Theory Model Of Mining Fracture Annular Body And Its Application In Pressure Relief Gas Drainage

With the development of coal safety,high efficiency and green mining technology,the problem of gas overrun caused by high-strength mining in low-permeability and unsaturated coal seam has been paid more and more attention.At the same time,the condition of short distance coal seam group in our country makes the upper adjacent layer directly enter the caving zone of the goaf with the roof caving,and a large amount of pressure relief gas is desorbed,which intensifies the gas emission in the goaf and causes the upper corner of the working face and the gas frequency of the return air flow to exceed the limit.Gas drainage in fault zone is one of the main methods of gas control in upper corner and return air flow of working face,and the selection of drainage position is an important guarantee for the drainage effect.The determination of the pumping position is affected by many factors,such as the fracture development pattern,the permeability of overburden,the interval between layers and the law of gas transportation and storage under pressure relief.In order to realize the accurate location of the extraction position and the high-efficient co mining of coal and gas,the shennanao coal mine is taken as an example to carry out in-depth research.This article comprehensively uses a variety of methods such as theoretical analysis,numerical simulation,laboratory experiments,field measurements,etc.,making full use of coal mining science,mine pressure and rock formation control,mine rock mechanics,elastoplastic mechanics,damage mechanics,fracture mechanics,fluid mechanics,Theoretical knowledge of computational fluid mechanics,seepage mechanics,spatial solid geometry,groundwater dynamics,and image analysis technology,the mechanism of the formation and expansion of the fissures in the overburden is systematically expounded from the micro and macro levels;Based on the actual engineering background of Shennanwa Coal Mine,the 3D morphological characteristics of mining overburden fractures and their evolution with the advancement of the working face were studied.The concept of mining fractured torus was proposed,and a 3D three-dimensional model was initially constructed.Characterization parameters and discrimination methods;Aiming at the differences in the physical properties of different areas of mining overburden,a calculation model for the permeability of mining fractured annulus is proposed,and its distribution characteristics are studied in the laboratory and on-site;Based on the constructed three-dimensional model of the mining fractured ring and the permeability calculation model,the gas storage and storage laws of the goaf before and after extraction were analyzed,the drilling optimization scheme was proposed,and the initial mining of the 20104 working face of the Shen Nanwa coal mine Gas management during the normal and normal mining periods.The main conclusions obtained from this study are as follows:(1)The change of vertical stress of the surrounding rock of the stope can be divided into two major processes(pressurization and unloading),and four small stages(increasing axial pressure,unloading from axial pressure to confining pressure,and unloading from confining pressure to Zero,the axial pressure becomes tensile stress).On the micro-level,during the increase of axial pressure,as the axial stress gradually increases,the crack expansion will occur sliding friction,self-similar expansion,bending expansion,and unstable expansion;When the axial compressive stress is unloaded to the confining pressure stage,the micro-cracks will undergo reverse slip deformation;the axial compressive stress is unloaded to the zero stage,when the micro-cracks initiate initiation and expansion;when the axial compressive stress becomes tensile stress Some micro-fissures need to be opened and some micro-fissures must be closed.From a macro perspective,the formation of delamination cracks can be judged by the maximum curvature and maximum deflection when the upper and lower adjacent rock layers bend and sink;The formation of vertical breaking fractures needs to meet the breaking deformation strength conditions and deformation coordination conditions;Mining overlying rocks are outside the goaf,and there are lateral fissure development areas.Lateral fissures are not obvious near the stope area,but they are obvious in areas far from the stope.The formation and expansion of lateral fissures can be considered as the main bending moment,Rock mass unloading,tensile cracking,rock mass creep,etc.(2)From the perspective of the corners on the working surface and the gas control of the return air flow,based on previous studies,the concept of "mining fractured ring"and its characterization parameters and criteria(the characterization parameters have a internal extension angle,external extension angle,ring width,ring height),a three-dimensional three-dimensional model of the fractured ring body was initially constructed;In the horizontal direction,according to the positions of the four sides of the mining fractured ring body,it is divided into stope ring body,return air ring body,cut eye ring body,and transport ring body;in the vertical direction,it obeys the overburden rock in the goaf The division of the "three zones" is divided into mining fractured ring bodies-collapse zone(ring body-collapse zone),mining fractured ring bodies-fault zone(ring body-fracture zone);(3)From the first time the roof is pressed to