A method and system for calculating critical thickness of rock wall for safe coal mining in tunnel

Abstract

The present invention relates to a method and system for calculating the critical thickness of a rock wall for safe coal mining in a tunnel, including: constructing a rock wall model; based on the limit equilibrium theory, obtaining a calculation formula for the width of the limit equilibrium zone according to the stress distribution characteristics in front of the face and the influencing factors of the width of the limit equilibrium zone; based on the calculation formula, determining the value of the width of the limit equilibrium zone according to coal seam parameters. Based on the gas pressure and blasting disturbance, the thickness of the rock wall reserved for coal mining blasting is determined according to the value of the width of the limit equilibrium zone. The present invention constructs a rock wall model, and based on the limit equilibrium theory, obtains the calculation formula for the width of the limit equilibrium zone according to the stress distribution characteristics in front of the face and the influencing factors of the width of the limit equilibrium zone, determines the calculation formula for the critical rock wall thickness affected by comprehensive factors, and reasonably reserves the rock wall thickness through numerical simulation, thereby achieving safe coal mining.

Description

Technical Field

[0001] The invention relates to the technical field of calculation of thickness of safety rock walls in gas tunnels, and in particular to a method and system for calculating critical thickness of safety rock walls in coal mining tunnels. Background Art

[0002] With the comprehensive advancement of transportation infrastructure, especially the high-speed railways that cross mountains and ridges with straight large-radius curves, the lines inevitably pass through a large number of coal-bearing strata. When the tunnel passes through the coal seam, the gas pressure and outburst volume increase, and there is a risk of coal and gas outburst. Before the tunnel is exposed, a certain thickness of safety rock wall should be reserved. If the thickness of the reserved rock wall is too small, it will be difficult to resist the ground stress and gas pressure to expose the coal seam by itself, causing safety hazards such as gas outburst; otherwise, it will affect the construction progress and the coal-excavation operation. Scientifically and reasonably reserving the thickness of the safety rock wall has become a key parameter for the safety of coal-excavation construction in the gas outburst area of ​​large-section tunnels.

[0003] In the prior art, the thickness of the reserved rock pillars of different thicknesses is numerically calculated, and the minimum thickness of the rock pillars is determined in combination with the damage of the reserved rock pillars; the prior art establishes a mechanical model for cross-tunnel mining in a large mining height working face, and determines the value of the thickness of the safe rock pillar; the prior art estimates the thickness of the safe rock pillar in combination with the construction of tunnels crossing steeply inclined coal seams, and establishes a three-dimensional model, and selects a 9m safe rock pillar; the prior art proposes the use of a grouting plate and an improved method of multivariate regression analysis to calculate the thickness of the safe rock plate for preventing gas outbursts in tunnels. In the prior art, through numerical simulation analysis of the Yangjiaozhao Tunnel, a fitting expression for the thickness of the safe rock pillar under the combined influence of the coal seam inclination and the size of the gas pressure is derived; in the prior art, relying on the Guigala Tunnel of the Tibet Laze Expressway, the calculation formula for the safe thickness of the rock pillar for tunnel stone gate coal uncovering is summarized for different coal seam inclinations.

[0004] In previous studies, the safe thickness of rock pillars was mainly determined by numerical simulation analysis, and the influencing factors involved in the derived theoretical calculation formula were not comprehensive. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method and system for calculating the critical thickness of rock walls for safe coal mining in tunnels. Based on the limit equilibrium theory, the present invention proposes a calculation formula for the critical rock wall thickness affected by comprehensive factors, and reasonably reserves the rock wall thickness through numerical simulation to achieve safe coal mining.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for calculating the critical thickness of a tunnel coal-uncovering safety rock wall comprises the following steps:

[0008] construct rock wall models;

[0009] Based on the limit equilibrium theory, the calculation formula of the limit equilibrium zone width is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the limit equilibrium zone width;

[0010] Based on the calculation formula, the value of the width of the limit equilibrium zone is determined according to the coal seam parameters.

