Method and system for evaluating supporting strength of coal mine tunnel

Abstract

The invention discloses a coal mine tunnel support strength evaluation method and system, and the method comprises the following steps: carrying out the actual modeling of a coal mine tunnel according to a field project through FLAC3D numerical simulation software; under the condition of no ground stress, endowing elastic model parameters to the model and calculating balance; designing different supporting schemes, applying pre-tightening force and calculating balance; determining a low stress threshold value corresponding to a roadway surrounding rock unstable layer and a high stress threshold value corresponding to roof fracture instability, and calculating the low stress threshold value and the high stress threshold value by combining the volume weight of the rock sample obtained by field sampling; respectively calculating a high stress volume and a low stress volume; defining the lowest pressure stress efficiency, the lowest standard pressure stress volume and the pressure stress efficiency, and obtaining the lowest standard pressure stress volume according to the supporting strength of different schemes; the higher the lowest pressure stress efficiency, the higher the pressure stress efficiency and the lowest standard pressure stress volume are, the better the supporting effect of the anchor rod and / or the anchor cable is, and otherwise, the poorer the supporting effect is.

Description

Technical Field

[0001] The present invention relates to the field of evaluating the strength of tunnel support, and in particular to a method and system for evaluating the strength of coal mine tunnel support. Background Art

[0002] Traditional bolt support theories are all based on certain hypotheses, among which the most commonly used theories in coal mine tunnels are suspension theory, natural balance arch theory and composite beam theory. The suspension theory believes that the role of the bolt is to suspend the unstable rock layer in the upper stable rock layer to prevent the collapse of the weak and broken rock layer. The natural balance arch theory believes that after the tunnel is excavated, the surrounding rock loses its interlayer connection. Under the pressure of the overlying rock layer, the shallow surrounding rock is destroyed, and a natural balance arch is formed within a certain range in the depth. The rock mass above the natural balance arch is stable, and the role of the bolt is mainly to prevent the surrounding rock in the damaged area from collapsing. The composite beam theory believes that in the layered rock layer, the role of the bolt is to provide axial and tangential constraints, prevent the rock layer from delamination and relative sliding, and anchor several thin rock layers into a thicker rock layer to form a composite beam. Compared with the unanchored rock beam, the maximum bending strain and stress of the composite beam will be greatly reduced, thereby improving the stability of the tunnel roof.

[0003] Based on the above, it can be seen that the main role of anchor rods and / or anchor cables in coal mine tunnels is to prevent the collapse of broken surrounding rocks and the large bending of the roof, which leads to the breaking instability. The final output of the traditional theoretical calculation method is the critical stress corresponding to the unstable layer and the maximum stress corresponding to the breaking instability, that is, the critical minimum and maximum stress values ​​of the surrounding rock instability, which can provide a theoretical basis for the support parameters of anchor rods and / or anchor cables, but cannot evaluate the support effect of a specific support scheme.

[0004] The anchor support parameters obtained based on the above theory are a range, which cannot be specific to a certain support scheme, and cannot visualize the support effect of anchors and / or anchor cables. In view of this, in order to improve the tunnel support evaluation system, a coal mine tunnel surrounding rock anchor and / or anchor cable support strength assessment method combining theory and numerical calculation is proposed, which makes the tunnel support parameter design and optimization more comprehensive and reliable. Summary of the invention

[0005] In response to the problems and needs raised above, this solution proposes a method and system for evaluating the support strength of coal mine tunnels. Due to the adoption of the following technical features, it can achieve the above technical objectives and bring about many other technical effects.

[0006] An object of the present invention is to provide a method for evaluating the strength of coal mine tunnel support, comprising the following steps:

[0007] S10: Obtain rock samples on site, test the basic physical and mechanical parameters of rocks, and use FLAC 3DNumerical simulation software to model coal mine tunnels based on field engineering;

[0008] S20: In the absence of geostress, elastic model parameters are assigned to the model and equilibrium is calculated;

[0009] S30: Simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnels, apply preload and calculate the balance;

[0010] S40: Determine the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock and the high stress threshold corresponding to the breaking and instability of the roof by using the natural equilibrium arch theory and the composite beam theory respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof by combining the bulk density of the rock samples obtained by field sampling;

[0011] S50: traversing the maximum principal stress of the grid unit according to the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculating the high stress volume and low stress volume corresponding to the high stress threshold and the low stress threshold respectively;

[0012] S60: Define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. Multiply the high stress volume and low stress volume by the corresponding high stress threshold and low stress threshold to obtain the minimum compressive stress effectiveness E. At the same time, traverse the grid units to extract the product of the stress volume and stress value within the high stress threshold and low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V;

[0013] S70: Determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the greater the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the anchor rod and / or anchor cable support effect, and vice versa.

