Study On Thermal-Humidity-Mechanics Coupling Characteristics In Soil High-Temperature Heat Storage Process

At present,shallow geothermal energy utilization is an important technical means to achieve clean heating,in which underground heat storage has become an important way of geothermal energy utilization technology.In this study,based on the application of high-temperature underground energy storage,the variation of thermal-humiditymechanics(THM)parameters and coupling characteristics of unsaturated thermal storage soil were studied in view of the problems of backfill shrinkage,slab formation,and structural settlement in the heat transfer process of thermal storage soil.Based on the experimental research and numerical calculation and analysis of the model,the variation laws of soil temperature,volumetric water content,and pore pressure in the process of high-temperature heat storage are understood,the coupling mechanism of THM parameters is explored,and the characteristics of heat and moisture migration and structural settlement in the process of heat storage and heating are studied,which lays a theoretical foundation for the efficient and stable operation of shallow ground energy utilization.The THM coupling experiment platform of high-temperature regenerator was independently built to study the various characteristics and correlation characteristics of temperature,volumetric moisture content,and pressure of the regenerator under continuous and intermittent heat storage conditions.At the same time,the influence of particle size on the variation of thermal and moisture parameters in the heat storage process was compared and analyzed.The results show that the volumetric water content increases sharply in the early stage due to the influence of temperature rise,and the continuous heat storage makes the pore water migrate from heat source to cold source continuously,and the unbalanced pore pressure is produced in the direction of heat transfer.Compared with the continuous heat storage mode,intermittent heat storage is more conducive to heat transfer and maintain the uniform distribution of water content,and reduces the pressure variation in the soil.The increase in soil particle size will promote the heat transfer of soil,weaken the heat and moisture migration,and increase the internal pore pressure of soil.Based on the thermal-pore water seepage and thermal-pore pressure coupling control equations,the THM coupling numerical model of the regenerative soil is constructed,and the model is verified by the established experimental platform.Using the numerical model,the temperature distribution,moisture content distribution,and settlement or stress variation characteristics of the cylindrical regenerator in the radial and axial directions during the cross-seasonal heat storage-heating process are studied.The characteristics of local heat and moisture accumulation and deformation accumulation in the process of repeated seasonal heat storage and heating are studied.The interaction characteristics,thermal accumulation,and stress accumulation characteristics of each heat source in the well group during the heat storage-heating process are studied.The results show that the soil temperature increases in the heat storage stage and the soil expands,and the pore water accelerates from the top of the soil to the bottom along the axial direction.In the insulation stage,the soil temperature is redistributed,and the pore pressure and settlement increase slowly;in the heating stage,the soil heat storage decreases gradually,and the pore pressure and settlement increase rapidly.The pore pressure and settlement showed a slowly increasing trend at the top stage;during the three-year repeated heat storage-heating process,the soil temperature increased at the end of the shutdown stage compared with the previous year,and the heating rate of the raw soil was greater than that of the backfill.After a heat storage-heating cycle,pore water presents an irreversible migration phenomenon;compared with the original soil,the settlement and pore pressure of backfill changed more.During the three-year repeated heat storage-heating process of well group,the thermal accumulation mainly occurs in the soil around the heat exchange tube.The soil pressure around the heat exchange tube increases gradually with the increase of cycles,and the stress also gradually accumulates.