Numerical Study On The Influence Of Temperature On The Interactions Between Energy Pile And Soil

Energy pile is a new type of structure and heat transfer component which utilizes the foundation of building pile to conduct heat exchange with the surrounding rock and soil mass.Because of the different energy demands of different buildings in different regions and the lack of understanding of the thermal-hydro-mechanical coupling behavior of the energy pile and the soil around the pile,the design and safe service of the energy pile are facing challenges.In this paper,by combining theoretical analysis,laboratory test and numerical simulation,the interaction between single pile and soil around the pile under temperature load is emphatically studied,and the influence of different temperature load on the thermal-hydro-mechanical coupling response of energy pile is emphatically discussed,to reflect the different building energy demand for the effect of pile and soil interaction.The main research contents and achievements of this paper are as follows:?1?The thermal-hydro-mechanical coupling process of energy pile in soil mainly involves pile,soil and pile-soil interface,which are highly coupled with each other.In this paper,for saturated soil,the governing equations of heat transfer in pile,deformation of pile,heat transfer in soil,pore water flow in soil,deformation of soil and pile-soil interface are established respectively?a total number of eleven?.On this basis,the thermal-hydro-mechanical model of energy pile in saturated soil is proposed.The coupling approach between them is discussed in detail.The model can consider the pile,soil and pile-soil interface highly coupled with each other,and there are eleven independent variables,including pile temperature T_p,pile displacement u_p,I?x?y and z directions?,soil temperature T,soil displacement u_i?x?y and z directions?,pore water pressure p_w,and relative displacement of pile-soil interface u_s and u_n.?2?The thermal-mechanical coupling model test of single energy pile in dry silt under static temperature load was carried out,focusing on the head vertical displacement variation rule of energy pile under temperature action.The test results show that:top of the pile rises when pile temperature rises;top of the pile settles when pile temperature drops.The time when the head vertical displacement flattens out is earlier than that when the temperature flattens out,and after the head vertical displacement flattens out with time,the head vertical displacement still changes slowly with the increase of time.Based on the thermal-hydro-mechanical coupling model of the energy pile in saturated soil,the thermal-mechanical coupling model of the energy pile in dry silt is established.The numerical simulation results are in good agreement with the model test data,which can well reflect the change rule of pile head displacement under the action of temperature,and reflect that pile head displacement is not only affected by thermal expansion and cold contraction of pile,but also affected by soil deformation caused by pile deformation and soil deformation caused by heat transfer of pile and soil.The rationality and reliability of the simplified model are verified.?3?Based on the thermal-hydro-mechanical coupling model of energy pile in saturated soil,assuming that the pile-soil interface is perfect contact,the mechanism and law of pile head displacement under different temperature loads are studied.For a single energy pile with long-term mechanical load in saturated clay,four temperature load cases are set up,including two symmetrical cyclic temperature loads and two asymmetrical cyclic temperature loads.The results of numerical analysis show that the temperature change of the pile causes the deformation of the pile,and the deformation of the pile causes the deformation of the soil on around the pile.At the same time,the deformation of soil skeleton and the change of pore water pressure caused by the heat transfer process of pile and soil lead to further deformation of soil,and the final deformation of soil also affects the deformation of pile.All of the above determine the change of pile head displacement.When the cooling range is large,the pile shrinkage deformation is large;and the increase of pore pressure in the upper part of the pile side is large,and the effective stress decreases greatly;the heat transfer range of the pile and the soil is the largest,and the soil skeleton shrinkage deformation is large,resulting in a large settlement of the pile head,which is 1.8mm.When the cooling range is small,the settlement of pile head is small,which is 0.8mm.When the temperature rise amplitude is large,the expansion deformation of pile is large;the pore pressure caused by the heat transfer of pile and soil is large,which causes the flow of pore water in a certain area to cause large thermal convection;the soil temperature increases rapidly,and the expansion deformation is obvious,which causes the pile head to rise greatly,which is 0.9mm.When the temperature rise amplitude is small,the pile head uplift is small,which is 0.45mm.Under the action of long-term mechanical load,the maximum settlement of winter and uplift of summer under four temperature load cases are respectively:1.80mm,0.90mm;0.80mm,0.45mm;0.80mm,0.90mm;1.80mm,0.45mm.It shows that the temperature change has little influence on the pile head displacement and the pile mechanical behavior.In saturated clay,when the cooling loading rate is too high,the soil will produce more plastic deformation,so it is necessary to pay attention to the safe use of energy pile in areas with more heating demand in winter.