Floor failure law of extra-thick coal seam in fully mechanized caving mining

The coal mining on the high-artesian water body will cause floor disturbance and damage, and lead to the thinner effective waterproof stratum, which enhances the risk coefficient of water bursting at the floor. Grouting modification of the target horizon is an effective governing measure. However, the grouting within the floor damage scope will waste a large amount of grout and affect the project effect. Therefore, it is especially important to carry out the study of the damage depth and regularity of the coal seam floor. Accordingly, the 5105 working bench of the Yushupo Coal Mine in Shanxi was adopted as the study object. The borehole stress-strain technique was used to carry out the 4 months' continuous monitoring of the 7 survey lines and 91 sensors that were arranged at the air intake tunnel before, during and after the mining, and the three-in-one “space-time” omnibearing floor disturbance and damage data were obtained for regularity analysis, providing important technological parameters for establishing the floor grouting governing plan. As shown by the results, the distance between the start point of the floor damage depth and the working bench was 24.2 m. The vertical distance and the horizontal distance of the maximum damage depth from the working bench were 28 m and 21.3 m, respectively. The floor damage depth fitting form conformed to the plastic gliding regularity. The study result provides the scientific basis for the study of the floor damage depth regularity under the similar operating conditions