Stable anchoring design method for narrow coal pillar tunnels with close proximity to coal seams

Abstract

This invention discloses a stable anchoring design method for narrow coal pillars in gob-side excavation roadways with close proximity to coal seams. The determination of the narrow coal pillar size in the gob-side excavation roadway includes: S10, analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters; S11, calculation of the width of the plastic zone within the coal pillar after mining of adjacent working faces based on the coal and rock physical and mechanical parameter test results, and numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working faces around the gob-side excavation roadway; S12, determination of the narrow coal pillar size based on the above content and a comprehensive consideration of the roadway anchor cable anchoring quality. The design method for forming the stable anchoring structure includes: S20, calculation of the shear dilatation pressure of the roadway surrounding rock; S21, derivation of the mechanical model of the single-end anchor bolt action by incorporating the shear dilatation pressure of the roadway surrounding rock; S22, calculation of the prestress of the roadway anchor cable based on the above results; and S23, determination of the timing of anchor mesh support.

Description

Technical Field

[0001] This invention relates to the field of coal mine roadway support technology, and in particular to a stable anchoring design method for roadways with narrow coal pillars left in close proximity to coal seams during goaf excavation. Background Technology

[0002] Narrow coal pillar roadways, utilizing the goaf topography and stress transfer patterns, allow the roadway to be located in a stress-reducing zone. This avoids the impact of intense overlying strata activity after the adjacent working face is mined, reducing roadway maintenance costs. Furthermore, maintaining a certain width of coal pillar between the roadway and the upper goaf prevents water accumulation, harmful gases, and large rocks from entering the roadway. Currently, with the continuous advancement of underground roadway support technology, the application of narrow coal pillar roadway technology is gradually increasing.

[0003] Determining the size of narrow coal pillars in gob-side excavation roadways under single coal seam conditions is relatively simple. It only requires considering the mining conditions of the coal seam and the influence of the coal pillar size on the stability of the gob-side excavation roadway. The range of values ​​can be determined based on limit equilibrium theory. Compared with single coal seam mining, the overlying strata movement and mine pressure manifestation characteristics of closely spaced coal seam group mining are significantly different: On the one hand, the roof surrounding rock of gob-side excavation roadways in closely spaced coal seams is significantly damaged by the mining of the overlying coal seam. Furthermore, the concentrated stress formed on the floor by the residual coal pillars after the mining of the upper coal seam and the coal body mined on one side leads to significant changes in the roof structure and stress environment of the lower coal seam mining area, thus triggering a strong new phenomenon of mine pressure. On the other hand, the stress level is further increased due to the mining of the working face of the coal seam. Because of the complex stress transmission law and the spatiotemporal relationship of mine pressure manifestation, when the size of the coal pillars in gob-side excavation roadways in the nearby lower coal seam is not properly determined, the mine pressure manifestation is severe, and the roadway surrounding rock support is extremely difficult. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a stable anchoring design method for roadways with narrow coal pillars in close-range coal seams, achieving a reasonable layout of roadways in the dynamic pressure zone of close-range coal seams and stable control of the surrounding rock.

[0005] This invention provides a stable anchoring design method for gob-side excavation roadways with narrow coal pillars in close proximity to the coal seam, comprising: determining the dimensions of the narrow coal pillar in the gob-side excavation roadway and designing a stable anchoring structure; wherein...

[0006] The determination of the dimensions for narrow coal pillars in roadways excavated along the goaf includes:

[0007] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0008] S11. Calculate the width of the plastic zone in the coal pillar after mining 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 goaf-running roadway.

[0009] S12. Based on the analysis of mining geological conditions, the testing of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the numerical value of the vertical stress distribution of the surrounding rock in the roadway, and the comprehensive consideration of the anchoring quality of the roadway anchor cables, the dimensions of the narrow coal pillar are determined.

[0010] Design methods for forming stable anchoring structures include:

[0011] S20. Calculate the shear dilatation pressure of the surrounding rock in the tunnel;

[0012] S21. Derivation of the mechanical model of single-end anchor bolt action by incorporating the shear dilatation pressure of the surrounding rock in the roadway.

[0013] S22. Based on the derivation of the mechanical model of single-end anchor bolt action and the calculation results of shear dilatation pressure of the surrounding rock in the roadway, calculate the prestress of the roadway anchor bolt cable.

[0014] S23. Determine the timing of anchor mesh support.

[0015] Optionally, the analysis of mining geological conditions specifically includes, based on on-site mining data, analyzing the surrounding rock environment of the roadway with narrow coal pillars in the lower coal seam, and the testing of coal and rock physical and mechanical parameters specifically includes: testing the basic physical and mechanical parameters of the surrounding rock of the target roadway, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard samples, obtaining the physical and mechanical parameters and deformation and failure laws of the roadway roof and floor and coal seam, and providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0016] Optional physical and mechanical parameters of coal and rock include uniaxial compressive strength, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

[0017] Optionally, the numerical simulation calculation of the vertical stress distribution of the surrounding rock after the mining of the working face around the goaf-running roadway includes: establishing a FLAC3D three-dimensional numerical calculation model based on the geological conditions of the goaf-running roadway; performing excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seam working faces; obtaining cloud maps of the vertical stress distribution of the surrounding rock of the goaf-running roadway at different mining stages; comparing the stress level of the surrounding rock under different coal pillar sizes or roadway locations; analyzing the difficulty of roadway maintenance; and obtaining the value of the stress concentration factor K based on the cloud map of the vertical stress distribution of the surrounding rock.

[0018] Optionally, calculating the width of the plastic zone within the coal pillar after mining adjacent working faces includes:

[0019] According to the limit equilibrium theory, the width X0 of the plastic zone within the coal pillar after mining adjacent working faces is calculated using the following formula:

[0020]

[0021] In the formula: m is the coal seam thickness in meters, λ is the lateral pressure coefficient, λ = μ / (1-μ), and μ is Poisson's ratio. θ is the internal friction angle of the coal body, C0 is the cohesion of the coal body (in MPa), K is the stress concentration factor, and γ is the average unit weight of the overlying strata (in MN / m³). 3 H represents the tunnel depth in meters (m), and P represents the tunnel depth. z The resistance of the support structure to the coal face is expressed in MPa.

[0022] The reasonable width of the coal pillar is calculated according to the formula B = X0 + X1 + X2, where the latter two have limited values. Specifically, X2 is the effective length of the anchor bolt, which is taken as 1.2m; and X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2).

