Study on the influence of low temperature and moisture content on the shear strength of remodeling coal

In order to ensure safe, efficient and stable mining of soft coal seam, the direct shear test was conducted to analyze the shear strength characteristics of remodeling coal under the coupling effect from low temperature (20 ℃, 0 ℃, -10 ℃, -20 ℃, -30 ℃, -40 ℃) and moisture (0, 0.8%, 4%, 8%, 12%, 16%).The mathematical statistics was used to discuss the influence mechanism of temperature and moisture on the shear strength.The results show that, when the moisture is 0, the cohesion exponentially increases with the decrease of temperature.The shear strength of remodeling coal is proportional to the vertical stress, thereby conforming to the Mohr-Coulomb criterion.When the temperature increase from 10 ℃ to 20 ℃, the water content increase from 12% to 16%, the cohesion reaches the maximum of 322.9 kPa.The minimum cohesive of 138.0 kPa occurs near the temperature of -40 ℃ and the moisture of 4%.When the temperature ranging from -20 ℃ to -40 ℃, the internal friction angle gradually decreases to the minimum value of 18.25° with the increase of water content.When the moisture content increase from 6% to 13% and the temperature decrease from -20 ℃ to 10 ℃, the internal friction angle reaches the maximum value of 31.45° and the corresponding shear strength reaches the maximum value.Under the coupling effect from temperature and moisture, the shear strength, internal friction angle and cohesion are more affected by the temperature.