Study On Heat Transfer Characteristics And Thermodynamic Response Of Energy Pile Group

The energy pile technology is to change the pile foundation of the building into a part of the ground source heat pump system.The heat exchange pipe is embedded in the pile foundation.The pile is used as a heat exchange well,and connected with the heat exchange pipe through the water collector,so that the energy pile and the surrounding rock and soil mass transfer heat mutually.In this way,not only the well digging and grouting backfilling of GSHP system are eliminated,but also the problem of large floor area is solved,and the construction period can be shortened by parallel construction.At present,the research work of energy pile mainly focuses on the heat exchange efficiency of single pile and the structural response,and a lot of heat response tests and corresponding experimental research are carried out,while the research work on the heat exchange mechanism and thermodynamic response of energy pile group is less.In the process of heat exchange,the temperature field of multiple piles is different from that of single pile,and the mechanical response of the structure is also different,which may cause unknown influence on the upper structure.In this paper,through the heat transfer test of multiple piles in the energy pile test base,combined with simulation calculation,the heat transfer characteristics and thermodynamic response of the energy pile group are analyzed,and the heat transfer mechanism and thermal response law of the pile group are clarified.Based on the heat transfer test of multiple piles in the energy pile test base and the simulation calculation,the heat transfer characteristics and thermodynamic response analysis of the energy pile group are carried out,and the heat transfer mechanism of the pile group is clarified.The thermal characteristics of single pile and pile group under different buried pipe forms and pile group arrangements are compared and analyzed,and the following conclusions are obtained:By comparing and analyzing the test and simulation results of the heat exchange process of the energy pile,the temperature distribution along the depth direction of the measured pile is basically consistent with the results of the numerical simulation.The temperature distribution of pile body along the depth direction is relatively stable and the temperature difference of different sections is small.The influence range of the whole temperature field is elliptical,the temperature of the top and bottom of the pile is slightly lower than that of the middle of the pile body,which is generally low at both ends and high in the middle,but the overall change is not obvious.In the actual test,the thermal influence radius of each pile is less than 2m,but in the simulation analysis,the temperature field between piles changes and some thermal interference occurs,and the thermal influence radius of pile group is larger than that of single pile,which shows that the thermal effect of pile group is not the superposition of single pile thermal effect.In the heat exchange process of energy pile,the vertical strain curve of different depth increases parabola with time.Because the constraint of the two ends of the pile isweaker than that of the middle,the strain distribution of the pile is generally large at both ends and small in the middle.Under the action of temperature load,a large additional temperature stress is produced in the pile body.With the increase of heating time,the maximum additional temperature stress of the two piles appears in the middle of the pile body,which is generally small at both ends and large in the middle.In the whole heating process,the curve trend is basically consistent with the position of the center point.During the heating process,the shaft friction of the pile redistributes along the depth direction.The increasing trend of the side friction near the positive and negative junction in the middle of the pile is obviously faster than that at the top and bottom of the pile.When the temperature rises to a certain value,the increasing change of the side friction of the energy pile is limited.Compared with the test results of single pile and double pile with similar temperature rise,the overall distribution of the shaft friction is similar,but that of double pile test is mainly concentrated in the two ends of the pile,while that of single pile test is mainly concentrated in the pile,and the pile-soil interaction at both ends of energy pile is more obvious in the double pile test.