[0023] Optional, comprehensive considerations include:

[0024] From the perspective of the vertical stress distribution of the surrounding rock, when the roadway with a narrow coal pillar 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 roadway is relatively favorable.

[0025] The roof strata of the roadway have been damaged by mining, and the roof rock mass is relatively broken, making it difficult to guarantee the anchoring quality of the anchor cables. Therefore, from the perspective of ensuring the safety of the roadway, this location is not suitable.

[0026] Based on the calculated result B of the reasonable coal pillar size and the degree of fracture of the surrounding rock of the coal pillar, the coal pillar size of the roadway excavated along the goaf should be ≥ B.

[0027] Optional, the derivation of the mechanical model for a single-end anchor bolt includes:

[0028] First, based on the different stress states of the anchor rod body, the end anchor rods in coal mine roadways are divided into the anchoring section L1, the free section L2, and the threaded section L3. Theoretically, the stress state of the end anchor rod is simplified to an end anchor rod mechanical model for analysis.

[0029] Then, according to St. Venant's principle, the stress distribution generated by the concentrated force of a single anchor rod is approximated by the solution of the Boussinnesq problem. That is, when the length z of the free segment L2 is 0 ≤ z ≤ 0.5L2, the compressive stress σ along the rod direction at any point in the upper and lower rectangular planes formed by the anchor rod spacing r and the length z of the free segment L2 are taken as the side lengths. z Calculate using the following formula:

[0030]

[0031] Where: σz —Compressive stress provided by the anchor bolt, MPa;

[0032] P—Preload applied during anchor bolt installation, MN;

[0033] r—anchor bolt spacing, m;

[0034] Anchor bolt support mainly bears the shear dilatation deformation pressure p of the rock mass within the anchor bolt anchorage range. s The self-weight of a small amount of delaminated rock mass is negligible, and the cohesion C within the anchored rock mass is ignored. According to the Mohr-Coulomb law, the compressive stress σ provided by the anchor bolt is... z The following equation must be satisfied for the anchorage structure to remain stable:

[0035] Right now

[0036] Where: σ zmin —Minimum compressive stress formed by the anchor bolt on the centerline of the anchoring structure, MPa;

[0037] —Internal friction angle of the rock mass, °;

[0038] p s —Shear dilatation pressure of the rock mass within the anchorage range, MPa.

[0039] Optionally, the calculation of shear dilatation pressure in the surrounding rock of the tunnel requires establishing a numerical analysis model based on the geological conditions of the tunnel being excavated along the goaf. This model simulates the vertical stress distribution of the surrounding rock during tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the area of ​​the surrounding rock in a state of shear dilatation gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain point, the tensile stress reaches its extreme value, i.e., p. s The extreme value of p is reached, after which the tensile stress value continuously decreases. When the calculation step increases to a certain value, the tensile stress value of the rock mass around the tunnel approaches 0, indicating that the shallow rock mass is continuously delaminating, fragmenting, and eventually completely losing its bearing capacity. During this process, p s The extreme value is the value of the roadway confining pressure shear expansion pressure.

[0040] Optionally, the prestress calculation of the roadway anchor cables needs to be based on the test results of the physical and mechanical parameters of coal and rock and the initial anchor mesh support design scheme, taking into account the anchor spacing r, the length z of the free section L2 of the anchor, and the internal friction angle of the rock mass. and the shear dilatation deformation pressure p of the rock mass within the anchorage range s Substitute the values ​​into the following formula:

[0041]

[0042] This allows us to calculate the preload P required during anchor bolt installation to form a stable anchoring structure for the tunnel roof and sidewalls.

[0043] Optional timing for anchor mesh support includes:

[0044] Based on the analysis of the shear dilatation pressure development law of the surrounding rock of the roadway at different calculation steps obtained from the numerical analysis model simulation, in order to maintain the integrity and self-bearing capacity of the surrounding rock of the roadway and avoid the continuous delamination, fragmentation, and even loss of bearing capacity of the shallow rock mass, the initial support resistance provided by the anchor mesh support should be greater than the maximum shear dilatation pressure generated by the deformation of the shallow surrounding rock of the roadway, and the timing of the support should also be before the extreme point of shear dilatation stress of the surrounding rock of the roadway appears.

[0045] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art:

[0046] This invention provides a stable anchoring design method for gob-side excavation roadways with narrow coal pillars in close-proximity coal seams. This method comprehensively considers the stress level, rock fragmentation degree, and stable anchoring structure formation mechanism of the surrounding rock under multi-coal seam mining conditions. It offers a stable anchoring design method for gob-side excavation roadways with narrow coal pillars in close-proximity coal seams, achieved through mining geological condition analysis and coal and rock physical and mechanical parameter testing, calculation of the width of the plastic zone within the coal pillar after adjacent working faces are mined, and numerical simulation calculation of the vertical stress distribution of the surrounding rock after the working faces around the gob-side excavation roadway are mined. The anchoring quality of roadway anchor cables is comprehensively considered to determine the size of narrow coal pillars in roadways excavated along the goaf. Through the derivation of the mechanical model of single-end anchor bolt action, the calculation of shear dilatation pressure of the roadway surrounding rock, the calculation of prestress of roadway anchor cables, and the timing of anchor mesh support, a design method for the formation of a stable anchoring structure is determined. This method can not only reasonably leave narrow coal pillars so that roadways excavated along the goaf are located in stress reduction zones, but also ensure the anchoring performance of roadway anchor cables and provide a calculation method for the formation of a stable anchoring structure in the roadway surrounding rock. This achieves the reasonable layout of roadways excavated along the goaf in the dynamic pressure zone of nearby coal seams and the stability control of the surrounding rock. Attached Figure Description

[0047] Figure 1 A schematic diagram of geological mining conditions and layout of tunnels along the goaf provided for embodiments of the present invention;

[0048] Figure 2 This is a cloud map showing the vertical stress distribution around the working face after mining in a goaf-running roadway during numerical simulation.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1. Roadway excavated along the goaf; 2. Narrow coal pillar; 3. Lower section working face; 4. Coal pillar left between working faces of the overlying coal seam; 5. Goaf of the working face on the left side of the overlying coal seam; 6. Goaf of the working face on the right side of the overlying coal seam; 7. Key strata between coal seams; 8. Roof strata of the overlying coal seam; 9. Floor strata of the lower coal seam; 10. Goaf of the upper section working face. Detailed Implementation

