A method for estimating the strength of surrounding rock in bolt-supported tunnels

Abstract

The present invention relates to the field of mining rock mass mechanics, and specifically discloses a method for estimating the surrounding rock strength of an anchor-supported tunnel, comprising: firstly, investigating and obtaining basic information of the surrounding rock of the anchor-supported tunnel and sampling the surrounding rock and anchor materials; secondly, measuring the coal-rock mechanical properties of the surrounding rock samples, and measuring the working properties of the anchor materials; at the same time, calculating and obtaining the designed anchor support strength; thirdly, judging the state of the surrounding rock of the anchor support according to the sampling and measurement results, and judging whether a fracture zone occurs; if so, directly estimating the compressive strength of the surrounding rock of the anchor support; if not, first predicting the force-deformation relationship of the tunnel surrounding rock support, and then estimating the compressive strength of the surrounding rock of the anchor support, and providing an estimation result; the present invention solves the difficulty in estimating the surrounding rock strength of the anchored tunnel, and can provide a basis for subsequent anchored surrounding rock support effect and hazard evaluation, thereby preventing the occurrence of problems such as roof collapse and spalling.

Description

Technical Field

[0001] The invention relates to the field of mine rock mass mechanics, and in particular to a method for estimating the strength of surrounding rock of an anchor-supported tunnel. Background Art

[0002] As one of the most important support methods for mine tunnels in my country, bolt support is effective in determining the degree of improvement in the surrounding rock's anti-destructive capacity after bolt support, and compressive strength is a key parameter for characterizing the surrounding rock's anti-destructive capacity. Therefore, it is very important to accurately estimate the compressive strength of the surrounding rock after bolt support.

[0003] The existing methods for obtaining the compressive strength of surrounding rock of anchor bolts mainly adopt theoretical calculation, numerical simulation and similar material simulation. Among them, the surrounding rock strengthening theory is often used in theoretical calculation, considering the coupling of the mechanical properties of anchor bolt materials and coal rock materials, and the improvement of the surrounding rock compressive capacity by the anchor support working load is not considered; and in the numerical simulation method, due to the limitations of the model and constitutive relationship, the anchor bolts mostly use simplified units, which is difficult to accurately reflect the characteristics of anchor bolt support, and the obtained surrounding rock compressive strength is quite different from the actual one; when using similar materials for simulation, due to the use of geometric similarity, the effect of anchor bolt support on improving the surrounding rock strength can be better given from a qualitative perspective, and its quantitative expression is very different from the actual value. At the same time, considering that the design of anchor bolt support requires an accurate estimation of the surrounding rock strength after anchor bolt support, so as to avoid serious damage to the surrounding rock after anchor bolt support and even cause spalling and roof collapse due to inappropriate estimation of surrounding rock strength.

[0004] Therefore, there is an urgent need for a method to accurately estimate the compressive strength of the surrounding rock after bolting before mine bolting, so that the deformation of the tunnel surrounding rock can be controlled within the allowable range and the normal use of the tunnel can be ensured. Summary of the invention

[0005] The purpose of the present invention is to provide a method for estimating the strength of surrounding rock in an anchor-supported roadway to solve the following technical problems:

[0006] How to accurately estimate the compressive strength of the surrounding rock after anchor support to ensure the normal use of the tunnel.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for estimating the surrounding rock strength of an anchor-supported roadway, the method comprising:

[0009] S1. Obtain basic investigation information on the surrounding rock of the bolt support tunnel, sample the surrounding rock and bolt materials, and obtain sampling data;

[0010] S2. Analyze the sampling data: determine the mechanical properties of the coal and rock in the tunnel, determine the working properties of the anchor material, and calculate the anchor support strength;

[0011] S3. According to the sampling data analysis results, the state of the surrounding rock of the anchor support is identified to determine whether a fracture zone exists:

[0012] If yes, then directly estimate the compressive strength of the surrounding rock supported by the anchor bolts;

[0013] If not, the force-deformation relationship of the tunnel surrounding rock support is estimated first, and the compressive strength of the surrounding rock is estimated by selecting the anchor support;

[0014] S4. Output the estimation result of step S3.

