Influences on key stratum movement to surface gas drainage hole and borehole prevention countermeasures

In order to reveal the reason of the water-inrush disasters induced by the damage of surface gas drainage hole during mining of No .8101 working face in Wolonghu Coal Min e, by the way of theoretical analysis and field measurement, this paper comprehensively analyzed the movement characteristics of key stratum, the structure of gas drainage hole as well as the water inflow of No.8101 working face and the borehole TV, and so on. Results showed that the breakage of thick and hard key stratum resulted in the movement of overlying strata it controls, which caused tensile failure of casing outside the borehole in several sections, thus, the gas drainage boreholes became main channels that interconnected the K3 sandstone aquifer with water-flowing fracture zone below. All this has caused the sustainably large amount of water inflow on No 8101 working face. To ensure the surface gas drainage hole not to be damaged, it shouId be considered in three stages: pre-mining design, diling construction and mining control. Meanwhile, relevant countermeasures should be carried out, including damage prediction in advance, strengthening the boreholes, and decreasing the damage by adopting harmonic mining, so as to realize the long-term stability of the gas drainage boreholes.