Deep gob-side entry driving support method based on plastic zone control

Abstract

The invention belongs to the technical field of coal mining, and relates to a deep gob-side entry driving support method based on plastic zone control, which comprises the following steps: acquiring roadway radius, principal stress ratio, principal stress deflection angle, support stress and cohesive force and internal friction angle of roadway surrounding rock before support; substituting into a preset equation; according to a preset equation, roadway surrounding rock cohesion and internal friction angles under different supporting stresses are determined, and then the roadway radius, the main stress ratio, the main stress deflection angle, the different supporting stresses and the corresponding roadway surrounding rock cohesion and internal friction angles are substituted into a constructed roadway surrounding rock plastic zone boundary analytical equation. The method comprises the following steps: determining surrounding rock plastic zone boundary forms corresponding to different support stresses, then determining the support stress corresponding to a stable form in a plurality of surrounding rock plastic zone boundary forms as the optimal support stress, and finally obtaining the optimal row distance between anchor rods and cables, thereby determining the number and the arrangement mode of the anchor rods and cables according to the optimal row distance between the anchor rods and cables. And stable control of deep gob-side entry driving surrounding rock is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining and relates to a deep goaf-side roadway support method based on plastic zone control. Background Art

[0002] As coal mining progresses deeper, the mining environment undergoes dramatic changes. The deep environment characterized by "three highs and one disturbance" (high ground stress, high gas pressure, high temperature, and intense mining disturbance) leads to frequent disasters in deep roadways, particularly in deep gob-side driving. While deep gob-side driving can significantly reduce the size of coal pillars and increase coal recovery rates, it poses significant challenges for roadway maintenance. Firstly, weak interlayers are common in coal roadway roofs. When such interlayers exist in gob-side driving roofs, the difficulty of controlling the surrounding rock in gob-side driving increases significantly due to their weak cementation and poor self-stability. Secondly, under the influence of mining at the upper working face, the surrounding rock in gob-side driving experiences a shift in principal stress direction under high deviatoric stress, forming a butterfly-shaped plastic zone with deflection and exhibiting asymmetric failure characteristics.

[0003] To address the above issues, numerous scholars have conducted relevant theoretical research. However, existing research still has shortcomings: existing research on the plastic zone of tunnel surrounding rock mostly focuses on theoretical derivation. There is a lack of systematic and in-depth research on the analytical expression of the boundary line of the surrounding rock plastic zone under the action of support stress, which makes it difficult to accurately reflect the influence of support stress on the evolution of the plastic zone in actual engineering. For gob-side tunneling with weak interlayer roof, although existing research has explored its failure mechanism, it has not yet formed a comprehensive and quantitative analysis method for the surrounding rock failure mode under such special roof conditions. In terms of surrounding rock control, existing control strategies and technologies are mostly based on experience and qualitative analysis, lacking a scientific and systematic control principle based on the morphology of the surrounding rock plastic zone. This makes it difficult to effectively solve the problem of surrounding rock stability control in deep gob-side tunneling, and the effect of ensuring surrounding rock stability in actual engineering applications is limited. Therefore, further in-depth research on the evolution law of the plastic zone in gob-side tunneling and its control principle is urgently needed to achieve stable control of the surrounding rock of deep gob-side tunneling. Summary of the Invention

[0004] The purpose of the present invention is to provide a deep goaf-side tunnel support method based on plastic zone control, which can deduce the evolution law of the plastic zone of the goaf-side tunnel and its control principle, and realize stable control of the surrounding rock of the deep goaf-side tunnel according to the evolution law of the plastic zone of the goaf-side tunnel and its control principle.

[0005] To achieve the above objectives, the present invention provides the following technical solutions: A deep gob-side roadway support method based on plastic zone control is characterized by comprising the following steps: Obtain the tunnel radius, principal stress ratio, principal stress deflection angle, support stress, and the cohesion and internal friction angle of the tunnel surrounding rock before support.

[0006] The tunnel radius, support stress, and surrounding rock cohesion and internal friction angle before support are substituted into the preset equation, which is used to describe the relationship between the support stress and the surrounding rock cohesion and internal friction angle before support.

[0007] The cohesion and internal friction angle of the tunnel surrounding rock under different support stresses are determined according to the preset equations.

[0008] The tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding tunnel surrounding rock cohesion and internal friction angle are substituted into the constructed analytical equation of the tunnel surrounding rock plastic zone boundary to determine the boundary morphology of the surrounding rock plastic zone corresponding to different support stresses.

[0009] The support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms is determined as the optimal support stress.

[0010] The optimal anchor cable spacing is obtained according to the optimal support stress, and the number and arrangement of anchor cables are determined according to the optimal anchor cable spacing.

[0011] The present invention is also characterized in that: The preset equation is: , Where, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses, is the anchor preload, is the anchor cable diameter, is the friction coefficient between the anchor and the surrounding rock. In the threaded steel anchor support system, , is the roadway radius, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, It is the internal friction angle of the tunnel surrounding rock before support.

[0012] The analytical equation of the plastic zone boundary of the tunnel surrounding rock is constructed as follows: , Where, 、 、 respectively The quadratic term coefficient, linear term coefficient and constant term, is the minimum principal stress, is the roadway radius, is the distance between the unit body of the surrounding rock and the center of the roadway, is the principal stress ratio, that is, the ratio of the maximum principal stress to the minimum principal stress, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, is the internal friction angle of the surrounding rock of the roadway before support, and are all about the principal stress deflection angle The coefficient of , , is the angle between the unit body direction and the horizontal direction, is the principal stress deflection angle, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses.

[0013] The number and arrangement of anchor cables are determined based on the optimal spacing between anchor cables: , Where, and are the anchor cable spacing and row spacing, is the anchor preload, is the optimal support stress.

