Study On Tectonic Stress And Its Influence On Coal And Gas Outburst In Pingdingshan Eastern Mining Area

The comprehensive hypothesis of coal and gas outburst holds that outburst is the result of comprehensive action of in-situ stress,gas and mechanical properties of coal,and tectonic stress is the link connecting the above three factors.The tectonic stress is divided into paleotectonic stress and modern tectonic stress according to the action period.The study of coal and gas outburst from the perspective of tectonic stress mainly includes paleotectonic stress and modern tectonic stress.Firstly,the action direction and magnitude of paleotectonic stress and modern tectonic stress in eastern Pingdingshan mining area are clarified.Then,the development law of structural coal and gas occurrence law in the eastern mining area of Pingdingshan are analyzed,and the control effect of paleotectonic stress on the above-mentioned outburst factors is discussed based on the above-mentioned law.Finally,based on the above research,taking the outburst accident working face as the prototype and using FLAC3D software to establish a numerical model,the control effect of modern tectonic stress on coal and gas outburst was studied.In this paper,the eastern Pingdingshan mining area is taken as the research mining area,and structural geology,rock mechanics,structural physics and other theoretical methods are used to study the control effect of structural stress field on coal and gas outburst by means of on-site investigation,theoretical analysis,laboratory experiments,numerical simulation and on-site testing.The research content of this paper mainly includes the following five aspects:(1)Study on Tectonic Stress and Tectonic Evolution of the Eastern Mining Area of PingdingshanBy observing conjugate shear joints in the field and underground,a total of 1816 shear joint data were collected,and the paleotectonic stress experienced after Permian in the mining area was inversed by stereographic projection method.By collecting and analyzing the geostress data of the mining area,the direction and magnitude of the modern tectonic stress in the eastern mining area of Pingdingshan were obtained,and the results were verified by the inversion of the focal mechanism.According to the above analysis,after the formation of the Carboniferous Permian coal-bearing strata in the eastern part of Pingdingshan,the Indosinian period,the Yanshan early-intermediate,the late Yanshanian and the Himalayan period tectonic stresses were observed,and the action directions were NS,NW,NE.NNE direction,in which the late Yanshanian tectonic stress has the strongest intensity and the Indosinian period has the least intensity.The NWW and NW controlled fault-fold structures in the study mining area were mainly formed under the action of paleotectonic stress s in the late Yanshan period,while the paleotectonic stress in the Indosinian period,the early-middle Yanshan period and the Himalayan period mainly formed secondary structures and minor structures in the study mining area;The action direction of modern tectonic stress in eastern Pingdingshan mining area is NEE direction.The size of modern tectonic stress in No.8,No.10,No.12 and No.1 mine in Shoushan is above 30MPa,and that in No.1 mine is about 20MPa.(2)Study on the control of paleotectonic stress on the development of tectonic coalBased on the study of paleo-tectonic stress and tectonic coal development law in the study area,the controlling mechanism of tectonic stress on tectonic coal type and development regularity in the study area is studied.This paper focuses on the mechanism of tectonic coal formation in fault-fold belts,the paleo-tectonic stress is the key factor in the formation and development of tectonic coal.Fragmented coal and crushed coal can be formed under the action of extrusion,shearing and tensile tectonic stress.The scale-type mylonite coal is mainly formed under the shear tectonic stress.The wrinkle-type mylonite coal is mainly formed under the action of extrusion and shear tectonic stress.Soil-like mylonite coal is mainly formed under the action of shear tectonic stress.The subsequent tectonic stress after the formation of tectonic coal may transform the low-destructive tectonic coal to the high-destructive tectonic coal.The formation process of faults and folds in coal-bearing strata is also the formation process of tectonic coal.Tectonic stress is the macroscopic control of the distribution of tectonic coal through the distribution of geological structures in the mining area.Based on the above analysis,the formation mechanism of the strip-like and layered distribution of tectonic coal in the fault zone of the study area is obtained.The development of tectonic coal of the regional and layer levels are controlled by the large-scale structure of the eastern mining area of Pingdingshan,while the development of tectonic coal of the local level is controlled by the small structure in the mining area.The late Yanshan tectonic stress is the most critical first-stage tectonic stress for the formation and development of tectonic coal in the mining area and the stratum,while the other three-stage tectonic stress mainly affects the formation and development of local tectonic coal.