[0014] In an example of the present invention, in step S40, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows:

[0015] σ h =γ·b

[0016] Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

[0017] In one example of the present invention, the expression for the thickness of the broken zone of the tunnel roof rock layer is as follows:

[0018]

[0019] Where: a is the half span of the tunnel, m; α is the coal seam inclination, (°); k y is the stability coefficient of the rock formation to be anchored; f n is the hardness coefficient of the anchoring rock layer; C is the depth of coal wall damage in the tunnel.

[0020] In one example of the present invention, the expression of the tunnel coal wall damage depth is as follows:

[0021]

[0022] Where Kcx is the extrusion stress concentration coefficient around the tunnel, which is determined by the tunnel cross-sectional shape and aspect ratio; γ is the average gravity density of the stratum between the tunnel and the surface, kN / m 3 ; H is the depth of the tunnel from the ground surface, m; B0 is a dimensionless parameter that characterizes the degree of mining impact; f y is the hardness coefficient of the coal seam; h is the thickness of the coal seam or the thickness of the coal interlayer within the tunnel contour, m; is the internal friction angle of coal, (°).

[0023] In one example of the present invention, in step S40, the expression of the high stress threshold corresponding to the top plate breaking instability is:

[0024]

[0025] In the formula, (q i )1 is the maximum load of the rock layer on the first layer at the i-th layer; B is the tunnel span; L2 is the effective length of the anchor rod.

[0026] In one example of the present invention, the expression for the load acting on the first layer of the tunnel roof by the nth layer of rock is:

[0027]

[0028] Where γ is the gravity density of the rock formation, kN / m 3 ; h is the thickness of the rock layer, m; E is the elastic modulus of the rock layer, MPa. In one example of the present invention, in step S60, the expression of the minimum compressive stress effectiveness is as follows:

[0029] E=σ H V H +σ h V h

[0030] Where V H —Stress volume corresponding to high stress threshold, V h —Stress volume corresponding to the low stress threshold;

[0031] The expression for the minimum standard compressive stress volume is as follows:

[0032]

[0033] Where E is the minimum compressive stress efficiency, σ 标准 For the support strength.

[0034] In one example of the present invention, the expression of the support strength is as follows:

[0035]

[0036] Where P 锚杆 is the anchor preload, P 锚索 is the anchor cable preload; a1 and a2 are the spacing between anchor rods; b1 and b2 are the spacing between anchor cables.

[0037] Another object of the present invention is to provide an evaluation system for the coal mine tunnel support strength evaluation method as described above, comprising:

[0038] The tunnel modeling unit is configured to obtain on-site rock samples, test the basic physical and mechanical parameters of the rock, and use FLAC 3D Numerical simulation software to model coal mine tunnels based on field engineering;

[0039] A first computing unit is configured to assign elastic model parameters to the model and compute equilibrium in the absence of ground stress;

[0040] The second computing unit is configured to simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnel, apply preload and calculate balance;

[0041] A threshold calculation unit is configured to determine a low stress threshold corresponding to an unstable layer of the tunnel surrounding rock and a high stress threshold corresponding to the breaking and instability of the roof through the natural equilibrium arch theory and the composite beam theory, respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof in combination with the bulk density of the rock sample obtained by field sampling;

[0042] A volume calculation unit is configured to traverse the maximum principal stress of the grid unit according to the low stress threshold and the high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculate the high stress volume and the low stress volume corresponding to the high stress threshold and the low stress threshold respectively;

[0043] The third operation unit is configured to define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. The minimum compressive stress effectiveness E is obtained by multiplying the high stress volume and the low stress volume by the corresponding high stress threshold and the low stress threshold, respectively. At the same time, the grid units are traversed to extract the product of the stress volume and the stress value within the range of the high stress threshold and the low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V;

[0044] The support effect evaluation unit is configured to determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the larger the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the support effect of the anchor rod and / or anchor cable, and vice versa.

[0045] In one example of the present invention, in the threshold calculation unit, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows:

[0046] σ h =γ·b

[0047] Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

[0048] The present invention has the following beneficial effects:

[0049] (1) This evaluation method uses Flac 3D The numerical simulation software inverts the actual situation on site, calls out the three-dimensional visualization cloud map of the high and low support stress fields of the anchor or anchor cable, determines the range of the anchor support stress field, and determines the high and low stress thresholds of tunnel damage in combination with theoretical calculations. On this basis, the minimum stress efficiency, compressive stress efficiency and minimum standard stress volume are defined, which can be used as an intuitive and visual evaluation method for the support strength of the anchor or anchor cable, making the anchor or anchor cable support system more comprehensive and reliable.

[0050] (2) This evaluation method uses Flac 3D The numerical simulation software brings out a three-dimensional visualization cloud map of anchor or cable support stress, which is combined with the anchor or cable support compressive stress field test to verify the diffusion law of the anchor or cable support stress field, greatly reducing the cost of such experiments.

