Study on the change law of temperature and mechanical properties of coal body in uncovering coal seam in low temperature freezing cross-cut

In order to study the change law of temperature and mechanical properties of coal body in uncovering coal seam in low-temperature freezing cross-cut, U-shaped copper tubes are pre-buried and frozen with liquid nitrogen during the preparation of coal samples. The characteristics of internal and surface temperature and stress-strain changes of coal samples under different freezing times are analyzed by temperature measurement, infrared thermal imaging and uniaxial compression. The test results show that with the increase of freezing time, the internal and surface temperatures of coal samples show a decreasing trend. The lowest surface temperature of coal samples is located near the U-shaped copper tube, and the highest surface temperature of coal samples is located at the boundary of coal samples. In the compaction stage, with the increase of freezing time, the strain of coal samples gradually decreases and the compaction stage shortens. In the elastic deformation stage and yield stage, with the increase of freezing time, the maximum stress and elastic modulus of coal samples both increase.