[0051] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0052] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0053] The determination of the narrow coal pillar size in gob-running roadways under single coal seam conditions is relatively simple and the method is basically mature. First, the range of values ​​is determined by calculation based on the limit equilibrium theory. Then, the stability characteristics of the surrounding rock under different coal pillar sizes are analyzed and a reasonable coal pillar size is selected. At present, there are many studies on the narrow coal pillar size in gob-running roadways under single coal seam conditions, but there are few studies on the narrow coal pillar size in gob-running roadways with close proximity to coal seams. In my country, the occurrence and mining of close proximity to coal seams is relatively large. Many mining areas have problems such as unreasonable narrow coal pillar size in gob-running roadways with close proximity to coal seams and difficulties in roadway maintenance. This is mainly because: (1) The factors that need to be considered in determining the narrow coal pillar size in gob-running roadways are more complex and diverse. Under the condition of close proximity mining of multiple coal seams, the mine pressure in gob-running roadways is more intense. The time and space relationship between mining between upper and lower coal seams is complex. If the coal pillar size is unreasonable, it will lead to high stress concentration in the surrounding rock of the roadway and severe rock fragmentation, which in turn leads to reduced reliability of anchor mesh support and difficulty in applying anchor bolts and cables, and other technical problems in roadway maintenance. (2) There is no theoretical basis for accurate quantitative design of key parameters of anchor mesh support such as anchor bolt preload and support timing. There is a lack of design methods for the formation of a stable anchoring structure between the surrounding rock of the roadway and the anchor mesh support system, which leads to frequent problems of roadway support instability.

[0054] Under the conditions of close-range coal seam mining, roadways driven along the goaf are subject to multiple superimposed effects from the mining of the overlying coal seam, the remaining coal pillars, the mining of the working face of the coal seam, and the disturbance caused by tunneling. It is necessary to comprehensively consider various factors such as the stress environment of the surrounding rock of the roadway under different coal pillar sizes and the design of stable anchorage. Therefore, it is urgent to study and develop a set of stable anchorage design methods for roadways driven along the goaf with narrow coal pillars under the conditions of close-range coal seam mining.

[0055] Therefore, embodiments of the present invention provide a stable anchoring design method for roadways with narrow coal pillars in close-range coal seams, realizing the rational layout of roadways in the dynamic pressure zone of close-range coal seams and the stability control of the surrounding rock.

[0056] At least one embodiment of the present invention provides a stable anchoring design method for a gob-side excavation roadway with a narrow coal pillar in close proximity to the coal seam, comprising: determining the size of the narrow coal pillar in the gob-side excavation roadway and a design method for forming a stable anchoring structure, wherein determining the size of the narrow coal pillar in the gob-side excavation roadway includes:

[0057] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0058] S11. Calculate the width of the plastic zone in the coal pillar after mining 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 goaf-running roadway.

[0059] S12. Based on the analysis of mining geological conditions, the testing of physical and mechanical parameters of coal and rock, the width of the plastic zone in the coal pillar, the numerical value of the vertical stress distribution of the surrounding rock in the roadway, and the comprehensive consideration of the anchoring quality of the roadway anchor cables, the dimensions of the narrow coal pillar are determined.

[0060] Design methods for forming stable anchoring structures include:

[0061] S20. Calculate the shear dilatation pressure of the surrounding rock in the tunnel;

[0062] S21. Derivation of the mechanical model of single-end anchor bolt action by incorporating the shear dilatation pressure of the surrounding rock in the roadway.

[0063] S22. Based on the derivation of the mechanical model of single-end anchor bolt action and the calculation results of shear dilatation pressure of the surrounding rock in the roadway, calculate the prestress of the roadway anchor bolt cable.

[0064] S23. Determine the timing of anchor mesh support.

[0065] The stable anchoring design method for roadways with narrow coal pillars in close-range coal seams provided in the above embodiments of the present invention comprehensively considers various aspects such as the size of the narrow coal pillar, the stress level of the surrounding rock in the roadway, the degree of rock fragmentation, and the formation mechanism and design of the stable and reliable anchoring bearing structure, thereby realizing the reasonable layout of roadways in close-range coal seam dynamic pressure zones and the stable control of the surrounding rock.

[0066] The present invention will be described below through several specific embodiments. To keep the following description of the embodiments clear and concise, detailed descriptions of known functions and components may be omitted. When any component of an embodiment of the present invention appears in more than one drawing, the component may be represented by the same reference numerals in each drawing.

[0067] This invention provides a stable anchoring design method for a gob-side excavation roadway with a narrow coal pillar in a close-range coal seam, comprising: determining the dimensions of the narrow coal pillar in the gob-side excavation roadway and a design method for forming a stable anchoring structure, wherein determining the dimensions of the narrow coal pillar in the gob-side excavation roadway includes:

[0068] S10. Analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters;

[0069] S11. Calculate the width of the plastic zone in the coal pillar after mining 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 goaf-running roadway.

[0070] S12. Based on the analysis of mining geological conditions, the testing of physical and mechanical parameters of coal and rock, the width of the plastic zone in the coal pillar, the numerical value of the vertical stress distribution of the surrounding rock in the roadway, and the comprehensive consideration of the anchoring quality of the roadway anchor cables, the dimensions of the narrow coal pillar are determined.

[0071] Design methods for forming stable anchoring structures include:

[0072] S20. Calculate the shear dilatation pressure of the surrounding rock in the tunnel;

[0073] S21. Derivation of the mechanical model of single-end anchor bolt action by incorporating the shear dilatation pressure of the surrounding rock in the roadway.

[0074] S22. Based on the derivation of the mechanical model of single-end anchor bolt action and the calculation results of shear dilatation pressure of the surrounding rock in the roadway, calculate the prestress of the roadway anchor bolt cable.

[0075] S23. Determine the timing of anchor mesh support.

[0076] First, it's important to clarify that the narrow coal pillar and the stable anchoring of the goaf-side tunnel are related, and the logical relationship is progressive: coal pillar first, then stable anchoring. The first step is to leave a narrow coal pillar. Furthermore, the size of the narrow coal pillar is crucial for tunnel stability control. Too narrow a pillar results in lower surrounding rock stress levels, which is beneficial for maintenance, but it can lead to the fractured zone on the coal pillar side exceeding the anchor cable length, causing frequent anchoring failures and making the surrounding rock unstable. Conversely, an excessively large coal pillar leaves too much coal, resulting in less coal extraction and wasted resources. Moreover, the stress level under a large coal pillar will increase. Therefore, a reasonable coal pillar size is a prerequisite for ensuring a reasonable surrounding rock stress level and the quality of anchor cable anchoring. The coal pillar size obtained solely from traditional theoretical calculations is only a range; it needs to be determined by comprehensively considering the surrounding rock stress level, anchor cable length, and anchoring quality (using anchor cable pull-out test results for feedback and evaluation). Then, our theoretical derivation and calculations are used to design the tunnel anchor mesh support, with some parameters requiring numerical simulation calculations. Two design principles are proposed regarding the design method for stable anchoring: one is to calculate the prestress value of the anchor cable required to form a stable anchoring structure for the roadway roof and sidewalls, ensuring that the initial support resistance provided by the anchor mesh support is greater than the maximum shear dilatation pressure generated by the deformation of the shallow surrounding rock in the roadway; the other is that the support should be provided before the extreme point of shear dilatation stress in the surrounding rock of the roadway occurs.

