A Design Method for the Support Structure of Deep-Buried Soft Rock Tunnels Based on Energy Regulation

Abstract

The present invention provides a design method for the support structure of a deeply buried soft rock tunnel based on energy regulation, belonging to the technical field of tunnel engineering; it includes: obtaining the components of the in-situ stress in the direction of the major principal stress, the intermediate principal stress, and the minor principal stress; manufacturing rock cylindrical specimens and cubic specimens; conducting a conventional uniaxial compression test on the cylindrical specimens to obtain the basic strength parameters of the surrounding rock; conducting a true triaxial loading and unloading test on the cubic specimens to obtain the ultimate dissipated energy of the surrounding rock; formulating a design scheme for the tunnel bolt support structure; establishing a calculation model for the deeply buried soft rock tunnel considering the cooperative action of the surrounding rock and bolts, and calculating the dissipated energy density of the surrounding rock and the absorbed energy of the support structure; calculating the instability energy judgment basis of the surrounding rock and the instability energy judgment basis of the bolts; judging the stability of the surrounding rock and judging the stability of the bolts. The present invention is applicable to tunnels in a deep high-energy geological environment and can reflect the energy-driven essence of the instability and failure of deeply buried soft rock tunnels under high in-situ stress.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering and relates to a design method for the supporting structure of a deep-buried soft rock tunnel based on energy regulation. Background Technique

[0002] In high geostress deep-buried soft rock tunnels that appear in railway tunnel engineering construction, the squeezing large deformation caused by high geostress has brought great harm to the construction of the tunnel and the operation safety in the later stage. The problem of the supporting structure design of high geostress deep-buried soft rock tunnels has always troubled the majority of tunnel constructors. The existing supporting structure design methods mainly rely on the prediction of squeezing potential, which can be divided into the engineering analogy method, the theoretical analysis method, and the machine learning method according to different prediction methods. The engineering analogy method is based on the comprehensive analysis of existing tunnel cases with similar surrounding rock conditions and service functions, establishes a large deformation grading evaluation method for high geostress deep-buried soft rock tunnels, and proposes corresponding supporting schemes and supporting parameters for different deformation grades for engineering design reference. The theoretical analysis method calculates the stress and deformation in the process of the interaction between the surrounding rock and the support through theoretical analysis, and then evaluates the stability of the tunnel, and optimizes the supporting scheme according to the evaluation results. The machine learning method collects a large amount of deformation monitoring data and formation condition parameters, proposes the key factors affecting tunnel deformation, selects a suitable machine learning model for training, and optimizes the prediction accuracy of the model by adjusting parameters and algorithms. Finally, the trained model is used to predict the tunnel deformation of the actual project, and the squeezing risk is evaluated and the supporting structure is designed according to the prediction results.

[0003] The existing supporting design methods mainly evaluate the stability of high geostress deep-buried soft rock tunnels from the perspectives of the stress-strain field and the evolution of the displacement field. However, at present, the large deformation disasters during the construction of high geostress soft rock tunnels have not been completely and effectively controlled, and it is still an engineering problem to be solved urgently. The deep rock mass in the high geostress environment stores a high amount of strain energy and belongs to a high-energy geological environment. The excavation of deep tunnels leads to the generation of a free face in the surrounding rock of the tunnel, causing stress redistribution in the surrounding rock and the accumulation of energy on the free face. When the energy accumulated in the surrounding rock in the near-hole area exceeds the energy storage limit, the dissipation and release of energy will be triggered, which will further induce the deformation, damage, and failure of the surrounding rock. Therefore, the deformation and failure process of the surrounding rock of high geostress deep-buried soft rock tunnels is driven by energy. The traditional stress-strain relationship cannot reflect the energy-driven essence of the deformation and failure of the surrounding rock, and there are certain limitations in quantifying the deformation grade, severity, and the supporting effects of different supporting parameters of the tunnel. A reasonable support should enable the surrounding rock and the supporting structure of the tunnel to meet the requirements of bearing capacity and allowable deformation at the same time. Designing the supporting structure from the perspective of energy can achieve the unity of strength design and stiffness design. Summary of the Invention

