Thermomechanical Response of Geothermal Energy Pile Groups in Sand

The thermomechanical response of geothermal energy pile groups in sand was studied in the present work by using a three-dimensional nonlinear finite-element analysis procedure. A raft was considered on the piles. The stress-strain responses of the piles and raft were considered linear elastic. The stress-strain response of sand was reproduced by using the state parameter-based constitutive clay and sand model (CASM). The CASM was implemented in finite-element software through a user-defined material subroutine. The geothermal energy pile group was analyzed for different combinations of thermal and nonthermal piles in the group in a single layer of sand. Analysis results were studied for the displacement at the base of the pile and the axial stresses in the pile. Parametric sensitivity studies were performed by varying the spacing between the piles. It can be observed from the results that the geothermal piles, when subjected to heating, exhibit higher displacement and axial stress than the piles under only mechanical loading. Differential settlement at the pile base was observed for the groups that contained both thermal and nonthermal piles.