[0051] (3) This evaluation method saves time for on-site testing of support solutions and combines theoretical calculations with Flac 3DThe numerical simulation software is used to invert the actual situation on site, and then the above-mentioned evaluation method is used to quickly make an economically feasible anchor rod or anchor cable support plan, which provides a guarantee for the reliability of the tunnel support plan, reduces the trial and error time of the support plan, improves the on-site construction efficiency, and saves on-site construction costs.

[0052] The best embodiment for carrying out the present invention will be described in more detail below with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0054] Figure 1 A flow chart of a method for evaluating the support strength of a coal mine tunnel according to an embodiment of the present invention;

[0055] Figure 2 A schematic diagram of the structure of anchor rods and anchor cables driven into a tunnel model according to one of the solutions (Solution 1) of the embodiments of the present invention;

[0056] Figure 3 A schematic diagram of the structure of anchor rods and anchor cables driven into a tunnel model according to another solution (Solution 2) of an embodiment of the present invention;

[0057] Figure 4 A comparison diagram of compressive stress volumes under different schemes according to an embodiment of the present invention;

[0058] Figure 5 A comparison diagram of support effects of different schemes according to an embodiment of the present invention;

[0059] Figure 6 A three-dimensional diagram of the compressive stress zone under one of the support schemes (Scheme 1) according to an embodiment of the present invention;

[0060] Figure 7 It is a three-dimensional diagram of the compressive stress zone under another support scheme (Scheme 2) according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described 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.

[0062] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not necessarily indicate a quantity limitation. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0063] According to a first aspect of the present invention, a method for evaluating the strength of coal mine tunnel support is as follows: Figure 1 As shown, the following steps are included:

[0064] S10: Obtain rock samples on site, test the basic physical and mechanical parameters of rocks, and use FLAC 3D Numerical simulation software to model coal mine tunnels based on field engineering;

[0065] S20: In the absence of geostress, elastic model parameters are assigned to the model and equilibrium is calculated;

[0066] S30: Simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnels, apply preload and calculate the balance;

[0067] S40: Determine the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock and the high stress threshold corresponding to the breaking and instability of the roof by using the natural equilibrium arch theory and the composite beam theory respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof by combining the bulk density of the rock samples obtained by field sampling;

[0068] S50: traversing the maximum principal stress of the grid unit according to the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculating the high stress volume and low stress volume corresponding to the high stress threshold and the low stress threshold respectively;

[0069] S60: Define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. Multiply the high stress volume and low stress volume by the corresponding high stress threshold and low stress threshold to obtain the minimum compressive stress effectiveness E. At the same time, traverse the grid units to extract the product of the stress volume and stress value within the high stress threshold and low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V;

[0070] S70: Determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the greater the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the anchor rod and / or anchor cable support effect, and vice versa.

[0071] By adopting the above method and combining theoretical calculation with numerical simulation, the diffusion range of anchor compressive stress, compressive stress effectiveness and compressive stress volume change under different support schemes are obtained. Then, the feasibility of the support scheme is judged intuitively and obviously through the compressive stress effectiveness, minimum compressive stress effectiveness and minimum standard compressive stress volume values, which improves the tunnel support evaluation system and provides a more comprehensive basis for the rationality of tunnel support.

[0072] Combining theoretical calculation and numerical simulation software, the diffusion effect of anchor preload in the surrounding rock during the tunneling stage is simulated under the condition of no ground stress. The minimum and maximum stresses of surrounding rock fall damage and top plate center tensile fracture are determined by theoretical calculation, corresponding to low and high compressive stress thresholds respectively. Then, the stress volume under high and low compressive stress thresholds is extracted by traversing the grid. Finally, the support effect of the support scheme is quantified by compressive stress efficiency E0, minimum compressive stress efficiency E and minimum standard compressive stress volume V. The anchor compressive stress diffusion cloud map is extracted by three-dimensional visualization. The comprehensive comparison realizes the evaluation of different support schemes of the tunnel, provides a basis for the rationality of tunnel support, and then supplements and improves the comprehensive evaluation system of tunnel support. This method can propose a relatively reliable support scheme in a short time, greatly reducing the trial and error time of the on-site support scheme, realizing the control of tunnel stability and improving the on-site construction efficiency.

[0073] This evaluation method uses Flac 3DThe numerical simulation software inverts the actual situation on site, calls out the three-dimensional visualization cloud map of the high and low support stress fields of the anchor or anchor cable, determines the range of the anchor support stress field, and determines the high and low stress thresholds of tunnel damage in combination with theoretical calculations. On this basis, the minimum stress efficiency, compressive stress efficiency and minimum standard stress volume are defined, which can be used as an intuitive and visual evaluation method for the support strength of the anchor or anchor cable, making the anchor or anchor cable support system more comprehensive and reliable.