[0004] The invention provides a design method for the supporting structure of a deep-buried soft rock tunnel based on energy regulation, including the following steps:

[0005] Step 1: Test the in-situ stress in the tunnel site area to obtain the components of the in-situ stress in the directions of the major principal stress, intermediate principal stress, and minor principal stress respectively;

[0006] Fabricate specimens in the form of cylinders and cubes respectively from the rock masses at the engineering site in the tunnel site area;

[0007] Step 2: Conduct a conventional uniaxial compression test on the cylindrical specimens to obtain the basic strength parameters of the surrounding rock;

[0008] Conduct a true triaxial loading and unloading test on the cubic specimens to obtain the ultimate dissipated energy of the surrounding rock;

[0009] Step 3: Take the energy dissipation limit value of the surrounding rock as the evaluation index for the bearing capacity of the surrounding rock of the deep-buried soft rock tunnel under high in-situ stress, and formulate a design scheme for the tunnel bolt support structure. Distribute the mortar bolts uniformly along the longitudinal and circumferential directions of the tunnel to form the tunnel support structure, and then formulate the relevant parameters of the tunnel support structure;

[0010] Step 4: Based on the relevant parameters of the formulated tunnel support structure, establish a calculation model for the deep-buried soft rock tunnel considering the synergistic effect of the surrounding rock and bolts, and calculate the dissipated energy density of the surrounding rock and the absorbed energy of the support structure;

[0011] Step 5: Calculate the judgment basis for the instability energy of the surrounding rock and the judgment basis for the instability energy of the bolts ;

[0012] Step 6: Judge the stability of the surrounding rock according to the judgment basis for the instability energy of the surrounding rock and judge the stability of the bolts according to the judgment basis for the instability energy of the bolts ; If the stability of the surrounding rock and the stability of the bolts both meet the requirements, output the design scheme for the tunnel bolt support structure. If the stability of the surrounding rock and the stability of the bolts do not meet the requirements, adjust the relevant parameters of the tunnel support structure formulated in Step 3, such as increasing the number of bolts, reducing the bolt spacing, increasing the bolt length, or selecting bolts with greater strength, and return to Step 4.

[0013] Furthermore, the basic strength parameters of the surrounding rock include: elastic modulus , Poisson's ratio , uniaxial compressive strength , dilation coefficient , peak geological strength index , rock mass quality characteristic parameter and disturbance coefficient ;

[0014] The specific process of obtaining the ultimate dissipated energy of surrounding rock is as follows:

[0015] S2.1. According to the in-situ stress test results, the initial values to be applied are set for the stresses on the six surfaces of the specimen respectively, so as to simulate the stress state of the surrounding rock before tunnel excavation; among them, the initial values of the upper and lower axial stress acting surfaces of the specimen are set as the major principal stress , the initial values of the lateral stresses on two mutually parallel side surfaces of the specimen are set as the intermediate principal stress , and the initial values of the lateral stresses on the other two mutually parallel side surfaces of the specimen are set as the minor principal stress ;

[0016] Keep the intermediate principal stress unchanged, and continuously increase the axial major principal stress at a constant loading rate by means of displacement loading, and continuously unload the minor principal stress at a constant unloading rate by means of stress unloading. When the minor principal stress is unloaded to zero, the test ends, and the stress-strain curves of the specimen in the directions of the major principal stress, intermediate principal stress, and minor principal stress at different time periods during the true triaxial loading and unloading process are obtained;

[0017] S2.2. Based on the stress-strain and each energy component of the specimen in the directions of the major principal stress , intermediate principal stress , and minor principal stress during the elastic deformation stage of the true triaxial loading and unloading process, the elastic strain energy and plastic dissipated energy of the specimen are obtained;

[0018] S2.3. Based on the elastic strain energy and plastic dissipated energy of the specimen, the energy dissipation rate of the specimen is calculated;

[0019] S2.4. Take the plastic dissipated energy corresponding to when the energy dissipation rate of the specimen reaches its maximum value as the energy consumption limit value of the surrounding rock, and take the energy consumption limit value of the surrounding rock as the evaluation index of the bearing capacity of the surrounding rock of the high in-situ stress and deep-buried soft rock tunnel.