[0011] Based on the gas pressure and blasting disturbance, the thickness of the rock wall reserved for coal blasting is determined according to the value of the limit equilibrium zone width.

[0012] Preferably, the top and bottom of the rock wall in the rock wall model are both subject to vertical ground stress, and the rock wall serves as the top constraint and the bottom constraint of the rock wall model.

[0013] Preferably, the factors affecting the width of the limit equilibrium zone include: tunnel excavation height, average bulk density of the strata overlying the tunnel, tunnel face burial depth, stress concentration coefficient, rock internal friction angle and cohesion, coal seam inclination and gas pressure.

[0014] Preferably, the calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0015] Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face;

[0016] According to the stress state of the unit body in the limit equilibrium zone, the force equation in the x-axis direction when the unit body is in the limit equilibrium state is determined; the force equation is:

[0017]

[0018] Among them, σ x is the horizontal stress; σ z is the vertical stress, is the internal friction angle of rock, c is the cohesion of rock, h is the excavation height of tunnel, and dx is the unit width.

[0019] Preferably, the calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0020] Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face;

[0021] The stress equilibrium equation in the rock wall is determined according to the stress state of the unit body in the limit equilibrium zone; the stress equilibrium equation is:

[0022]

[0023]

[0024]

[0025] Here, τ xz is the shear stress in the xz plane.

[0026] At the junction of the coal seam and the limit equilibrium zone, it satisfies: σ x =βσ z =βKγH;

[0027] Preferably, the calculation formula for obtaining the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone includes:

[0028] The vertical stress equation is determined according to the force equation and the stress equilibrium equation; the vertical stress equation is:

[0029]

[0030] Among them, β is the lateral pressure coefficient, and x is the distance from any point in the limit equilibrium zone to the rock wall in front of the tunnel face.

[0031] Preferably, the calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0032] The calculation formula for determining the width of the limit equilibrium zone is determined by taking into account the coal seam inclination, coal seam gas pressure and boundary conditions; the calculation formula for the width of the limit equilibrium zone is:

[0033]

[0034] Among them, σ x =βσ z =βKγH, α is the coal seam inclination, P is the coal seam gas pressure, K is the stress concentration factor; γ is the average bulk density of the overlying stratum of the tunnel, H is the depth of the tunnel face; the boundary condition is σ z =KγH+Pcosα.

[0035] Preferably, the coal seam parameters include: coal seam inclination, gas pressure, internal friction angle of carbonaceous mudstone, cohesion, and compressive strength.

[0036] A system for calculating critical thickness of rock wall for safe coal mining in tunnels, comprising:

[0037] Construction module, used to build rock wall models;

[0038] The first calculation module is used to obtain a calculation formula for the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone;

[0039] A determination module is used to determine the value of the width of the limit equilibrium zone based on the calculation formula and coal seam parameters.

[0040] The second calculation module is used to determine the thickness of the rock wall reserved for coal blasting based on the gas pressure and blasting disturbance and the numerical simulation of the width of the limit equilibrium zone.

[0041] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0042] The present invention provides a method and system for calculating the critical thickness of a rock wall for safe coal uncovering in a tunnel. The present invention constructs a rock wall model, based on the limit equilibrium theory, obtains a calculation formula for the width of the limit equilibrium zone according to the stress distribution characteristics in front of the face and the influencing factors of the width of the limit equilibrium zone, determines a calculation formula for the critical rock wall thickness affected by comprehensive factors, and reasonably reserves the rock wall thickness through numerical simulation, thereby achieving safe coal uncovering. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 A flow chart of a method for calculating critical rock wall thickness for coal mining in a tunnel provided by the present invention;

[0045] Figure 2 A schematic diagram of stress redistribution of surrounding rock at the tunnel face in an embodiment provided by the present invention;

[0046] Figure 3 A diagram of a rock wall model in an embodiment provided by the present invention;

[0047] Figure 4 The stress state of the unit body in the limit equilibrium zone in the embodiment provided by the present invention;

