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Abstract In view of the research situation and existing problems involved with the hard and stable roof control in coal mine，the test of directional hydraulic fracturing employed for the roof control is presented；the characteristics of hydraulic fracturing in the roof are obtained via the monitoring boreholes decorated on both sides of the fracturing borehole and the pressure record during hydraulic fracturing. The test results show that：(1) The transverse notch is introduced successfully in the roof by means of KZ54 drill and is capable of reducing the pressure required for crack breakdown during the directional hydraulic fracturing. (2) The inflatable straddle packer adopted for hole sealing ensures the stepwise fracturing in the hard strata，the stepwise fracturing can create multiple cracks in the roof，which ultimately weakens the hard strata. (3) The breakdown pressure and propagation pressure change in proportion to the depth of fracturing location；the crack can propagate to a large scope radius of 20 m approximately. (4) The pressure versus time curve is recorded and presents a variety of forms potentially related to the rock uniformity，permeability，geostress field and rock structure surface. (5) The rock strength is the main factor that controls the fracturing process when the values of geostress and rock tensile strength are nearly identical.
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Received: 25 November 2011
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2012, Vol. 31 
