Experimental study on infrared radiation characteristics of overburden movement of self-forming roadway under pressure relief

The physical simulation test was carried out in the 5-200 working face of Dianping Coal Mine,China,and the whole process of overburden rock movement during self-forming roadway pressure relief and pressure relief was gradually excavated along the coal seam. Gypsum powder,fine river sand,barite powder and other similar materials were used to construct four types of rock formations such as sandy mudstone,medium sandstone,limestone and coal rock. Six types of excavation steps were designed along the coal seam according to different propulsion scales,which were used to observe the collapse law of the overlying rock layer under different excavation stages. Infrared thermal imager and high-precision speckle system were used as the main observation methods. Infrared radiation temperature,infrared thermal image and rock formation displacement were selected as monitoring indicators. The temporal and spatial characteristics of infrared radiation during the overlying rock movements were mainly studied. The results show that the infrared radiation characteristics of the overlying rock movements on the kerf and non-cut sides are different due to the pressure relief of the cutting roof,and combining with the overburden rock movement,it can be divided into four stages:①finite deformation stage,cutting seam side with the cutting seam side surface temperature of the overburden strata both presenting "up-down-up-down" M form. Changing characteristics of the infrared thermal image are no obvious differentiation. ②In the direct top collapsing stage,both sides of the strata show a sudden drop in infrared radiation temperature,the maximum temperature drop is 1.8℃. The infrared thermal image of the upper caving coal gangue shows a low temperature zone. ③In the basic roof breaking and slewing stage,the infrared radiation temperature of cutting seam side suddenly increases then slowly decreases. The infrared thermal image shows a coexisting of local high and low temperature zones. The infrared radiation temperature of the non-cutting seam side suddenly increases,turns slowly increasing,after from stability turning suddenly decreases. Infrared thermography shows low-temperature band stacking distribution. ④In the rock formation stabilization phase,the infrared thermal image at the slit side has a local blocky high-temperature area,and the infrared thermal image gradually shows a "three-zone" distribution characteristic as a whole. The research results have enriched the understanding of the process of overburden movement under the condition of pressure cut and pressure relief,and laid an experimental basis for the application of infrared to the study of overburden movement.