The surrounding rock failure range of floor drainage roadway under the mining influence and its effect on the aquiclude are the key to determine the aquiclude thickness of the floor. This paper studied the distribution characteristics of the surrounding rock plastic zone by the numerical simulation when the floor drainage roadway was located at different positions under the working face and determined the rational position. Results show that (1) when the floor drainage roadway is staggered inward, the floor surrounding rock is prone to appear the butterfly plastic zone under single work face mining. And the butterfly plastic zone increases sharply after being affected by secondary mining of adjacent working face. (2) When the floor drainage roadway is staggered outward, the floor surrounding rock plastic zone extends gently affected by a single working face. And the depth of the plastic zone has no obvious change after being affected by secondary mining of adjacent working face. (3) According to the risk of water inrush, the three layout schemes can be ranked as follows: stagger   inward   25   m > stagger   inward   80   m > stagger   outward   15   m . (4) Considering the floor stress environment, gas extraction efficiency, and water prevention and control, the reasonable location of floor drainage roadway below the No. 11060 working face of Zhaogu No. 2 Coal Mine was finally determined. It was arranged in the sandy mudstone layer on the upper part of L9 limestone under the middle part of coal pillar and was drived along the seam floor.

The Zhaogu No. 2 coal mine is a single thick coal seam mining mine with high gas content. Due to the lack of protective layer mining conditions, we can only arrange the floor gas extraction roadway (FGER) to extract the gas from the overlying coal seam of the FGER to ensure safe production. However, improper placement of FGER will cause water inrush from the floor of FGER. Given above contradictions, this paper analyzes the stress-strain relationship of the fractured rock mass in the caving zone and the stress-recovery characteristics of the goaf from the perspective of the structural characteristics of the overlying strata above goaf. Based on this, a FLAC3D numerical model of equivalent delayed filling of caving rock mass was established by using the double-yield model filling method. The distribution of floor stress under the influence of mining is obtained after the model calculation, i.e., with the increase of the distance from the floor, the ratio of bidirectional stress to the peak value, and the stability value decrease, but the decrease amplitude becomes smaller and smaller. Therefore, floor roadway used for gas extraction should be located 10-15 m below the floor. Combined with the distribution of floor strata in 11060 working face, it is finally determined that FGER should be located 13 m below the floor. Such arrangement of FGER can not only ensure the effect of gas drainage but also prevent the occurrence of water inrush from floor.

The open-off cut is used for equipment installation of working face before underground mining, and its sectional size is larger than that of the mining roadway. Therefore, the stability of open-off cut surrounding rock determines whether the panel can be put into operation. To solve the roof instability of open-off cut in the Wanli No.1 coal mine, the roof failure mechanism of open-off cut under weak composite rock strata with thin thickness was studied by field monitoring, theoretical analysis, and numerical simulation. First, the characteristics of surrounding rock and the basic law of strata behaviors were obtained by detailed field monitoring. Afterward, FLAC3D numerical simulation and mechanical analysis were used to obtain the main mechanical control parameters of surrounding rock instability, and the existence of a soft interlayer above the roof is the main cause of roof instability. Based on this, the supporting parameters of the open-off cut were optimized and adjusted. The optimized parameters were applied to the adjacent 31207 open-off cut. The engineering practice showed that the optimized supporting parameters have an ideal control effect on roof stability.

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