Abstract：As longwall caving technology prevails rapidly in China，gas emission from longwall faces and goaf area increases continuously. Traditional gas drainage techniques，such as drilling roof holes from tailgate or drilling inseam and cross-measure holes，sometimes can not meet the requirements of methane drainage for a modern longwall operation. The alternative method to drill gas drainage holes underground is to drill boreholes from surface to the goaf area. When a coal seam is being extracted out，the upper rock strata above the goaf will be undergoing discontinuous damage and continuous movement. During overlying rock strata being fractured，the surface gas drainage boreholes may be damaged due to ground movement. A method for the calculation of the stability of surface boreholes for drainage of gas from goaf area is introduced. An example of determination of borehole and casing diameters is given to demonstrate the application of the computational method. By using this method，the damage of surface gas drainage holes caused by induced excessive mining displacement can be effectively reduced if not being avoided. Surface borehole diameter and casing diameter as well as characteristics of filling materials can be achieved by calculating the horizontal movement and vertical stain at different depths.
