| Energy pile is a new type of pile foundation buried pipe technology,which combines ground source heat pump technology with building pile foundation,turning the buried concrete pile foundation into a part of the heat storage and heat exchange ground source heat pump system.The heat exchange tubes of various shapes are embedded in the pile foundation to convert the shallow low-temperature geothermal energy,so that the building pile foundation can also function as a ground source heat pump heat exchanger under the premise of meeting the bearing performance,ensuring cooling in summer,The demand for heating in winter.At present,there have been a lot of researches on energy piles at home and abroad,but they mainly focus on the heat transfer efficiency of energy piles.There are few studies on the pile material of energy piles and the surrounding soil.Therefore,this article focuses on the study of the thermodynamic characteristics of the soil around the energy pile under different consolidation conditions and the influence of the pile body material on the heat transfer efficiency.Two model piles have been studied under working load and without working load.The energy pile model test and the thermodynamic characteristic test of the steel fiber energy pile in the soil with different consolidation states have obtained the changes of the pile-soil temperature transfer,pile displacement,pile stress and lateral friction resistance,and the conclusions are drawn as follows:(1)Temperature field distribution: The temperature transfer between the pile and the soil diffuses outward with the heat exchange tube as the center.At the same moment,the temperature of the soil decreases with the increase of the radial distance,and gradually decreases along the depth direction.The transfer speed of the steel fiber model pile is faster than that of the ordinary model pile.The stronger the heat conductivity,the faster the heat exchange between the heat tube and the pile body and the surrounding soil,and the heat exchange efficiency is significantly improved.(2)Pile top displacement: The change in temperature causes the expansion or contraction of the pile body,resulting in upward or downward displacement.When there is only a temperature load,the displacement of the pile top increases with the increase of temperature,and decreases with the decrease of temperature.At the end of a cycle,additional settlement will occur.When the structure and temperature load act together,the upward displacement of the pile body is small,and due to the effect of the upper load,the settlement caused by the shrinkage of the pile body when the temperature drops,produces a larger displacement change than when the load is zero.Due to the strong thermal conductivity and fast heat transfer efficiency,the steel fiber model pile produces larger displacements than ordinary model piles.When the steel fiber model pile is in the soil with different consolidation states,the larger the consolidation ratio,the smaller the final settlement of the pile.(3)Pile end compressive stress:The maximum compressive stress of the steel fiber model pile is greater than that of the ordinary model pile.With the increase of the number of temperature cycles,the maximum compressive stress of the two model piles decreases gradually.When there is load on the top,the model pile will produce greater compressive stress.Under the same temperature cycle,the larger the consolidation ratio is,the smaller the compressive stress is.(4)Pile body stress: Regardless of whether there is a load on the upper part,the pile body stress first increases and then decreases along the depth direction,and the maximum value is in the lower half of the pile body.And the pile stress of the steel fiber model pile is greater than that of the ordinary model pile.When the steel fiber model pile is in the soil with different consolidation states,the greater the consolidation ratio,the greater the stress generated by the pile.(5)Mobilized side shear stress:When there is no upper load on the pile top,during the heating process,the pile body produces negative side friction in the upper part and positive side friction in the lower part.During the cooling process,the pile body produces positive side friction in the half.Side friction resistance,the lower part produces negative side friction resistance;when there is an upper load on the top of the pile,the direction of the side friction resistance is the same as when there is no upper load,but the size of the side friction resistance is smaller than the side friction resistance of the upper part without load,temperature cycle has little effect on the side friction resistance.The steel fiber model piles in soils with different consolidation states increases with the increase of consolidation ratio.(6)Through the ABAQUS finite element software,combined with actual tests,a finite element model was established,a series of numerical simulation analysis was carried out on the energy pile in the clay foundation,and the thermodynamics of the steel fiber model pile and the ordinary model pile under the action of temperature load were calculated.On this basis,external load is added to further analyze the influence of the upper load on the thermodynamic characteristics of the energy pile.The test data and simulation data were compared and analyzed to verify the reliability and accuracy of the model. |