[0048] Figure 5 The model is established in the embodiment provided by the present invention;

[0049] Figure 6 A schematic diagram of the three-step excavation steps in the embodiment provided by the present invention;

[0050] Figure 7It is a contour map of vertical stress in front of the three-step excavation face in the embodiment provided by the present invention;

[0051] Figure 8 It is a contour map of vertical stress of tunnel surrounding rock at different stages in the embodiment provided by the present invention;

[0052] Fig. 9 This is a straight line diagram of vertical stress in front of the face of the coal mining operation section in the embodiment provided by the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] The purpose of the present invention is to provide a method and system for calculating the critical thickness of rock walls for safe coal uncovering in tunnels. Based on the limit theory, the present invention proposes a calculation formula for the critical rock wall thickness affected by comprehensive factors, and reasonably reserves the rock wall thickness through numerical simulation to achieve safe coal uncovering.

[0055] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] like Figure 1 As shown, the present invention provides a method for calculating the critical thickness of a tunnel coal mining safety rock wall, comprising the following steps:

[0057] construct rock wall models;

[0058] Based on the limit equilibrium theory, the calculation formula of the limit equilibrium zone width is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the limit equilibrium zone width;

[0059] Based on the calculation formula, the value of the width of the limit equilibrium zone is determined according to the coal seam parameters.

[0060] Based on the gas pressure and blasting disturbance, the thickness of the rock wall reserved for coal blasting is determined according to the value of the limit equilibrium zone width.

[0061] Before tunnel excavation, the underground coal and rock mass is in a three-dimensional stress equilibrium state. After excavation, the coal and rock equilibrium state is broken and the surrounding rock stress is redistributed. As the tunnel face advances, the rock wall thickness becomes thinner and thinner. Under the action of stress, the edge of the rock mass in front of the tunnel face is damaged and gradually extends to the depth until the boundary of the elastic stress zone. Part of the rock mass is in a limit equilibrium state. The stress distribution model is as follows: Figure 2 As shown in the figure, a plane rectangular coordinate system is established with the center of the tunnel face as the coordinate origin O. Due to the open space on one side and local stress concentration after tunnel excavation, the rock wall tends to shear along the tunnel excavation contour or weak surface, and shear stress is generated on the shear surface.

[0062] Further, such as Figure 3 As shown, the top and bottom of the rock wall in the rock wall model are both subject to vertical ground stress, and the rock wall serves as the top constraint and bottom constraint of the rock wall model.

[0063] The factors affecting the width of the limit equilibrium zone include: tunnel excavation height, average bulk density of the strata overlying the tunnel, tunnel face burial depth, stress concentration coefficient, rock internal friction angle and cohesion, coal seam inclination and gas pressure.

[0064] Further, such as Figure 4 As shown, based on the limit equilibrium theory, the calculation formula for the width of the limit equilibrium zone is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0065] Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face;

[0066] According to the stress state of the unit body in the limit equilibrium zone, the force equation in the x-axis direction when the unit body is in the limit equilibrium state is determined; the force equation is:

[0067]

[0068] Based on the limit equilibrium theory, a unit cell with a width of dx and a length of 1 is randomly selected in the rock wall, and the tunnel excavation height is h. In the x direction, the stress on the side of the unit cell close to the face is x, and the stress on the other side is σ x +dx, the stress in the z direction is σ z , the shear stress on the shear surface is The internal stress state of the unit body is as follows Figure 4 shown.

[0069] Among them, σ x is the horizontal stress; σ z is the vertical stress, is the internal friction angle of rock, c is the cohesion of rock, h is the excavation height of tunnel, and dx is the unit width.

[0070] The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0071] Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face;

[0072] The stress equilibrium equation in the rock wall is determined according to the stress state of the unit body in the limit equilibrium zone; when the body force is ignored, the stress equilibrium equation is:

[0073]

[0074]

[0075]

[0076] Among them, τ xz is the shear stress in the xz plane.