[0020] Furthermore, the relevant parameters of the initially proposed tunnel support structure include: the layout spacing of adjacent bolts along the tunnel axis is , the included angle between adjacent bolts along the circumferential direction of the tunnel is , the length of the bolt is , the diameter of the anchorage area is , the elastic modulus of the bolt , the hardening modulus of the bolt , the yield strength of the bolt , the ultimate tensile strength of the bolt , the yield strain of the bolt and the failure strain of the bolt .

[0021] Furthermore, the specific process of calculating the dissipated energy density of the surrounding rock and the absorbed energy of the support structure is as follows:

[0022] S4.1. Establish a calculation model for deep tunnels considering the co - action of the surrounding rock and bolts, and input the basic parameters of the tunnel model, the strength parameters of the surrounding rock, and the material parameters of the bolts;

[0023] The basic parameters of the tunnel model include: the excavation radius of the tunnel is , the virtual support reaction force acting on the tunnel wall is , the in - situ stress of the tunnel is , the layout spacing of adjacent bolts along the tunnel axis is , the angle between adjacent bolts along the circumferential direction of the tunnel is , the length of the bolt is and the radius of the anchorage area is ;

[0024] The strength parameters of the surrounding rock include: the elastic modulus , the Poisson's ratio , the uniaxial compressive strength , the peak geological strength index , the rock mass quality characteristic parameter and the disturbance coefficient ;

[0025] The material parameters of the bolts include: the shear stiffness between the bolt and the grout interface , the bond strength between the bolt and the grout interface or between the surrounding rock and the grout interface , the friction angle of the failure surface of the grout body , the elastic modulus of the bolt , the hardening modulus of the bolt , the yield strength of the bolt , the ultimate tensile strength of the bolt , the yield strain of the bolt and the failure strain of the bolt ;

[0026] S4.2. Based on the deep - tunnel calculation model, solve the stress evolution path of the deep - tunnel surrounding rock under the co - action of the surrounding rock and bolts after tunnel excavation, and obtain the surrounding rock at the th unloading Radial deformation of the layer ;

[0027] S4.3, based on The surrounding rock mass at the time of first unloading Radial deformation of the layer Solve the stress evolution path of deep tunnel anchors under the synergistic effect of surrounding rock and anchors after tunnel excavation;

[0028] S4.4. Calculate the energy density and total energy of the surrounding rock based on the stress evolution path of the surrounding rock;

[0029] S4.5. Calculate the energy density and total absorbed energy of the anchor based on the stress evolution path of the anchor.

[0030] Furthermore, the established deep tunnel calculation model satisfies the following conditions:

[0031] (I) Assuming the tunnel depth is greater than 500m, the ground stress before excavation is a uniformly distributed hydrostatic pressure environment;

[0032] (II) The surrounding rock is a homogeneous and isotropic elastic material and the stress state in the plastic stage satisfies the three-dimensional HB strength criterion and the strain increment complies with the non-associated flow law;

[0033] (III) The mechanical behavior of the interaction between the anchor and the surrounding rock satisfies the bond-slip model. The relationship between the shear stress per unit length of the anchor and the relative displacement between the anchor and the surrounding rock satisfies the following formula:

[0034] ;

[0035] in, is the shear stress per unit length of the anchor; is the relative displacement between a certain point on the anchor and the surrounding rock at that position; is the shear stiffness between the anchor and grout interface or between the surrounding rock and grout interface; It is the bond strength between the anchor and grout interface or between the surrounding rock and grout interface; is the friction angle of the failure surface of the grouting body; is the effective diameter of the interface between the anchor and the grouting layer; The confining pressure per unit length of the anchor rod is equal to the radial stress of the surrounding rock. ;