[0074] This evaluation method uses Flac 3D The numerical simulation software brings out a three-dimensional visualization cloud map of anchor or cable support stress, which is combined with the anchor or cable support compressive stress field test to verify the diffusion law of the anchor or cable support stress field, greatly reducing the cost of such experiments.

[0075] This evaluation method saves time for on-site testing of support solutions and combines theoretical calculations with Flac 3D The numerical simulation software is used to invert the actual situation on site, and then the above-mentioned evaluation method is used to quickly make an economically feasible anchor rod or anchor cable support plan, which provides a guarantee for the reliability of the tunnel support plan, reduces the trial and error time of the support plan, improves the on-site construction efficiency, and saves on-site construction costs.

[0076] In an example of the present invention, in step S40, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows:

[0077] σ h =γ·b

[0078] Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

[0079] In one example of the present invention, the expression for the thickness of the broken zone of the tunnel roof rock layer is as follows:

[0080]

[0081] Where: a is the half span of the tunnel, m; α is the coal seam inclination, (°); k y is the stability coefficient of the rock formation to be anchored; f n is the hardness coefficient of the anchoring rock layer; C is the depth of coal wall damage in the tunnel.

[0082] In one example of the present invention, the expression of the tunnel coal wall damage depth is as follows:

[0083]

[0084] Where Kcx is the extrusion stress concentration coefficient around the tunnel, which is determined by the tunnel cross-sectional shape and aspect ratio; γ is the average gravity density of the stratum between the tunnel and the surface, kN / m3 ; H is the depth of the tunnel from the ground surface, m; B0 is a dimensionless parameter that characterizes the degree of mining impact; f y is the hardness coefficient of the coal seam; h is the thickness of the coal seam or the thickness of the coal interlayer within the tunnel contour, m; is the internal friction angle of coal, (°).

[0085] In one example of the present invention, in step S40, the expression of the high stress threshold corresponding to the top plate breaking instability is:

[0086]

[0087] In the formula, (q i )1 is the maximum load of the rock layer on the first layer at the i-th layer; B is the tunnel span; L2 is the effective length of the anchor rod.

[0088] In one example of the present invention, the expression for the load acting on the first layer of the tunnel roof by the nth layer of rock is:

[0089]

[0090] Where γ is the gravity density of the rock formation, kN / m 3 ; h is the thickness of the rock layer, m; E is the elastic modulus of the rock layer, MPa. In one example of the present invention, in step S60, the expression of the minimum compressive stress effectiveness is as follows:

[0091] E=σ H V H +σ h V h

[0092] Where V H —Stress volume corresponding to high stress threshold, V h —Stress volume corresponding to the low stress threshold;

[0093] The expression for the minimum standard compressive stress volume is as follows:

[0094]

[0095] Where E is the minimum compressive stress efficiency, σ 标准 For the support strength.

[0096] In one example of the present invention, the expression of the support strength is as follows:

[0097]

[0098] Where P 锚杆 is the anchor preload, P 锚索is the anchor cable preload; a1 and a2 are the spacing between anchor rods; b1 and b2 are the spacing between anchor cables.

[0099] According to the second aspect of the present invention, an evaluation system of the above-mentioned coal mine tunnel support strength evaluation method comprises:

[0100] The tunnel modeling unit is configured to obtain on-site rock samples, test the basic physical and mechanical parameters of the rock, and use FLAC 3D Numerical simulation software to model coal mine tunnels based on field engineering;

[0101] A first computing unit is configured to assign elastic model parameters to the model and compute equilibrium in the absence of ground stress;

[0102] The second computing unit is configured to simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnel, apply preload and calculate balance;

[0103] A threshold calculation unit is configured to determine a low stress threshold corresponding to an unstable layer of the tunnel surrounding rock and a high stress threshold corresponding to the breaking and instability of the roof through the natural equilibrium arch theory and the composite beam theory, respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof in combination with the bulk density of the rock sample obtained by field sampling;

[0104] A volume calculation unit is configured to traverse the maximum principal stress of the grid unit according to the low stress threshold and the high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculate the high stress volume and the low stress volume corresponding to the high stress threshold and the low stress threshold respectively;

[0105] The third operation unit is configured to define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. The minimum compressive stress effectiveness E is obtained by multiplying the high stress volume and the low stress volume by the corresponding high stress threshold and the low stress threshold, respectively. At the same time, the grid units are traversed to extract the product of the stress volume and the stress value within the range of the high stress threshold and the low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V;

[0106] The support effect evaluation unit is configured to determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the larger the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the support effect of the anchor rod and / or anchor cable, and vice versa.