[0077] At the junction of the coal seam and the limit equilibrium zone, it satisfies: σ x =βσ z =βKγH;

[0078] The calculation formula for the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone includes:

[0079] The vertical stress equation is determined according to the force equation and the stress equilibrium equation; the vertical stress equation is:

[0080] Among them, β is the lateral pressure coefficient, and x is the distance from any point in the limit equilibrium zone to the rock wall in front of the tunnel face.

[0081] The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including:

[0082] The calculation formula for determining the width of the limit equilibrium zone is determined by taking into account the coal seam inclination, coal seam gas pressure and boundary conditions; the calculation formula for the width of the limit equilibrium zone is:

[0083]

[0084] Among them, α is the coal seam inclination, P is the coal seam gas pressure, K is the stress concentration factor; γ is the average bulk density of the overlying stratum of the tunnel, H is the depth of the tunnel face; the boundary condition is σ z =KγH+Pcosα and X=L (at the vertical stress peak).

[0085] According to the actual situation of C5 coal seam, the measured gas pressure is 2.42MPa, the coal seam inclination is 45°, and the average bulk density γ of the overlying stratum on the tunnel face is 25kN / m 3, the stress concentration factor is 2.5, the face depth is 140m, the tunnel upper step excavation height is 4m, and considering the influence of gas pressure and blasting vibration, the rock strength is reduced by 30%, the internal friction angle φ of carbonaceous mudstone is 31.5°, the cohesion is 3.23MPa, and the compressive strength is 10.1MPa. According to the calculation formula of the limit equilibrium zone width, the limit equilibrium zone width L=1.43m is calculated.

[0086] The coal seam parameters include: coal seam inclination, gas pressure, internal friction angle of carbonaceous mudstone, cohesion, and compressive strength.

[0087] A system for calculating critical thickness of rock wall for safe coal mining in tunnels, comprising:

[0088] Construction module, used to build rock wall models;

[0089] The first calculation module is used to obtain a calculation formula for the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone;

[0090] A determination module is used to determine the value of the width of the limit equilibrium zone based on the calculation formula and coal seam parameters.

[0091] The second calculation module is used to determine the thickness of the rock wall reserved for coal blasting based on the gas pressure and blasting disturbance and the value of the limit equilibrium zone width.

[0092] This embodiment also discloses the simulation process of the thickness of the reserved rock wall for coal blasting in gas tunnel:

[0093] (1) Model building:

[0094] According to the excavation of Yujingshan Tunnel, the C5 coal seam was uncovered first, and the coal uncovering operations were mainly carried out in strong-medium weathered shale (P2l), mud sandstone (P2l) and C5 and C6 coal seams. The vertical distance between the C5 and C6 coal seams is 26.6m, the tunnel coal spacing is 30.7m, and the coal seam inclination is 45°. A three-dimensional model was established based on the actual strata and engineering conditions of the tunnel, and the surface terrain was simplified to a slope. The model length × width = 100m × 200m, the maximum height is 105m, the maximum width of the tunnel section is 15m, and the maximum height is 12m. The initial support and secondary lining are simplified and merged into a 1m concrete lining, such as Figure 5 As shown. Considering the boundary effect, 45m of surrounding rock is reserved on both sides of the tunnel. The upper boundary is a free boundary with no constraints, the left and right boundaries constrain the lateral displacement, and the lower boundary has both vertical and lateral displacement constraints and is a fixed boundary. The elastic-plastic constitutive model and the Mohr-Coulomb criterion are adopted.

[0095] There are 6 types of rock formations in the tunnel simulation area, including shale, sandstone, C5 coal seam, mixed layer, C6 coal seam and mud sandstone. Shale is gray and dark gray, including mud structure and foliation structure; sandstone is gray-yellow, belongs to strong weathering rock, fine-grained structure and medium-layered structure; coal seam is black, carbonaceous structure, thin-layered structure; mud siltstone is purple-red, powdery structure. According to the engineering geological survey report, while considering the influence of gas pressure and blasting disturbance, the numerical simulation calculation parameters are comprehensively determined, as shown in Table 1.