[0036] (IV) The relationship between the axial force and tensile deformation of the anchor rod satisfies the linear strengthening elastic-plastic mechanics model shown in the following formula:

[0037] ;

[0038] in, is the axial stress of the bolt is the tensile strain of the bolt

[0039] Furthermore, to solve for the radial deformation of the th layer of the surrounding rock during the th unloading, the specific process is as follows:

[0040] S4.2.1. Assume that the stress in the anchored zone of the surrounding rock satisfies the following equilibrium equation:

[0041] ;

[0042] where is the bolt geometric coefficient ; is the distance from any position in the surrounding rock to the center of the circle is the radial stress of the surrounding rock;

[0043] The stress in the unanchored zone of the surrounding rock satisfies the following equilibrium equation:

[0044] ;

[0045] The stress in the elastic zone of the surrounding rock satisfies the following quantitative relationship;

[0046] ;

[0047] The stress in the plastic zone of the surrounding rock satisfies the three-dimensional H-B strength criterion;

[0048] S4.2.2. Calculate the stress of the surrounding rock;

[0049] Assume that the virtual support reaction force acting on the tunnel wall is gradually unloaded from the in-situ stress of the tunnel to 0 in steps, and the surrounding rock is divided into layers. Then, using the finite difference method, the stress of the th layer of the surrounding rock during the th unloading is where is the unloading step of the support reaction force unloading is the number of the surrounding rock layer ;

[0050] S4.2.3. According to the calculation results of the surrounding rock stress, solve for the elastic strain increment of the th layer of the surrounding rock relative to the th layer;

[0051] S4.2.4. Simultaneously solve the deformation compatibility equations and the plastic potential function to obtain the total strain of the surrounding rock ;

[0052] S4.2.5. Based on the total strain of the surrounding rock , solve for the radial deformation of the th layer of the surrounding rock during the th unloading.

[0053] Furthermore, the specific process for solving the stress evolution path of the deep tunnel bolts under the combined action of the surrounding rock and the bolts after tunnel excavation is as follows:

[0054] S4.3.1. Based on the radial deformation of the th layer of the surrounding rock during the th unloading, solve for the relative displacement between any point on the bolt and the surrounding rock during the th unloading, as well as the shear stress of the bolt;

[0055] S4.3.2. Based on the shear stress of the bolt, calculate the axial force of the th layer of the bolt during the th unloading;

[0056] S4.3.3. Calculate the tensile strain of the bolt based on the linear hardening elastoplastic mechanical model of the bolt.

[0057] Furthermore, the method for determining the position of the neutral point of the bolt is as follows:

[0058] The position of the neutral point is determined according to the self - equilibrium equation of the bolt;

[0059] The self - equilibrium equation of the bolt is as follows:

[0060] ;

[0061] where is the distance between the neutral point of the bolt and the bolt head, and is the distance between any point on the bolt and the bolt;

[0062] When specifically solving for the position of the neutral point of the bolt, the specific process is as follows:

[0063] (i). Assume the position of the neutral point is ;

[0064] (ii). According to the expression of and The expressions are used to calculate the relative displacements and shear stresses of each node of the bolt in turn; the trial calculation results of the shear stresses are substituted into the self - equilibrium equation of the bolt;

[0065] (iii). Judge whether the shear stress satisfies the self - equilibrium equation;

[0066] (iv). If not satisfied, adjust the position of the neutral point to , and return to (ii); if satisfied, directly determine the position of the neutral point of the bolt as the final position.

