Study On The Performance Of Energy Piles Subjected To The Thermal Cycles In Sand

The energy pile is a new type of building energy-saving technology,which uses the built-in heat exchange pipe in the pile body to exchange heat with the shallow geothermal energy,and heats up or cools the building while undertaking the upper part of the building load.During the actual operation of the energy pile,the temperature of the pile changes periodically with the different operating modes.The influence of the pile on the bearing capacity and deformation of the pile is not clear.In order to ensure the safety of the pile foundation,it is necessary to conduct research on relevant issues in-depth.Based on the laboratory model test method and numerical simulations,the performance of energy piles subjected to thermal cycles in sand was studied.the main work and conclusions are as follows:(1)Based on the laboratory model test method,the working characteristics of energy piles under different pile head loading levels were studied.The results show that the larger the pile head load,the greater the residual settlement after temperature cycling,and the additional settlement caused by temperature after 3 cycles under the limit load reaches 0.58 of the pile diameter.In the case of no load at the pile head,the pressure at the the pile bottom is restored to the initial value at the end of the temperature cycle.When the load at the pile head is large,the the pressure at the the pile bottom increases after cycling,and the soil at the pile bottom is additionally compressed.(2)Based on the finite element software ABAQUS,the secondary development of the boundary surface model and the simulation comparison of the literature test data show that the developed subroutine can simulate the volumetric dilatancy and shrinkage and the non-linearity of the strain relationship of the sand under monotonic and cyclic loading.The developed subroutine can be reasonably used to study the working characteristics of the energy pile under the circulating temperature.(3)Based on indirect coupling calculation,the boundary surface model is adopted to simulate the mechanical response of energy piles under different foundation and pile head constraints.The results indicate that under the condition of free pile head,after temperature cycles are over,the pile head in the loose sand and dense sand foundations is significantly settled,and the ultimate bearing capacity of single piles in reloaded loose sand and dense sand decreased by 13%and 3%respectively.When the pile head is constrained,the pile shaft is increased with the number of cycles.As the force continues to decrease,tensile damage may occur in loose sand,and the ultimate bearing capacity of single piles in reloaded loose sand and dense sand decreased by 16%and 3%respectively.