Research On The Evolution Law Of Fault Slip And Mechanism Of Coal Bumps Induced By Mining

Underground faults are widely distributed to affect the normal mining of coal mines.Mining process near faults is easy to induce strong power disasters,such as coal bumps and mine earthquakes,which seriously threat the mining safety in coal mines.Methods such as field investigation,theoretical analysis,numerical simulation,similar simulation experiment and engineering verification were applied in this thesis to illuminate the following four problems.They are the correlation between the temporal and spatial characteristics of coal bump and faults structure,the damage evolution characteristics of fault damage under mining disturbance,the mining-induced occurrence mechanics of coal bump in mining areas affected by faults and the hazard assessment of coal bump in areas affected by faults.The research achievements are as follows:(1)The obvious temporal and spatial distribution feature of coal bump is closed related to the faults structure.The author collected the data of coal bumps happening near F16 Fault and other faults in Yima Coal Mine and found that the distance between mining place and F16 Fault is obvious negatively related to the frequency of coal bumps.In the view of mining sequence,the frequency of coal bumps in excavating process was 9,accounting for 45%,while the frequency of coal bumps in mining process was 11,accounting for 55%.In the view of disaster location,the frequency of coal bumps in workface was 2,accounting for 10%,and the frequency of coal bumps in roadway was 18,accounting for 90%.The statistical data showed that coal bumps near faults mainly happened in roadways,and the disaster position was in ahead of workface 200 m,which was beyond the traditional distribution area of coal bumps.The magnitude of coal bumps near faults was extensive,with a parameter more than 500 m,which easily lead to equipment damage,casualties.(2)The failure process of faults was divided into three stages: fault damage initiation,fault propagation and fault slippageThe Workface 21141 in Qianqiu Coal Mine and the Workface 25110 in Yuejin Coal Mine were taken as examples.The author monitored the micro-seismic signals when the workfaces were mining across faults and analyzed the characteristics of faults slippage and the distribution characteristics of micro-seismic signals.The micro-seismic signals appeared when the distance between workface and fault is around 120m-240 m.At the stage of fault damage initiation,the micro-seismic signal had the feature of advanced-appearance,and the range was larger than the area of advanced abutment pressure.At the stage of fault propagation,the micro-seismic signals accumulated around faults when the distance between fault and workface was 10m-40 m,presenting an obvious regional characteristic.At the stage of fault slippage,there were plenty of micro-seismic signals near the fault,and the upper and lower plates of the fault were freed to release energy and induce large magnitude.(3)The fault damage variable was proposed to quantitatively evaluate the disturbance effect of the mining activity on the fault.Based on the theory of damage mechanics,the fault damage variable was defined to evaluate the disturbance effect of mining activity on fault.According to the general characteristics of the geological conditions of coal mining,the working model of fault surface was constructed to study the fault damage evolution,fault-surrounding rock stress-displacement distribution,and the stress characteristics around workface under mining disturbance conditions.With the working surface gradually close to the fault,the fault damage variable increased rapidly,the stress barrier effect of fault was obvious,the upper and lower disk displacement appeared discontinuous phenomenon,the coal seam stress shows a trend to rise slowly and then descend.Under the condition of mining disturbance,the change of fault damage was earlier than the support pressure of coal seam of 50 m,and the fault damage variable could be used as a sensitive index to monitor fault slippage.Fault damage variables are affected by mining factors,fault factors and geo-stress level.Through the orthogonal simulation test,it was determined that the influence of the distance of the workface from the fault,the length of the workface,the dip angle of the fault factor,the friction in the fault and the lateral pressure coefficient in the stress level were relatively significant.(4)The mechanism of excavation induced coal bump in fault areas was illustrated.On the basis of analyzing a large number of coal bumps cases,the author proposed that coal bumps are caused by the high static load and the intensive dynamic load superimposed on the coal and rock mass under certain disturbance triggering.According to Mohr-Coulomb failure criterion and fault slippage characteristics,the method of fault slip start-up condition and fault slip energy release assessment method were analyzed.The analysis of fault slip start condition showed that the slip failure of the fault is affected by the geologic dynamic effect,which explains that not all the coal bumps happened when workfaces were mined through faults.Based on the morphological characteristics of the coal strata between the workface and the fault,the criteria for the failure identification of the upper slip-shear,the downward slip-shear and the segregation of the fault were deduced when the excavation face was located in the lower strata of the fault.Based on the above research,this paper clarified the three types of fault-coal-bump interaction mechanism,such as fault activation type,fault-pillar type and fault-slip type,when workface are adjacent to faults.Then the author put forward recommendations from the monitoring and control aspect to prevent coal bumps when mining across faults.