[0067] Furthermore, the specific process of calculating the energy density and total energy of the surrounding rock according to the stress path of the surrounding rock is as follows:

[0068] S4.4.1. According to the calculation results of the stress path of the surrounding rock, obtain the elastic energy density of the th layer of the surrounding rock after times of unloading, the plastic dissipation energy density and the plastic release energy density ;

[0069] S4.4.2. Integrate the energy density components within the plastic zone range to obtain the increment of elastic strain energy , plastic dissipation energy and plastic release energy of the plastic zone of the surrounding rock in the plastic deformation stage;

[0070] The specific process of calculating the energy density and absorbed total energy of the bolt according to the stress path of the bolt is as follows:

[0071] S4.5.1. According to the calculation results of the stress path of the bolt, the distribution density of the absorbed energy of the bolt along the length direction ;

[0072] S4.5.2. Integrate the energy density of any point of the bolt along the length direction to solve the absorbed energy of a single bolt at the th unloading;

[0073] According to the number of bolts contained in a unit length along the longitudinal direction of the tunnel, obtain the total absorbed energy of the bolts per unit cross - section of the tunnel under plane - strain conditions .

[0074] Furthermore, the specific process of judging the stability of the surrounding rock according to the instability energy judgment basis of the surrounding rock is as follows:

[0075] When the instability energy judgment basis of the surrounding rock, it is determined that the surrounding rock has no risk of instability failure; when the instability energy judgment basis If so, it is determined that there is a risk of instability in the surrounding rock, and the basis for judging the instability energy of the surrounding rock The larger it is, the higher the risk of instability;

[0076] According to the basis for judging the instability energy of the bolt The specific process of judging the stability of the bolt is as follows:

[0077] When the basis for judging the instability energy of the bolt If so, it is determined that the bolt is in the normal working stage; when the basis for judging the instability energy of the bolt If so, it is determined that the bolt will be pulled off;

[0078] When the basis for judging the instability energy of the surrounding rock and the basis for judging the instability energy of the bolt are both less than 1, it means that the design requirements of the support structure for the deep-buried soft rock tunnel are met; when the basis for judging the instability energy of the surrounding rock and the basis for judging the instability energy of the bolt are both greater than or equal to 1, it means that the design requirements of the support structure for the deep-buried soft rock tunnel are not met.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] (1) The present invention proposes a design method for the support structure of deep-buried soft rock tunnels based on energy regulation, which is applicable to tunnels in deep high-energy geological environments and can reflect the energy-driven essence of the instability and failure of deep-buried soft rock tunnels under high ground stress. The essence of the instability and failure of the surrounding rock in deep-buried soft rock tunnels under high ground stress is the result that the dissipated energy exceeds the energy consumption limit of the surrounding rock, and the essence of the failure of the support structure is that the absorbed energy exceeds the support energy storage limit. Therefore, the new design method proposed by the present invention aims to control the dissipated energy density of the surrounding rock and the absorbed energy density of the support structure within the limit values from the perspective of energy regulation to ensure the stability of the two load-bearing bodies of the surrounding rock and the support.

[0081] (2) The design method for the support structure of deep-buried soft rock tunnels based on energy regulation proposed by the present invention can achieve the unity of strength design and stiffness design, and solves the design problem that it is difficult to quantify the support parameters for deep-buried soft rock tunnels under high ground stress. A reasonable support structure should, on the one hand, fully mobilize the bearing capacity of the surrounding rock and have a certain ability to release the deformation of the surrounding rock, and on the other hand, also have compressive strength to prevent the surrounding rock from loosening and failing. Therefore, for the design of the support structure of deep-buried soft rock tunnels under high ground stress, the unity of strength design and stiffness design should be achieved, and energy is an effective index to achieve the unity of the two and an important basis for the design of the support structure.

[0082] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the drawings. Brief Description of the Drawings

[0083] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0084] Figure 1 is a schematic flow chart of a design method for a support structure of a deeply buried soft rock tunnel based on energy regulation in an embodiment of the present invention;

[0085] Figure 2 is a schematic diagram of a calculation model for a deep tunnel in an embodiment of the present invention;

[0086] Figure 3(a) is a schematic diagram of the zoning in the elastic deformation stage of the surrounding rock in an embodiment of the present invention;

[0087] Figure 3(b) is a schematic diagram of the zoning in the plastic deformation stage of the surrounding rock and the radius of the plastic zone is smaller than the radius of the anchorage zone in an embodiment of the present invention;