[0014] When determining the support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms as the optimal support stress, it is determined by analyzing the change law of the surrounding rock plastic zone boundary under different support stresses.

[0015] The changing pattern of the boundary of the surrounding rock plastic zone is as follows: when the principal stress ratio is in the range of 0.5~1.75, the surrounding rock plastic zone mainly presents a circle or ellipse; when the principal stress ratio is less than 0.5 or greater than 1.75, the boundary line of the tunnel surrounding rock plastic zone changes into a butterfly shape; when the principal stress deflection angle gradually increases, the butterfly leaf plastic zone shifts from the shoulder to the roof and the two sides; when the support stress gradually increases, the boundary line of the surrounding rock plastic zone transitions from a butterfly shape to an ellipse.

[0016] When determining the number and arrangement of anchor cables based on the optimal anchor cable spacing, the optimal anchor cable density is obtained by taking the inverse of the optimal anchor cable spacing. The required optimal total number of anchor cables is obtained based on the tunnel surface area and the optimal anchor cable density. The optimal arrangement of the roof anchor cables is determined based on the distribution state of the weak interlayer in the roof.

[0017] The deep goaf-side roadway support method based on plastic zone control of the present invention has the following advantages: The present invention obtains the tunnel radius, principal stress ratio, principal stress deflection angle, support stress and the cohesion and internal friction angle of the tunnel surrounding rock before support, and then substitutes the tunnel radius, support stress and the cohesion and internal friction angle of the tunnel surrounding rock before support into a preset equation. The preset equation is used to describe the relationship between the support stress and the cohesion and internal friction angle of the tunnel surrounding rock before support. The cohesion and internal friction angle of the tunnel surrounding rock under different support stresses are then determined according to the preset equation. The tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding cohesion and internal friction angle of the tunnel surrounding rock are then substituted into the constructed analytical equation of the plastic zone boundary of the tunnel surrounding rock to determine the boundary morphology of the surrounding rock plastic zone corresponding to different support stresses. The support stress corresponding to the stable morphology among multiple boundary morphologies of the surrounding rock plastic zone is determined as the optimal support stress. Finally, the optimal anchor cable spacing is obtained according to the optimal support stress, and the number and arrangement of anchor cables are determined according to the optimal anchor cable spacing, thereby realizing stable control of the surrounding rock of deep goaf-side tunneling. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall process structure of the present invention.

[0019] Figure 2 Schematic diagram of the stress state of the surrounding rock of the tunnel of the present invention.

[0020] Figure 3 Schematic diagram of the maximum shear stress strength criterion in the present invention.

[0021] Figure 4 Schematic diagram of principal stress deflection in the present invention.

[0022] Figure 5 Schematic diagram of the plastic zone morphology and radius variation under different lateral pressure coefficients in the present invention.

[0023] Figure 6 Schematic diagram of the plastic zone boundary for different principal stress deflection angles in the present invention.

[0024] Figure 7 Schematic diagram of the plastic zone boundary under different support stresses in the present invention.

[0025] Figure 8 This is a schematic diagram of the geological conditions and numerical model of the return air channel 1692 (1) in the present invention.

[0026] Figure 9 Schematic diagram of the evolution law of the plastic zone of the tunnel surrounding rock under different principal stress ratios in the present invention.

[0027] Figure 10 Schematic diagram of the distribution of plastic zones of surrounding rocks under different principal stress deflection angles in the present invention.

[0028] Figure 11Schematic diagram of the distribution of plastic zone of surrounding rock of roadway with weak interlayer roof under different principal stress deflection angles in the present invention.

[0029] Figure 12 Schematic diagram of the influence of weak interlayers on the plastic zone in the present invention, where (a) represents different weak interlayer thicknesses, (b) represents different weak interlayer positions, and (c) represents different numbers of weak layers.

[0030] Figure 13 Schematic diagram of the development of the butterfly-shaped plastic zone and the distortion of the weak interlayer plastic zone in the present invention.

[0031] Figure 14 This is a schematic diagram of the original support design and surrounding rock failure characteristics of the return air tunnel in the present invention.

[0032] Figure 15 This is a schematic diagram of the optimized support parameters and tunnel support effect of the return air tunnel in the present invention.

[0033] Figure 16 Schematic diagram of the roof delamination and surrounding rock peeping results of the return air tunnel in the present invention, where (a) is the surrounding rock deformation during excavation, (b) is the roof delamination during excavation, (c) is the surrounding rock deformation during mining, and (d) is the roof delamination during mining. DETAILED DESCRIPTION

[0034] The technical solutions in the present invention will be described clearly and in detail below with reference to the accompanying drawings. In the description of the embodiments of the present invention, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, such as A and / or B, which can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present invention, "multiple" refers to two or more than two. The following terms "first" and "second" are used for descriptive purposes only and cannot be understood as implying or suggesting relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0035] like Figure 1 As shown, the present invention provides a deep goaf-side roadway support method based on plastic zone control, comprising the following steps: Obtain the tunnel radius, principal stress ratio, principal stress deflection angle, support stress, and the cohesion and internal friction angle of the tunnel surrounding rock before support; Substituting the tunnel radius, support stress, and surrounding rock cohesion and internal friction angle before support into a preset equation, the preset equation is used to describe the relationship between the support stress and the surrounding rock cohesion and internal friction angle before support; The cohesion and internal friction angle of the tunnel surrounding rock under different support stresses are determined according to the preset equations.

[0036] The tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding tunnel surrounding rock cohesion and internal friction angle are substituted into the constructed analytical equation of the tunnel surrounding rock plastic zone boundary to determine the boundary morphology of the surrounding rock plastic zone corresponding to different support stresses.

[0037] The support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms is determined as the optimal support stress.

[0038] The optimal anchor cable spacing is obtained according to the optimal support stress, and the number and arrangement of anchor cables are determined according to the optimal anchor cable spacing.

