Stable anchoring design method for near-distance coal seam gob-side tunneling roadway with narrow coal pillar reserved

Abstract

The invention discloses a stable anchoring design method for a near-distance coal seam narrow coal pillar gob-side tunneling roadway, and the method comprises the steps: S10, analyzing mining geological conditions, and testing physical and mechanical parameters of coal rock; s11, calculating the width of a plastic zone in a coal pillar after adjacent working faces are mined according to a coal rock physical and mechanical parameter test result, and carrying out numerical simulation calculation on vertical stress distribution of surrounding rock after stoping of the working faces around the gob-side tunneling roadway, and S12, determining the reserved size of the narrow coal pillar according to the content and comprehensive consideration of the anchoring quality of roadway anchor rods and cables. The design method for forming the stable anchoring structure comprises the steps that S20, roadway surrounding rock shear expansion pressure is calculated, S21, the roadway surrounding rock shear expansion pressure is introduced to conduct single end anchor rod action mechanical model derivation, S22, roadway anchor rod cable prestress calculation is conducted according to the result, and S23, the anchor net supporting opportunity is determined.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine tunnel support, and in particular to a stable anchoring design method for tunneling along the air with narrow coal pillars left in a close-range coal seam. Background Art

[0002] The tunnel driven along the goaf with narrow coal pillars can be arranged in the stress reduction zone by utilizing the collapse characteristics of the goaf area and the law of stress transfer, so as to avoid the influence of the intense activity of the overlying strata after the adjacent working face is mined, reduce the maintenance cost of the tunnel, and retain a certain width of coal pillars between the upper goaf area to protect the tunnel, so as to prevent water accumulation in the goaf area, harmful gases, large rocks, etc. from entering the tunnel. At present, with the continuous advancement of underground tunnel support technology, the application of tunnel driven along the goaf with narrow coal pillars is gradually increasing.

[0003] The determination of the size of the narrow coal pillar in the goaf-side tunnel under the condition of a single coal seam is relatively simple. It only needs to consider the influence of the mining conditions of the coal seam and the size of the coal pillar on the stability of the goaf-side tunnel. The value range can be determined by the limit equilibrium theory. Compared with the mining of a single coal seam, the movement of the overlying strata and the characteristics of the mine pressure manifestation in the mining of a close-range coal seam group are significantly different: on the one hand, the roof surrounding rock of the goaf-side tunnel in the close-range coal seam is significantly damaged by the mining of the overlying coal seam, and is continuously affected by the concentrated stress formed on the floor by the section coal pillar remaining after the mining of the upper coal seam and the coal body mined on one side, resulting in significant changes in the roof structure and stress environment of the mining area of ​​the lower coal seam, which in turn causes a new phenomenon of strong mine pressure; on the other hand, affected by the mining of the working face of the coal seam, the stress level is further increased. Due to the complex temporal and spatial relationship between the stress transfer law and the mine pressure manifestation, when the size of the coal pillar in the goaf-side tunnel in the close-range coal seam below is not reasonably set, the mine pressure is violent and the tunnel surrounding rock support is extremely difficult.

[0004] The proportion of close-range coal seams deposited and mined in my country is large. In many mining areas, there are problems such as unreasonable setting of narrow coal pillars in the tunnels along the empty space and difficulty in tunnel maintenance during close-range coal seam mining, which leads to frequent problems of tunnel support instability. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams, which realizes the reasonable arrangement of tunneling along the goaf in the dynamic pressure zone of close-range coal seams and the stability control of the surrounding rock.

[0006] The present invention provides a stable anchoring design method for a tunnel along the goaf with a narrow coal pillar in a close-distance coal seam, comprising: determining the size of the narrow coal pillar in the tunnel along the goaf and designing a stable anchoring structure; wherein:

[0007] The determination of the size of the narrow coal pillar in the gob-side tunneling includes:

[0008] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0009] S11. Calculate the width of the plastic zone in the coal pillar after mining of adjacent working faces based on the test results of coal and rock physical and mechanical parameters, and carry out numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working face around the gob-side tunneling tunnel;

[0010] S12. Determine the size of the narrow coal pillar based on the analysis of mining geological conditions, the test of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the value of the vertical stress distribution of the tunnel surrounding rock, and the anchoring quality of the tunnel bolt cable;

[0011] Design methods for forming stable anchor structures include:

[0012] S20, calculating the shear dilatancy pressure of the tunnel surrounding rock;

[0013] S21. The shear expansion pressure of the surrounding rock of the tunnel is taken into account to derive the mechanical model of the single end anchor bolt;

[0014] S22. Calculate the prestress of the anchor cable in the tunnel based on the derivation of the mechanical model of the single end anchor and the calculation results of the shear expansion pressure of the tunnel surrounding rock;

[0015] S23. Determine the timing of anchor net support.

[0016] Optionally, the mining geological conditions analysis specifically includes analyzing the surrounding rock environment of the tunnel excavated along the airspace with a narrow coal pillar left in the lower coal layer based on on-site mining data. The coal and rock physical and mechanical parameter testing specifically includes: testing the basic physical and mechanical parameters of the target tunnel surrounding rock, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard specimens, and obtaining the physical and mechanical parameters and deformation and failure laws of the tunnel roof and floor and coal seams, providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0017] Optionally, the physical and mechanical parameters of coal rock include uniaxial compression, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

[0018] Optionally, the numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining around the working face of the goaf tunnel includes: establishing a FLAC3D three-dimensional numerical calculation model according to the geological conditions of the goaf tunnel, and conducting excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seam working faces to obtain the vertical stress distribution cloud map of the surrounding rock of the goaf tunnel at different mining stages, comparing the stress levels of the tunnel surrounding rock under different coal pillar sizes or tunnel positions, analyzing the difficulty of tunnel maintenance, and obtaining the value of the stress concentration factor K according to the vertical stress distribution cloud map of the surrounding rock.

[0019] Optionally, the calculation of the width of the plastic zone in the coal pillar after mining of adjacent working faces includes:

[0020] According to the limit equilibrium theory, the width X0 of the plastic zone in the coal pillar after adjacent working faces are mined is calculated as follows:

[0021]

[0022] Where: m is the coal seam thickness, unit is m, λ is the lateral pressure coefficient, λ=μ / (1-μ), μ is the Poisson's ratio, is the internal friction angle of the coal body, C0 is the cohesion of the coal body, the unit is MPa, K is the stress concentration factor, γ is the average bulk density of the overlying rock layer, the unit is MN / m 3 , H is the tunnel depth, in m, P z is the support resistance of the support body to the coal seam, in MPa;

[0023] The reasonable coal pillar width is calculated according to the formula B = X0 + X1 + X2, where the latter two have limited values, namely, X2 is the effective length of the anchor rod, which is 1.2m; X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2).

