Monitoring and Analysis of the Damage Height of overburden Rock Mass on the Mined-out Area

The vertical boreholes were drilled from the surface for correlation detection of the damage height of overburden rock mass. The expanding height of the inner collapsed zone and the permeable fractured zone as well as their distribution in the overburden rock mass after excavation of the coal seam were determined based on the leakage volume of drilling fluid, the change of water level in the boreholes and the borehole images by color TV.