Coupled Water,air And Heat Transport In Reconstruction Soil Filled With Coal Gangue

In the coal mining area of China,there is a large area of reconstruction soil filled with coal gangue.According to incomplete statistics,there are over 300 hm~2reconstruction soil in Huainan mining area.Because of the physical and chemical properties is quite different between coal gangue and soil,the moisture,gas and heat transfer is more complex in reconstructed soil,which plays an important role in repair area ecological system.However,the study on the physical properties of coal gangue and the moisture,gas and heat migration is still lacking in reconstruction soil.Therefore,the hydraulics parameters,thermal diffusivity,gas conductivity of coal gangue were determined and monitored the water,gas and heat condition in reconstructed soil profile for further discuss the water,gas and heat migration laws in reconstruction soil.It not only can increase the safety of the reclaimed soil,improve soil curing technology and lay a foundation for soil carbon fixed or carbon segregation,but also can deeply understand the characteristic mechanism of special layered soil and provide theoretical basis and experimental basis for similar layered soil research.The main conclusions of this paper are as follows:(1)The hydraulic parameters,thermal diffusivity and gas permeability is significant difference between coal gangue and soil.The saturated water content of coal gangue was significantly lower than soil for 6.90%~16.40%,but the saturation hydraulic conductivity,thermal diffusivity and gas conductivity are higher than soil.The saturation hydraulic conductivity of coal gangue decreased significantly with the bulk density increasing.When the bulk density increased from 1.8 to 2.2g/cm~3,the saturation conductivity decreased from 0.249 to 0.017mm/min.The sensitivity of gas permeability to water of coal gangue increased with water content increasing,but the sensitivity of soil is inverse.(2)In reconstruction soil,coal gangue can increase the water holding capacity of the upper soil,because the inhibition of coal gangue layer for water infiltration.With soil thickness increasing,the temperature variation of the surface soil was gradually decreasing.The temperature influence coefficient(T_c),which is the effects of coal gangue layer on the surface soil temperature,can be used to quantitatively analyze the influence and estimate the soil thickness.The gas permeability of reconstruction soil was determined by topsoil and filling matrix,so that the calculation model of reconstruction soil permeability was built.In addition,gas diffusion is hindered by soil layer when gas diffused to the interface of soil layer,which lead gas accumulation in soil and coal gangue interface.(3)Hydrus-1D software can better simulate the water content distribution in reconstruction soil profile,but unable to accurately simulate the water infiltration process.Reconstruction soil water infiltration process was influenced by the interface,so that water infiltration was blocked,which leading to the existing theory of water flow can’t well describe the reconstruction soil water infiltration.(4)The heat release process of coal gangue was simulated by the heating system of the reconstructing soil water vapor heat coupling transport device at the bottom.In the process of heating,because the thermal diffusion coefficient of coal gangue is greater than soil,stable temperature gradient was forming in reconstruction soil.Under the action of temperature gradient,water had a tendency of upward movement,which leaded to the water content of H5 layer decreased significantly for 0.142%/h,but the water content of other layers increased for 0.039,0.052,0.057 and 0.040%/h respectively.Temperature and water content can affect gas diffusion,but the increase of profile temperature gradient will weaken the influences of water content on gas movement.