[0024] Optional, comprehensive considerations include:

[0025] From the perspective of surrounding rock vertical stress distribution, when the tunnel along the goaf with narrow coal pillars in the lower layer is completely below the goaf, the vertical stress of the surrounding rock is the lowest, and the stress environment of the tunnel is relatively favorable;

[0026] The tunnel roof rock layer has been damaged by mining, and the tunnel roof rock mass is relatively broken, so the anchoring quality of the anchor cable is difficult to guarantee. Therefore, from the perspective of ensuring tunnel safety, this location is not suitable.

[0027] Combined with the calculation result B of reasonable coal pillar size and the degree of fracture of the surrounding rock of the coal pillar, the size of the coal pillar in the tunnel along the gob should be ≥B.

[0028] Optionally, the derivation of the mechanical model of a single end anchor includes:

[0029] Firstly, according to the different stress states of the bolt body, the end anchor bolt in the coal mine tunnel is divided into the anchoring section L1, the free section L2 and the threaded section L3. In theory, the stress state of the end anchor bolt is simplified to the mechanical model of the end anchor bolt for analysis.

[0030] Then, according to the St.Venant principle, the solution of the boussinnesq problem is used to approximate the stress distribution caused by the concentrated force of a single anchor rod. That is, when the length z of the free section L2 is 0≤z≤0.5L2, the compressive stress σ along the rod body direction at any point in the upper and lower rectangular planes composed of the anchor rod spacing r and the length z of the free section L2 is z Calculate as follows:

[0031]

[0032] Where: z —compressive stress provided by the anchor, MPa;

[0033] P—preload force applied during anchor installation, MN;

[0034] r—anchor spacing, m;

[0035] The anchor support mainly bears the shear expansion deformation pressure p of the rock mass within the anchoring range of the anchor s and the deadweight of a small amount of delaminated rock mass. Since the amount of rock delaminated is negligible, and the cohesion C of the anchored rock mass is ignored, according to the Moore-Coulomb law, the compressive stress σ provided by the anchor is z The following formula should be satisfied to keep the anchor structure stable:

[0036] Right now

[0037] Where: zmin —Minimum compressive stress formed by the anchor rod on the center line of the anchoring structure, MPa;

[0038] —internal friction angle of rock mass, °;

[0039] p s —Shear deformation pressure of rock mass within the anchoring range of anchor bolt, MPa.

[0040] Optionally, the calculation of the dilatancy pressure of the tunnel surrounding rock needs to establish a numerical analysis model based on the geological conditions of the tunnel along the goaf, and simulate and calculate the vertical stress distribution diagram of the surrounding rock during the tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the range of the surrounding rock in the dilatancy state around the tunnel gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain time step, the tensile stress reaches the extreme value, that is, p s After that, the tensile stress value continues to decrease. When the calculation time step increases to a certain value, the tensile stress value of the rock mass around the tunnel approaches 0, which means that the shallow rock mass continues to delaminate, break and expand, and finally completely loses its bearing capacity. In this process, p s The extreme value of is the value of the tunnel confining pressure and shear pressure.

[0041] Optional, the calculation of prestress of the anchor cable in the roadway needs to be based on the test results of the physical and mechanical parameters of the coal and rock and the initial anchor mesh support design plan, and the anchor spacing r, the length z of the anchor free section L2, the internal friction angle of the rock mass and the shear expansion deformation pressure p of the rock mass within the anchoring range s Substitute the values ​​into the following formula:

[0042]

[0043] In this way, the preload force P applied during the installation of the anchor rods required to form a stable anchoring structure on the top of the tunnel can be calculated.

[0044] Optional anchor net support opportunities include:

[0045] According to the development law of shear dilatancy pressure of tunnel surrounding rock under different calculation time steps obtained by numerical analysis model simulation calculation, in order to maintain the integrity and self-bearing capacity of tunnel surrounding rock and avoid continuous delamination, crushing and expansion of shallow rock mass, and even loss of bearing capacity, the initial support resistance provided by anchor net support should be greater than the maximum shear dilatancy pressure caused by deformation of shallow tunnel surrounding rock, and the support timing should also be before the extreme point of shear dilatancy stress of tunnel surrounding rock appears.

[0046] The technical solution provided by the embodiment of the present invention has the following advantages compared with the prior art:

[0047] A stable anchoring design method for a tunnel along the goaf with a narrow coal pillar left in a close-range coal seam provided in an embodiment of the present invention comprehensively considers the surrounding rock stress level, surrounding rock crushing degree and stable anchoring structure formation mechanism of the tunnel along the goaf under multi-coal seam mining conditions, and provides a stable anchoring design method for a tunnel along the goaf with a narrow coal pillar left in a close-range coal seam. Through mining geological condition analysis and coal and rock physical and mechanical parameter testing, calculation of the width of the plastic zone in the coal pillar after mining of adjacent working faces, numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working faces around the tunnel along the goaf and The anchoring quality of the tunnel anchor cable is comprehensively considered to determine the size of the narrow coal pillar in the tunnel along the goaf. The design method for forming a stable anchoring structure is determined by deriving the mechanical model of the single end anchor, calculating the shear pressure of the tunnel surrounding rock, calculating the prestress of the tunnel anchor cable and the timing of anchor net support. This can not only reasonably leave a narrow coal pillar so that the tunnel along the goaf is arranged in the stress reduction zone, but also ensure the anchoring performance of the tunnel anchor cable and provide a calculation method for the formation of a stable anchoring structure in the tunnel surrounding rock, thus realizing the reasonable arrangement of the tunnel along the goaf in the dynamic pressure zone of the close coal seam and the stability control of the surrounding rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of geological mining conditions and layout of tunnels along the goaf provided in an embodiment of the present invention;

[0049] Figure 2 This is a cloud diagram of vertical stress distribution after mining around the working face of the goaf-side tunneling in numerical simulation calculation.

[0050] Description of reference numerals:

[0051] 1. Tunnel excavated along the goaf; 2. Narrow coal pillars; 3. Lower section working face; 4. Remaining coal pillars between working faces of overlying coal seams; 5. Goaf area of ​​the left working face of overlying coal seams; 6. Goaf area of ​​the right working face of overlying coal seams; 7. Key rock strata between coal seams; 8. Rock strata group of the roof of overlying coal seams; 9. Rock strata of the bottom of lower coal seams; 10. Goaf area of ​​the upper section working face. DETAILED DESCRIPTION

[0052] A specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation.