[0107] By adopting the above system and combining theoretical calculation with numerical simulation, the diffusion range of anchor compressive stress, compressive stress effectiveness and compressive stress volume change under different support schemes are obtained. Then, the feasibility of the support scheme is judged intuitively and obviously through the compressive stress effectiveness, minimum compressive stress effectiveness and minimum standard compressive stress volume values, which improves the tunnel support evaluation system and provides a more comprehensive basis for the rationality of tunnel support.

[0108] Combining theoretical calculation and numerical simulation software, the diffusion effect of anchor preload in the surrounding rock during the tunneling stage is simulated under the condition of no ground stress. The minimum and maximum stresses of surrounding rock fall damage and top plate center tensile fracture are determined by theoretical calculation, corresponding to low and high compressive stress thresholds respectively. Then, the stress volume under high and low compressive stress thresholds is extracted by traversing the grid. Finally, the support effect of the support scheme is quantified by compressive stress efficiency E0, minimum compressive stress efficiency E and minimum standard compressive stress volume V. The anchor compressive stress diffusion cloud map is extracted by three-dimensional visualization. The comprehensive comparison realizes the evaluation of different support schemes of the tunnel, provides a basis for the rationality of tunnel support, and then supplements and improves the comprehensive evaluation system of tunnel support. This method can propose a relatively reliable support scheme in a short time, greatly reducing the trial and error time of the on-site support scheme, realizing the control of tunnel stability and improving the on-site construction efficiency.

[0109] The evaluation system uses Flac 3D The numerical simulation software inverts the actual situation on site, calls out the three-dimensional visualization cloud map of the high and low support stress fields of the anchor or anchor cable, determines the range of the anchor support stress field, and determines the high and low stress thresholds of tunnel damage in combination with theoretical calculations. On this basis, the minimum stress efficiency, compressive stress efficiency and minimum standard stress volume are defined, which can be used as an intuitive and visual evaluation method for the support strength of the anchor or anchor cable, making the anchor or anchor cable support system more comprehensive and reliable.

[0110] The evaluation system uses Flac 3D The numerical simulation software brings out a three-dimensional visualization cloud map of anchor or cable support stress, which is combined with the anchor or cable support compressive stress field test to verify the diffusion law of the anchor or cable support stress field, greatly reducing the cost of such experiments.

[0111] The evaluation system saves time for on-site testing of support solutions and combines theoretical calculations with Flac 3D The numerical simulation software is used to invert the actual situation on site, and then the above-mentioned evaluation method is used to quickly make an economically feasible anchor rod or anchor cable support plan, which provides a guarantee for the reliability of the tunnel support plan, reduces the trial and error time of the support plan, improves the on-site construction efficiency, and saves on-site construction costs.

[0112] In one example of the present invention, in the threshold calculation unit, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows:

[0113] σ h =γ·b

[0114] Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

[0115] Specific examples

[0116] To further illustrate a method for evaluating the strength of tunnel support based on the volume of anchor (cable) compressive stress, a working face in a coal mine is taken as an example. The average burial depth of the working face is 690m, the average thickness of the coal seam in the working face is 5.2m, the thickness of the coal seam is stable, the average inclination is 4°, the endogenous cracks are developed, and the Proctor hardness of the coal seam is f=2~3.

[0117] 1) Sampling was carried out at 40m vertically upward and 20m vertically downward of a coal seam at a certain working face of a certain mine to test the basic physical and mechanical parameters of the rock, as shown in Table 1. The FLAC 3D Numerical simulation software, based on the actual modeling of the on-site project, in order to ensure that the anchor rods and anchor cables can be evenly placed and reduce experimental errors, the least common multiple of the anchor rod and anchor cable spacing of the two schemes, 12m, is taken as the tunnel length. The overall size of the model is length × width × height: 17m × 12m × 15m, and the tunnel size is width × height: 5m × 4m;

[0118] Table 1 Rock formation mechanical parameters

[0119]

[0120] 2) In the absence of geostress, elastic model parameters are assigned to the model according to the measured physical and mechanical parameters, and the equilibrium is calculated;

[0121] 3) Simulate the tunneling stage and design two different anchor (cable) support schemes. Install the anchors (cables) at the same time, apply preload, and calculate the balance. The specific support schemes are as follows;

[0122] Option 1: Attachment Figure 2 (The tunnel is 5m wide and 4m high) The tunnel roof and side parts are both made of HRB500 left-handed high-strength threaded steel resin anchor rods without longitudinal reinforcement. Five anchor rods (φ22×2400mm) are arranged in each row on the roof, with a row spacing of 1000×1000mm and a preload force of 60kN; four anchor rods (φ22×2400mm) are arranged in each row on the side parts, with a row spacing of 1000×1000mm and a preload force of 60kN; two anchor cables (φ22×5000mm) are arranged in each row on the roof, with a row spacing of 3000×2000mm and a preload force of 200kN; the roof anchor rods (cables) and side anchor rods are arranged perpendicular to the tunnel surface.