(5)Based on the detailed numerical analysis,the risk of coal bump around fault area was evaluatedBased on the geologic mining conditions of Panel 21 in Qianqiu Mine,a three-dimensional refinement numerical model reflecting the actual stratigraphic conditions of the Panel 21 in Qianqiu Mine was constructed by the spatial modeling and the envelope surface modeling method.Based on the measured geo-stress data of Panel 21,the ground stress was applied to the numerical model coordinate system through the spatial stress conversion formula.The vertical stress of the coal seam before mining was 18-22 MPa,the maximum horizontal stress was 20-26 MPa,the minimum horizontal stress was 12-16 MPa.The stress level of the deep near the fault was high,dominated by the tectonic stress,which was consistent with the ?H> ?V> ?h type of the stress in Qianqiu Coal Mine.The reasonableness of the stress loading method was verified.The authors analyzed the stress evolution law of the surrounding rock during the mining process near Fault F16.The distribution of stress in coal seam is: The initial vertical stress of the Workface 21181 was 18.2 MPa,the peak value of the bearing pressure was 24.2 MPa,the stress increased by 32.9%,and the stress concentration coefficient was 1.32.During mining process of Workface 21201,the stress of the original rock increased to 23.1 MPa,the peak value of the bearing pressure was 32.3 MPa,the stress increased by 39.8%,and the stress concentration coefficient was 1.39.During the mining process of Workface 21221,the stress of the original rock increased to 28.7MPa,the peak value of the advanced bearing pressure was 39.2 MPa,the stress increased by 36.6%,and the stress concentration coefficient was 1.36.The stress distribution on the coal seam is: the horizontal stress of the workface was 22.5 MPa and the vertical stress was 27.8 MPa.During the mining process of Workface 21201,the horizontal stress of the workface was 33.4 MPa,the vertical stress was 38.9 MPa,the horizontal stress increased by 48.4% and the vertical stress increased by 39.9%.When mining Workface 21221,the horizontal stress peak was 23.5 MPa and the vertical stress peak was 32.2 MPa.Compared with Workface 21201,both the horizontal stress and the vertical stress decreased.It showed that there was a critical distance when mining near faults.When the critical distance was less than the critical distance,the stress of the coal seam increased,and when the distance was close,the stress of the coal seam decreased.The numerical simulation results showed that the F16 fault was a high stress concentration area.Supported by the lateral coal body of Workface 21201,and the rock mass under the fault had the tendency to reverse the goaf.Due to the influence of the Fault F16 and the massive conglomerate layer,the bulk rock mass accumulated plenty of elastic energy near the fault side,and it was concluded that the coal body was in the stress limit state when the Workface 21201 was recovered,with high risk of coal bump.The closer the working surface was to the fault,the more obvious the effect of mining on the disturbance of the fault was,and the greater the slip of the fault was,which indicated that the risk of coal bump induced by fault slippage was high in the Workface 21221.Similar simulations showed that the activation of the fault zone was not the overall activation of the rock mass on both sides of the fault.The fault block that was closer to the coal seam was activated first.That is,the activation of the rock mass was unstable,and then,with the increase of the disturbance degree of the mining,the activation movement expanded to the high-level bit.And the closer the mining coal seam was,the more intense the activation of the fault rock mass was.Before and after the fault slip,the displacement of the overlying strata was abruptly changed,and the transient loading to the faulted coal body was added.In addition,the area was in the high stress state,which was easy to induce the underlying coal seam.(6)Fault-affected area excavation monitoring and control of coal bumps engineering practice verified the above theoryBased on the mining disturbance induced fault slip evolution law,mining-induced coal bump mechanism in faults area and the assessment results of coal bumps,the author summarized monitoring and preventing measurements in faults area.The Workface 25110 in the Yuejin Mine was affected by the overlying giant conglomerate,Fault F16 and small faults in workface,which made this workface was seriously threated by coal bumps,especially floor coal bumps.The author established the mechanics model of the roadway floor,and analyzed the mechanical mechanism of the bottom deformation.The principle of roadway support based on energy balance was proposed: Optimizing the layout of the roadway,improving the ability of the supporting structure to adapt to the deformation of the surrounding rock and building weak structure in the surrounding rock,so as to reduce the accumulation of elastic strain energy and improve the energy release level.Through the use of rigid and flexible integration support,the implementation of the roof-coal-roof pressure relief measurement,the effect of preventing coal bumps effect was obvious after the implementation of the above measurement,which curbed the occurrence of coal bumps and realized the production safety in coal mines.Zhujixi Mine is affected by the associated threat of high geo-stress and coal-and-gas outburst.To avoid coal bumps,the zone 50 m around the fault was regarded as the focused monitoring zone.Moreover,the author used hydraulic support work resistance monitoring system,drilling stress meter and drill cutting method to monitor the strata pressure behavior when mining through the fault and set the critical value for forecasting coal bumps.By raising the mining position in advance to upper wall of the fault and constructing pressure relieve holes of large diameter,the workface mining through the Fault FD35 safely.