[0053] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the technical solutions of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0054] The determination of the size of the narrow coal pillar in the goaf-driven tunnel under the condition of a single coal seam is relatively simple and the method is basically mature. First, the value range is determined by the limit equilibrium theory, and then the stability characteristics of the tunnel surrounding rock under different coal pillar sizes are analyzed and the reasonable coal pillar size is selected. At present, there are many studies on the narrow coal pillar in the goaf-driven tunnel under the condition of a single coal seam, and there are few related studies on the narrow coal pillar in the goaf-driven tunnel of close-distance coal seams. The occurrence and mining ratio of close-distance coal seams in my country is large. Many mining areas have the problems of unreasonable narrow coal pillars in the goaf-driven tunnel under close-distance coal seam mining and difficult tunnel maintenance. The main reasons are: (1) The factors that need to be considered in the size of the narrow coal pillar in the goaf-driven tunnel are more complex and diverse. Under the condition of close-distance mining of multiple coal seams, the mine pressure in the goaf-driven tunnel is more severe, and the time and space relationship between the upper and lower coal seams is complex. The unreasonable size of the coal pillar will lead to high concentration of stress in the tunnel surrounding rock and severe surrounding rock crushing, which will lead to technical difficulties in tunnel maintenance such as reduced reliability of anchor net support and difficulty in applying anchor cables. (2) There is no theoretical basis for accurate quantitative design of key parameters of anchor mesh support, such as anchor cable preload and support timing. There is also a lack of design methods for forming a stable anchoring structure between tunnel surrounding rock and anchor mesh support system, which leads to frequent problems of tunnel support instability.

[0055] Under the condition of close-distance coal seam mining, the tunnels driven along the goaf are affected by the multiple superposition of mining of overlying coal seams, residual coal pillars, mining of the working face of the coal seam and disturbance caused by excavation. It is necessary to comprehensively consider many factors such as the stress environment of the tunnel surrounding rock and the stable anchoring design under the conditions of different coal pillar sizes. Therefore, it is urgent to study and develop a stable anchoring design method for tunnels driven along the goaf with narrow coal pillars under the condition of close-distance coal seam mining.

[0056] To this end, an embodiment of the present invention provides a stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams, thereby achieving reasonable arrangement of tunneling along the goaf in the dynamic pressure zone of close-range coal seams and stable control of the surrounding rock.

[0057] At least one embodiment of the present invention provides a stable anchoring design method for a roadway driven along the goaf with a narrow coal pillar in a close-distance coal seam, including: determining the size of the narrow coal pillar in the roadway driven along the goaf and designing a stable anchoring structure, wherein the determination of the size of the narrow coal pillar in the roadway driven along the goaf includes:

[0058] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0059] S11. Calculate the width of the plastic zone in the coal pillar after mining of adjacent working faces based on the test results of coal and rock physical and mechanical parameters, and carry out numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working face around the gob-side tunneling tunnel;

[0060] S12. The size of the narrow coal pillar is determined based on the analysis of mining geological conditions, testing of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the value of the vertical stress distribution of the tunnel surrounding rock, and the anchoring quality of the tunnel anchor cable.

[0061] Design methods for forming stable anchor structures include:

[0062] S20, calculating the shear dilatancy pressure of the tunnel surrounding rock;

[0063] S21. The shear expansion pressure of the surrounding rock of the tunnel is taken into account to derive the mechanical model of the single end anchor bolt;

[0064] S22. Calculate the prestress of the anchor cable in the tunnel based on the derivation of the mechanical model of the single end anchor and the calculation results of the shear expansion pressure of the tunnel surrounding rock;

[0065] S23. Determine the timing of anchor net support.

[0066] In the stable anchoring design method for tunneling along the air with narrow coal pillars in close-range coal seams provided by the above-mentioned embodiment of the present invention, multiple aspects such as the size of narrow coal pillars, the stress level of the tunnel surrounding rock, the degree of surrounding rock fragmentation, the formation mechanism and design of a stable and reliable anchoring bearing structure are comprehensively considered, thereby achieving the reasonable arrangement of tunneling along the air in the dynamic pressure zone of close-range coal seams and the stability control of the surrounding rock.

[0067] The present invention is described below by several specific embodiments. In order to keep the following description of the embodiments of the present invention clear and concise, the detailed description of known functions and known components may be omitted. When any component of the embodiments of the present invention appears in more than one accompanying drawings, the component may be represented by the same reference numeral in each of the accompanying drawings.

[0068] The embodiment of the present invention provides a stable anchoring design method for a roadway driven along the goaf with a narrow coal pillar in a close-distance coal seam, including: determining the size of the narrow coal pillar in the roadway driven along the goaf and designing a stable anchoring structure, wherein the determination of the size of the narrow coal pillar in the roadway driven along the goaf includes:

[0069] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0070] S11. Calculate the width of the plastic zone in the coal pillar after mining of adjacent working faces based on the test results of coal and rock physical and mechanical parameters, and carry out numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working face around the gob-side tunneling tunnel;

[0071] S12. The size of the narrow coal pillar is determined based on the analysis of mining geological conditions, testing of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the value of the vertical stress distribution of the tunnel surrounding rock, and the anchoring quality of the tunnel anchor cable.

[0072] Design methods for forming stable anchor structures include:

[0073] S20, calculating the shear dilatancy pressure of the tunnel surrounding rock;

[0074] S21. The shear expansion pressure of the surrounding rock of the tunnel is taken into account to derive the mechanical model of the single end anchor bolt;

[0075] S22. Calculate the prestress of the anchor cable in the tunnel based on the derivation of the mechanical model of the single end anchor and the calculation results of the shear expansion pressure of the tunnel surrounding rock;

[0076] S23. Determine the timing of anchor net support.