the goaf once and then to the goaf twice,the spatial form of the mining fissure ring will go through the process of cap,square ring and long ring.On the vertical cut surface of the parallel stope,the boundary morphology of the overburden mining fractures is not a positive trapezoidal distribution in the traditional understanding,but a positive trapezoidal distribution in the near stope area and an inverted trapezoidal distribution in the area away from the stope.The distance of trapezoidal distribution is about 150～200m behind the stope;The external extension angle of the incision ring has gone from 90° to 95° to 99°,which indicates that with the continuous advancement of the working face,the breaking angle of the overburden on the side of the incision is constantly increasing;The width of the ring in the stope is 64.5m,and it is 37m after the second square,and it goes through a process of first increasing,then decreasing,and then stable;The internal extension angle of the stope ring is approximately the same as the external extension angle of the stope ring,and it is stable at about 57°.Within 60m of the stope,the vertical stress of the roof overburden is mostly in the tensile stress zone.2.5 times the length of the tensile stress zone of the eyelet ring;Away from the working face area,the stress recovery process of the overburden in the goaf is transmitted from top to bottom.As the distance from the stope increases,the width of the stress recovery in the goaf in the direction of the parallel working surface gradually increases,and the width of the stress recovery zone Logarithmic growth with distance from the work surface;(4)In the study of the evolution and distribution characteristics of overburden mining fractures,simulations of similar materials show that along the advancing direction of the overburden,the overburden rupture area expands outward in a "(?)" shape,between the overburden fracture line and the horizontal line The included angle remains basically unchanged,and the breaking angle of the overlying rock on the side of the stope is about 50°;There are fissure development areas with a width of 25～26m on both sides of the working face in the direction of the parallel working face,and the extension angle of the ring body is 63～64 °;using a non-contact strain displacement video measuring instrument,the mining area of the overburden during excavation.The monitoring found that along the advancing direction of the working face,the influence boundary of the mining area during the mining process presented an arch-like hyperbola-like-inverted ladder shape.Field measurements show that the high-angle fractures are the dominant fractures in the return air ring-fault zone.The vertical fractures with α>75° account for 27.5%,and the high-angle fractures with an inclination of 45°≤α<75° account for 61.1%.Low-angle fractures with an inclination angle of 15°≤α<45° accounted for 10.2%,and horizontal fractures with α<15° accounted for only 1.2%.(5)A solution model of the fractured ring body permeability was proposed,and it was pointed out that the permeability of the ring body-collapse zone was solved using the Blake-Kozeny formula,and the permeability of the ring body-fracture zone was performed using the fracture tensor theory.Introduced the method of using borehole panoramic imaging technology to solve the fractured rock mass permeability in hydraulics.The permeability of the upper part of the return air ring-collapse zone was measured in the field to be 4.43 10-5m2,and the permeability of the return air ring-fault zone was measured.3.81 ×10-8～3.01×10-5 m2,the permeability of overburden decreases with increasing distance from the goaf;The simulation experiments show that the horizontal permeability under the influence of mining has increased by 400-2050 times compared with the original horizontal permeability.The horizontal permeability in the upper part of the overburden is lower than that in the lower part.The vertical permeability is significantly affected by the vertical fracture gap.When the overlying soft rocks are broken in groups due to the breaking of subcritical layers,the vertical permeability of this area is low.The vertical permeability on both sides of the mined-out area is significantly larger than that in the middle of the mined-out area.Under the influence of mining,the vertical permeability of overburden in the mined-out area has increased by 125-1900 times from the initial vertical permeability.The permeability of the collapse zone can be calculated as k1=-7e-6z+0.0001;the permeability of the ring body-fault zone can be calculated as k2=-1e"6z+6e"5.(6)Through a comparative analysis of different drainage levels and horizontal offset offset drainage schemes,it is found that the drilling effect is optimal when the position of the drilling holes is 35m in height and the internal offset distance is 30m.Five groups of drilling fields are set within 150m before the initial mining period of the working face,and the average final hole height of each drilling field is sequentially increased,which are 15m,18m,24m,34m,and 38m respectively;the average inner distance from the return air lane is 21m in turn,22m,25m,28m,30m;In the normal mining period,6 drilling holes of φ153mm are designed for each group of drilling sites,and the spacing between the drilling sites is 30m.In order to ensure the effective extraction length of high-level drilling,the average height of the final drilling holes is 40m,and the inner distance is fan-shaped with a center of 30m Layout.