[0015] Preferably, the method for measuring the mechanical properties of coal and rock in the roadway is:

[0016] The principal stress expression of Coulomb failure of coal rock is:

[0017]

[0018] Wherein, (1) is the principal stress expression of Coulomb failure of coal rock when no fracture zone appears, (2) is the principal stress expression of Coulomb failure of coal rock when fracture zone appears; σ c is the uniaxial compressive strength of coal rock; c is the cohesion; is the internal friction angle; σ1 is the maximum principal stress; σ3 is the minimum principal stress; is the equivalent internal friction angle of the surrounding rock in the fracture zone, and

[0019] Preferably, the process of determining the working characteristics of the anchor material is:

[0020] SS1. Determine the free length of the anchor support;

[0021] SS2. Install the anchor sample on the testing machine and ensure that the free section length of the anchor support is consistent with the actual free section length of the anchor;

[0022] SS3. Conduct a tensile test to determine the maximum allowable elongation L0 of the anchor rod after pre-tightening.

[0023] Preferably, the anchor support strength calculation includes:

[0024] Anchor rock support force F 01 The formula is:

[0025] F 01 = nηF0;

[0026] Among them, F0 is the working load of a single anchor; n is the number of anchors on the top and side of the roadway along the roadway; η is the uneven coefficient of the working load of the anchor;

[0027] When the top plate of the anchor support is flat and the cross section of the anchor support is flat, η is 0.8-0.9; when the top plate of the anchor support is uneven and the cross section of the anchor support is partially uneven, η is 0.6-0.8; when the top plate of the anchor support is uneven and has large fluctuations and the cross section of the anchor support is uneven and has large fluctuations, η is 0.5-0.6;

[0028] According to the on-site anchor support parameters, F0 is taken as the anchor design anchoring force, and the formula for the anchor support strength P0 is:

[0029]

[0030] Among them, D is the tunnel width of the anchor support top plate and the tunnel side height of the anchor support side; d0 is the anchor row spacing.

[0031] Preferably, the method for identifying the state of the surrounding rock of the anchor support in step S3 is:

[0032] By formula Calculate the radius R of the surrounding rock fracture zone of the tunnel f ;

[0033] Where a is the equivalent radius of the roadway; P v is the vertical stress at the location of the tunnel, and P v =γH, γ is the bulk density of surrounding rock, H is the buried depth of tunnel; P i The maximum support strength that can be provided by anchor support; is the equivalent internal friction angle of the surrounding rock in the fracture zone;

[0034] Compare the radius Rf of the roadway surrounding rock fracture zone with the roadway equivalent radius a:

[0035] When R f > a, it is judged that the surrounding rock of the tunnel has a fracture zone;

[0036] When R f When ≤a, it is judged that there is no fracture zone in the surrounding rock of the tunnel.

[0037] Preferably, the method for pre-analyzing the force-deformation relationship of the tunnel surrounding rock support in step S3 is:

[0038] The expression of tunnel surrounding rock support force-deformation is obtained:

[0039]

[0040]

[0041] Among them, u a is the deformation of the surrounding rock of the tunnel; μ is the Poisson's ratio of coal rock; E is the elastic modulus of coal rock.

[0042] Preferably, the method for estimating the compressive strength of surrounding rock supported by anchor bolts is:

[0043] When the surrounding rock of the tunnel has a fracture zone, let P design =σ3, and the currently acquired Substituting σ3 into the principal stress expression (2) of Coulomb failure of the coal rock, the maximum principal stress σ1' is obtained, and σ1' is the compressive strength of the surrounding rock in the fracture zone of the anchor support;

[0044] When there is no cracked area in the surrounding rock of the tunnel, the maximum allowable elongation L0 after high pre-tightening support of the anchor bolt is L0 = u a Substitute it into the tunnel surrounding rock support force-deformation expression to calculate the support force P 0spport ; P 0spport Compare with P0 and take P 0spport The minimum value between P0 and P1 is taken as σ3 and substituted into the principal stress expression (1) of Coulomb failure of the coal rock to obtain the maximum principal stress σ1''. The value of σ1'' is the compressive strength of the surrounding rock supported by the anchor bolt.

[0045] Preferably, the maximum allowable elongation L0 of the anchor rod after the anchor rod is pre-tightened is obtained in the following manner:

[0046] Obtain the curve EL1 of the anchor working load changing with the extension distance when there is no preload;

[0047] Obtain the curve EL2 showing the variation of the anchor working load with the elongation distance when the preload force P1 is applied; determine the maximum allowable elongation L0 of the anchor after the anchor is preloaded according to the intersection value of the curve EL1 and the curve EL2.