[0077] First of all, it should be noted that leaving narrow coal pillars is related to the stable anchoring of the roadway along the goaf, and the logical relationship is a progressive relationship, first the coal pillar and then the stable anchoring. First of all, it is necessary to leave narrow coal pillars. In addition, the number of narrow coal pillars left is critical to the stability control of the roadway. If the coal pillars are too narrow, the stress level of the surrounding rock of the roadway will be low, which is conducive to maintenance, but it will cause the crushing area on the side of the coal pillar of the roadway to exceed the anchoring length of the anchor cable, frequent anchoring failure, and the surrounding rock will also be difficult to stabilize; if the coal pillars are too large, too much coal resources will be left behind, less coal will be mined, resulting in a waste of resources, and the stress level of the roadway under the large coal pillars will also increase. Therefore, a reasonable coal pillar size is a prerequisite for ensuring a reasonable stress level of the surrounding rock of the roadway and the anchoring quality of the anchor cable. The size of the coal pillar is a range obtained only by traditional theoretical calculations. It is necessary to comprehensively consider the stress level of the surrounding rock of the roadway, the length of the anchor cable, and the anchoring quality (feedback and evaluation based on the pull-out test results of the anchor cable) to determine the size of the coal pillar, and then use our theoretical derivation and calculation to carry out the design of the roadway anchor net support. Some of the parameters need to be obtained in combination with numerical simulation calculations. Two design principles are proposed in the stable anchoring design method: one is to calculate the prestress value of the anchor cable required to form a stable anchoring structure on the top of the tunnel to ensure that the initial support resistance provided by the anchor mesh support should be greater than the maximum shear pressure generated by the deformation of the shallow surrounding rock of the tunnel; the other point is that the support timing should also be before the extreme point of shear stress of the tunnel surrounding rock appears.

[0078] A stable anchoring design method for a tunnel along the goaf with a narrow coal pillar left in a close-range coal seam provided in an embodiment of the present invention comprehensively considers the surrounding rock stress level, surrounding rock crushing degree and stable anchoring structure formation mechanism of the tunnel along the goaf under multi-coal seam mining conditions, and provides a stable anchoring design method for a tunnel along the goaf with a narrow coal pillar left in a close-range coal seam. Through mining geological condition analysis and coal and rock physical and mechanical parameter testing, calculation of the width of the plastic zone in the coal pillar after mining of adjacent working faces, numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working faces around the tunnel along the goaf and The anchoring quality of the tunnel anchor cable is comprehensively considered to determine the size of the narrow coal pillar in the tunnel along the goaf. The design method for forming a stable anchoring structure is determined by deriving the mechanical model of the single end anchor, calculating the shear pressure of the tunnel surrounding rock, calculating the prestress of the tunnel anchor cable and the timing of anchor net support. This can not only reasonably leave a narrow coal pillar so that the tunnel along the goaf is arranged in the stress reduction zone, but also ensure the anchoring performance of the tunnel anchor cable and provide a calculation method for the formation of a stable anchoring structure in the tunnel surrounding rock, thus realizing the reasonable arrangement of the tunnel along the goaf in the dynamic pressure zone of the close coal seam and the stability control of the surrounding rock.

[0079] Optionally, the mining geological conditions analysis specifically includes analyzing the surrounding rock environment of the tunnel excavated along the airspace with a narrow coal pillar left in the lower coal layer based on on-site mining data. The coal and rock physical and mechanical parameter testing specifically includes: testing the basic physical and mechanical parameters of the target tunnel surrounding rock, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard specimens, and obtaining the physical and mechanical parameters and deformation and failure laws of the tunnel roof and floor and coal seams, providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0080] Optionally, the physical and mechanical parameters of coal rock include uniaxial compression, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

[0081] Optionally, the numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining around the working face of the goaf tunnel includes: establishing a FLAC3D three-dimensional numerical calculation model according to the geological conditions of the goaf tunnel, and conducting excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seam working faces to obtain the vertical stress distribution cloud map of the surrounding rock of the goaf tunnel at different mining stages, comparing the stress levels of the tunnel surrounding rock under different coal pillar sizes or tunnel positions, analyzing the difficulty of tunnel maintenance, and obtaining the value of the stress concentration factor K according to the vertical stress distribution cloud map of the surrounding rock.

[0082] The vertical stress concentration factor of the tunnel surrounding rock is a key parameter in the calculation of the plastic zone of the coal pillar and the evaluation of the tunnel anchoring design. The process of obtaining it by field measurement is complex and the cycle is long. In the embodiment of the present invention, the numerical simulation method can be used to calculate it accurately and efficiently.

[0083] Optionally, the calculation of the width of the plastic zone in the coal pillar after mining of adjacent working faces includes:

[0084] According to the limit equilibrium theory, the width X0 of the plastic zone in the coal pillar after adjacent working faces are mined is calculated as follows:

[0085]

[0086] Where: m is the coal seam thickness, unit is m, λ is the lateral pressure coefficient, λ=μ / (1-μ), μ is the Poisson's ratio, is the internal friction angle of the coal body, C0 is the cohesion of the coal body, the unit is MPa, K is the stress concentration factor, γ is the average bulk density of the overlying rock layer, the unit is MN / m 3 , H is the tunnel depth, in m, P z is the support resistance of the support body to the coal seam, in MPa;

[0087] The reasonable coal pillar width is calculated according to the formula B = X0 + X1 + X2, where the latter two have limited values, namely, X2 is the effective length of the anchor rod, which is 1.2m; X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2).

[0088] Generally speaking, the size of the coal pillar in the goaf-driven tunnel is not only related to the stress state of the tunnel surrounding rock and the difficulty of maintenance, but also to the anchoring quality of the anchor cable and the stability control of the tunnel surrounding rock. Therefore, the size of the narrow coal pillar should be determined based on the calculation results of the coal pillar and the comprehensive consideration of the anchoring quality of the anchor cable (i.e., the on-site anchor cable pull-out test results).

[0089] Based on the above problems, in the embodiments of the present invention, comprehensive considerations include: from the perspective of vertical stress distribution of surrounding rock, when the lower layer narrow coal pillar is left and the roadway is excavated along the goaf is completely below the goaf, the vertical stress of the surrounding rock is the lowest, the stress environment of the roadway is relatively favorable, the roadway roof rock layer has suffered mining damage, the roadway roof rock mass is relatively broken, and the anchoring quality of the anchor cable is difficult to guarantee. Therefore, from the perspective of ensuring the safety of the roadway, this position is not suitable. Combined with the reasonable coal pillar size calculation result B and the degree of coal pillar surrounding rock rupture, the coal pillar size value of the roadway excavated along the goaf should be ≥ B. However, when the coal pillar size is larger, the loss of coal resources will further increase, and the stress level of the roadway will gradually increase. Therefore, the selection of the reasonable coal pillar size for the roadway excavated along the goaf should be based on the perspective of ensuring the anchoring quality of the roadway anchor cable, combined with the anchor cable pull-out test results and the theoretical calculation results of the coal pillar width. Generally, the value is B or 6m.