[0088] Figure 3(c) is a schematic diagram of the zoning in the plastic deformation stage of the surrounding rock and the radius of the plastic zone is larger than the radius of the anchorage zone in an embodiment of the present invention;

[0089] Figure 4 is a schematic diagram of the relative displacement and shear stress between the surrounding rock and the bolt in an embodiment of the present invention;

[0090] Figure 5 is a schematic diagram of the distribution curve of the dissipated energy density of the surrounding rock in an embodiment of the present invention;

[0091] Figure 6 is a schematic diagram of the distribution curve of the absorbed energy density of the bolt in an embodiment of the present invention.

[0092] Among them:

[0093] ① is the elastic zone of the surrounding rock, ② is the plastic zone of the surrounding rock, ③ is the elastic-plastic boundary, ④ is the bolt, ⑤ is the elastic zone with anchor, ⑥ is the elastic zone without anchor, ⑦ is the plastic zone with anchor, ⑧ is the plastic zone without anchor, ⑨ is the neutral point of the bolt, ⑩ is the distribution curve of the shear stress of the bolt, is the test result of the energy consumption limit of the surrounding rock, is the calculation result of the maximum dissipated energy density of the surrounding rock, is the energy storage limit of the bolt, is the calculation result of the maximum absorbed energy density of the bolt. Detailed Description of the Preferred Embodiments

[0094] To make the above objects, features, and advantages of the present invention more clearly understandable, the following provides a detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the drawings of the present invention are all in simplified forms and use non-precise scales, only for conveniently and clearly assisting in the description of the embodiments of the present invention; the several mentioned in the present invention are not limited to the specific quantities in the drawing examples; the orientation or positional relationships indicated by 'front','middle', 'back', 'left', 'right', 'up', 'down', 'top', 'bottom','middle', etc. in the present invention are all based on the orientation or positional relationships shown in the drawings of the present invention, and do not indicate or imply that the devices or components referred to must have a specific orientation, nor can it be understood as a limitation to the present invention.

[0095] See Figure 1 As shown, a design method for a deep-buried soft rock tunnel support structure based on energy regulation provided by the present invention includes the following steps:

[0096] Step 1: Use the stress relief method to test the in-situ stress in the tunnel site area near the tunnel face, and respectively obtain the components of the in-situ stress in the major principal stress direction, intermediate principal stress direction, and minor principal stress direction according to the elastic mechanics theory and the measured strain data, and denote the component of the in-situ stress in the major principal stress direction as the major principal stress denote the component of the in-situ stress in the intermediate principal stress direction as the intermediate principal stress and denote the component of the in-situ stress in the minor principal stress direction as the minor principal stress ;

[0097] At the same time, select a complete and relatively large rock mass from the engineering site in the tunnel site area, and prepare the rock mass into a cylindrical specimen with a size of 50mm×100mm (diameter×height) and a cubic specimen with a size of 100mm×100mm×100mm (length×width×height), and the surface flatness error of the cylindrical specimen and the cubic specimen is ±0.05mm, and the perpendicularity error is ±0.25°.

[0098] Step 2: Conduct a conventional uniaxial compression test on the cylindrical specimen to obtain the basic strength parameters of the surrounding rock;

[0099] Conduct a true triaxial loading and unloading test on the cubic specimen to obtain the ultimate dissipation energy of the surrounding rock.

[0100] The basic strength parameters of the surrounding rock include: elastic modulus Poisson's ratio uniaxial compressive strength dilatancy coefficient peak geological strength index rock mass quality characteristic parameter and disturbance coefficient .