[0123] Option 2: Attachment Figure 3 The tunnel roof and side parts are both made of HRB500 left-handed high-strength threaded steel resin anchor rods without longitudinal reinforcement. Six anchor rods (φ22×2400mm) are arranged in each row of the roof, with a row spacing of 800×1200mm and a preload force of 60kN, which are arranged perpendicular to the roof; five anchor rods (φ22×2400mm) are arranged in each row of the side parts, with a row spacing of 800×1200mm and a preload force of 60kN, which are also arranged perpendicular to the side parts; two anchor cables (φ22×5000mm) are arranged in each row of the roof, with a row spacing of 2400×2400mm and a preload force of 200kN, which are all arranged perpendicular to the tunnel roof.

[0124] 4) The critical stress (corresponding to the low stress threshold) corresponding to the unstable layer of the tunnel surrounding rock and the maximum stress (corresponding to the high stress threshold) corresponding to the roof breaking and instability are determined by the natural equilibrium arch theory and the composite beam theory respectively. Then, the low and high stress thresholds corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof are calculated in combination with the rock density obtained by field sampling. The calculation process is as follows:

[0125] Depth of coal wall damage in tunnel:

[0126]

[0127] Where: Kcx-extrusion stress concentration coefficient around the tunnel, determined by the tunnel cross-section shape and aspect ratio, taken as 1.2; γ-average gravity density of the stratum between the tunnel and the surface, taken as 23kN / m 3 ; H-depth of tunnel from the ground surface, 690m; B0-dimensionless parameter representing the impact of mining, 0.8; f y -Coal seam hardness coefficient, 1.5; h-coal seam thickness or thickness of coal interlayer within the tunnel contour, 5.2m; -Internal friction angle of coal, 22(°).

[0128] The coal wall damage depth of the roadway is obtained: C = 0.05m

[0129] Depth of rock layer damage in tunnel roof:

[0130] Where: a-half span of the tunnel, 2.5m; α-coal seam inclination, 4 (°); k y -Stability coefficient of the rock formation to be anchored 0.9; f n -Hardness coefficient of anchoring rock formation 3.0.

[0131] The damage depth of the tunnel roof rock layer is obtained: b = 0.94m

[0132] Then the low stress threshold: σ h =γ·b

[0133] Where: γ-gravity density of the roof crushing zone, 24.6kN / m3; b-thickness of the roof crushing zone, 0.94m;

[0134] The low stress threshold is obtained: σ h =0.02MPa

[0135] The maximum stress corresponding to the top plate breaking instability in step 4 (high stress threshold, composite beam theory):

[0136] The load of n layers of rock on the first layer of the tunnel roof:

[0137] Where: γ-gravity density of rock layer, kN / m 3 ; h-rock layer thickness, m; E-elastic modulus of rock layer, MPa.

[0138] By calculation, when the load of the rock layer on the first layer reaches the maximum when the second layer is reached, it is recorded as (Table 1):

[0139]

[0140] Maximum tensile stress value of the lower surface of the clamped beam at the midpoint:

[0141] Where: B-tunnel span, 5.0m; L2-anchor effective length, 2.0m;

[0142] The high stress threshold σ H =0.11MPa

[0143] In summary, the high and low thresholds of compressive stress around the roadway are 0.11MPa and 0.02MPa respectively;

[0144] 5) According to the selected threshold, traverse the maximum principal stress of the grid unit and calculate the stress volume corresponding to the high and low stress thresholds respectively. The grid traversal instructions are as follows;

[0145] p_z = zone.head

[0146] loop while p_z#null

[0147] p_z = zone.next(p_z)

[0148] endloop

[0149] like Figure 4 As shown in Figure 1, the stress volumes corresponding to the high and low stress thresholds of Scheme 1 are: 17.38m 3 、368.83m 3 The stress volumes corresponding to the high and low stress thresholds of Scheme 2 are: 18.03m 3、364.56m 3 .

[0150] Step 6: Define the minimum compressive stress effectiveness and the minimum standard compressive stress volume. Multiply the high and low stress volumes by the corresponding stress thresholds to obtain the minimum compressive stress effectiveness E. At the same time, the grid units can be traversed to extract the product of the stress volume and stress value within the high and low stress thresholds to obtain the compressive stress effectiveness E0. Then, according to the active support force / support density (support strength σ 标准 ) is corrected to obtain the minimum standard compressive stress volume V. The quality of the support scheme is determined by comparing the minimum compressive stress effectiveness E, compressive stress effectiveness E0 and the minimum standard compressive stress volume V.