[0039] In summary, the present invention obtains the tunnel radius, principal stress ratio, principal stress deflection angle, support stress and the tunnel surrounding rock cohesion and internal friction angle before support, and then substitutes the tunnel radius, support stress and the surrounding rock cohesion and internal friction angle before support into a preset equation. The preset equation is used to describe the relationship between the support stress and the tunnel surrounding rock cohesion and internal friction angle before support, and then determines the tunnel surrounding rock cohesion and internal friction angle under different support stresses according to the preset equation. Then, the tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding tunnel surrounding rock cohesion and internal friction angle are substituted into the constructed tunnel surrounding rock plastic zone boundary analytical equation to determine the surrounding rock plastic zone boundary morphology corresponding to different support stresses, and then determines the support stress corresponding to the stable morphology among multiple surrounding rock plastic zone boundary morphologies as the optimal support stress. Finally, the optimal anchor cable spacing is obtained according to the optimal support stress, and the number and arrangement of anchor cables are determined according to the optimal anchor cable spacing, thereby realizing stable control of the surrounding rock of deep goaf excavation.

[0040] Among them, the preset equation is: , Where, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses, is the anchor preload, is the anchor cable diameter, is the friction coefficient between the anchor and the surrounding rock. In the threaded steel anchor support system, , is the roadway radius, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, It is the internal friction angle of the tunnel surrounding rock before support.

[0041] Among them, the constructed analytical equation of the plastic zone boundary of the tunnel surrounding rock is: , Where, 、 、 respectively The quadratic term coefficient, linear term coefficient and constant term, is the minimum principal stress, is the roadway radius, is the distance between the unit body of the surrounding rock and the center of the roadway, is the principal stress ratio, that is, the ratio of the maximum principal stress to the minimum principal stress, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, is the internal friction angle of the surrounding rock of the roadway before support, and are all about the principal stress deflection angle The coefficient of , , is the angle between the unit body direction and the horizontal direction, is the principal stress deflection angle, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses.

[0042] The number and arrangement of anchor cables are determined according to the optimal spacing between anchor cables: , Where, and are the anchor cable spacing and row spacing, is the anchor preload, is the optimal support stress.

[0043] Further, if Figure 2 、 Figure 3 、 Figure 4 As shown in Figure 2, the specific steps for constructing the analytical equation of the plastic zone boundary of the roadway surrounding rock are as follows: Step 1: Analyze the tunnel surrounding rock mechanics with the help of polar coordinate system, where: P 1 and P 3 are the ratios of the maximum principal stress to the minimum principal stress (hereinafter referred to as principal stress ratio), and their values ​​are p and p , is the ratio of the maximum principal stress to the minimum principal stress, 、 and are the radial stress, tangential stress and shear stress borne by the unit body respectively. According to the A-type stress state of the tunnel, it can be divided into the superposition of B-type stress state and C-type stress state by the elastic mechanics superposition method, as shown in Figure 2 Type B and C stress states. Type B stress state is the stress solution of tunnel surrounding rock under maximum and minimum principal stress, and the radial stress, tangential stress and shear stress of surrounding rock are respectively 、 and , its mechanical formula in polar coordinates is:

[0044] , Type C stress state is the stress state of the tunnel surrounding rock under the action of anchor cable support, in which the radial stress and tangential stress of the surrounding rock are respectively and , its mechanical formula in polar coordinates is: , Step 2: According to the superposition principle of elastic mechanics, the stress solution under the B-type stress state and the stress solution under the C-type stress state are superimposed to obtain the surrounding rock stress solution under the A-type stress state. The specific formula is: , Step 3, according to the Mohr stress circle (see Figure 4 ), we can get the relationship between the maximum principal stress, the minimum principal stress and the stress components of the unit body. Assuming that the tunnel surrounding rock is a continuous transition from elastic to plastic, the elastic limit state is given by and A moiré intensity envelope is determined, such as Figure 3 As shown, the relationship between the maximum principal stress and the minimum principal stress can be obtained, and the specific formula is as follows: , , Step 4: Combine the formulas of step 2 and step 3 to obtain the plastic condition obtained by the Mohr stress circle under the limit state, that is, the implicit analytical expression of the plastic zone boundary of the circular roadway surrounding rock. The specific formula is as follows: , , Where, for The algebraic expression of the eighth-order coefficient, for The sixth-order coefficient algebraic expression, for The algebraic expression of the fourth-order coefficient, for Algebraic expression of quadratic coefficients, is the algebraic expression of the constant term.

[0045] Step 5: Affected by the mining of the upper working face, shear stress appears in the surrounding rock of the gob-driven tunnel. The principal stress direction of the surrounding rock is not parallel to the vertical or horizontal direction, but deflected relative to the vertical or horizontal direction, such as Figure 4 When the principal stress deflects, the angle between the principal stress deflection and the numerical direction is , clockwise is positive, thus the implicit analytical expression of the boundary of the deflection plastic zone of the surrounding rock of the circular tunnel under the support effect can be obtained.

[0046] , Where, for The algebraic expression of the eighth-order coefficient, for The sixth-order coefficient algebraic expression, for The algebraic expression of the fourth-order coefficient, for The algebraic expression of the quadratic coefficient, is the algebraic expression of the constant term.

[0047] Step 6: Stress on the inner wall of the tunnel surrounding rock It mainly includes the support resistance brought by the anchor cable, and its result can be calculated by the anchor cable preload and the spacing between anchor cables. The specific formula is as follows: , Where, is the anchor preload, and are the anchor cable spacing and row spacing respectively.