[0077] This invention provides a stable anchoring design method for gob-side excavation roadways with narrow coal pillars in close-proximity coal seams. This method comprehensively considers the stress level, rock fragmentation degree, and stable anchoring structure formation mechanism of the surrounding rock under multi-coal seam mining conditions. It offers a stable anchoring design method for gob-side excavation roadways with narrow coal pillars in close-proximity coal seams, achieved through mining geological condition analysis and coal and rock physical and mechanical parameter testing, calculation of the width of the plastic zone within the coal pillar after adjacent working faces are mined, and numerical simulation calculation of the vertical stress distribution of the surrounding rock after the working faces around the gob-side excavation roadway are mined. The anchoring quality of roadway anchor cables is comprehensively considered to determine the size of narrow coal pillars in roadways excavated along the goaf. Through the derivation of the mechanical model of single-end anchor bolt action, the calculation of shear dilatation pressure of the roadway surrounding rock, the calculation of prestress of roadway anchor cables, and the timing of anchor mesh support, a design method for the formation of a stable anchoring structure is determined. This method can not only reasonably leave narrow coal pillars so that roadways excavated along the goaf are located in stress reduction zones, but also ensure the anchoring performance of roadway anchor cables and provide a calculation method for the formation of a stable anchoring structure in the roadway surrounding rock. This achieves the reasonable layout of roadways excavated along the goaf in the dynamic pressure zone of nearby coal seams and the stability control of the surrounding rock.

[0078] Optionally, the analysis of mining geological conditions specifically includes, based on on-site mining data, analyzing the surrounding rock environment of the roadway with narrow coal pillars in the lower coal seam, and the testing of coal and rock physical and mechanical parameters specifically includes: testing the basic physical and mechanical parameters of the surrounding rock of the target roadway, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard samples, obtaining the physical and mechanical parameters and deformation and failure laws of the roadway roof and floor and coal seam, and providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0079] Optional physical and mechanical parameters of coal and rock include uniaxial compressive strength, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

[0080] Optionally, the numerical simulation calculation of the vertical stress distribution of the surrounding rock after the mining of the working face around the goaf-running roadway includes: establishing a FLAC3D three-dimensional numerical calculation model based on the geological conditions of the goaf-running roadway; performing excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seam working faces; obtaining cloud maps of the vertical stress distribution of the surrounding rock of the goaf-running roadway at different mining stages; comparing the stress level of the surrounding rock under different coal pillar sizes or roadway locations; analyzing the difficulty of roadway maintenance; and obtaining the value of the stress concentration factor K based on the cloud map of the vertical stress distribution of the surrounding rock.

[0081] The vertical stress concentration factor of the surrounding rock in the roadway is a key parameter in the calculation of the plastic zone of the coal pillar and the evaluation of the roadway anchorage design. Obtaining it by field measurement is a complex and time-consuming process. In this embodiment of the invention, numerical simulation is used to calculate it accurately and efficiently.

[0082] Optionally, calculating the width of the plastic zone within the coal pillar after mining adjacent working faces includes:

[0083] According to the limit equilibrium theory, the width X0 of the plastic zone within the coal pillar after mining adjacent working faces is calculated using the following formula:

[0084]

[0085] In the formula: m is the coal seam thickness in meters, λ is the lateral pressure coefficient, λ = μ / (1-μ), and μ is Poisson's ratio. θ is the internal friction angle of the coal body, C0 is the cohesion of the coal body (in MPa), K is the stress concentration factor, and γ is the average unit weight of the overlying strata (in MN / m³). 3 H represents the tunnel depth in meters (m), and P represents the tunnel depth. z The resistance of the support structure to the coal face is expressed in MPa.

[0086] The reasonable width of the coal pillar is calculated according to the formula B = X0 + X1 + X2, where the latter two have limited values. Specifically, X2 is the effective length of the anchor bolt, which is taken as 1.2m; and X1 is the stability coefficient, which is calculated as 30% to 50% of (X0 + X2).

[0087] Generally, the dimensions of coal pillars left in roadways excavated along the goaf are not only related to the stress state of the surrounding rock and the difficulty of maintenance, but also to the anchoring quality of anchor cables and the stability control of the surrounding rock. Therefore, the dimensions of narrow coal pillars should be determined based on the coal pillar calculation results and by comprehensively considering the anchoring quality of anchor cables (i.e., the results of on-site anchor cable pull-out tests).

[0088] Based on the above problems, in this embodiment of the invention, comprehensive considerations include: From the perspective of the vertical stress distribution of the surrounding rock, when the roadway with a narrow coal pillar is completely below the goaf, the vertical stress of the surrounding rock is the lowest, and the stress environment of the roadway is relatively favorable. However, the roof strata of the roadway have undergone mining damage, and the roof rock mass is relatively fractured, making it difficult to guarantee the anchoring quality of the anchor cables. Therefore, from the perspective of ensuring roadway safety, this location is not suitable. Combining the reasonable coal pillar size calculation result B and the degree of fracture of the surrounding rock of the coal pillar, the coal pillar size of the roadway should be ≥ B. However, when the coal pillar size is large, the amount of coal resource loss will further increase, and the stress level of the roadway will also gradually increase. Therefore, the reasonable selection of the coal pillar size for the roadway should be based on ensuring the anchoring quality of the roadway anchor cables, combined with the anchor cable pull-out test results and the theoretical calculation results of the coal pillar width. Generally, a value of B or 6m is appropriate.

