Model Experiments On Internal Force Response Of Single Pile In Inhomogeneous Temperature Field

Shallow geothermal energy development technology has developed rapidly.From ground source heat pump(GSHP)to energy pile with buried pipes,to the foundation slabs,tunnels,underground continuous walls,retaining walls,wells,sewage pipelines and other structures as a new technology for heat exchange between the ground and the soil.The development of these technologies has led to an increase in geothermal energy extraction.In addition,geothermal energy is increasingly used in heating and cooling of buildings as a renewable energy source.Therefore,the massive exploitation of shallow geothermal energy has caused the original stable geothermal field to change.Building piles and other underground structures in this changing temperature field will undergo deformation due to thermal expansion and contraction,and also variety in internal force.At present,research on thermal and mechanical responses of piles and soils has yielded a lot of results,mainly in the field of energy piles.However,there are few studies on the thermal and mechanical behavior of non-heat-exchanged piles,especially the bending deformation of non-heat-exchanged piles in Inhomogeneous temperature field.In this paper,the thermal and mechanical behaviors of a single pile in an inhomogeneous temperature field are studied by means of lab model tests and numerical simulation.The main research contents and conclusions are as follows:Firstly,the inhomogeneous temperature field in the soil was constructed by an indoor model test.The temperature,vertical displacement of the pile top,vertical displacement of the soil surface and the deformation of the pile body under three cycles of rising and cooling conditions were analyzed.The experimental results show that the uplift and settlement of the pile and the soil occur during the overall increase and decrease of the temperature field,and there is a clear corresponding relationship with the temperature change law.The temperature difference between the two sides of the pile body during heating and cooling results in different tension and compression strains on both sides of the pile body,revealing the phenomenon of complex bending deformation of the pile body in the inhomogeneous temperature field.Secondly,a finite element model of piles and soils was established based on the engineering geology conditions of an energy pile site at the Federal Institute of Technology in Lausanne,Switzerland.And using COMSOL software to simulate the thermal and mechanical behavior of non-heat exchanger piles in non-uniform temperature field.The simulation results show that the bending deformation of adjacent piles gradually increases until the temperature field becomes stable.The bending moments of the adjacent piles under different temperature conditions are different.The bending moment of the pile is the result of the interaction between the temperature difference on both sides of the pile and the contact between the pile and the soil.This paper studied the temperature distribution,variation characteristics of soil and piles and the variation of force in piles during the use of shallow geothermal energy.The research results have certain reference significance for the optimization design of pile foundation and evaluation of the engineering performance of pile foundation in inhomogeneous temperature field.