Study On The Hidden Hazards Mechanism Due To Coal Mining Under High Thick Brittle And Hard Rock

Water inrush is a great potential safety hazard existing in coal mines of China,and because of reasons such as increasing mine production,enlarged mining depth,multiseam mining,etc.,a new roof water hazard type-separation-layer water hazard in overlying strata,and its outstanding features like great momentary water yield,unobvious water inrush omen and huge harm have gradually drawn high attention from cycles of mining safety.At present,research achievements from both home and abroad mainly concentrate on separation-layer formation mechanism,distribution rules and engineering application of reduction of surface subsidence by grouting at separation layer,while there are few researches on “water vapor” formation conditions at separation layer and its water inrush-vapor burst(gas)mechanism,etc.,hence,it needs urgent research on this aspect.Based on existing researches from both home and abroad,taking Wolong Lake coal mine as the background and by means of field measurement,theoretical analysis,numerical simulation,etc.,this paper,on basis of analysis of background conditions under which separation-layer water—aerodynamic force accident happens and the principal line of “formation of separation layer? collection of “water and vapor “at separation layer? “water and vapor sudden surging” at separation layer,conduct in-depth theoretical research and discussion about formation of mined separation-layer water and sudden surging mechanism under thick,crisp and hard overlying strata.By studying rock stratum distribution and variation rules of lithological characters and thickness at 5,6 and 7 rock stratums on No.8 coal,this paper sampled 5,6 and 7rock stratum,conducted comprehensive analysis and test of physical and mechanical properties of samples,and based on which it established engineering geological model.The model adopted FLAC3 D software to conduct numerical simulation and analysis of stress field,displacement and plastic zone of different scales and spatial forms.In the meantime,it determined rock mass fracture distance on No.8 coal.The following results were obtained through study and analysis:(1)average compression strength was 69.12 MPa and tensile strength was 4.46 MPa of sandstone on No.8 coal by measuring physical and mechanical properties of rock samples;average compression strength of siltstone was 24.77 MPa and average tensile strength was1.97MPa;average compression strength of mudstone was 18.80 MPa and averagetensile strength was 1.57 MPa.(2)Development and evolution rules at separation layer of No.8 coal overlying strata under thick,crisp and hard roof mining situation were comprehensively studied by using surface drilling,flow-velocity and flow-quantity logging and numerical simulation,and put forward that basic conditions of separation-layer water were respectively: development position of separation layer was on water-diversion fracture zone,and feeding water source existed around the separation layer,and infiltration capacity of rock masses around it was strong.(3)Through analysis of rock stratum distribution on No.8 coal,there were mostly K3 sandstone aquifers on No.8 coal,after No.8 coal roof formed separation-layer space,it would accept water source supplement from K3 sandstone aquifers,and impact energy generated by its fracture would impact inferior rock mass at separation layer,consequently,this rock mass would experience great deformation and deformation velocity with momentary bucking failure,thus forming dynamic breakthrough zone connecting water diversion fracture.(4)It used theories like elasticity to deduce the process in which separation-layer inferior rock mass formed dynamic breakthrough zone under impact effect and proposed relevant theoretical expression.(5)It put forward that the most direct reason for occurrence of separation-layer water hazard was formation of “water-vapor gathering” separation layer and established corresponding engineering geographical model.Based on above,the key technology of preventing and controlling water & vapor gathering at separation layer was to build up intercepting holes beyond working plane to intercept and predict the position in which separation layer development above working plane,to set diversion holes to intercept supplementary water source for separation layer and release separation layer water in advance.This study further enriched prevention and control technologies of separation layer in Huainan and Huaibei regions.