Influence factors and model prediction of soil thermal conductivity during freezing
In order to investigate the basic rules of thermal conductivity of the soil,the transient planar heat source method was used to test the thermal conductivity of the soil during freezing.The variation of the thermal conductivity of soils at different temperatures,moisture content,and dry density physical indicators is studied.The mechanism by which the dynamics of these three physical indicators affect the thermal conductivity of the soil is analyzed.Based on the experimental data,six machine learning models,DT,RF,GBDT,AdaBoost,SVR and BPNN,were developed to predict the thermal conductivity of the soil.The predictive performance of six machine learning models and three empirical models is evaluated through four performance indicators.In ad-dition,feature importance analysis is carried out based on RF and GBDT.The results indicate that there is no significant change in the thermal conductivity of the soil during the unfrozen phase.During the phase change stage,the thermal conductivity of soil exhibits a decreasing and increasing trend with decreasing temperature de-pending on the moisture content and dry density,respectively,with the increasing trend increasing with increas-ing moisture content.During the frozen phase,the thermal conductivity of the soil decreases as the temperature decreases due to the evaporation and migration of water from the soil sample during the test.The thermal conduc-tivity of the soil increases with both dry density and moisture content.Based on the evaluation results,the perfor-mance of RF is better among the six machine learning models(RMSE=0.036,MAE=0.028,R2=0.993,AD= 0.004),significantly outperforming the three empirical models.Compared to empirical models,RF can also more accurately predict the thermal conductivity of soil in other regions.It is recommended to use RF to predict the thermal conductivity of soil during the freezing process.The analysis of feature importance highlights that moisture content,temperature,and porosity are significant factors that influence the thermal conductivity of fro-zen soil.
NETL
NSTL
万方数据