[0096] Table 1 Physical and mechanical parameters of rock formations

[0097]

[0098] (2) Simulation conditions and result analysis:

[0099] A tunnel of the Chenggui High-speed Railway was excavated using the three-step method. The excavation steps are as follows: Figure 6 FLAC3D was used to simulate and analyze the stress distribution characteristics of the surrounding rock at different excavation stages, the excavation disturbance range, the stress distribution state in front of the tunnel face, and the critical thickness of the safety rock wall reserved for blasting and coal uncovering in large-section tunnels.

[0100] (3) Stress in front of the heading face in normal excavation section:

[0101] Depend on Figure 7 It can be seen that after the excavation of the upper step, there is obvious stress concentration on the face, the maximum vertical stress is 3.5MPa, and the vertical stress concentration coefficient reaches 2.35. The vertical stress in front of the face shows an overall trend of increasing first, reaching the peak, then starting to decrease, and finally tending to be stable. After the excavation of the middle and lower steps, the distribution state of the vertical stress in front of the face remains basically unchanged. It can be seen that the distribution state of the vertical stress in front of the face is mainly affected by the excavation of the upper step. After the excavation of the upper step, the secondary distribution of the vertical stress in front of the face has been completed. The excavation of the upper step has caused the upper part of the middle step and the lower step to be exposed to the air, and the stress has been unloaded and released in the vertical direction. The excavation of the middle step and the lower step has no obvious effect on the distribution state of the vertical stress in front of the face. After the lining is applied, the vertical stress distribution in front of the face remains unchanged as a whole, and the vertical stress at the same position in front of the face has a decreasing trend.

[0102] (4) Tunnel surrounding rock stress distribution:

[0103] The vertical stress contour diagrams of the tunnel surrounding rock before tunnel excavation, after excavation of the upper step, middle step, lower step and after lining are shown in the figure below. Figure 8 As shown in (a)(b)(c)(d).

[0104] Depend on Figure 8It can be seen that before tunnel excavation, the stratum was in the original rock stress state, and the vertical stress increased with the increase of depth. After the upper step excavation, the vertical stress distribution of the surrounding rock changed significantly. The stress distribution state was symmetrically distributed along the center line of the tunnel, the stress at the top of the tunnel decreased, and the stress on the side wall increased. After the middle step excavation, the stress distribution state was still symmetrically distributed along the center line of the tunnel, the stress at the top of the tunnel decreased, the stress on the side wall increased, and stress concentration occurred at the two arch feet, with the maximum stress reaching 3.6MPa. After the lower step excavation, the tunnel reached the excavation section size, the vertical stress contour map was symmetrically distributed along the center line of the tunnel, the stress of the tunnel vault and bottom plate decreased, the stress of the tunnel side wall increased, the vertical stress of the vault was less than the stress of the side wall, and the stress concentration coefficient reached 2.4 when the tunnel was buried at a depth of 60m. After the lining was applied, the stress distribution state of the tunnel surrounding rock did not change significantly, but the maximum vertical stress of the tunnel side wall decreased, the maximum vertical stress of the side wall was 3.25MPa, and the vertical stress of the tunnel vault and bottom plate did not change much.

[0105] (5) Stress distribution in front of the face of coal mining operation section:

[0106] Fig. 9 (a)(b)(c)(d) are the stress cloud map and contour map in front of the tunnel face when the tunnel face is advanced to 30m, 20m, 10m and 0m away from the C5 coal seam respectively.