(3)Study on the Influence of Paleotectonic stress on Gas OccurrenceThrough extensive testing of gas content and pressure data of each mine,the gas occurrence law of coal seam in the eastern mining area of Pingdingshan is studied,and the reason for the imbalance of gas occurrence in the eastern mining area of Pingdingshan is analyzed.Gas occurrence is the result of gas generation,gas migration enrichment and gas preservation environment.Permeability is the key factor affecting coal seam gas migration.The permeability of coal-rock samples in the non-structural zone and fault zone of the mining area was tested by using the true triaxial coal-rock pressure-seepage experimental equipment.The influence of tectonic stress on gas permeability is studied.On this basis,the effects of tectonic stress on the occurrence of gas in the mining area are studied from the aspects of tectonic stress affecting gas generation,gas migration and preservation environment.According to the above research,the permeability of the coal sample in the fault zone is most sensitive to stress,the coal sample in the non-structural area is the second,and the permeability of the roof rock sample is the least sensitive to the stress.The parallel permeability of the coal sample in the non-structural and fault areas is most affected by the maximum tectonic stress,the influence of vertical stress is the second,the minimum tectonic stress is the least affected.The vertical bedding permeability is most affected by the maximum tectonic stress,the minimum tectonic stress is the second,the vertical stress is the least,and the influence of tectonic stress on the permeability is more critical;When the coal sample is loaded with 30MPa of tectonic stress,the permeability is about 0.1 md,and the permeability of the coal is extremely low,which leads to the high-gas zone of the compressive fault structure.The paleo-tectonic stress drived the migration of gas from the high-stress zone to the low-stress zone,and resulted in gas enrichment in the compressive structural zone and less gas in the tensile structural zone through the above-mentioned actions.Based on the above studies,the influence of paleotectonic stress on gas occurrence in the mining area in the east of Pingdingshan can be divided into three key periods:the Indosinian period and the early-middle period of Yanshan,late Yanshan and Xishan periods.(4)Study on the Influence Mechanism of Tectonic Stress on Coal and Gas OutburstIt is found that the most frequent accidents occurred in the tunneling face of the fault area in research mining area.Coal and gas extrusion accidents accounted for 73.88%of the total number of accidents,indicating that tectonic stress is the most critical driving force for coal and gas outburst accidents in mining areas.In order to study the dynamic effect of tectonic stress in the outburst,this paper combines the research on the development of tectonic coal and the occurrence of gas in the fault zone,the FLAC3D software is used to establish the numerical model of the normal fault and reverse fault zone excavation with the coal seam as the inclined state and the structural soft coal zone.The model is divided into 0°,30°,60° and 75° according to the angle between the direction of the excavation and the fault strike.The stress evolution during the excavation process near normal fault and reverse fault under different tectonic stress conditions is simulated.Based on the outburst energy equation,the outburst risk of the tunneling face in the normal fault and reverse fault zone under modern tectonic stress is analyzed.The magnitude of modern tectonic stress has an important influence on the prominent hazard of the tunneling face in the normal fault and reverse fault zone.Under the same gas condition,the greater the tectonic stress intensity,the greater the risk of outburst.The outburst hazard of the tunneling face in the normal fault and reverse fault zone increases with the increase of the angle between the direction of the modern tectonic stress and the heading direction,but the influence of the direction of the tectonic stress on the outburst is far less than the magnitude of the tectonic stress.Under the same tectonic stress and gas conditions,the stress concentration of the heading face near the reverse fault is slightly larger than that of the normal fault,and the outburst risk is larger than that of the normal fault zone.(5)Study on the mechanism of influence of tectonic stress on coal and gas outburstBased on the study of tectonic stress in the eastern mining area of Pingdingshan,combined with tectonic stress to control the development of tectonic coal and influence the law of gas occurrence,the mechanism of tectonic stress affecting coal and gas outburst is clarified.Paleo-tectonic stress mainly affects coal and gas outburst by affecting the tectonic coal development,the gas occurrence and geological structure distribution.The residual stress of paleo-tectonic stress is negligible compared with modern tectonic stress.The influence of paleo-tectonic stress is mainly in the physical body of coal.The direction and size of modern tectonic stress have an impact on the outburst,and the influence of stress size is more critical.Modern tectonic stress mainly provides elastic strain energy of coal rock,which is an important source of coal and gas outburst energy,especially in the structural areas such as faults and folds,and the elastic strain energy increases,and the prominent risk increases.Modern tectonic stress affects the gas expansion energy by affecting the permeability of the coal seam,and the mining disturbance is the fuse of coal and gas outburst in the coal seam.When the tectonic stress exceeds 20MPa during the excavation process,the pressure relief measures should be taken until the tectonic stress is reduced to a safe level.The excavation direction of the heading face should be as close as possible to the direction of the tectonic stress.When the excavation reaches a region where the fault strike intersects with the direction of the tectonic stress at a large angle,the fault zone tends to have structural stress concentration and large gas pressure,and gas drainage and pressure relief measures should be strengthened.