Research on soil water content variation in coal mining area based on ground-penetrating radar

Coal mining has an important influence on the soil water content in the vadose zone. In this study, during April, August and October 2015 and June 2016, ground-penetrating radar was used to detect the soil water content of the shallow sand layer (< 10 m) of the Daliuta mining area, Shaanxi Province, China. Average envelope amplitude, auto-regression and moving average joint inversion methods were used to invert the soil water content, and the soil water content detected by ground-penetrating radar was corrected by a time domain reflectometer and laboratory measurements. The results indicated that ground-penetrating radar could measure the soil water content with an accuracy similar to that of the time domain reflectometer. The accuracy of soil water content estimates obtained by utilizing average envelope amplitude, auto-regression and moving average joint inversion methods was improved by 23.5% on average. Coal mining reduced the soil water content of the sand layer and increased the coefficient of soil water content variation. The soil water content returned to its original state after the mining settlement had stabilized, while the spatial distribution of soil water content was unable to return to its original state within a short time period. The water content of the sand layer in the centre of the subsidence basin (110-350 m) increased significantly (1.05%) after mining and was identified as the most favourable area for ecological restoration. This study provides a reference for the ecological reconstruction of subsidence areas resulting from coal mining.