[0101] The specific process of obtaining the ultimate dissipated energy of surrounding rock is as follows:

[0102] S2.1. According to the in-situ stress test results, set the initial values to be applied to the stresses on the six surfaces of the specimen respectively, so as to simulate the stress state of the surrounding rock before tunnel excavation; among them, set the initial value of the upper and lower axial stress acting surfaces of the specimen as the major principal stress , set the initial value of the lateral stress of two mutually parallel side surfaces of the specimen as the intermediate principal stress , and set the initial value of the lateral stress of the other two mutually parallel side surfaces of the specimen as the minor principal stress ;

[0103] Keep the intermediate principal stress unchanged, and continuously increase the axial major principal stress at a constant loading rate by means of displacement loading, and continuously unload the minor principal stress at a constant unloading rate by means of stress unloading. When the minor principal stress is unloaded to zero, the test ends, and the stress-strain curves of the specimen in the directions of the major principal stress, intermediate principal stress, and minor principal stress at different time periods during the true triaxial loading and unloading process are obtained.

[0104] Furthermore, the different time periods during the true triaxial loading and unloading include the elastic deformation stage, plastic yielding stage, post-peak strain softening stage, and residual stage.

[0105] S2.2. Based on the stress-strain and each energy component of the specimen in the directions of the major principal stress , intermediate principal stress , and minor principal stress during the elastic deformation stage of the true triaxial loading and unloading process, obtain the elastic strain energy and plastic dissipated energy of the specimen;

[0106] The expression of the elastic strain energy of the specimen is as follows:

[0107] ;

[0108] ;

[0109] Among them, is the elastic modulus of the specimen, is the Poisson's ratio of the specimen, is the elastic strain in the direction of the major principal stress, is the elastic strain in the direction of the intermediate principal stress, is the elastic strain in the direction of the minor principal stress.

[0110] The plastic dissipation energy of the rock has the following expression:

[0111] ;

[0112] ;

[0113] wherein, is the total energy of the input rock, and its value is equal to the integral of the principal stresses in each direction with respect to the strain; is the total strain in the direction of the major principal stress, is the total strain in the direction of the intermediate principal stress, is the total strain in the direction of the minor principal stress; specifically, , and are measured by LVDT displacement sensors installed in the true triaxial test equipment.

[0114] S2.3. Based on the elastic strain energy and the plastic dissipation energy of the specimen, calculate the energy dissipation rate of the specimen.

[0115] The energy dissipation rate of the specimen has the following expression:

[0116] .

[0117] S2.4. Take the plastic dissipation energy corresponding to when the energy dissipation rate of the specimen reaches its maximum value as the energy consumption limit value of the surrounding rock, and take the energy consumption limit value of the surrounding rock as the evaluation index for the bearing capacity of the surrounding rock of the deep buried soft rock tunnel under high geostress.

[0118] Specifically, assume that the slope in the evolution curve of the energy dissipation rate of the specimen is 0, then it is when the energy dissipation rate of the specimen reaches its maximum value ; that is:

[0119] ;

[0120] .

[0121] Step 3. Take the energy consumption limit value As an evaluation index for the bearing capacity of surrounding rock in deep-buried soft rock tunnels with high ground stress. Initially, a design scheme for the tunnel bolt support structure is formulated. Mortar bolts are evenly distributed along the longitudinal and circumferential directions of the tunnel to form the tunnel support structure, and the relevant parameters of the tunnel support structure are initially determined.

[0122] The relevant parameters of the initially formulated tunnel support structure include: the layout spacing between adjacent bolts along the tunnel axis is , the included angle between adjacent bolts along the circumferential direction of the tunnel perimeter is , the length of the bolt is , the diameter of the anchorage area is , the elastic modulus of the bolt , the hardening modulus of the bolt , the yield strength of the bolt , the ultimate tensile strength of the bolt , the yield strain of the bolt and the failure strain of the bolt .

[0123] Step 4: Based on the relevant parameters of the initially formulated tunnel support structure, establish a calculation model for deep-buried soft rock tunnels considering the synergistic effect of surrounding rock and bolts, and calculate the dissipated energy density of the surrounding rock and the absorbed energy of the support structure.

