Finite Element Simulation of Vertical Pile Load Tests for Piles Casted Partly in Soil Cement and Natural Alluvium Soil Deposits

Abstract

AbstractOne of the proposed site in Northern India for four unit 700 MWe nuclear power plant (NPP) is being founded on alluvial soil. Soil medium at the site mainly consists of silty sand/sandy silt. Detailed analysis shows that top few meters of soil may liquefy under extreme earthquake scenario. To mitigate the liquefaction potential, ground improvement by means of using compacted soil–cement mix is placed for a certain liquefiable depth of the soil sub-strata. Safety-related structures of NPPs typically configured with thick shear walls for shielding as well as structural purposes that make the structures quite stiff and heavy. The combined pile-raft foundation (CPRF) system has been adopted for some of the safety-related structures of NPP to control both total as well as differential settlement. Performance of CPRF system is assessed through detailed soil structure interaction analysis where different pile-soil-raft interactions are appropriately simulated. As per ‘ISSMGE Combined Pile Raft Foundation Guideline’, for the design of CPRF system, detailed knowledge of single standalone pile behavior is required. Pile-soil interface parameters are calibrated based on site-specific pile load tests data. In the present work, an effort is made to simulate the field pile test results through finite element analysis. Single pile behavior along with the supporting anchor/reaction piles is modeled in Abaqus software to perform finite element analysis with due consideration of pile-soil interaction aspect. The interface parameters are suitably calibrated such that simulated pile behavior closely matches the observed pile behavior established in pile load tests. The final calibrated soil-pile interface parameters, thus, obtained are to be used to perform detailed soil-structure interaction analysis and subsequent qualification of CPRF system of safety-related structures.KeywordsCombined piled-raft foundation (CPRF)Soil–cementSoil-pile interactionPile-soil interface parametersLoad transfer behaviorMohr–Coulomb material modelCohesive behavior