[0107] Depend on Fig. 9It can be seen that after tunnel excavation, the vertical stress in front of the face first increases, reaches the peak value, then begins to decrease, and finally tends to be stable. There will be a stress reduction zone, a stress increase zone and an original rock stress zone in front of the face. As the face continues to advance, the vertical stress peak in front of the face also continues to advance, and is always located at a certain distance in front of the face. There is an obvious stress concentration phenomenon in the face of the upper step. When it is 30m away from the C5 coal seam, the maximum vertical stress is 2.5MPa; when it is 20m away from the C5 coal seam, the maximum vertical stress is 1.28MPa; when it is 10m away from the C5 coal seam, the maximum vertical stress is 1.25MPa; when it is close to the C5 coal seam, the maximum vertical stress is 2.5MPa; the buried depth of the face is 50-30m, and the vertical stress concentration coefficient is 2-1.65. When the face is 30m away from the C5 coal seam, the C5 coal seam is basically in the original rock stress zone, and the excavation of the tunnel has little effect on the C5 coal seam. When the tunnel face is 20m away from the C5 coal seam, part of the C22 coal seam is in the original rock stress zone, and some areas are slightly affected, with a slight increase in vertical stress. When the tunnel face is 10m away from the C5 coal seam, the vertical stress increase area of ​​the C5 coal seam increases and begins to approach the vertical stress peak position. At this time, if the tunnel face continues to advance, the distance between the tunnel face and the C5 coal seam will continue to decrease, and the C5 coal seam will get closer and closer to the peak position. When it reaches the peak position, it is just in a state of limit equilibrium. When the tunnel face is 10m away from the C5 coal seam, the vertical stresses of the tunnel vault at different positions in front of the tunnel face and 2m above are extracted, and the distance to the tunnel face position and the vertical stress diagram are drawn.

[0108] The vertical stress in front of the tunnel face increases first, reaches the peak value, then begins to decrease and eventually stabilizes. The maximum vertical stress at the tunnel crown appears at 1.7m in front of the face, and the maximum vertical stress at 2m above the tunnel crown appears at 1.1m. The width from the face to the vertical stress peak can be considered as the limit equilibrium zone. The width of the limit equilibrium zone is used as the thickness of the reserved rock wall, and the influence of gas pressure and blasting disturbance is considered, and a certain safety factor is taken.

[0109] It is recommended that the thickness of the reserved rock wall for coal blasting be set to 2.0m.

[0110] Corresponding to the above method, this embodiment further provides a system for calculating the critical thickness of a tunnel coal uncovering safety rock wall, which is characterized by comprising:

[0111] Construction module, used to build rock wall models;

[0112] The first calculation module is used to obtain a calculation formula for the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone;

[0113] A determination module is used to determine the value of the width of the limit equilibrium zone based on the calculation formula and coal seam parameters.

[0114] The second calculation module is used to determine the thickness of the rock wall reserved for coal blasting based on the gas pressure and blasting disturbance and the value of the limit equilibrium zone width.

[0115] The beneficial effects of the present invention are as follows:

[0116] The present invention constructs a rock wall model, based on the limit equilibrium theory, obtains the calculation formula for the width of the limit equilibrium zone according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, determines the calculation formula for the critical rock wall thickness affected by comprehensive factors, and reasonably reserves the rock wall thickness through numerical simulation, thereby achieving safe coal uncovering.

[0117] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0118] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for calculating the critical thickness of a tunnel coal-uncovering safety rock wall, characterized in that: The following steps are involved: construct rock wall models; Based on the limit equilibrium theory, the calculation formula of the limit equilibrium zone width is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the limit equilibrium zone width; Based on the calculation formula, the value of the width of the limit equilibrium zone is determined according to coal seam parameters; Based on the gas pressure and blasting disturbance, the thickness of the rock wall reserved for coal blasting is determined according to the value of the limit equilibrium zone width; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face; According to the stress state of the unit body in the limit equilibrium zone, the force equation in the x-axis direction when the unit body is in the limit equilibrium state is determined; the force equation is: Among them, σ x is the horizontal stress; σ z is the vertical stress, is the internal friction angle of the rock, c is the cohesion of the rock; h is the excavation height of the tunnel, dx is the unit width; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The stress equilibrium equation in the rock wall is determined according to the stress state of the unit body in the limit equilibrium zone; the stress equilibrium equation is: Among them, τ xz is the shear stress in the xz plane direction; At the junction of the coal seam and the limit equilibrium zone, it satisfies: σ x =βσ z =βKγH; Based on the limit equilibrium theory, the calculation formula for the width of the equilibrium zone is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The vertical stress equation is determined according to the force equation and the stress equilibrium equation; the vertical stress equation is: Among them, β is the lateral pressure coefficient, x is the distance from any point in the limit equilibrium zone to the rock wall in front of the tunnel face; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The calculation formula for determining the width of the limit equilibrium zone is determined by taking into account the coal seam inclination, coal seam gas pressure and boundary conditions; the calculation formula for the width of the limit equilibrium zone is: Among them, σ x =βσ z =βKγH, α is the coal seam inclination, P is the coal seam gas pressure, K is the stress concentration factor; γ is the average bulk density of the overlying stratum of the tunnel, H is the buried depth of the tunnel face; the boundary condition is σ z =KγH+Pcosα.

