| China is a large coal consumer,coal as the main energy supplier is an important support for the development of the national economy.At present,in the primary energy consumption structure of our country,the proportion of coal consumption still occupies the first place,and it is expected that in the next few decades,coal will still be the main donor of energy demand.However,with the continuous mining of coal resources and the decrease of reserves,the waste of resources caused by the traditional method of pillar mining needs to be solved urgently.Non-pillar mining has become the development direction of coal resources mining in the future.As a new type of non-pillar mining technology with high efficiency and safety,non pillar by roof-cutting mining is more and more widely used.With the consumption of shallow coal resources,some mining areas have entered the coal seam mining under deep or complex geological conditions,in which the inclined coal seam resources account for a large proportion,and the non-pillar mining by roof-cutting technology used in the inclined coal seam.It not only accords with the strategic direction of sustainable development of coal resources,but also solves a series of problems such as dynamic disasters in inclined coal seam mining.To study the structural characteristics of gob-side entry by roof-cutting,stope stress evolution and mine pressure behavior law,at the same time,it can be used as a reference for mines with similar geological conditions.Based on the engineering background of gob-side entry by roof cutting of inclined thick coal seam in Jinfeng Coal Mine,Yinchuan,Ningxia,this paper uses the research methods of theoretical analysis,numerical simulation,etc.,combined with indoor rock mechanic experiment,field test and so on.In this paper,the characteristics of surrounding rock structure,the evolution of overlying rock stress,the key parameters of roof cutting and roadway formation and the law of in-situ mine pressure behavior in inclined thick coal seam of Jinfeng Coal Mine are studied and analyzed systematically.the main contents are as follows:(1)First of all,the technical principle and key technology of gob-side entry by roof cutting a are introduced in detail,and the action mechanism of constant resistance and large deformation anchor cable support and two-way energy accumulation directional blasting are analyzed.Then,a variety of surrounding rock control techniques for roof cutting and roadway formation are summarized,and the multi-directional control system of roadway surrounding rock in inclined thick coal seam is put forward.(2)Based on the mechanical analysis of the structural characteristics and stability of the surrounding rock of the gob-side entry by roof cutting of the inclined thick coal seam,it is concluded that when the basic roof of the non-pillar mining by roof cutting is broken for the first time,the internal deflection of the stope shows asymmetric distribution.The maximum flexure position is in the middle and upper part of the stope,and the first tensile fracture position of the basic roof is in the middle and upper part of the front coal wall and the rear coal wall along the inclined direction.The basic roof fault span of the non-pillar mining by roof cutting is different in the lower part of the working face and the middle and upper part of the working face,the basic roof fracture form,the lower opening is larger,the upper opening is smaller,as the irregular "o-x" periodic fracture;(3)The mechanical model of surrounding rock structure of gob-side entry by roof cutting in inclined thick coal seam is established,three instability modes of entry roof are put forward,and the corresponding instability conditions are given.Through the theoretical analysis,the expression of the interlayer interface stress,the width of the plastic zone and the deformation of the solid coal slope in the plastic zone of the solid coal side of the gob-side entry by roof cutting are obtained,and the length of the gangue cushion in the lower goaf of the stope is obtained,and according to the momentum theorem,The impact force of the lateral support system is obtained.Through the systematic and detailed analysis of the surrounding rock environment of the roadway,it provides a theoretical support for the selection of key parameters.(4)By using the numerical simulation software,the evolution law and caving characteristics of the overlying rock stress field in the non-pillar mining by roof cutting of inclined thick coal seam are analyzed,and it is concluded that in the process of advancing the mining face,along the direction of the working face,a stress arch is formed as the arch foot in the rear coal wall and in front the work face,and in the middle of mining distance as the highest point.Along the inclination direction of the working face,the arch foot forms the coal wall on both sides of the working face,and the arch roof is located in the middle and upper part of the working face.(5)The influence of the change of dip angle on the distribution of stope stress field is analyzed by simulating.It is concluded that the stress concentration factor of the middle and upper face of the three kinds of coal seam dip angle shows the law that the smaller the coal seam dip angle is,the smaller the stress concentration factor is,and the lowest stress concentration factor is when the coal seam dip angle is the highest in the lower part of the working face.The stress concentration factor in front of the working face of the three kinds of coal seam dip angle is inversely proportional to the dip angle of the coal seam,and the greater the dip angle of the coal seam is,the farther the stress concentration position is from the roadway.The lateral pressure stress concentration factors behind the three kinds of coal seam dip face are as follows:coal seam dip angle 15°>coal seam dip angle 30°>coal seam dip angle 45 °,and the stress release area in the roof strata of the stope shows obvious asymmetry,and the larger the dip angle is,the greater the dip angle is.The more obvious the asymmetry is.The overlying rock caving arch is asymmetrical,the highest position of the arch roof is in the middle and upper part of the working face,and the upper part of the caving arch is a crack development zone.After the development of caving arch in horizontal non-pillar mining stope is completed,the highest position of arch roof is located in the middle of working face,showing a state of left and right symmetry.(6)The rock mechanical parameters of the roof of transport roadway in 011810 working face of Jinfeng Coal Mine are obtained by test.According to the field geological boreholes and roadway lithology exploration holes,the roof lithology is explored in detail and the design division is carried out according to the results.Then,according to the rock mechanics parameters,the cutting height and depth of roof in different zones are determined by using the method of theoretical calculation and numerical simulation.Through theoretical calculation,the roof constant resistance anchor cable support parameters of roof cutting roadway in inclined thick coal seam are determined,and finally the support parameters of surrounding rock maintenance of roof cutting roadway are determined.(7)Through the analysis of the field pressure data,the characteristics of stope pressure behavior and the law of surrounding rock deformation and stress variation in the process of non pillar mining by roof cutting in inclined thick coal seam are obtained.The mine pressure in the mining stope shows the phenomenon of asymmetric pressure,which is as follows:the middle and upper part of the working face>the middle of the working face>the upper part of the working face>the lower part of the working face.Compared with the middle area of the working face,the pressure intensity and the periodic pressure step distance of the two ends of the working face are changed,the overall compression strength of the middle area of the working face is the highest,and the pressure step distance is small,and the periodic pressure step distance of the two ends is larger than that of the middle part of the working face.The roof and floor deformation of cut roadway in inclined coal seam is asymmetric,the subsidence of solid coal side roof is less than that of gravel side roof,the stress change of constant resistance and large deformation anchor cable is divided into three regions,and the stress increase is different in different areas.The variation law of hydraulic unit pressure and the changing trend of lateral pressure in the temporary support area of roadway cutting are closely related to the distance affected by dynamic pressure. |
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