| By installing heat exchange pipes in the pile foundation of a building to form energy piles,the dual functions of supporting the upper building load and extracting geothermal energy from the shallow surface soil can be played.Retaining row-piles are commonly used for foundation pit support,and they will no longer continue to play a supporting role after the completion of foundation pit construction.By installing heat exchange tubes inside traditional foundation pit retaining row-piles to form energy retaining row-piles,energy retaining row-piles can support slopes during foundation pit excavation and building foundation construction.After the building is officially used,energy retaining row-piles can also be used to extract shallow geothermal energy for heating and cooling buildings,achieving the effects of "discarding piles for new use" and "one pile for two purposes",expanding and extending the use value of retaining row-piles.However,there are few studies on the thermal mechanical response characteristics of energy retaining row-piles at present.In this paper,the method of combining field test and numerical simulation is used to study the thermal mechanical response characteristics and mechanism of energy retaining row-piles under temperature load.The work carried out and the main results achieved are as follows:(1)Field tests were conducted and a three-dimensional thermal-mechanical coupled finite element model of energy retaining row-piles was established to study the thermal-mechanical response characteristics of energy retaining row-piles under different temperature load modes.Comparing the finite element simulation results with the field measured data,and conducting parameter sensitivity analysis based on the finite element model,it was found that the intermittent operation mode can improve the heat exchange efficiency and reduce thermal stress of the energy retaining row-piles,and reasonable arrangement of the intermittent ratio helps to further expand the advantages of the intermittent operation mode,reduce the impact of thermal stress on the row-piles,and improve the stability and safety of the row-piles.(2)Field tests and numerical simulations were conducted to study the impact of energy pile configuration on the thermal mechanical response and mechanism of energy retaining row-piles,and the influence of the location and number of energy piles in the row-piles on their thermal mechanical response characteristics was analyzed.It is found that with the decrease of the distance between the activated energy piles and the increase of the number of energy piles,the interaction between the energy piles,the crown beam,and the non heated piles gradually increases,resulting in differences in the thermal mechanical response characteristics between the energy retaining row-piles and the characteristics of a single energy pile.(3)Through three-dimensional finite element simulation,the influence of the operation of the integrated pipe gallery on the thermal mechanical response characteristics of adjacent energy retaining row-piles was studied,with emphasis on the analysis of the effects of air convection heat transfer and different boundary conditions(including constant temperature boundary and thermal insulation boundary)within the integrated pipe gallery.It is found that the greater the air flow rate,the greater the impact of the pipe gallery on the heat exchange rate and thermal stress of the energy retaining row-piles.When simplified boundary conditions are used for the inner wall of the pipe gallery,the model can also be used to accurately predict the heat exchange efficiency of the energy retaining row-piles,and can more accurately predict the mechanical responses of the energy retaining row-piles such as thermal stress and displacement. |