[0089] Optionally, the derivation of the mechanical model for a single end anchor bolt includes: First, based on the different stress states of the anchor bolt body, the end anchor bolts in coal mine roadways are divided into the anchored section L1, the free section L2, and the threaded section L3. Theoretically, the stress state of the end anchor bolt is simplified to an end anchor bolt mechanical model for analysis. Then, according to St. Venant's principle, the solution to the Boussinnesq problem is used to approximate the stress distribution generated 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 formed by the anchor bolt spacing r and the length z of the free section L2 are taken as the side lengths. z Calculate using the following formula:

[0090]

[0091] Where: σ z —Compressive stress provided by the anchor bolt, MPa;

[0092] P—Preload applied during anchor bolt installation, MN;

[0093] r—anchor bolt spacing, m;

[0094] Anchor bolt support mainly bears the shear dilatation deformation pressure p of the rock mass within the anchor bolt anchorage range. sThe self-weight of a small amount of delaminated rock mass is negligible, and the cohesion C within the anchored rock mass is ignored. According to the Mohr-Coulomb law, the compressive stress σ provided by the anchor bolt is... z The following equation must be satisfied for the anchorage structure to remain stable:

[0095] Right now

[0096] Where: σ zmin —Minimum compressive stress formed by the anchor bolt on the centerline of the anchoring structure, MPa;

[0097] —Internal friction angle of the rock mass, °;

[0098] p s —Shear dilatation pressure of the rock mass within the anchorage range, MPa.

[0099] Optionally, the calculation of shear dilatation pressure in the surrounding rock of the tunnel requires establishing a numerical analysis model based on the geological conditions of the tunnel being excavated along the goaf. This model simulates the vertical stress distribution of the surrounding rock during tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the area of ​​the surrounding rock in a state of shear dilatation gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain point, the tensile stress reaches its extreme value, i.e., p. s The extreme value of p is reached, after which the tensile stress value continuously decreases. When the calculation step increases to a certain value, the tensile stress value of the rock mass around the tunnel approaches 0, indicating that the shallow rock mass is continuously delaminating, fragmenting, and eventually completely losing its bearing capacity. During this process, p s The extreme value is the value of the roadway confining pressure shear expansion pressure.

[0100] In engineering practice, the shear dilatation pressure p of the rock mass within the anchorage range of the anchor bolt s As the deformation of the surrounding rock in the tunnel changes continuously, it is often difficult to measure it in a timely and accurate manner. However, the numerical calculation method in this invention can obtain the shear dilatation pressure of the surrounding rock in the tunnel at different calculation steps with relatively accurate results.

[0101] Optionally, the prestress calculation of the anchor cable 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 scheme, taking into account the anchor spacing r, the length z of the free section L2 of the anchor, and the internal friction angle of the rock mass. and the shear dilatation deformation pressure p of the rock mass within the anchorage range s Substitute the values ​​into the following formula:

[0102]

[0103] This allows us to calculate the preload P required during anchor bolt installation to form a stable anchoring structure for the tunnel roof and sidewalls.

[0104] As an active support method, the prestress of the anchor bolts is the most important parameter for anchor mesh support to play its active support role. In the early stage of roadway excavation, the support must provide sufficient support resistance to suppress delamination and fragmentation of the shallow rock mass, thereby forming an anchored bearing structure with high load-bearing capacity. To achieve this, it is necessary to rely on the pre-tightening force applied during the installation of the anchor bolts (cables). In addition, reasonable prestress of the anchor bolts can enable the anchor bolts to quickly increase resistance and maintain good load-bearing conditions, which is conducive to the formation of a reliable anchored bearing structure between the anchor bolts and the surrounding rock of the roadway, and to giving full play to the self-bearing capacity of the surrounding rock and maintaining the long-term stability of the surrounding rock.

[0105] Optionally, the timing of anchor mesh support includes: analyzing the development law of shear dilatation pressure of the surrounding rock in the roadway at different calculation steps obtained from numerical analysis model simulation, in order to maintain the integrity and self-bearing capacity of the surrounding rock in the roadway and avoid continuous delamination, fragmentation, or even loss of bearing capacity of the shallow rock mass, the initial support resistance provided by the anchor mesh support should be greater than the maximum shear dilatation pressure generated by the deformation of the shallow surrounding rock in the roadway, and the support timing should also be before the extreme point of shear dilatation stress of the surrounding rock in the roadway appears.

[0106] The timing of anchor mesh support is crucial for the effectiveness of controlling the surrounding rock in roadways. Timely anchor mesh support, coupled with relatively intact surrounding rock, easily forms a stable, reliable, and high-bearing-capacity anchored structure. Conversely, if anchor mesh support is implemented too late, the surrounding rock may have lost its bearing capacity, resulting in poor support effectiveness. However, there has been a lack of accurate quantitative scientific basis regarding when to implement support; support design data only suggests "timely support." Therefore, based on numerical simulation calculations to obtain the development law of shear dilatation pressure in the surrounding rock at different calculation steps, this paper analyzes and presents a quantitative support timing for anchor mesh support: "before the occurrence of the extreme point of shear dilatation stress in the surrounding rock of the roadway."

[0107] Example:

[0108] The following will take Pingmei Coal Industry Co., Ltd.'s Fourth Mine as an example. 16-17 Taking the -31020 working face as an example, combined with Figure 1 and Figure 2 The present invention and its technical solutions are described in detail, wherein, Figure 1 This is a schematic diagram of the geological and mining conditions and the layout of the tunnels along the goaf provided in an embodiment of the present invention. Figure 2 It is a cloud map of the vertical stress distribution around the working face after mining in a goaf tunnel, calculated in numerical simulation.

[0109] like Figure 1 and Figure 2 As shown, the main mining area of ​​Pingmei No. 4 Mine has... 15 Heji 16-17 Coal seam, already 15 The coal seam is an overlying coal seam with an average thickness of 1.5m. 16-17The coal seam is the lower seam, with an average thickness of 3.3m and a spacing between the seams ranging from 3 to 11m, belonging to the category of closely spaced coal seam group mining. The test roadway has been... 16-17 -31020 working face return airway (i.e., goaf excavation roadway 1) is located below already 16-17 In the coal seam, 16-17 -31020 working face (i.e., lower section working face 3) is located on the right side of this coal seam. 16 -23160 working face goaf (i.e., upper section working face goaf 10), test roadway and its own 16-17 A narrow coal pillar 2 is left in the goaf of the -23160 working face, overlying with [unclear]. 15 -31020 working face goaf (i.e., the goaf 5 on the left side of the overlying coal seam working face) and the existing 15 -23160 working face goaf (i.e., goaf 6 on the right side of the overlying coal seam working face). 16-17 The immediate roof of the coal seam is composed of silty mudstone with an average thickness of 5.45 m, and the main roof is composed of medium-grained sandstone with an average thickness of 11.5 m. These two elements constitute the key inter-coal seam strata 7. The floor strata 9 of the lower coal seam mainly include: the immediate floor is composed of sandy mudstone with an average thickness of 2.8 m, and the main floor is composed of silty mudstone with an average thickness of 5.6 m. The overlying coal seam roof strata group 8 mainly consists of silty mudstone and fine sandstone, respectively constituting the key inter-coal seam strata 7. 15 The immediate roof and the primary roof of the coal seam.