2. The method for calculating the critical thickness of the safe rock wall for coal mining in a tunnel according to claim 1 is characterized in that: The top and bottom of the rock wall in the rock wall model are both subject to vertical ground stress, and the rock wall serves as the top constraint and bottom constraint of the rock wall model.

3. The method for calculating the critical thickness of the safe rock wall for coal mining in a tunnel according to claim 1 is characterized in that: The factors affecting the width of the limit equilibrium zone include: tunnel excavation height, average bulk density of the strata overlying the tunnel, tunnel face burial depth, stress concentration coefficient, rock internal friction angle and cohesion, coal seam inclination and gas pressure.

4. The method for calculating the critical thickness of the safe rock wall for coal mining in a tunnel according to claim 1, characterized in that: The coal seam parameters include: coal seam inclination, gas pressure, internal friction angle of carbonaceous mudstone, cohesion, and compressive strength.

5. A system for calculating the critical thickness of a tunnel coal-uncovering safety rock wall, characterized in that: include: Construction module, used to build rock wall models; The first calculation module is used to obtain a calculation formula for the width of the limit equilibrium zone based on the limit equilibrium theory and according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone; A determination module, used to determine the value of the limit equilibrium zone width according to the coal seam parameters based on the calculation formula; The second calculation module is used to determine the thickness of the rock wall reserved for coal blasting based on the gas pressure and blasting disturbance and the value of the limit equilibrium zone width; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: Determine the stress state of the unit body in the limit equilibrium zone according to the limit equilibrium theory and the stress distribution characteristics in front of the tunnel face; According to the stress state of the unit body in the limit equilibrium zone, the force equation in the x-axis direction when the unit body is in the limit equilibrium state is determined; the force equation is: Among them, σ x is the horizontal stress; σ z is the vertical stress, is the internal friction angle of the rock, c is the cohesion of the rock; h is the excavation height of the tunnel, dx is the unit width; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The stress equilibrium equation in the rock wall is determined according to the stress state of the unit body in the limit equilibrium zone; the stress equilibrium equation is: Among them, τ xz is the shear stress in the xz plane direction; At the junction of the coal seam and the limit equilibrium zone, it satisfies: σ x =βσ z =βKγH; Based on the limit equilibrium theory, the calculation formula for the width of the equilibrium zone is obtained according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The vertical stress equation is determined according to the force equation and the stress equilibrium equation; the vertical stress equation is: Among them, β is the lateral pressure coefficient, x is the distance from any point in the limit equilibrium zone to the rock wall in front of the tunnel face; The calculation formula for the width of the limit equilibrium zone is obtained based on the limit equilibrium theory according to the stress distribution characteristics in front of the tunnel face and the influencing factors of the width of the limit equilibrium zone, including: The calculation formula for determining the width of the limit equilibrium zone is determined by taking into account the coal seam inclination, coal seam gas pressure and boundary conditions; the calculation formula for the width of the limit equilibrium zone is: Among them, σ x =βσ z =βKγH, α is the coal seam inclination, P is the coal seam gas pressure, K is the stress concentration factor; γ is the average bulk density of the overlying stratum of the tunnel, H is the buried depth of the tunnel face; the boundary condition is σ z =KγH+Pcosα.

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