[0151] Option 1:

[0152] Minimum pressure stress performance: E = σ H V H +σ h V h =0.11×17.38+0.02×368.83=9.29MJ

[0153] Support strength:

[0154] Minimum standard compressive stress volume:

[0155] Compressive stress efficiency extracted by software: E0 = 10.38 MJ

[0156] Option 2:

[0157] Minimum pressure stress performance: E = σ H V H +σ h V h =0.11×18.03+0.02×364.56=9.27MJ

[0158] Support strength:

[0159] Minimum standard compressive stress volume:

[0160] Compressive stress efficiency extracted by software: E0 = 10.17 MJ

[0161] Comparing Scheme 1 with Scheme 2, Scheme 1 has a larger spacing and a smaller row spacing, while Scheme 2 has a smaller spacing and a larger row spacing. Normally, it is difficult to compare the advantages and disadvantages of the two schemes. However, this method can intuitively derive the advantages and disadvantages of the two schemes through the ratio, which has a good reference significance.

[0162] The final calculation shows: Figure 5As shown in the figure, Scheme 1: The minimum compressive stress performance is 9.29 MJ, and the minimum standard compressive stress volume is 44.19 m 3 , the compressive stress performance is 10.38MJ; Option 2: The minimum compressive stress performance is 9.27MJ, and the minimum standard compressive stress volume is 42.14m 3 , the compressive stress efficiency is 10.17MJ; it is obvious that the minimum compressive stress efficiency, minimum standard compressive stress volume and compressive stress efficiency of Scheme 1 are better than those of Scheme 2. It can be seen that the support effect of Scheme 1 is significantly better than that of Scheme 2. This shows that the comprehensive evaluation method combining theoretical calculation and numerical simulation can provide guidance for on-site support, such as Figure 6 and Figure 7 As shown in the figure, the extracted three-dimensional compressive stress distribution diagram of the anchor bolt shows intuitively that the stress diffusion of Scheme 1 is more comprehensive than that of Scheme 2, completely covering the side area of ​​the tunnel, and the stress succession is more continuous. Therefore, it can be further concluded that Scheme 1 is better than Scheme 2.

[0163] This evaluation method combines theoretical calculations with FLAC 3D Combined with numerical simulation software, a numerical model that conforms to the actual situation on site is established. The minimum and maximum stresses of surrounding rock fall damage and central tensile fracture of the roof are determined by theoretical calculation, and the high and low compressive stress thresholds are determined. Then, the compressive stress volume under the high and low compressive stress thresholds is extracted by traversing the grid. Finally, the support effect of the support scheme is quantified by the minimum compressive stress efficiency E, the minimum standard compressive stress volume V and the compressive stress efficiency E0. Then, the anchor compressive stress diffusion cloud map is extracted by three-dimensional visualization. The comprehensive comparison realizes the evaluation of different support schemes for the tunnel, provides a basis for the rationality of the tunnel support, and improves the tunnel support evaluation system. It provides a more comprehensive basis for the rationality of the tunnel support, thereby supplementing and improving the comprehensive evaluation system of the tunnel support. Using this method, a relatively reliable support scheme can be proposed in a short time, which greatly reduces the trial and error time of the on-site support scheme, realizes the stability control of the tunnel, and improves the on-site construction efficiency.

[0164] The exemplary implementation scheme of a coal mine tunnel support strength assessment method and system proposed in the present invention is described in detail above with reference to the preferred embodiments. However, those skilled in the art will appreciate that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A method for evaluating the strength of coal mine tunnel support, characterized in that: The steps include: S10: Obtain rock samples on site, test the basic physical and mechanical parameters of rocks, and use FLAC 3D Numerical simulation software to model coal mine tunnels based on field engineering; S20: In the absence of geostress, elastic model parameters are assigned to the model and equilibrium is calculated; S30: Simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnels, apply preload and calculate the balance; S40: Determine the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock and the high stress threshold corresponding to the breaking and instability of the roof by using the natural equilibrium arch theory and the composite beam theory respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof by combining the bulk density of the rock samples obtained by field sampling; S50: traversing the maximum principal stress of the grid unit according to the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculating the high stress volume and low stress volume corresponding to the high stress threshold and the low stress threshold respectively; S60: Define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. Multiply the high stress volume and low stress volume by the corresponding high stress threshold and low stress threshold to obtain the minimum compressive stress effectiveness E. At the same time, traverse the grid units to extract the product of the stress volume and stress value within the high stress threshold and low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V; S70: Determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the greater the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the anchor rod and / or anchor cable support effect, and vice versa.

2. The method for evaluating the strength of coal mine tunnel support according to claim 1, characterized in that: In step S40, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows: s h =γ·b Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

3. The method for evaluating the strength of coal mine tunnel support according to claim 2, characterized in that: The expression for the thickness of the broken zone of the tunnel roof is as follows: Where: a is the half span of the tunnel, m; α is the coal seam inclination, (°); k y is the stability coefficient of the rock formation to be anchored; f n is the hardness coefficient of the anchoring rock layer; C is the depth of coal wall damage in the tunnel.

