The performance analysis of energy piles in cross-anisotropic soils

Abstract

Energy piles possess two important properties – structural load-bearing and ground heat exchangers, which is a cost-effective building energy-saving solution. Besides, natural soils generally exhibit anisotropic properties which impact the overall performance of energy piles. Therefore, the performance of energy piles in layered cross-anisotropic soils is investigated in this paper. Firstly, based on the basic equations of elasticity and heat transfer theory, the extended precise integration method (EPIM) is applied to acquire the thermo-elastic fundamental solution of layered cross-anisotropic soils, which will be utilized as the kernel function of the boundary element method (BEM). Then, the stiffness matrix equation of the energy pile considering the thermal strain and mechanical loads is derived with the aid of the finite element method (FEM). Afterwards, according to soil-pile deformation coordination conditions, the coupled BEM-FEM formulation to represent the soil-pile interaction is developed. Compared with in-situ tests and numerical simulations, the accuracy of the proposed method is verified. Finally, parametric analyses are conducted on the performance of energy piles subjected to the mechanical and temperature load simultaneously, and influences of pile-soil stiffness ratio, length-diameter ratio and soil cross-anisotropy on energy pile responses are discussed.