[0090] Optionally, the derivation of the mechanical model of a single end anchor bolt includes: first, according to the different stress states of the bolt body, the end anchor bolt in the coal mine tunnel is divided into an anchoring section L1, a free section L2 and a threaded section L3. In theory, the stress state of the end anchor bolt is simplified to the mechanical model of the end anchor bolt for analysis. Then, according to the St. Venant principle, the solution of the boussinnesq problem is used to approximate the stress distribution caused by the concentrated force of a single anchor bolt, that is, when the length z of the free section L2 is 0≤z≤0.5L2, the compressive stress σ along the direction of the bolt body at any point in the upper and lower rectangular planes composed of the anchor bolt spacing r and the length z of the free section L2 is taken as the side length z Calculate as follows:

[0091]

[0092] Where: z —compressive stress provided by the anchor, MPa;

[0093] P—preload force applied during anchor installation, MN;

[0094] r—anchor spacing, m;

[0095] The anchor support mainly bears the shear expansion deformation pressure p of the rock mass within the anchoring range of the anchor sand the deadweight of a small amount of delaminated rock mass. Since the amount of rock mass delaminated is negligible, and the cohesion C of the anchored rock mass is ignored, the compressive stress σ provided by the anchor rod according to the Moore-Coulomb law is z The following formula should be satisfied to keep the anchor structure stable:

[0096] Right now

[0097] Where: zmin —Minimum compressive stress formed by the anchor rod on the center line of the anchoring structure, MPa;

[0098] —internal friction angle of rock mass, °;

[0099] p s —Shear deformation pressure of rock mass within the anchoring range of anchor bolt, MPa.

[0100] Optionally, the calculation of the dilatancy pressure of the tunnel surrounding rock needs to establish a numerical analysis model based on the geological conditions of the tunnel along the goaf, and simulate and calculate the vertical stress distribution diagram of the surrounding rock during the tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the range of the surrounding rock in the dilatancy state around the tunnel gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain time step, the tensile stress reaches the extreme value, that is, p s After that, the tensile stress value continues to decrease. When the calculation time step increases to a certain value, the tensile stress value of the rock mass around the tunnel approaches 0, which means that the shallow rock mass continues to delaminate, break and expand, and finally completely loses its bearing capacity. In this process, p s The extreme value of is the value of the tunnel confining pressure and shear pressure.

[0101] In engineering practice, the shear pressure p of the rock mass within the anchoring range of the anchor bolt is s As the deformation of the tunnel surrounding rock continues to change, it is often difficult to measure it in a timely and accurate manner. However, the numerical calculation in the embodiment of the present invention can more accurately obtain the shear dilatancy pressure of the tunnel surrounding rock at different calculation time steps.

[0102] Optional, anchor cable prestress calculation needs to be based on the test results of coal rock physical and mechanical parameters and the initial anchor mesh support design plan, anchor spacing r, anchor free section L2 length z, rock mass internal friction angle and the shear expansion deformation pressure p of the rock mass within the anchoring range s Substitute the values ​​into the following formula:

[0103]

[0104] In this way, the preload force P applied during the installation of the anchor rods required to form a stable anchoring structure on the top of the tunnel can be calculated.

[0105] As an active support method, anchor cable prestress is the most important parameter for anchor cable support to play an active support role. In the early stage of tunnel excavation, sufficient support resistance must be provided to suppress the delamination and expansion of the shallow rock mass in the tunnel, so as to form an anchor bearing structure with a higher bearing capacity. To achieve this, it is necessary to rely on the preload applied when the anchor (cable) is installed. In addition, reasonable anchor cable prestress can make the anchor cable quickly increase resistance and maintain good bearing conditions, which is conducive to the formation of a reliable anchor bearing structure between the anchor cable and the tunnel surrounding rock, and to give full play to the self-bearing capacity of the tunnel surrounding rock and maintain the long-term stability of the tunnel surrounding rock.

[0106] Optionally, the timing of anchor net support includes: analyzing the development law of shear dilation pressure of tunnel surrounding rock at different calculation time steps obtained from the simulation calculation of the numerical analysis model, maintaining the integrity and self-bearing capacity of tunnel surrounding rock and avoiding continuous delamination, crushing and expansion of shallow rock mass, and even loss of bearing capacity, the initial support resistance provided by the anchor net support should be greater than the maximum shear dilation pressure generated by the deformation of shallow tunnel surrounding rock, and the support timing should also be before the extreme point of shear dilation stress of tunnel surrounding rock appears.

[0107] The timing of anchor net support is crucial to the control effect of tunnel surrounding rock. If the anchor net support is timely and the surrounding rock is relatively intact, the anchor net support and the surrounding rock will easily form a stable, reliable, and strong bearing capacity anchored bearing structure; on the contrary, if the timing of anchor net support is too late, the tunnel surrounding rock has lost its bearing capacity and the support effect is poor. However, there has been a lack of accurate and quantitative scientific basis for when to implement support, and the support design data only recommends "timely support". Therefore, based on the development law of shear dilatation pressure of tunnel surrounding rock under different calculation time steps obtained through numerical simulation calculation, the quantitative support timing of anchor net support is given, which is "before the extreme point of shear dilatation stress of tunnel surrounding rock appears".

[0108] Example:

[0109] The following will take Pingmei Co., Ltd. 16-17 -31020 working surface as an example, combined with Figure 1 and Figure 2 The present invention and its technical solution are described in detail, wherein: Figure 1 A schematic diagram of geological mining conditions and layout of tunnels along the goaf provided in an embodiment of the present invention, Figure 2 It is a cloud diagram of vertical stress distribution after mining around the working face of the goaf-side tunneling in numerical simulation calculation.

[0110] like Figure 1 and Figure 2 As shown, Pingmei No. 4 mine is mainly engaged in mining 15 Heji 16-17 Coal seam, 15 The coal seam is the overlying coal seam with an average thickness of 1.5m. 16-17The coal seam is the lower coal seam, with an average thickness of 3.3m and a coal seam spacing of 3 to 11m, belonging to the close-range coal seam group mining. 16-17 -31020 working face return air lane (i.e. tunnel 1 along the air path) is located below 16-17 In coal seams, 16-17 -31020 working face (i.e. lower section working face 3) on the right side is the coal seam 16 -23160 working face goaf area (i.e. upper section working face goaf area 10), test tunnel and 16-17 -23160 A narrow coal pillar 2 is left in the goaf of the working face, and the overlying 15 -31020 working face goaf area (i.e. working face goaf area 5 on the left side of the overlying coal seam) and 15 -23160 working face goaf area (i.e. working face goaf area 6 on the right side of the overlying coal seam). 16-17 The immediate roof of the coal seam is composed of silty mudstone with an average thickness of 5.45 m, and the basic roof is composed of medium-grained sandstone with an average thickness of 11.5 m, which together constitute the key rock layer 7 between coal seams; the lower coal seam floor rock layer 9 mainly includes: the immediate bottom is composed of sandy mudstone with an average thickness of 2.8 m, and the basic bottom is composed of silty mudstone with an average thickness of 5.6 m; the overlying coal seam roof rock layer group 8 is mainly composed of silty mudstone and fine sandstone, which respectively constitute the key rock layer 7 between coal seams. 15 The direct roof and basic roof of the coal seam.

