Seismic Response Assessment of Structure-Foundation-Dense Granular Column Considering Interaction Effect on the Liquefiable Soil

Two of the important issues in the construction of structures located in seismic coastal areas are the study of the potential of liquefaction phenomenon in saturated sandy soils and seismic structure-foundation-soil interaction (SSFSI). Control of structure damage on the liquefiable soil and large deformations of soil due to seismic loading and, also, the other responses such as: the accelerations at top of the structure/foundation and excess pore water pressure related of this phenomenon are very important. The phenomenon of liquefaction happens due to the occurrence of an earthquake and due to the lack of sufficient opportunity for drainage of excess pore water pressure. One of the effective and useful mitigation methods to control of the liquefaction phenomenon is the usage of dense granular column (DGC) in appropriate dimensions and distances on the ground susceptible to liquefaction. The role of the DGC in controlling the liquefaction phenomenon are follow as: firstly, the DGC is made of materials that are more permeable to sandy soils and cause the excess pore water pressure to be dissipate faster, and secondly, DGC increases the stiffness of the system, which proportionally reduces the excess water pore pressure due to the dilative behavior. To reduce the risks of liquefaction, it is necessary to fully understand its consequences. These consequences depend on permanent soil displacements, structural performance, structural characteristics, foundation and structure dimensions, soil conditions of the structure site, type of loading and earthquake intensity. The presence of the structure and impact of SSFSI affects the intensity of liquefaction and static and dynamic stresses in the soil. Most prior studies (e.g., physical, numerical, or analytical models), ignore the existence of the structure or consider the effect of soil-structure interaction (SSI) on the liquefiable soil layer as an equivalent model. Hitherto, the essence and extend of these interactions are not sufficiently understood. These methods can not properly assess the damage caused by liquefaction; Therefore, these methods cannot be used in the design of structures resistant to liquefaction. Therefore, to accurately study the effect of liquefaction, a method and model is needed that can fully consider the soil, foundation, and structure so that it can be used to correctly estimate the amount of subsidence and displacement of the structure. In this study, to evaluate the seismicity and the mitigation effect of DGCs, using OpenSees finite element software, modeling of DGCs and surrounding soils without structure and models with 5, 10 and 15 storey structures were performed. The three-dimensional soil and DGCs modeled in the software are placed under different earthquakes and the effects of structural layers on the lateral displacement, excess pore water pressure, response of acceleration spectrum, drift and shear force of stories are investigated. The liquefiable soil is modelled through the pressure-dependent multi yield surface soil constitutive law (PDMY02) applied in OpenSees. The results of this study are shown the positive effect of DGC on the reduction of lateral displacement components of soil and structure, foundation subsidence and excess water pore pressure. Also, the presence of the structure on the soil and the increase of its floors have increased the mentioned components except for lateral displacement of soil.