Using ground penetrating radar combined with borehole to detect soil profile and water content in coal mining subsidence area

In this study, to analyze the influence of coal seam mining on formation structure and water content, ground penetrating radar (GPR) combined with borehole sampling was firstly used to detect and analyze the change of shallow stratum medium and its structure in the process of coal mining. Then the soil water content of different soil media in the shallow strata of coal mining area is determined by GPR and sampling. Finally, the changes of strata structure and moisture content of different soil media under the influence of coal seam mining conditions is compared. The objectives of this research were to analyze 1) the change of the sedimentary structure of the shallow strata before and after coal mining, and determine the influence of coal mining on the soil profile of the shallow strata; 2) the influence of coal mining on the distribution of soil moisture in surface soil; and; 3) the relationship between different soil media and soil moisture content in shallow strata under coal mining conditions to provide scientific basis for reclamation after mining. The radar detection drilling results showed that the soil medium structure of the shallow layer (< 10 m) in the mining area of coal mine mainly included sand layer, clay layer and weathering layer from the top to the bottom. The water cut detected by GPR was similar to the measured water cut with depth. The correlation coefficients of water cut detected by the two methods for the four boreholes were 0.875, 0.88, 0.94 and 0.84, respectively. The results also showed that the water content of clay and sand clay was much higher than that of sand. Coal mining had a certain impact on the shallow soil profile, but the soil profile remained unchanged. After coal mining, the water content of shallow soil decreased significantly. The water content of sand layer in L1 measured in the 1st and 3rd times decreased by 2.15% on average, and the water content loss rate was 28.26% on average. The moisture content loss rate of clay layer in the first and third detection was 12.85% on average. This showed that coal mining had a great influence on soil moisture content of sand structure. The average moisture content of the sand layer detected in the second and fourth times was 5.31% and 7.44%, respectively. The increase range of moisture content was between 5% and 56%, and the average increase range was 27.89%. The water content of clay layer detected twice was 11.46% and 11.96%, respectively, with an increase of 0.5%, 19.13% - 19.59% and an average increase of 4.79%. That was to say, the moisture content of clay structure layer changes little while that of sand structure changed greatly. This indicated that the clay stratum was less affected by rainfall and the water content of sand stratum wsa more affected by rainfall. The shallow soil moisture was mainly affected by rainfall.