[0111] In oneself 16-17 During the excavation and mining of the return air tunnel of the 31020 working face, the stability of the tunnel surrounding rock was affected by the support pressure of the coal pillar 4 left between the working faces of the overlying coal seam, the adjacent 16-17 The superposition of the lateral support pressure of the upper section working face of the coal seam and the advanced support pressure of the lower section working face 3 makes the stress environment of the tunnel very complex. 15 Coal seam and 16-17 The interlayer spacing of the coal seams is small, and the key rock layers 7 between the coal seams are silty mudstone and mudstone. 15 Coal mining has 16-17 There is a certain degree of damage and destruction on the coal seam roof. 16-17 During the service period of coal seam mining tunnels, the tunnel floor heave and the inward displacement of the two sides are generally large. Especially under the action of the advanced support pressure of the working face, the tunnel cross-section shrinks sharply, making tunnel maintenance very difficult.

[0112] like Figure 1As shown in the figure, a stable anchoring design method for a roadway along the goaf with a narrow coal pillar in a close-range coal seam includes two parts: determination of the size of the narrow coal pillar in the roadway along the goaf and design method for forming a stable anchoring structure. The determination of the size of the narrow coal pillar in the roadway along the goaf includes: analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters, calculation of the width of the plastic zone in the coal pillar after mining of the adjacent working face, numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working face around the roadway along the goaf, and comprehensive consideration of the anchoring quality of the roadway anchor cable. The design method for forming a stable anchoring structure includes: derivation of the mechanical model of the single end anchor bolt, calculation of the shear expansion pressure of the roadway surrounding rock, calculation of the prestress of the roadway anchor cable, and determination of the timing of anchor net support.

[0113] The analysis of mining geological conditions and the testing of coal and rock physical and mechanical parameters require, on the one hand, the analysis of the surrounding rock environment of the tunnel 1 along the goaf with narrow coal pillars in the lower coal layer based on on-site mining data. It can be seen that the tunnel 1 along the goaf is not only affected by the excavation of the tunnel itself and the mining of the lower section working face 3, but also by the concentrated stress formed on the floor by the coal pillars 4 left between the working faces of the overlying coal seams and the goaf 10 of the upper section working face. The stress environment of the tunnel surrounding rock is complex. Under the influence of mining disturbances of surrounding tunnels and working faces, the stress environment of the surrounding rock of the tunnel 1 along the goaf with narrow coal pillars has undergone many complex evolution processes. Each change in the stress state of the rock mass will cause changes in the structural characteristics of the rock mass, thereby leading to the continuous weakening and fragmentation of the surrounding rock strength of the tunnel 1 along the goaf. On the other hand, it is necessary to test the basic physical and mechanical parameters of the surrounding rock of the goaf-side excavation tunnel 1, carry out laboratory uniaxial compression tests, variable-angle shear tests, and Brazilian splitting tests on standard specimens, and obtain the physical and mechanical parameters of the tunnel roof and floor and coal seams (including uniaxial compression, tensile strength, elastic modulus, cohesion, internal friction angle, Poisson's ratio) and deformation and failure laws, etc., to provide parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0114] The width of the plastic zone in the narrow coal pillar 2 after the adjacent working face is mined. The reasonable width of the coal pillar is generally calculated according to the formula B = X0 + X1 + X2. The latter two in the formula generally have limited values, that is, X2 is the effective length of the anchor, which is 1.2m; X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2); therefore, the reasonable width of the coal pillar is mainly determined by X0. According to the limit equilibrium theory, the width X0 of the plastic zone in the coal pillar after the adjacent working face is mined is calculated as follows:

[0115]

[0116] Where: m is the coal seam mining thickness, m; λ is the lateral pressure coefficient, λ = μ / (1-μ), μ is the Poisson's ratio; is the internal friction angle of the coal body, °; C0 is the cohesion of the coal body, MPa; K is the stress concentration factor; γ is the average bulk density of the overlying rock layer, MN / m 3; H is the tunnel depth, m; P z It is the support resistance of the support body to the coal seam, MPa.

[0117] The numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining around the working face of the goaf-side tunneling tunnel 1 requires the establishment of a FLAC3D large-scale three-dimensional numerical calculation model based on the geological conditions of the goaf-side tunneling tunnel 1. According to the mining sequence of the upper and lower coal seam working faces, the established numerical model is excavated and simulated to obtain the cloud diagram of the vertical stress distribution of the surrounding rock of the goaf-side tunneling tunnel 1 at different mining stages, as shown in Figure 2. Figure 2 As shown in the figure, the stress level of the tunnel surrounding rock and the difficulty of tunnel maintenance under different coal pillar sizes (i.e., different tunnel layout positions) can be analyzed. At the same time, the value of the stress concentration factor K can be obtained based on the calculation results of the vertical stress distribution.

[0118] Comprehensive consideration of the anchoring quality of the anchor cable in the goaf-driven tunnel 1: On the one hand, from the perspective of tunnel stress distribution, when the goaf-driven tunnel 1 with a narrow coal pillar in the lower layer is completely below the goaf, the vertical stress of the tunnel surrounding rock is the lowest, and the stress environment of the tunnel is relatively favorable; on the other hand, the roof rock layer of the goaf-driven tunnel 1 (the key rock layer 7 between coal seams) has suffered mining damage, the rock mass of the tunnel roof is relatively broken, and the anchoring quality of the anchor cable is difficult to guarantee. Therefore, from the perspective of ensuring the safety of the tunnel, this position is not suitable.