[0110] In oneself 16-17 During the excavation and mining of the return airway in the -31020 working face, the stability of the surrounding rock was affected by the supporting pressure of the coal pillar 4 left between the working faces of the overlying coal seam and the adjacent... 16-17 The combined effect of the lateral support pressure from the upper section of the coal seam working face and the advance support pressure from the lower section working face 3 results in a highly complex stress environment in the roadway. Furthermore, due to the already... 15 Coal seam and itself 16-17 The coal seams have small interlayer spacing, and the key rock strata between the coal seams, stratum 7, are silty mudstone and mudstone. 15 Coal seam mining is beneficial to oneself 16-17 The roof of the coal seam has suffered some degree of damage and destruction. 16-17 During the service period, coal seam mining roadways generally experience significant floor heave and inward displacement of the sidewalls. In particular, under the pressure of the working face's advance support, the roadway cross-section shrinks sharply, making roadway maintenance extremely difficult.

[0111] like Figure 1As shown, a stable anchoring design method for narrow coal pillars in gob-side excavation roadways with close proximity to the coal seam is presented. This method comprises two parts: determining the dimensions of the narrow coal pillar in the gob-side excavation roadway and designing the stable anchoring structure. Determining the dimensions of the narrow coal pillar includes: analysis of mining geological conditions and testing of coal and rock physical and mechanical parameters; calculation of the width of the plastic zone within the coal pillar after mining adjacent working faces; numerical simulation calculation of the vertical stress distribution of the surrounding rock after mining of the working faces around the gob-side excavation roadway; and comprehensive consideration of the anchoring quality of the roadway anchor cables. The design method for forming the stable anchoring structure includes: derivation of the mechanical model of a single end anchor bolt; calculation of the shear dilatation pressure of the roadway surrounding rock; calculation of the prestress of the roadway anchor cables; and determination of the timing of anchor mesh support.

[0112] The analysis of mining geological conditions and the testing of physical and mechanical parameters of coal and rock require, on the one hand, the analysis of the surrounding rock environment of the narrow coal pillar roadway 1 in the lower coal seam based on the on-site mining data. It can be seen that the roadway 1 is not only affected by the excavation of this roadway and the mining of the lower section working face 3, but also by the coal pillar 4 left between the working faces of the overlying coal seam and the concentrated stress formed on the floor by the goaf 10 of the upper section working face. The stress environment of the roadway surrounding rock is complex. During the process of disturbance caused by the mining of the surrounding roadways and working faces, the stress environment of the surrounding rock of the narrow coal pillar roadway 1 has undergone multiple complex evolution processes. Each change in the stress state of the rock mass will cause changes in the structural characteristics of the rock mass, resulting in the continuous weakening and fragmentation of the surrounding rock strength of the roadway 1. On the other hand, it is necessary to test the basic physical and mechanical parameters of the surrounding rock of the roadway 1 along the goaf, and to carry out laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard samples to obtain the physical and mechanical parameters (including uniaxial compressive strength, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio) and deformation and failure laws of the roadway roof and floor and coal seam, so as to provide parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

[0113] The width of the plastic zone within the narrow coal pillar 2 after mining adjacent working faces is calculated. A reasonable coal pillar width is generally calculated using the formula B = X0 + X1 + X2, where the latter two values ​​are generally limited: X2 is the effective length of the anchor bolt, taken as 1.2m; X1 is the stability coefficient, calculated as 30%–50% of (X0 + X2). Therefore, the reasonable coal pillar width is mainly determined by X0. According to the limit equilibrium theory, the width X0 of the plastic zone within the coal pillar after mining adjacent working faces is calculated using the following formula:

[0114]

[0115] Where: m is the coal seam thickness, m; λ is the lateral pressure coefficient, λ=μ / (1-μ), μ is Poisson's ratio; γ 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 unit weight of the overlying strata, MN / m³. 3H represents the tunnel depth in meters (m); P z The resistance of the support structure to the coal face is expressed in MPa.

[0116] Numerical simulation calculation of the vertical stress distribution of the surrounding rock after the mining of the working face around the gob-side excavation roadway 1 requires establishing a large-scale FLAC3D three-dimensional numerical calculation model based on the geological conditions of the gob-side excavation roadway 1. Following the mining sequence of the upper and lower coal seams, the established numerical model is used for excavation simulation to obtain cloud maps of the vertical stress distribution of the surrounding rock in different mining stages of the gob-side excavation roadway 1, such as... Figure 2 As shown, the stress level of the surrounding rock in the roadway and the difficulty of roadway maintenance can be analyzed under different coal pillar sizes (i.e., different roadway layout locations). Simultaneously, the value of the stress concentration factor K can be obtained based on the calculation results of the vertical stress distribution.

[0117] Comprehensive consideration of the anchoring quality of the anchor cables in the goaf-advancing roadway 1: On the one hand, from the perspective of roadway stress distribution, with the narrow coal pillar in the lower layer, the goaf-advancing roadway 1 is completely below the goaf, the vertical stress of the surrounding rock is the lowest, and the stress environment of the roadway is relatively favorable; on the other hand, the roof strata of the goaf-advancing roadway 1 (key inter-coal seam 7) have undergone mining damage, the roof rock mass is relatively broken, and the anchoring quality of the anchor cables is difficult to guarantee. Therefore, from the perspective of ensuring the safety of the roadway, this location is not suitable.

[0118] Furthermore, the Poisson's ratio of the coal seam is taken as 0.26, the internal friction angle as 32.5°, the cohesion as 1.19 MPa, the stress concentration factor as 1.89, and the average unit weight of the overlying strata as 0.025 MN / m³. 3 The tunnel depth is taken as 952m, and the coal face support resistance is negligible. Substituting the above parameters into the calculation formula for X0, we obtain... 16-17 After mining the -23160 working face, the width of the plastic zone X0 within the narrow coal pillar 2 is approximately 2.936m. Therefore, it can be theoretically calculated that... 16-17 The width B of the narrow coal pillar in the goaf-side excavation roadway of the -31020 return airway ranges from 5.377 to 6.204 m. Considering the calculated reasonable coal pillar size B and the degree of rock fracturing around the coal pillar, the coal pillar size in the goaf-side excavation roadway should be ≥ B. However, a larger coal pillar size will further increase coal resource loss, and the stress level in the roadway will also gradually increase. Therefore, the selection of the reasonable narrow coal pillar size 2 in the goaf-side excavation roadway 1 should be based on ensuring the anchoring quality of the roadway anchor bolts (cables), and a value of 6 m should be selected based on the anchor bolt pull-out test results and the theoretical calculation results of the coal pillar width.