[0048] Beneficial effects of the present invention:

[0049] (1) The method for estimating the strength of the surrounding rock of the anchored tunnel provided by the present invention fully considers the anchor support and the deformation and destruction process of the surrounding rock, so that the group effect of the anchor support is adapted to the deformation and destruction of the tunnel surrounding rock, and provides a method for determining the strength of the surrounding rock after the tunnel excavation is anchored, including the two situations where the anchored surrounding rock has a fracture zone and the non-fracture zone, thereby solving the difficulty in estimating the strength of the surrounding rock of the anchored tunnel and providing a basis for the subsequent anchored surrounding rock support effect and hazard evaluation, thereby preventing the occurrence of problems such as roof collapse and slab spalling.

[0050] (2) The present invention uses the uneven working load coefficient of the anchor to determine the anchor support strength, which solves the problem of different working loads of the anchor group caused by the uneven surrounding rock wall of the tunnel, ensures that the consideration of the anchor group effect is more in line with the actual project, and effectively avoids overestimation of the anchor support effect.

[0051] (3) When the surrounding rock of the tunnel given in this method does not have a fracture zone, the working load and deformation capacity of the anchor rod are fully considered. On the one hand, the anchor rod support performance can be maximized, and on the other hand, the anchor rod is prevented from breaking and failing due to excessive elongation, making the estimation of the strength of the surrounding rock of the anchored tunnel more reasonable.

[0052] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0054] Figure 1 This is a flow chart for estimating the compressive strength of surrounding rock in the anchor support tunnel of the present invention;

[0055] Figure 2 It is a schematic diagram of the working characteristic curve of the support anchor rod of the present invention;

[0056] Figure 3 This is the working characteristic curve of the test anchor rod of the present invention. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] To solve the problem of determining the compressive strength of the surrounding rock after bolt support, please refer to Figure 1 As shown, the present invention is a method for estimating the surrounding rock strength of an anchor-supported roadway, the method comprising:

[0059] S1. Obtain basic investigation information on the surrounding rock of the bolt support tunnel, sample the surrounding rock and bolt materials, and obtain sampling data;

[0060] S2. Analyze the sampling data: determine the mechanical properties of the coal and rock in the tunnel, determine the working properties of the anchor material, and calculate the anchor support strength;

[0061] S3. According to the sampling data analysis results, the state of the surrounding rock of the anchor support is identified to determine whether a fracture zone exists:

[0062] If yes, then directly estimate the compressive strength of the surrounding rock supported by the anchor bolts;

[0063] If not, the force-deformation relationship of the tunnel surrounding rock support is estimated first, and the compressive strength of the surrounding rock is estimated by selecting the anchor support;

[0064] S4. Output the estimation result of step S3.

[0065] Through the above technical scheme, in this embodiment, it is necessary to first conduct a survey on the surrounding rock conditions of the anchor-supported tunnel to obtain sampling data, and specifically conduct an on-site survey on the estimated surrounding rock of the anchor-supported tunnel to obtain the engineering geological conditions and support conditions of the tunnel, wherein the engineering geology mainly includes the buried depth, shape and size of the tunnel, the rock properties and thickness of the surrounding rock, etc., and the support conditions mainly include the anchor support materials used, the spacing between supports, the preload force, etc., and samples of the surrounding rock and anchor materials are taken.

[0066] The content of the above investigation is specific to this embodiment. The sampling data content includes: the designed buried depth of a certain mine belt drift is 400m, the cross-section shape is rectangular, the tunnel size is width × height is 5.4 × 3.8m, the tunnel wall is flat after excavation, the side anchor is a left-handed high-strength threaded steel anchor, the yield strength is 500MPa, the diameter is 22mm, the length is 2.6m, the actual support free section length is 1.6m, the spacing is 1.0 × 1.0m, the rectangular arrangement, 4 in each row, the designed preload force is 120kN, and the average bulk density of the overlying rock is 20kN / m 3 .

