Research And Application Of Empirical Model Of Soil Thermal Conductivity

The exchange of surface water and groundwater is one of the research focuses of hydrology,environmental science,hydrogeology,water resources management and other disciplines.As a new and efficient analysis method,the temperature tracer method is of great significance for studying the hydrogeological characteristics of rivers,lakes,wetlands and other near-surface water bodies.The thermal conductivity of the soil as an important influence factor of the hydro-thermal coupling model directly determines whether the model is successful and accurate.Based on the analysis and summary of relevant research results at home and abroad,this paper proposes a new thermal conductivity model,and based on the new thermal conductivity model,a hydro-thermal coupling model of saturated-unsaturated flow in the riverbed and riparian zone under heterogeneous parameters is built.Finally,combined with field experiments,the applicability of the new thermal conductivity model is verified,and the temporal and spatial changes of the temperature field and seepage field of saturated-unsaturated riverbed and riparian zone are explored,and the correlation is analyzed.The main research results are as follows:(1)Based on the basic physical parameters of the soil,considering the influence of organic matter content and the composition of each particle on the shape factor,a new empirical model of thermal conductivity is proposed.The new model and nine other models were used to calculate the thermal conductivity values of 10 different texture soils at different water contents.The results show that the new model has a better fitting effect on various soils than other models.The model has the highest accuracy,the best performance,and a wide range of application.(2)The verification results of engineering examples show that compared with Chung&Horton(1987)model based on HYDRUS software and the Lu(2007)and Lu(2014)models based on COMSOL Multiphysics software,the new thermal conductivity model based on COMSOL Multiphysics Multiphysics software is more suitable for the hydro-thermal coupling study of saturated-unsaturated flow in riverbeds and riparian zones,and the overall fitting accuracy is higher,and it can accurately describe the dynamic change process of saturated-unsaturated temperature field.(3)For the temperature field,the water temperature and the temperature of each monitoring tube below the surface have obvious "decay" and "lag" compared with the ambient temperature.The farther away from the river bed and the deeper the embedding depth,the smaller the influence of atmospheric temperature and water temperature,the more stable the temperature field changes;and the temperature field of the river bed and riparian zone both appear "warm and cool" in summer,and the temperature stratification phenomenon of "upper cold and lower warm" in winter.For the seepage field,the flow velocity changes regularly with the fluctuation of the water level.In the riparian zone,the closer the monitoring point is to the surface,the smaller the flow velocity fluctuation range and the smaller the flow velocity value.But the riverbed area is just the opposite,and the vertical velocity is greater than the riparian zone.(4)Correlation analysis shows,for the riparian zone,temperature and water level are moderately negatively correlated,as the depth increases,the flow rate and the temperature difference between the two monitoring points above and below gradually change from a very significant weak correlation to a very significant moderate positive correlation and the flow rate shows extremely significant negative correlation with water level,and the closer it is to the river bed,the greater the correlation coefficient;For the riverbed area,the temperature of each measurement point is greatly affected by the water temperature,which is extremely significant and strongly correlated;the flow velocity and the water level are extremely significantly and strongly negatively correlated,and as the depth increases,the correlation between adjacent velocity points gradually increases.