[0119] The derivation of the mechanical model for a single end anchor bolt involves several steps. First, based on the different stress states of the anchor bolt body, end anchor bolts in coal mine roadways can be divided into ineffective anchorage sections (L1) and effective anchorage sections (L2). Theoretically, the end anchor bolt can be simplified to the mechanical model shown in the figure below for analysis. Then, based on St. Venant's principle, the stress distribution generated by the concentrated force acting on a single anchor bolt is approximated using the solution to the Boussinnesq problem. That is, within the range 0 ≤ z ≤ 0.5L2, the compressive stress σ along the z-direction at any point M is... z Calculate using the following formula:

[0120]

[0121] Where: σ z —Compressive stress provided by the anchor bolt, MPa;

[0122] P—Preload applied during anchor bolt installation, MN;

[0123] r—anchor spacing, m.

[0124] Anchor bolt support mainly bears the shear dilatation deformation pressure p of the rock mass within the anchor bolt anchorage range. s The self-weight of a small amount of delaminated rock mass is negligible due to its small amount of delamination, and the cohesion C within the anchoring rock mass is ignored. According to Mohr-Coulomb's law, the compressive stress σ provided by the rod... z The following equation must be satisfied for the anchorage structure to remain stable:

[0125] Right now

[0126] Where: σ zmin —Minimum compressive stress formed by the anchor bolt on the centerline of the anchoring structure, MPa;

[0127] —Internal friction angle of the rock mass, °;

[0128] p s —Shear dilatation pressure of the rock mass within the anchorage range, MPa.

[0129] Calculation of shear dilatation pressure in the surrounding rock of the roadway, due to the shear dilatation pressure p of the surrounding rock of the roadway. sThe shear dilatation pressure changes continuously with the deformation of the surrounding rock in the tunnel, making it difficult to measure accurately. Numerical calculation models are needed to obtain a more accurate picture of the shear dilatation pressure at different calculation steps. Therefore, based on the geological conditions of the tunnel 1 being excavated along the goaf, a numerical analysis model needs to be established to simulate and calculate the vertical stress distribution of the surrounding rock during tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases (100 steps per cycle), the area of ​​the surrounding rock in a state of shear dilatation gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches 500, the tensile stress reaches its extreme value (i.e., p). s The extreme value was 0.0988 MPa. Afterward, the tensile stress value continuously decreased. When the calculation time step increased to 1000 time steps, the tensile stress value of the rock mass surrounding the tunnel approached 0, indicating that the shallow rock mass continuously delaminated, fragmented, and eventually completely lost its bearing capacity. During this process, p s The extreme value is the value of the roadway confining pressure shear expansion pressure.

[0130] The prestress calculation of the anchor cables is based on the test results of the surrounding rock mechanical parameters of the tunnel 1 excavated along the goaf and the initial anchor mesh support design scheme. The anchor spacing of 0.8m, the anchorage length of 0.9m, the internal friction angle of the surrounding rock of 32.5°, and the shear dilatation pressure of 0.0988MPa are substituted into the following formula:

[0131]

[0132] The prestress values ​​of the anchor cables required to form a stable anchoring structure for the roadway roof and walls can be calculated to be 78.2 kN and 101.1 kN, respectively.

[0133] Based on the development law of shear dilatation pressure of the surrounding rock in different calculation steps, it can be seen that in order to maintain the integrity and self-bearing capacity of the surrounding rock and avoid continuous delamination, fragmentation, and even loss of bearing capacity of the shallow rock mass, the initial support resistance provided by the anchor mesh support should be greater than the maximum shear dilatation pressure generated by the deformation of the shallow surrounding rock in the roadway. Furthermore, the support should be provided before the extreme point of shear dilatation stress in the surrounding rock of the roadway appears.

[0134] Furthermore, the initial anchor-mesh support design for roadways should employ a dynamic information design method that includes test point investigation and geomechanical assessment, initial design, underground monitoring and information feedback, and design revision. The test point investigation includes testing of surrounding rock strength, rock structure, in-situ stress, and anchoring performance. Based on this, a geomechanical assessment is conducted to provide reliable parameters for the initial design. The initial design uses a combination of numerical calculation and empirical methods to determine a reasonable anchor-mesh support scheme based on surrounding rock parameters and existing measured data. Finally, the anchor-mesh support scheme needs to be implemented underground, with detailed monitoring of surrounding rock deformation and anchor cable stress. The support design is verified or revised based on the monitoring results.

[0135] Finally, based on the initial anchor mesh support design scheme for the roadway, and combined with the roadway layout method and stable anchoring design method provided by this invention, a layout scheme for roadways excavated along the goaf and a new anchor mesh cable support scheme were proposed. The field application results show that the roadway remained basically stable after the mining of this working face, with the deformation of the two sides not exceeding 500mm and the roof subsidence not exceeding 200mm, achieving a good surrounding rock control effect.