[0048] In step 7, after the surrounding rock is supported by anchor cables, the anchor cables and the surrounding rock form a unified bearing structure. According to the surrounding rock strength enhancement theory, the mechanical properties of the anchored rock mass are improved, and the cohesion and internal friction angle of the roadway surrounding rock before support are increased. The improved cohesion and internal friction angle of the roadway surrounding rock, that is, the cohesion and internal friction angle of the roadway surrounding rock under different support stresses, are expressed as follows: , Where, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses, is the anchor preload, is the anchor cable diameter, is the friction coefficient between the anchor and the surrounding rock. In the threaded steel anchor support system, , is the roadway radius, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the tunnel surrounding rock before support, is the internal friction angle of the tunnel surrounding rock before support.

[0049] Step 8: Combining steps 5, 6, and 7, the analytical equation of the plastic zone boundary of the tunnel surrounding rock under the action of support stress can be obtained.

[0050] Among them, when determining that the support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms is the optimal support stress, it is determined by analyzing the change law of the surrounding rock plastic zone boundary under different support stresses.

[0051] Among them, the influence of the principal stress ratio on the boundary of the plastic zone is as follows: when the principal stress ratio is in the range of 0.5~1.75, the plastic zone of the surrounding rock mainly presents a circular or elliptical shape; when the principal stress ratio is less than 0.5 or greater than 1.75, the boundary line of the plastic zone of the tunnel surrounding rock presents a butterfly shape.

[0052] Further, when studying the influence of principal stress ratio on the boundary of plastic zone, the details are as follows: Take the roadway radius a is 2.7m, the minimum principal stress P 3 is 25MPa, support stress p 0 is 0MPa, the cohesion of the surrounding rock of the roadway before support C The pressure is 1.0 MPa, the internal friction angle is 29°, the principal stress deflection angle is 0°, and the above parameters are fixed. The principal stress ratio is set to 0.3, 0.4, 0.6, 0.8, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5 and 2.8. Substituting the above parameters into the above formula, the distribution state of the plastic zone of the surrounding rock under different principal stress ratios can be obtained, as shown in the following example: Figure 5 shown.

[0053] like Figure 5As shown in the figure, the principal stress ratio has a significant impact on the morphology of the plastic zone of the roadway surrounding rock. When the principal stress ratio increases from 0.3 to 1.0, the boundary of the surrounding rock plastic zone gradually changes from a butterfly shape to a circle; when it increases from 1.0 to 2.8, the boundary of the plastic zone gradually changes from a circle to a butterfly shape. Analysis of the variation of the plastic zone radius at the roof and shoulder shows that when it is in the range of 0.6-1.75, the surrounding rock plastic zone mainly presents a circular or elliptical shape, and the plastic zone radius changes slowly, indicating a slow expansion zone. When it is in the range of 0.3-0.4 and 2-2.8, the plastic zone radius changes significantly, and the plastic zone expands rapidly, especially the butterfly leaf plastic zone rapidly expanding radially toward the deep surrounding rock. As the further increase of , the butterfly leaf plastic zone gradually expands in the tangential direction of the roadway while expanding radially.

[0054] Among them, the influence of the principal stress deflection angle on the boundary of the plastic zone is as follows: when the principal stress deflection angle gradually increases, the plastic zone of the butterfly leaf shifts from the shoulder socket to the top plate and the two sides.

[0055] Furthermore, the influence of the principal stress deflection angle on the plastic zone boundary is studied as follows: For gob-side tunneling, the stress of the surrounding rock in the gob-side tunneling is deflected by the lateral support pressure. The principal stress ratio is fixed at 2.5, other parameters remain unchanged, and the principal stress deflection angle is set to 0-90°. The distribution of the boundary line of the plastic zone of the tunnel surrounding rock under different deflection angles can be obtained, such as Figure 6 shown.

[0056] Under different principal stress deflection angles, the plastic zone of the roadway surrounding rock consistently exhibits a significant butterfly-shaped characteristic. With the deflection of the principal stress direction, the position of the butterfly blades in the butterfly-shaped plastic zone changes accordingly, reflecting the dynamic shift in the direction of the maximum development radius of the plastic zone. For the roof, when the principal stress deflection angle is 0°, the butterfly blade plastic zone points to the shoulder area of ​​the roadway, indicating that the maximum development radius of the plastic zone is located at the shoulder. As the principal stress deflection angle gradually increases, the butterfly blades of the butterfly-shaped plastic zone gradually migrate from the shoulder area to the roof. When the principal stress deflection angle reaches 30°-60°, the maximum development radius of the plastic zone is located in the roof, and the two sides of the roadway are also within the maximum radius of the plastic zone. Further, when the principal stress deflection angle is between 60° and 90°, the development direction of the butterfly blade plastic zone gradually shifts from the roof area to the shoulder area. It should be emphasized that when the butterfly-leaf plastic zone is located at the roof position, the increase in the principal stress ratio will cause the butterfly-leaf plastic zone in the roof area to expand rapidly, thereby having a significant adverse effect on the stability of the roof. The above shows that the principal stress deflection angle not only significantly affects the distribution pattern and development direction of the plastic zone of the tunnel surrounding rock, but also has an important impact on the stability of the surrounding rock at different locations.

[0057] Among them, the influence of support stress on the boundary of the plastic zone is as follows: when the support stress gradually increases, the boundary line of the plastic zone of the surrounding rock transitions from a butterfly shape to an ellipse.

[0058] Furthermore, the influence of support stress on the boundary of the plastic zone is studied as follows: Assuming that the tunnel is supported immediately after excavation, the value is taken as 2.5, the deflection angle is 40°, the anchor support resistance is 120 MPa, and other parameters are kept unchanged. The support stress is set to 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa and 1.2 MPa.

[0059] Substituting the above support stress into the formula of internal friction angle and cohesion value under different support stress, the cohesion and internal friction angle of the tunnel surrounding rock after surrounding rock support can be obtained, as shown in Table 1. Substituting the changed cohesion and internal friction angle of the tunnel surrounding rock into the implicit solution formula of the plastic zone boundary under the surrounding rock strength enhancement of the anchor cable can obtain the distribution form of the plastic zone after the surrounding rock strength enhancement under the support effect, as shown in Figure 7 shown.

