3D NONLINEAR SEISMIC RAFT-PILE-SOIL-STRUCTURE INTERACTION FOR NUCLEAR POWER PLANTS

Abstract

Soil-Structure interaction plays a vital role in understanding the behaviour of massive structures such as nuclear power plants (NPPs) founded on soft/loose soil during seismic or dynamic loading. The behaviour of soil-foundation-structure becomes nonlinear during the seismic loading which complicates the problem. Most of the existing NPPs in India were constructed on the rock, which may not have the requirement of seismic soil-structure interaction analysis, but many of the upcoming proposed nuclear structures would be founded on the alluvial soil, necessitating considering SSI for analysis, further there could be an issue related to liquefaction. Therefore, in this thesis, finite element (FE) and finite difference (FD) based analyses considering Raft-Pile-Soil-Structure-Interaction (RPSSI) for nuclear power plants in the non-liquefiable and liquefiable soils are carried out. The first objective of this thesis is to develop and analyze computationally efficient 3D finite element and finite difference models of combined piled raft foundation (CPRF) of an NPP structure in the time domain, considering the material nonlinearity of soil and the effect of the boundary. This is further extended to analyze the seismic behaviour of RPSSI on the liquefying soil medium. Furthermore, to develop the 3D finite difference model of various types of foundations to examine the earthquake induced settlement with and without considering the NPP structure in both the non-liquefiable and liquefiable soils. The second objective is to carry out an RPSSI analysis on modelling the contact between the raft-soil and pile-soil, considering the effects of geometrical nonlinearity, i.e., slip and separation. The third objective is to develop an equivalent nonlinear spring-dashpot model (using the available non-linear constitute soil models) of a NPP Structure founded on raft foundation and CPRF in the time domain.