4. The method for evaluating the strength of coal mine tunnel support according to claim 3, characterized in that: The expression of the tunnel coal side failure depth is as follows: Where Kcx is the extrusion stress concentration coefficient around the tunnel, which is determined by the tunnel cross-sectional shape and aspect ratio; γ is the average gravity density of the stratum between the tunnel and the surface, kN / m 3 ; H is the depth of the tunnel from the ground surface, m; B0 is a dimensionless parameter that characterizes the degree of mining impact; f y is the hardness coefficient of the coal seam; h is the thickness of the coal seam or the thickness of the coal interlayer within the tunnel contour, m; is the internal friction angle of coal, (°).

5. The method for evaluating the strength of coal mine tunnel support according to claim 1, characterized in that: In step S40, the expression of the high stress threshold corresponding to the roof breaking instability is: In the formula, (q i )1 is the maximum load of the rock layer on the first layer at the i-th layer; B is the tunnel span; L2 is the effective length of the anchor rod.

6. The method for evaluating the strength of coal mine tunnel support according to claim 5, characterized in that: The expression of the load acting on the first layer of the tunnel roof by the nth layer of rock is: Where γ is the gravity density of the rock formation, kN / m 3 ; h is the thickness of the rock layer, m; E is the elastic modulus of the rock layer, MPa.

7. The method for evaluating the strength of coal mine tunnel support according to claim 1, characterized in that: In the step S60, the expression of the minimum compressive stress performance is as follows: E=σ H V H +s h V h Where V H —Stress volume corresponding to high stress threshold, V h —Stress volume corresponding to the low stress threshold; The expression for the minimum standard compressive stress volume is as follows: Where E is the minimum compressive stress efficiency, σ 标准 For the support strength.

8. The method for evaluating the strength of coal mine tunnel support according to claim 7, characterized in that: The expression of support strength is as follows: Where P 锚杆 is the anchor preload, P 锚索 is the anchor cable preload; a1 and a2 are the spacing between anchor rods; b1 and b2 are the spacing between anchor cables.

9. An evaluation system for the coal mine tunnel support strength evaluation method according to any one of claims 1 to 8, characterized in that: include: The tunnel modeling unit is configured to obtain on-site rock samples, test the basic physical and mechanical parameters of the rock, and use FLAC 3D Numerical simulation software to model coal mine tunnels based on field engineering; A first computing unit is configured to assign elastic model parameters to the model and compute equilibrium in the absence of ground stress; The second computing unit is configured to simulate the tunneling stage, design different support schemes, drive anchor rods and / or anchor cables on the coal mine tunnel, apply preload and calculate balance; A threshold calculation unit is configured to determine a low stress threshold corresponding to an unstable layer of the tunnel surrounding rock and a high stress threshold corresponding to the breaking and instability of the roof through the natural equilibrium arch theory and the composite beam theory, respectively, and calculate the low stress threshold and high stress threshold corresponding to the collapse of the unstable layer of the tunnel and the breaking and instability of the roof in combination with the bulk density of the rock sample obtained by field sampling; A volume calculation unit is configured to traverse the maximum principal stress of the grid unit according to the low stress threshold and the high stress threshold corresponding to the collapse of the unstable layer and the breakage and instability of the roof obtained in the above steps, and calculate the high stress volume and the low stress volume corresponding to the high stress threshold and the low stress threshold respectively; The third operation unit is configured to define the minimum compressive stress effectiveness E and the minimum standard compressive stress volume. The minimum compressive stress effectiveness E is obtained by multiplying the high stress volume and the low stress volume by the corresponding high stress threshold and the low stress threshold, respectively. At the same time, the grid units are traversed to extract the product of the stress volume and the stress value within the range of the high stress threshold and the low stress threshold to obtain the compressive stress effectiveness E0. Then, according to the support strength σ of different schemes, 标准 Correction to obtain the minimum standard compressive stress volume V; The support effect evaluation unit is configured to determine the quality of the support scheme by comparing the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, wherein the larger the minimum compressive stress effectiveness E, the compressive stress effectiveness E0 and the minimum standard compressive stress volume V, the better the support effect of the anchor rod and / or anchor cable, and vice versa.

10. The evaluation system of the coal mine tunnel support strength evaluation method according to claim 9, characterized in that: In the threshold calculation unit, the expression of the low stress threshold corresponding to the unstable layer of the tunnel surrounding rock is as follows: s h =γ·b Where: γ is the gravity density of the top plate crushing area, kN / m 3 ; b is the thickness of the broken rock zone of the tunnel roof, m.

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