[0060] Table 1 Changes in internal friction angle and cohesion of tunnel surrounding rock under different support stresses Depend on Figure 7 It can be seen that with the increase of support stress, the radius of the butterfly-shaped plastic zone of the tunnel surrounding rock decreases significantly, and the radial range and tangential range of the butterfly-shaped plastic zone gradually shrink. When the support stress reaches 0.8 MPa, the shape of the plastic zone begins to gradually change from butterfly to approximately elliptical. With the further increase of support stress, the plastic zone of the surrounding rock gradually presents a circular feature. At this time, the plastic zone of the surrounding rock reaches a stable form, and its corresponding support stress is the optimal support stress. This change shows that the increase in support stress not only changes the constraint effect of anchor rods and anchor cables on the tunnel surface, but also has a significant impact on the internal friction angle and cohesion parameters of the tunnel surrounding rock.

[0061] Therefore, by combining grouting and other measures to improve the internal friction angle and cohesion of the tunnel surrounding rock, the radius of the plastic zone can be further reduced, providing an effective means for controlling the stability of the tunnel surrounding rock.

[0062] Among them, the principal stress ratio, principal stress deflection angle, support stress, cohesion and internal friction angle of the tunnel surrounding rock before support are substituted into the analytical equation of the plastic zone boundary of the tunnel surrounding rock under the action of support stress. Combined with the influence of the principal stress ratio, principal stress deflection angle and support stress on the plastic zone boundary, the optimal support stress required to maintain the stability of the plastic zone is obtained: First, according to the influence of principal stress ratio, principal stress deflection angle and support stress on the boundary of plastic zone, the control principle of plastic zone in gob-side roadway driving is obtained. The control principle of plastic zone in gob-side roadway driving is to weaken shear dilatancy and eliminate distortion.

[0063] Then, the principal stress ratio, principal stress deflection angle, support stress, cohesion and internal friction angle of the tunnel surrounding rock before support are substituted into the analytical equation of the plastic zone boundary of the tunnel surrounding rock under the action of support stress, and combined with the plastic zone control principle of goaf-side roadway excavation, the optimal support stress required to maintain the stability of the plastic zone is obtained.

[0064] Among them, when determining the number and arrangement of anchor cables based on the optimal anchor cable spacing, the optimal anchor cable density is obtained by taking the inverse of the optimal anchor cable spacing. The required optimal total number of anchor cables is obtained based on the surface area of ​​the tunnel and combined with the optimal anchor cable density. The optimal arrangement of the roof anchor cables is determined based on the distribution state of the weak interlayer in the roof.

[0065] Example 1 The main mining coal seam 11-2 of the 1692 (1) working face at the -862m level of a coal mine is the 11-2 coal seam. The average thickness of the coal seam is 2.8m, the coal seam inclination is 2°~7°, and the average is 5°. The direct roof and basic roof are 5.4m and 13.8m sandy mudstone respectively. The weak interlayer in the coal roadway roof is mainly composed of thin coal lines with a thickness of 0.4m. The 1682 (1) working face in the north has been completed. The 1692 (1) return air roadway is excavated along the 1682 (1) goaf. According to the 1692 (1) return air roadway roof and floor plate column chart, the FLAC 3D The numerical simulation software was used to establish a numerical model with a length × width × height of 50m × 1m × 50m and a tunnel size of 5.4m × 3.6m, and the units around the tunnel were encrypted, such as Figure 8 The lithologic parameters are shown in Table 2. The Mohr-Coulomb constitutive model is adopted, and the ratio of the maximum principal stress to the minimum principal stress imposed by the model is 2.5.

[0066] Table 2 Model parameters like Figure 9 As shown in Figure 2, the evolution law of the plastic zone of the surrounding rock of the return airway under the conditions of a principal stress deflection angle of 40° and different principal stress ratios, where the principal stress ratio is the ratio of the maximum principal stress to the minimum principal stress. Figure 7Analysis shows that when θ = 0.4, the surrounding rock plastic zone exhibits a butterfly-shaped distribution. As the principal stress ratio increases to 1, the plastic zone gradually evolves into a circular shape. When the principal stress ratio is between 1 and 1.75, the plastic zone gradually transforms from a circular shape to an elliptical shape, but the range of the plastic zone does not change significantly. However, when the principal stress ratio exceeds 1.75, the surrounding rock butterfly-shaped plastic zone significantly expands deeper, showing a malignant development trend. Therefore, θ = 1.75 is a critical dividing point where the expansion of the surrounding rock plastic zone shifts from slow to accelerated. This result is highly consistent with theoretical calculations. Extracting the maximum shear stress at different principal stress ratios also reveals that during the expansion of the butterfly-shaped plastic zone, the maximum shear stress gradually develops deeper into the surrounding rock, resulting in shear failure-dominated expansion of the butterfly-shaped plastic zone. During the expansion process, the plastic zone width gradually increases and exhibits significant volume expansion. These phenomena indicate that the butterfly-shaped plastic zone is driven by a strong shear dilatancy effect under high deviatoric stress conditions and expands deeper along the direction of shear stress.

[0067] like Figure 10 The figure shows the distribution pattern of the plastic zone in the surrounding rock of the return airway under the conditions of a principal stress ratio of 2.5 and different principal stress deflection angles (0°-90°). As the principal stress deflection angle increases, the butterfly-shaped plastic zone of the surrounding rock undergoes significant deflection. The deflection angle is basically consistent with the principal stress deflection angle and highly consistent with the theoretical calculation results. This shows that the butterfly-shaped plastic zone in the surrounding rock of the roadway has a clear directional characteristic, and the deflection of the principal stress directly determines the spatial distribution direction of the maximum radius of the plastic zone.