[0067] Then, the mechanical properties of coal rock in the tunnel are measured, the working characteristics of anchor materials are measured, and the anchor support strength is calculated; to ensure that accurate formulas and data acquisition basis are provided for subsequent estimation results; then, the state of the surrounding rock of the anchor support is identified based on the analysis results of the sampling data to determine whether a rupture zone appears: if so, the compressive strength of the surrounding rock of the anchor support is directly estimated; if not, the force-deformation relationship of the tunnel surrounding rock support is first predicted, and the compressive strength of the surrounding rock of the anchor support is estimated; finally, the estimation results are output; by considering the two situations of the presence of rupture zones and the absence of rupture zones in the anchored surrounding rock, the problem of estimating the strength of the surrounding rock of the anchored tunnel is solved, which can provide a basis for the subsequent anchored surrounding rock support effect and hazard evaluation, thereby preventing problems such as roof collapse and spalling.

[0068] As an implementation mode of the present invention, the method for measuring the mechanical properties of coal and rock in the roadway is:

[0069] The uniaxial compression test and conventional triaxial compression test are used to obtain the uniaxial compressive strength σ of coal rock. c , cohesion c and internal friction angle The principal stress expression of Coulomb failure criterion is given as follows:

[0070]

[0071] In the formula, σ1 is the maximum principal stress; σ3 is the minimum principal stress; is the equivalent internal friction angle of the surrounding rock in the fracture zone, and

[0072] Specifically in this embodiment, according to the coal rock mechanical property measurement test, the mechanical properties of the roadway coal are tested and obtained as follows: uniaxial compressive strength 17.3MPa, cohesion 5.2MPa, internal friction angle 32°, elastic modulus 0.8GPa, Poisson's ratio 0.23; the principal stress expression of Coulomb failure of the roadway coal is obtained according to formula 1:

[0073]

[0074] As an embodiment of the present invention, please refer to Figure 2-3 As shown in the figure, the process of determining the working characteristics of anchor materials is as follows:

[0075] SS1. Determine the free length of the anchor support;

[0076] SS2. Install the anchor sample on the testing machine and ensure that the free section length of the anchor support is consistent with the actual free section length of the anchor;

[0077] SS3. Conduct a tensile test to determine the maximum allowable elongation L0 of the anchor rod after pre-tightening.

[0078] Through the above technical scheme, the indoor test method is adopted, combined with the actual anchor support, the full-size working characteristic curve of the anchor material is determined, and the working load-deformation relationship of the support anchor is obtained according to the anchor design preload P1, and then the maximum allowable elongation L0 of the anchor after the anchor is preloaded is obtained; specifically in this embodiment, according to the anchor material testing method, the working characteristic curve of the left-handed high-strength threaded steel anchor (yield strength 500MPa) with a free section length of 1.6m is tested and obtained, such as Figure 2 As shown in the figure, according to the anchor rod design preload of 120kN, the maximum allowable elongation of the anchor rod after preload is about 280mm.

[0079] As an implementation mode of the present invention, the anchor support strength calculation includes:

[0080] Anchor rock support force F 01 The formula is:

[0081] F 01 =nηF0; (Formula 2)

[0082] Among them, F0 is the working load of a single anchor; n is the number of anchors on the top and side of the roadway along the roadway; η is the uneven coefficient of the working load of the anchor;

[0083] When the top plate of the anchor support is flat and the cross section of the anchor support is flat, η is 0.8-0.9; when the top plate of the anchor support is uneven and the cross section of the anchor support is partially uneven, η is 0.6-0.8; when the top plate of the anchor support is uneven and has large fluctuations and the cross section of the anchor support is uneven and has large fluctuations, η is 0.5-0.6;

[0084] According to the on-site anchor support parameters, F0 is taken as the anchor design anchoring force, and the formula for the anchor support strength P0 is:

[0085]

[0086] Among them, D is the tunnel width of the anchor support top plate and the tunnel side height of the anchor support side; d0 is the anchor row spacing.

[0087] Through the above technical scheme, in the process of determining the anchor support strength in this embodiment, the anchor working load unevenness coefficient is used to solve the problem of anchor group working load differences caused by the unequal surrounding rock wall of the tunnel, so that the consideration of the anchor group effect is more in line with the actual project, and it is effectively avoided to overestimate the effect of anchor support. In this embodiment, the design force of coal seam anchor support is calculated as F design =4×0.9×200=720kN, anchor design support strength P design =720 / (3.8×1.0)kPa=0.189MPa;

[0088] As an implementation mode of the present invention, the method for identifying the state of the surrounding rock of the anchor support in step S3 is:

[0089] Calculate the radius R of the surrounding rock fracture zone of the tunnel f :

[0090]

[0091] Where a is the equivalent radius of the roadway; P v is the vertical stress at the location of the tunnel, usually P v =γH, γ is the bulk density of surrounding rock, H is the buried depth of tunnel; P i The maximum support strength that can be provided by anchor support; is the equivalent internal friction angle of the surrounding rock in the fracture zone;

[0092] The radius R of the fracture zone of the surrounding rock of the roadway f Compare with the equivalent radius a of the roadway:

[0093] When R f> a, it is judged that the surrounding rock of the tunnel has a fracture zone;

[0094] When R f When ≤a, it is judged that there is no fracture zone in the surrounding rock of the tunnel.

