deal with these problems, piled foundations have been utilized in the presence of liquefiable soils in seismic zones. More recently, rigid inclusion foundations have been also considered. A fundamental approach to study the soil-foundation-structure interaction requires the determination of the influence of the kinematic and inertial effects in the system. In order to investigate the effects of this interaction, numerical models with a 3-storey reinforced concrete building founded on pile systems (soil-pile-structure) and rigid inclusion systems (soil-inclusion-platform-structure) were analyzed. Finite difference numerical models were developed using Flac 3D. The SANISAND constitutive model was utilized to represent the behavior of the liquefiable soil layer. This model predicts with accuracy the soil response for various soil densities, stress levels and loading conditions. The linear elastic perfectly plastic constitutive model with a Mohr-Coulomb failure criterion was used to represent the behavior of the non-liquefiable soil layers. Different relative density values of the sand layer were considered. Two earthquake signals were used to study the influence of the frequency of the systems excitation. For each case, the spectrum response, shear forces and rocking of foundations were obtained. Maximum shear strains and excess pore pressures were presented at different depths. The efforts and displacements in the rigid elements (piles or rigid inclusions) were also compared for the different systems. The results show that the relative density, the pile length and the frequency of the input motion greatly influence the response of the reinforced systems.