[0068] When the principal stress deflection angle is between 30° and 60°, the butterfly-leaf plastic zone is primarily distributed in the roof, floor, and side walls of the roadway. For the roof, the maximum fracture depth of the plastic zone is concentrated in these areas, indicating that within this angle range, the roof and side walls are key locations for stress concentration and fracture development. Principal stress deflection has a direct impact on the distribution of the plastic zone in the roadway surrounding rock, particularly at specific deflection angles, which can alter the location and morphology of the plastic zone. This result allows for precise determination of the maximum plastic failure range of the roadway surrounding rock, providing a basis for optimizing roadway support schemes.

[0069] According to the 1692 (1) columnar diagram of the top and bottom plates of the return air channel, there is a weak interlayer at the 5.4m position of the top plate. Figure 11 Analysis shows that when the weak interlayer in the roof is subjected to different principal stress deflection angles, the distribution law of its plastic zone shows significant differences. When the principal stress deflection angles are 0° and 90°, the weak interlayer within the width of the tunnel roof will suffer significant delamination failure, and the delamination failure is mainly concentrated in the area directly above the roof. When the principal stress deflection angle is 10°~80°, the delamination failure of the weak interlayer in the roof shows directional characteristics, and the damage area gradually migrates from the left roof of the tunnel to the right, showing a trend of gradual shift with the deflection angle.

[0070] Especially when the principal stress deflection angle is in the range of 40°~60°, the delamination failure of the butterfly-shaped plastic zone of the roof and the weak interlayer are connected through the shear rupture zone, which significantly reduces the bearing capacity of the roof and eventually leads to the collapse and instability of the roof. This phenomenon reveals the vicious expansion mode of the butterfly-shaped plastic zone under the coupling of the weak interlayer and the principal stress deflection angle.

[0071] According to the on-site data, the weak interlayers in the roof are not distributed non-uniformly along the roadway direction. Their thickness, layer position and number of layers are different. In order to study the impact of these differences on the stability of the surrounding rock, the thickness, layer position and number of different weak interlayers were studied. Figure 12 As shown in Figure 2, the analysis shows that with the increase of the thickness of the weak interlayer, the width of the delamination failure gradually decreases, while the thickness of the delamination failure shows an increasing trend, as shown in Figure 2. Figure 12 As shown in (a), it shows that a larger thickness of the weak interlayer is more likely to form a significant delamination space, thereby increasing the risk of roof collapse. When the height of the weak interlayer increases, the degree of delamination damage gradually decreases. When the weak interlayer is located at a height of 10m above the roof, the delamination damage tends to completely disappear, indicating that the interlayer height has a significant impact on the roof failure mode. A higher interlayer position can significantly alleviate the occurrence of delamination damage, such as Figure 12 As shown in (b), at the same time, as the number of weak interlayers increases, the plastic zone of the roof gradually expands in the horizontal direction. When multiple weak interlayers work together, each interlayer will experience delamination failure, and the shear fracture of the roof will penetrate each weak interlayer, significantly increasing the possibility of roof instability and collapse, as shown in Figure 2. Figure 12 (c) shown.

[0072] The results of theoretical analysis and numerical simulation show that under high deviatoric stress conditions, the tunnel surrounding rock forms a plastic zone characterized by a butterfly shape under the driving force of strong shear dilatancy and expands to a deeper level. The morphology of this butterfly-shaped plastic zone reflects the typical characteristics of surrounding rock failure under high deviatoric stress, and is similar to the "X"-shaped fracture expansion form in the uniaxial compression test of rock, indicating that its failure mode has a certain universality under high deviatoric stress. However, when there are complex geological conditions such as weak interlayers in the tunnel surrounding rock, the morphology of the butterfly-shaped plastic zone will be significantly distorted. This distortion is manifested as the plastic zone being disturbed by special geological conditions during the expansion process, thereby causing unconventional malignant expansion. Taking the weak interlayer as an example, when the butterfly-shaped plastic zone extends to the interlayer area, the butterfly-shaped plastic zone no longer extends to the depth, but expands along the direction of the weak interlayer, such as Figure 13As shown in Figure 2 . Furthermore, when encountering other special geological conditions, the butterfly plastic zone may exhibit different distortion forms, the specific morphology of which depends on the type and characteristics of the geological conditions. Therefore, the butterfly plastic zone is a typical form of surrounding rock failure under high deviatoric stress, and the distortion of the butterfly plastic zone is caused by the interference of special geological conditions on its expansion path. The expansion of the butterfly plastic zone and the interconnection of the distorted plastic zone will significantly exacerbate the instability of the tunnel surrounding rock.

[0073] 1692 (1) The original support design of the return air tunnel is as follows: ① The middle position of the roof is supported by 3 anchor cables with a diameter of 21.8mm and a length of 6300mm, with a spacing of 1100mm×800mm; 2 anchor cables with a diameter of 21.8mm and a length of 6300mm are used on both sides of the roof, with a spacing of 4400mm×1100mm, arranged along the direction of the tunnel; 7 MG355 threaded steel anchor rods with a diameter of 22mm and a length of 24mm are used for support, with a spacing of 800mm×800mm. ② The two sides are supported by 5 MG355 threaded steel anchor rods with a diameter of 22mm and a length of 24mm, with a spacing of 800mm×800mm; In addition to the anchor rod support, the small coal pillar side is supported by 1 anchor cable with a diameter of 21.8mm and a length of 6300mm, with a spacing of 1100mm. 1692 (1) Under the influence of lateral support pressure, the surrounding rock of the return air lane showed obvious asymmetric damage, accompanied by the surrounding rock at the solid coal shoulder angle and the low angle area of ​​the small coal pillar side being squeezed into the lane space, the top plate appearing a fracture zone along the strike near the solid coal side, and the bottom plate appearing cracks along the strike. These phenomena are basically consistent with the theoretical analysis results and numerical simulation results, such as Figure 14 In addition, drilling holes into the roof revealed that cracks were developed in the roof, with multiple longitudinal and circumferential cracks, and severe delamination damage in the weak interlayers.