[0095] Through the above technical solution, in this embodiment, the equivalent radius of the tunnel a = 2.7m, the bolt breaking load 260kN, is used to calculate the equivalent internal friction angle of coal rock in the coal seam fracture zone. is 60°, the radius of the rupture zone is R f It is 2.93m>2.7m, so the fracture zone appears when the surrounding rock of the tunnel is stable.

[0096] As an implementation mode of the present invention, the method for predicting the relationship between the force and deformation of the surrounding rock support of the tunnel in step S3 is:

[0097] According to the tunnel engineering conditions and the elastic-plastic theory, the vertical stress, cohesion c and internal friction angle of the tunnel are calculated. Poisson's ratio and elastic modulus are incorporated into the expression of tunnel surrounding rock support force-deformation:

[0098]

[0099]

[0100] Among them, u a is the deformation of the surrounding rock of the tunnel; μ is the Poisson's ratio of coal rock; E is the elastic modulus of coal rock.

[0101] As an embodiment of the present invention, a method for estimating the compressive strength of surrounding rock supported by bolts is as follows:

[0102] First, when the surrounding rock of the tunnel has a fracture zone, let P design =σ3, and the currently acquired Substituting σ3 into the principal stress expression (2) of Coulomb failure of coal rock, the maximum principal stress σ1' is obtained. σ1' is the compressive strength of the surrounding rock in the fracture zone of the bolt support.

[0103] First, when there is no fracture zone in the surrounding rock of the tunnel, the maximum allowable elongation L0 after high pre-tightening support of the anchor bolt is L0 = u a Substitute it into the tunnel surrounding rock support force-deformation expression to calculate the support force P 0spport ; P 0sppor Compare t with P0 and take P 0sppor The minimum value between t and P0 is taken as σ3 and substituted into the principal stress expression (1) of Coulomb failure of coal rock to obtain the maximum principal stress σ1''. The value of σ1'' is the compressive strength of the surrounding rock supported by the anchor bolt.

[0104] Through the above technical solution, since in this embodiment, it is judged that the crack zone appears when the surrounding rock of the tunnel is stable; then according to the method for estimating the compressive strength of the surrounding rock supported by the anchor bolt, P design =0.189MPa=σ3, Substituting into formula 1, we get the maximum principal stress σ1', which is the compressive strength of the surrounding rock in the fractured area of ​​anchor support, which is 2.63MPa;

[0105] Of course, in the present embodiment, when there is no fracture zone in the surrounding rock of the tunnel, the working load and deformation capacity of the anchor rod are fully considered. On the one hand, the anchor rod support performance is maximized, and on the other hand, the anchor rod is prevented from breaking and failing due to excessive elongation, so that the estimation of the strength of the surrounding rock of the anchored tunnel is more reasonable.

[0106] As an implementation mode of the present invention, the maximum allowable elongation L0 of the anchor rod after the anchor rod is pre-tightened is obtained as follows:

[0107] Obtain the curve EL1 of the anchor working load changing with the extension distance when there is no preload;

[0108] Obtain the curve EL2 showing the variation of the anchor working load with the elongation distance when the preload force P1 is applied; determine the maximum allowable elongation L0 of the anchor after the anchor is preloaded according to the intersection value of the curve EL1 and the curve EL2.