[0136] The above inventions are merely a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations 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 roadways with narrow coal pillars in close-range coal seams, characterized in that, include: The determination of the dimensions for narrow coal pillars in goaf-running roadways and the design method for forming stable anchoring structures; among them, The determination of the dimensions for the narrow coal pillar in the goaf tunnel 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 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 goaf-running roadway. S12. Based on the analysis of mining geological conditions, the testing of coal and rock physical and mechanical parameters, the width of the plastic zone in the coal pillar, the numerical value of the vertical stress distribution of the surrounding rock in the roadway, and the comprehensive consideration of the anchoring quality of the roadway anchor cables, the dimensions of the narrow coal pillar are determined. The design method for forming the stable anchoring structure includes: S20. Calculate the shear dilatation pressure of the surrounding rock in the tunnel; S21. Derivation of the mechanical model of single-end anchor bolt action by incorporating the shear dilatation pressure of the surrounding rock in the tunnel. S22. Based on the derivation of the mechanical model of the single-end anchor bolt and the calculation results of the shear dilatation pressure of the surrounding rock in the roadway, calculate the prestress of the roadway anchor bolt cable. S23. Determining the timing of anchor mesh support; The calculation of shear dilatation pressure in the surrounding rock of the tunnel requires establishing a numerical analysis model based on the geological conditions of the tunnel being excavated along the goaf. This model simulates the vertical stress distribution of the surrounding rock during tunnel excavation. After the tunnel is excavated, as the number of calculation steps increases, the area of ​​the surrounding rock in a state of shear dilatation gradually expands, and the corresponding tensile stress value also gradually increases. When the number of calculation steps reaches a certain threshold, the tensile stress reaches its extreme value, i.e. p s The extreme value is reached, after which the tensile stress value continuously decreases. When the calculation step increases to a certain value, the tensile stress value of the rock mass around the tunnel approaches 0, indicating that the shallow rock mass is continuously delaminating, fragmenting, and eventually completely losing its bearing capacity. During this process, p s The extreme value is the value of the shear dilatation pressure of the roadway confining pressure; The prestress calculation of the roadway anchor cables requires consideration of the test results of the physical and mechanical parameters of the coal and rock and the initial anchor mesh support design scheme, including the anchor spacing. r Anchor bolt free section L 2 length z internal friction angle of rock mass and the shear dilatation deformation pressure of the rock mass within the anchoring range of the anchor bolt p s Substitute the values ​​into the following formula: ， This allows for the calculation of the preload applied during anchor bolt installation required to form a stable anchoring structure for the roadway roof and walls. P ; The timing of anchor mesh support includes: Based on the analysis of the shear dilatation pressure development law of the surrounding rock of the roadway at different calculation steps obtained from the numerical analysis model simulation, in order to maintain the integrity and self-bearing capacity of the surrounding rock of the roadway and avoid the continuous delamination, fragmentation, and even loss of bearing capacity of the shallow rock mass, the initial support resistance provided by the anchor mesh support should be greater than the maximum shear dilatation pressure generated by the deformation of the shallow surrounding rock of the roadway, and the timing of the support should also be before the extreme point of shear dilatation stress of the surrounding rock of the roadway appears.

2. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 1, characterized in that, The mining geological condition analysis specifically includes analyzing the surrounding rock environment of a roadway with a narrow coal pillar in the lower coal seam, 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 surrounding rock of the target roadway, conducting laboratory uniaxial compression tests, variable angle shear tests, and Brazilian splitting tests on standard samples, and obtaining the physical and mechanical parameters and deformation and failure laws of the roadway roof and floor and the coal seam, providing parameter basis for subsequent numerical simulation and theoretical calculation of coal pillar size.

3. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 2, characterized in that, The physical and mechanical parameters of the coal and rock include uniaxial compressive strength, tensile strength, elastic modulus, cohesion, internal friction angle, and Poisson's ratio.

4. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 1, characterized in that, The numerical simulation calculation of the vertical stress distribution of the surrounding rock after the mining of the working face around the goaf-running roadway includes: establishing a FLAC3D three-dimensional numerical calculation model based on the geological conditions of the goaf-running roadway; performing excavation simulation on the established numerical model according to the mining sequence of the upper and lower coal seams to obtain cloud maps of the vertical stress distribution of the surrounding rock in different mining stages; comparing the stress level of the surrounding rock under different coal pillar sizes or roadway locations to analyze the difficulty of roadway maintenance; and obtaining the stress concentration factor based on the vertical stress distribution cloud maps of the surrounding rock. K The value of .

5. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 4, characterized in that, The calculation of the width of the plastic zone within the coal pillar after mining adjacent working faces includes: According to the limit equilibrium theory, the width of the plastic zone within the coal pillar after mining adjacent working faces is... X 0 Calculate using the following formula: ， In the formula: m Coal seam thickness, in meters (m). λ The lateral pressure coefficient, λ = μ / (1- μ ), μ Poisson's ratio, The internal friction angle of the coal body. C 0 represents the cohesion of the coal body, in MPa. K The stress concentration factor is... γ This represents the average unit weight of the overlying rock strata, expressed in MN / m³. 3 , H The depth of the tunnel is expressed in meters (m). P z The resistance of the support structure to the coal face is expressed in MPa. The appropriate coal pillar width is determined according to the formula. Calculations show that the latter two values ​​in the formula have limited values, namely... X 2 The effective length of the anchor bolt is taken as 1.2m; X 1 As a stability coefficient, it is set at 30% to 50% ( X 0 + X 2 )calculate.

6. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 5, characterized in that, The comprehensive considerations include: From the perspective of the vertical stress distribution of the surrounding rock, when the roadway with a narrow coal pillar 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 roadway is relatively favorable. The roof strata of the roadway have been damaged by mining, and the roof rock mass is relatively broken, making it difficult to guarantee the anchoring quality of the anchor cables. Therefore, from the perspective of ensuring the safety of the roadway, this location is not suitable. Based on the calculated reasonable coal pillar size B and the degree of rock fracturing around the coal pillar, the coal pillar size in the goaf-advancing roadway should be ≥ B.

7. The stable anchoring design method for narrow coal pillar roadways with close-range coal seams as described in claim 1, characterized in that, The derivation of the mechanical model for the action of a single-end anchor bolt includes: Firstly, based on the different stress states of the anchor bolt body, the end anchor bolts in coal mine roadways are divided into anchoring sections. L 1. Free paragraph L 2 and threaded section L 3 In theory, the stress state of the end anchor bolt can be simplified and analyzed using the mechanical model of the end anchor bolt. Then, according to St. Venant's principle, the solution to the Boussinnesq problem is used to approximate the stress distribution caused by the concentrated force on a single anchor bolt, i.e., when the free segment... L The length z of 2 takes the value 0≤ z ≤ At that time, based on the anchor bolt spacing r and the free section L The compressive stress along the direction of the rod at any point within the two rectangular planes formed by the length z of the rod is the side length. Calculate using the following formula: ， In the formula: —Compressive stress provided by the anchor bolt, MPa; P —The preload force applied during anchor bolt installation, MN; r — Anchor bolt spacing, m; Anchor bolt support mainly bears the shear dilatation deformation pressure of the rock mass within the anchor bolt anchorage range. p s The self-weight of a small amount of delaminated rock mass is negligible due to its extremely small amount of delamination, and the cohesion within the anchoring rock mass is also ignored. C At that time, according to the Mohr-Coulomb law, the compressive stress provided by the anchor bolt... σ z The following equation must be satisfied for the anchorage structure to remain stable: ,Right now , In the formula: —Minimum compressive stress formed by the anchor bolt on the centerline of the anchoring structure, MPa; —Internal friction angle of the rock mass, °; p s —Shear dilatation pressure of the rock mass within the anchorage range, MPa.

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