[0074] Among them, small coal pillars are specifically: in coal mining, in order to ensure the stability of the tunnel, control the deformation of the surrounding rock and improve the recovery rate of coal resources, a coal pillar of a certain width will be left between the adjacent goaf and the working face being mined. Usually, coal pillars with a width of 3m~8m are called small coal pillars.

[0075] Based on theoretical analysis and numerical simulation results, the following key measures are proposed for surrounding rock control in gob-side tunneling. First, improving support capacity can effectively limit the expansion of the butterfly-shaped plastic zone caused by strong shear dilatancy. However, simply relying on increasing support density to increase support stress is not feasible in engineering practice, and the support resistance provided by anchor rods and cables is an order of magnitude different from the lateral support pressure of the surrounding rock. Therefore, in the high deviatoric stress environment of gob-side tunneling, the core of surrounding rock control should be stress regulation as the main method, supplemented by strengthening support, forming a comprehensive control strategy of "stress optimization + support enhancement".

[0076] On the basis of stress control, the support strength should be increased as much as possible to control the development and expansion of the surrounding rock plastic zone into a butterfly-shaped form. In particular, precise control should be implemented for complex geological conditions such as composite roofs with weak interlayers to avoid the distortion and expansion of the butterfly-shaped plastic zone. Based on this, the "weakening shear dilatancy and eliminating distortion" principle for controlling the plastic zone in gob-side roadway driving was derived, as follows:

[0077] (1) Section optimization: The original rectangular section of the tunnel that breaks the top and bottom is optimized to a trapezoidal section that tunnels along the top to ensure the integrity of the roof and reduce the initiation of shear cracks in the roof.

[0078] (2) Optimization of roof support: The roof anchor adopts high preload full-length anchoring technology to prevent the further development of shear fracture. At the same time, the anchor cable length is extended so that the weak interlayer of the roof is located in the anchoring area, effectively preventing the deformation of the plastic zone.

[0079] (3) Strengthening of coal side support: Extended anchor rods are used for deep anchoring to suppress side deformation and the development of butterfly-leaf plastic zones within the coal body. Short anchor cables are used to strengthen support at the shoulder angle and side angle to reduce the initiation and expansion of shear fractures at the shoulder angle and ensure the stability of the surrounding rock at the shoulder angle.

[0080] (4) Grouting modification of small coal pillars: In addition to implementing extended anchoring, the spray grouting process is used to improve the mechanical properties of the coal pillar, thereby reducing the expansion range of the plastic zone of the coal pillar and enhancing the overall stability of the small coal pillar.

[0081] Before the excavation of the 1692 (1) return air tunnel, the top plate of the 1682 (1) working face had been cut off and pressure relieved. The tunnel radius, support stress, and surrounding rock cohesion and internal friction angle before support were substituted into the preset equation. The tunnel surrounding rock cohesion and internal friction angle under different support stresses were determined according to the preset equation. The tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding tunnel surrounding rock cohesion and internal friction angle were substituted into the constructed tunnel surrounding rock plastic zone boundary analytical equation. The surrounding rock plastic zone boundary morphology corresponding to different support stresses was determined. The support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary morphologies was determined to be the optimal support stress. That is, when the plastic zone morphology is circular, it is a stable form. The support stress corresponding to the stable form is the optimal support stress. The optimal anchor cable spacing was obtained according to the optimal support stress. The number and arrangement of anchor cables were determined according to the optimal anchor cable spacing, as follows:

[0082] ① The top plate is supported by 7 MG400 anchor rods with a spacing of 800mm×900mm, a diameter of 22mm, and a length of 2400mm for full-length anchoring. The pre-tightening torque is not less than 200N·m.

[0083] ② The solid coal seam is supported by 4 MG400 anchor rods with a spacing of 800mm×900mm, a diameter of 22mm and a length of 2400mm. The shoulder angle is supported by a high preloaded short anchor cable with a diameter of 22mm and a length of 3100mm. The seam is supported by a high preloaded short anchor cable with a diameter of 22mm, a length of 4300mm and a spacing of 1800mm.

[0084] ③ The small coal pillar is supported by 4 MG400 anchor rods with a spacing of 800mm×900mm, a diameter of 22mm and a length of 2400mm. The side is supported by 2 high-preload short anchor cables with a spacing of 800×1800mm, a diameter of 22mm and a length of 4300mm for extended anchoring support. The preload torque is not less than 90N·m.

[0085] 1692 (1) After the support scheme was applied on site in the return air tunnel, the surrounding rock deformation was small. By drilling holes in the roof, it was found that there were no cracks in the roof, the surrounding rock in the weak interlayer was intact, and no delamination occurred. An observation point was set up 100m away from the cut hole to monitor the surrounding rock deformation and roof delamination during tunnel excavation and mining.

[0086] like Figure 16 (a) ~ Figure 16 (b) shows the surrounding rock deformation and roof delamination during the excavation of 1692 (1). The surrounding rock deformation rate was relatively high from 0d to 40d after the tunnel was formed. After 40d, the surrounding rock deformation tended to be stable. The maximum deformations of the tunnel roof, solid coal wall, small coal pillar wall and floor were 36mm, 51mm, 55mm and 76mm respectively. The roof delamination changed at a high rate from 0d to 50d, and then remained stable. The maximum displacement at the 9.0m measuring point was 27mm, the maximum displacement at the 4.8m measuring point was 13mm, and the maximum delamination was 14mm.

[0087] like Figure 16 (c) ~ Figure 16 (d) shows the surrounding rock deformation and roof delamination during mining. During mining, the roadway 50 m ahead of the working face was significantly affected by advanced mining, with surrounding rock deformation and roof delamination beginning to increase dramatically. Overall, from roadway construction to roadway abandonment, the maximum deformations of the roof, solid coal rib, and small coal pillar rib were 240 mm, 160 mm, and 305 mm, respectively, indicating good roadway control.