[0109] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for estimating the surrounding rock strength of an anchor-supported roadway, characterized in that: The method comprises: S1. Obtain basic investigation information on the surrounding rock of the bolt support tunnel, sample the surrounding rock and bolt materials, and obtain sampling data; S2. Analyze the sampling data: determine the mechanical properties of the coal and rock in the tunnel, determine the working properties of the anchor material, and calculate the anchor support strength; S3. According to the sampling data analysis results, the state of the surrounding rock of the anchor support is identified to determine whether a fracture zone exists: If yes, then directly estimate the compressive strength of the surrounding rock supported by the anchor bolts; If not, the force-deformation relationship of the tunnel surrounding rock support is estimated first, and then the compressive strength of the surrounding rock of the anchor support is estimated; S4, output the estimation result of step S3; The method for measuring the mechanical properties of coal and rock in the roadway is: The principal stress expression of Coulomb failure of coal rock is: ； in, is the principal stress expression of Coulomb failure of coal rock, It is the principal stress expression of Coulomb failure of coal rock when the fracture zone appears; is the uniaxial compressive strength of coal rock; For cohesion; is the internal friction angle; is the maximum principal stress; is the minimum principal stress; is the equivalent internal friction angle of the surrounding rock in the fracture zone, and ; The method for determining the state of the surrounding rock supported by bolts in step S3 is as follows: By formula Calculate the radius of the surrounding rock fracture zone of the tunnel ; in, is the equivalent radius of the roadway; is the vertical stress at the location of the tunnel, and , is the bulk density of surrounding rock, The depth of the tunnel; The maximum support strength that can be provided by anchor support; is the equivalent internal friction angle of the surrounding rock in the fracture zone; The radius of the fracture zone of the surrounding rock of the roadway Equivalent radius of the roadway To compare: when When , it is judged that the surrounding rock of the tunnel has a fracture zone; when When , it is judged that there is no fracture zone in the surrounding rock of the roadway; The method for predicting the relationship between the supporting force and deformation of the surrounding rock of the tunnel in step S3 is: The expression of tunnel surrounding rock support force-deformation is obtained: ； in, is the deformation of the surrounding rock of the tunnel; is the Poisson's ratio of coal rock; is the elastic modulus of coal rock.

2. The method for estimating the surrounding rock strength of an anchor-supported roadway according to claim 1, characterized in that: The process of determining the working characteristics of the anchor material is as follows: SS1. Determine the free length of the anchor support; SS2. Install the anchor sample on the testing machine and ensure that the free section length of the anchor support is consistent with the actual free section length of the anchor; SS3. Conduct a tensile test to determine the maximum allowable elongation of the anchor after pre-tightening. .

3. The method for estimating the surrounding rock strength of an anchor-supported roadway according to claim 2, characterized in that: The anchor support strength calculation includes: Anchor rock support force The formula is: ； in, is the working load of a single anchor; The number of anchors on the roadway roof and sidewalls along the roadway direction; is the unevenness coefficient of the anchor working load; And when the top plate of the anchor support is flat and the cross section of the anchor support is flat, Take 0.8-0.9; when the top plate of the anchor support is uneven and the cross section of the anchor support is partially uneven, Take 0.6-0.8; when the top plate of the anchor support is uneven and has large fluctuations and the cross section of the anchor support is uneven and has large fluctuations, Take 0.5-0.6; According to the on-site anchor support parameters, Design anchoring force for anchor bolts and anchor support strength The formula is: ； in, The width of the roadway with anchor support top plate and the height of the roadway side with anchor support side plate; Anchor rod spacing.

4. A method for estimating the surrounding rock strength of an anchor-supported tunnel according to claim 1 or 3, characterized in that: The method for estimating the compressive strength of surrounding rock supported by anchor bolts is as follows: When the surrounding rock of the tunnel has a cracked area, , and the currently acquired , Substituting it into the principal stress expression (2) of Coulomb failure of the coal rock, the maximum principal stress is obtained. , It is the compressive strength of surrounding rock in the fractured area of ​​anchor support; When there is no cracked area in the surrounding rock of the tunnel, the maximum allowable elongation of the anchor bolt after high pre-tightening support Substitute it into the tunnel surrounding rock support force-deformation expression to calculate the support force ;Will and To compare, take and The minimum value between Substitute it into the principal stress expression (1) of Coulomb failure of the coal rock to obtain the maximum principal stress , The value is the compressive strength of the surrounding rock supported by the anchor.

5. The method for estimating the surrounding rock strength of an anchor-supported roadway according to claim 2, characterized in that: The maximum allowable elongation of the anchor rod after the anchor rod is pre-tightened The way to obtain is: Obtain the curve of the anchor working load changing with the extension distance when there is no preload ; Get the preload Curve of anchor working load changing with extension distance ; According to the curve and curve The intersection value determines the maximum allowable elongation of the anchor after the anchor is pre-tightened. .

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