[0119] Furthermore, the Poisson's ratio of the coal body is 0.26, the internal friction angle is 32.5°, the cohesion is 1.19MPa, the stress concentration factor is 1.89, and the average bulk density of the overlying rock is 0.025MN / m 3 , the tunnel depth is 952m, the coal support resistance is negligible, and the above parameters are substituted into the calculation formula of X0 to obtain 16-17 -23160 After mining at the working face, the width of the plastic zone X0 in the narrow coal pillar 2 is about 2.936m. Therefore, it can be theoretically calculated that 16-17 -31020 The value range of the narrow coal pillar width B of the return air lane along the goaf is 5.377~6.204m. Combined with the reasonable coal pillar size calculation result B and the degree of coal pillar surrounding rock fracture, the coal pillar size of the goaf-driven roadway should be ≥ B. However, when the coal pillar size is larger, the loss of coal resources will increase further, and the stress level of the roadway will gradually increase. Therefore, the size selection of the reasonable narrow coal pillar 2 in the goaf-driven roadway 1 should be based on the perspective of ensuring the anchoring quality of the roadway anchor (cable), and combined with the anchor cable pull-out test results and the theoretical calculation results of the coal pillar width, it is selected as 6m.

[0120] Derivation of the mechanical model of the action of a single end anchor bolt. First, according to the different stress states of the bolt body, the end anchor bolt in the coal mine tunnel can be divided into an ineffective anchoring section (L1) and an effective anchoring section (L2). In theory, the end anchor bolt can be simplified to the mechanical model shown in the figure below for analysis. Then, according to the St. Venant principle, the solution of the boussinnesq problem is used to approximate the stress distribution caused by the concentrated force of a single anchor bolt. That is, within the range of 0≤z≤0.5L2, the compressive stress σ along the z direction at any point M is z Calculate as follows:

[0121]

[0122] Where: z —compressive stress provided by the anchor, MPa;

[0123] P—preload force applied during anchor installation, MN;

[0124] r—anchor spacing, m.

[0125] The anchor support mainly bears the shear expansion deformation pressure p of the rock mass within the anchoring range of the anchor s and the deadweight of a small amount of delaminated rock mass. Since the amount of rock mass delaminated is negligible, and the cohesion C of the anchored rock mass is ignored, the compressive stress σ provided by the rod according to the Moore-Coulomb law is z The following formula should be satisfied to keep the anchor structure stable:

[0126] Right now

[0127] Where: zmin —Minimum compressive stress formed by the anchor rod on the center line of the anchoring structure, MPa;

[0128] —internal friction angle of rock mass, °;

[0129] p s —Shear deformation pressure of rock mass within the anchoring range of anchor bolt, MPa.

[0130] Calculation of shear dilatancy pressure of tunnel surrounding rock. sIt changes continuously with the deformation of the tunnel surrounding rock and is often difficult to measure accurately. It requires the help of a numerical calculation model to more accurately obtain the shear dilatancy pressure of the tunnel surrounding rock at different calculation steps. Therefore, it is necessary to establish a numerical analysis model based on the geological conditions of the tunnel 1 along the air, and simulate and calculate the vertical stress distribution diagram of the surrounding rock during tunnel excavation. After the tunnel is excavated, with the increase of the number of calculation steps (the number of calculation steps for a single cycle is 100), the range of surrounding rock in the shear dilatancy state around the tunnel gradually expands, and the corresponding tensile stress value is also gradually increasing. When the number of calculation steps reaches 500 steps, the tensile stress reaches the extreme value (that is, p s =0.0988MPa), after which the tensile stress value continued to decrease. When the calculation time step increased to 1000 time steps, the tensile stress value of the rock mass around the tunnel approached 0, indicating that the shallow rock mass continued to delaminate, break and expand, and finally completely lost its bearing capacity. In this process, p s The extreme value of is the value of the tunnel confining pressure and shear pressure.

[0131] The anchor cable prestress calculation is based on the test results of the surrounding rock mechanical parameters of the tunnel 1 along the gob and the initial anchor mesh support design technical plan. The anchor spacing of 0.8m, the anchor anchoring section length of 0.9m, the internal friction angle of the tunnel surrounding rock of 32.5° and the shear pressure of 0.0988MPa are substituted into the following formula:

[0132]

[0133] It can be calculated that the prestress values ​​of the anchor cables required to form a stable anchoring structure on the top of the tunnel are 78.2kN and 101.1kN respectively.

[0134] The timing of anchor net support, according to the development law of shear dilatation pressure of tunnel surrounding rock under different calculation time steps, analysis shows that in order to maintain the integrity and self-bearing capacity of tunnel surrounding rock and avoid continuous delamination, crushing and expansion of shallow rock mass, and even bearing capacity, the initial support resistance provided by anchor net support should be greater than the maximum shear dilatation pressure caused by deformation of shallow surrounding rock of tunnel, and the support timing should also be before the extreme point of shear dilatation stress of tunnel surrounding rock appears.

[0135] Furthermore, the technical scheme for the initial anchor net support design of the tunnel should adopt a dynamic information design method including test point investigation and geomechanical evaluation, initial design, underground monitoring and information feedback, and revised design. The test point investigation includes surrounding rock strength, surrounding rock structure, ground stress and anchoring performance testing, and on this basis, a geomechanical evaluation is carried out to provide reliable parameters for the initial design. The initial design is carried out by combining numerical calculation and empirical methods, and a more reasonable anchor net support technical scheme is determined based on the surrounding rock parameters and existing measured data. Finally, the anchor net support technical scheme needs to be implemented underground, and detailed surrounding rock deformation and anchor cable force monitoring is carried out, and the support design is verified or revised based on the monitoring results.

[0136] Finally, based on the initial anchor mesh support design technical scheme for the tunnel, combined with the tunnel layout method and stable anchoring design method provided by the present invention, a layout scheme for the tunnel along the air and a new anchor mesh cable support technical scheme were proposed. The on-site application results showed that the tunnel was basically stable until it had undergone mining at this working face, with the deformation of the two sides not exceeding 500mm and the roof subsidence not exceeding 200mm, achieving better surrounding rock control effect.

[0137] The above inventions are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A stable anchoring design method for tunneling along the empty space with narrow coal pillars in close-range coal seams, characterized in that: include: Determination of the size of the narrow coal pillar in the gob-side tunnel and the design method for forming a stable anchoring structure; The determination of the size of the narrow coal pillar in the gob-side tunneling roadway includes: S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters; S11. Calculate the width of the plastic zone in the coal pillar after mining of adjacent working faces based on the test results of coal and rock physical and mechanical parameters, and carry out numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working face around the gob-side tunneling tunnel; S12. Determine the size of the narrow coal pillar based on the analysis of mining geological conditions, the test of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the value of the vertical stress distribution of the tunnel surrounding rock, and the anchoring quality of the tunnel bolt cable; The design method for forming the stable anchoring structure comprises: S20, calculating the shear dilatancy pressure of the tunnel surrounding rock; S21, taking into account the shear expansion pressure of the surrounding rock of the tunnel to derive the mechanical model of the single end anchor bolt; S22, calculating the prestress of the anchor cable in the tunnel according to the derivation of the mechanical model of the single end anchor and the calculation result of the shear expansion pressure of the tunnel surrounding rock; S23. Determine the timing of anchor net support.

2. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 1 is characterized in that: The mining geological conditions analysis specifically includes analyzing the surrounding rock environment of the tunnel excavated along the airspace with a narrow coal pillar left in the lower coal layer based on on-site mining data; the coal and rock physical and mechanical parameter testing specifically includes: testing the basic physical and mechanical parameters of the target tunnel surrounding rock, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard specimens, and obtaining the physical and mechanical parameters and deformation and failure laws of the tunnel roof and floor and coal seams, providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

3. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 2 is characterized in that: The physical and mechanical parameters of coal rock include uniaxial compression, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

4. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 1 is characterized in that: The numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining around the working face of the goaf-side tunneling roadway includes: establishing a FLAC3D three-dimensional numerical calculation model according to the geological conditions of the goaf-side tunneling roadway, and performing excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seam working faces to obtain a cloud map of the vertical stress distribution of the surrounding rock of the goaf-side tunneling roadway at different mining stages, comparing the stress levels of the surrounding rock of the roadway under different coal pillar sizes or roadway positions, analyzing the difficulty of roadway maintenance, and obtaining the value of the stress concentration factor K according to the cloud map of the vertical stress distribution of the surrounding rock.

5. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 4 is characterized in that: The calculation of the width of the plastic zone in the coal pillar after mining of adjacent working faces includes: According to the limit equilibrium theory, the width X0 of the plastic zone in the coal pillar after adjacent working faces are mined is calculated as follows: Where: m is the coal seam thickness, unit is m, λ is the lateral pressure coefficient, λ=μ / (1-μ), μ is the Poisson's ratio, is the internal friction angle of the coal body, C0 is the cohesion of the coal body, the unit is MPa, K is the stress concentration factor, γ is the average bulk density of the overlying rock, the unit is MN / m 3 , H is the tunnel depth, in m, P z is the support resistance of the support body to the coal seam, in MPa; The reasonable coal pillar width is calculated according to the formula B = X0 + X1 + X2, where the latter two have limited values, namely, X2 is the effective length of the anchor rod, which is 1.2m; X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2).

6. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 5 is characterized in that: The comprehensive considerations include: From the perspective of the vertical stress distribution of the surrounding rock, when the tunnel along the goaf with the narrow coal pillar left in the lower layer is completely below the goaf, the vertical stress of the surrounding rock is the lowest, and the stress environment of the tunnel is relatively favorable; The tunnel roof rock layer has been damaged by mining, and the tunnel roof rock mass is relatively broken, so the anchoring quality of the anchor cable is difficult to ensure. Therefore, from the perspective of ensuring tunnel safety, this location is not suitable; Combined with the calculation result B of reasonable coal pillar size and the degree of fracture of the surrounding rock of the coal pillar, the size of the coal pillar in the tunnel along the gob should be ≥B.

7. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 1 is characterized in that: The derivation of the mechanical model of the single end anchor bolt includes: Firstly, according to the different stress states of the bolt body, the end anchor bolt in the coal mine tunnel is divided into the anchoring section L1, the free section L2 and the threaded section L3. In theory, the stress state of the end anchor bolt is simplified to the mechanical model of the end anchor bolt for analysis. Then, according to the St.Venant principle, the solution of the boussinnesq problem is used to approximate the stress distribution caused by the concentrated force of a single anchor rod. That is, when the length z of the free section L2 is 0≤z≤0.5L2, the compressive stress σ along the rod body direction at any point in the upper and lower rectangular planes composed of the anchor rod spacing r and the length z of the free section L2 is z Calculate as follows: Where: z —compressive stress provided by the anchor, MPa; P—preload force applied during anchor installation, MN; r—anchor spacing, m; The anchor support mainly bears the shear expansion deformation pressure p of the rock mass within the anchoring range of the anchor s and the deadweight of a small amount of delaminated rock mass. Since the amount of rock delaminated is negligible, and the cohesion C of the anchored rock mass is ignored, according to the Moore-Coulomb law, the compressive stress σ provided by the anchor is z The following formula should be satisfied to keep the anchor structure stable: Right now Where: zmin —Minimum compressive stress formed by the anchor rod on the center line of the anchoring structure, MPa; —internal friction angle of rock mass, °; p s —Shear deformation pressure of rock mass within the anchoring range of anchor bolt, MPa.

8. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 7 is characterized in that: The calculation of the dilatancy pressure of the tunnel surrounding rock needs to establish a numerical analysis model according to the geological conditions of the tunnel along the goaf, and simulate and calculate the vertical stress distribution diagram of the surrounding rock during the tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the range of the surrounding rock in the dilatancy state around the tunnel gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain time step, the tensile stress reaches an extreme value, that is, p s After that, the tensile stress value keeps decreasing. When the calculation time step increases to a certain value, the tensile stress value of the rock mass around the roadway approaches 0, which means that the shallow rock mass keeps delaminating, breaking and expanding, and finally completely loses its bearing capacity. In this process, p s The extreme value of is the value of the tunnel confining pressure and shear pressure.

9. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 8 is characterized in that: The calculation of the prestress of the tunnel anchor cable needs to be based on the test results of the physical and mechanical parameters of the coal rock and the initial anchor mesh support design plan, and the anchor spacing r, the length z of the anchor free section L2, the internal friction angle of the rock mass, and the and the shear expansion deformation pressure p of the rock mass within the anchoring range s Substitute the values ​​into the following formula: In this way, the preload force P applied during the installation of the anchor rods required to form a stable anchoring structure on the top of the tunnel can be calculated.

10. The stable anchoring design method for tunneling along the goaf with narrow coal pillars in close-range coal seams as claimed in claim 9, characterized in that: The anchor net support opportunities include: According to the development law of shear dilatancy pressure of tunnel surrounding rock under different calculation time steps obtained by simulation calculation of the numerical analysis model, in order to maintain the integrity and self-bearing capacity of tunnel surrounding rock and avoid continuous delamination, crushing and expansion of shallow rock mass, and even loss of bearing capacity, the initial support resistance provided by anchor net support should be greater than the maximum shear dilatancy pressure caused by deformation of shallow tunnel surrounding rock, and the support timing should also be before the extreme point of shear dilatancy stress of tunnel surrounding rock appears.

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