[0088] In summary, the present invention establishes a mechanical model of tunneling along the goaf under non-isobaric conditions based on the elastic-plastic theory, derives an analytical equation for the boundary of the plastic zone of the tunnel surrounding rock under non-isobaric conditions considering the support stress conditions, and obtains the effects of different lateral pressure coefficients, principal stress deflection angles, and support stress on the boundary of the plastic zone. The principal stress ratio has an important influence on the shape and radius of the plastic zone of the tunnel surrounding rock. When = 0.5 ~ 1.75, the boundary line of the plastic zone of the tunnel surrounding rock changes to a circular and elliptical shape. When < 0.5 or > 1.75, the boundary line of the plastic zone of the tunnel surrounding rock changes to a butterfly shape. When the principal stress of the surrounding rock deflects, the butterfly leaf plastic zone shifts from the shoulder to the roof and the two sides. As the support stress increases, the boundary line of the plastic zone of the surrounding rock transitions from a butterfly shape to an elliptical shape. The butterfly-shaped plastic zone develops in depth under the drive of dilatancy stress, which is a typical feature of the plastic zone of the surrounding rock under high deviatoric stress conditions. Special geological conditions interfere with the development path of the plastic zone, resulting in the distortion of the plastic zone. When there are weak interlayers in the surrounding rock of the goaf-driven tunnel, the butterfly-shaped plastic zone is distorted along the weak interlayers, aggravating the instability and failure of the tunnel surrounding rock. Based on the control principle of "weakening dilatancy-eliminating distortion" under the control of the plastic zone, the support optimization of the 1692 (1) return air tunnel was carried out by using high-strength anchor rods + long and short anchor cables + coal pillar grouting. The field application effect is good. The maximum delamination during the tunnel operation is 22mm, and the maximum deformation is 305mm. It provides important theoretical guidance for the stability control of goaf-driven tunnels under complex conditions.

[0089] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention are intended to be protected by the present invention.

Claims

1. A deep gob-side roadway support method based on plastic zone control, characterized in that: The following steps are involved: Obtain the tunnel radius, principal stress ratio, principal stress deflection angle, support stress, and the cohesion and internal friction angle of the tunnel surrounding rock before support; Substituting the tunnel radius, support stress, and surrounding rock cohesion and internal friction angle before support into a preset equation, the preset equation is used to describe the relationship between the support stress and the surrounding rock cohesion and internal friction angle before support; Determine the cohesion and internal friction angle of the tunnel surrounding rock under different support stresses according to the preset equations; Substituting the tunnel radius, principal stress ratio, principal stress deflection angle, different support stresses and their corresponding tunnel surrounding rock cohesion and internal friction angle into the constructed tunnel surrounding rock plastic zone boundary analytical equation, the boundary morphology of the surrounding rock plastic zone corresponding to different support stresses was determined. Determine the support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms as the optimal support stress; The optimal anchor cable spacing is obtained according to the optimal support stress, and the number and arrangement of anchor cables are determined according to the optimal anchor cable spacing.

2. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: The preset equation is: ， Where, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of the tunnel surrounding rock under different support stresses, is the anchor preload, is the anchor cable diameter, is the friction coefficient between the anchor and the surrounding rock. In the threaded steel anchor support system, , is the roadway radius, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, It is the internal friction angle of the tunnel surrounding rock before support.

3. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: The constructed analytical equation of the plastic zone boundary of the tunnel surrounding rock is: ， Where, 、 、 respectively The quadratic term coefficient, linear term coefficient and constant term, is the minimum principal stress, is the roadway radius, is the distance between the unit body of the surrounding rock and the center of the roadway, is the principal stress ratio, that is, the ratio of the maximum principal stress to the minimum principal stress, is the support stress, that is, the support stress exerted by the anchor cable on the inner wall of the tunnel. is the cohesion of the surrounding rock of the roadway before support, is the internal friction angle of the surrounding rock of the roadway before support, and are all about the principal stress deflection angle The coefficient of , , is the angle between the unit body direction and the horizontal direction, is the principal stress deflection angle, is the cohesion of the tunnel surrounding rock under different support stresses, is the internal friction angle of tunnel surrounding rock under different support stresses.

4. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: Determine the number and arrangement of anchor cables based on the optimal spacing between anchor cables: ， Where, and are the anchor cable spacing and row spacing, is the anchor preload, is the optimal support stress.

5. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: When determining that the support stress corresponding to the stable form among multiple surrounding rock plastic zone boundary forms is the optimal support stress, it is determined by analyzing the change law of the surrounding rock plastic zone boundary under different support stresses.

6. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: The changing law of the boundary of the surrounding rock plastic zone is as follows: when the principal stress ratio is in the range of 0.5~1.75, the surrounding rock plastic zone mainly presents a circle or ellipse; when the principal stress ratio is less than 0.5 or greater than 1.75, the boundary line of the tunnel surrounding rock plastic zone changes into a butterfly shape; when the principal stress deflection angle gradually increases, the butterfly leaf plastic zone shifts from the shoulder to the roof and the two sides; when the support stress gradually increases, the boundary line of the surrounding rock plastic zone transitions from a butterfly shape to an ellipse.

7. The deep gob-side roadway support method based on plastic zone control according to claim 1 is characterized in that: When determining the number and arrangement of anchor cables based on the optimal anchor cable spacing, the optimal anchor cable density is obtained by taking the inverse of the optimal anchor cable spacing. The required optimal total number of anchor cables is obtained based on the tunnel surface area and combined with the optimal anchor cable density. The optimal arrangement of the roof anchor cables is determined based on the distribution state of the weak interlayer in the roof.

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