[0124] The specific process is as follows:

[0125] S4.1: Establish a calculation model for deep tunnels considering the synergistic effect of surrounding rock and bolts (see the structure of the deep tunnel calculation model in Figure 2 ), and input the basic parameters of the tunnel model, the strength parameters of the surrounding rock, and the material parameters of the bolts;

[0126] Preferably, the basic parameters of the tunnel model include: the excavation radius of the tunnel is , the virtual support reaction force acting on the tunnel wall is , the initial rock stress where the tunnel is located is , the layout spacing between adjacent bolts along the tunnel axis is , the included angle between adjacent bolts along the circumferential direction of the tunnel perimeter is , the length of the bolt is and the radius of the anchorage area is ;

[0127] Preferably, the strength parameters of the surrounding rock include: elastic modulus , Poisson's ratio , uniaxial compressive strength , peak geological strength index , rock mass quality characteristic parameter and disturbance coefficient . Among them: elastic modulus , Poisson's ratio and uniaxial compressive strength Obtained through the uniaxial compression test of the rock, the peak geological strength index , rock mass characteristic parameters and disturbance coefficient Obtained by using the chart prediction method based on the data obtained from the on-site survey of the surrounding rock of the tunnel face. Specifically, the chart prediction method is an existing technology. Preferably, the bolt material parameters include: the shear stiffness between the bolt and the grout interface

[0128] , the bond strength between the bolt and the grout interface or between the surrounding rock and the grout interface , the friction angle of the grout failure surface , the elastic modulus of the bolt , the hardening modulus of the bolt , the yield strength of the bolt , the ultimate tensile strength of the bolt , the yield strain of the bolt , and the failure strain of the bolt . Among them: the shear stiffness . Among them: the shear stiffness , the bond strength and the bond strength are obtained through the pull-out test of the bolt, and other strength parameters are found according to the "Code for Design of Steel Structures" (GB 50017-2017).

[0129] The calculation model of the deep tunnel needs to meet the following conditions:

[0130] (I), Assume that the tunnel burial depth is large enough (burial depth greater than 500m), and the in-situ stress before excavation is a hydrostatic pressure environment with uniform distribution;

[0131] (II), Assume that the surrounding rock is a homogeneous and isotropic elastic material. And the stress state of the rock in the plastic stage satisfies the three-dimensional H-B strength criterion, and the strain increment of the rock in the plastic stage conforms to the non-associated flow rule;

[0132] (III), The mechanical behavior of the interaction between the bolt and the surrounding rock satisfies the bond-slip model, and the relationship between the shear stress per unit length of the bolt and the relative displacement between the bolt and the surrounding rock satisfies the following formula:

[0133] ;

[0134] Among them, is the shear stress per unit length of the bolt; is the relative displacement between a certain point on the bolt and the surrounding rock at this position; is the shear stiffness between the bolt and the grout interface or between the surrounding rock and the grout interface; is the bond strength between the bolt and the grout interface or between the surrounding rock and the grout interface; is the friction angle of the failure surface of the grouting body; is the effective diameter of the interface between the bolt and the grouting layer; is the confining pressure per unit length of the bolt. For a bolt embedded in the surrounding rock, the confining pressure on the bolt is equal to the radial stress of the surrounding rock .

[0135] (IV) The relationship between the axial force and the tensile deformation of the bolt satisfies the linear hardening elastoplastic mechanical model shown in the following formula:

[0136] ;

[0137] Among them, is the axial stress of the bolt, is the tensile strain of the bolt.

[0138] Furthermore, the expression of the three-dimensional H-B strength criterion is as follows:

[0139] ;

[0140] ;

[0141] ;

[0142] ;

[0143] ;

[0144] ;

[0145] Among them, is the octahedral shear stress, is the average value of the first principal stress and the third principal stress in the octahedron, is the uniaxial compressive strength of the octahedron, , , are the strength parameters reflecting the rock characteristics in the three-dimensional H-B strength criterion, and are calculated according to the geological strength index of the rock, the rock mass quality characteristic parameter and the disturbance coefficient ; is the maximum principal stress of the specimen, is the intermediate principal stress of the specimen, is the minimum principal stress of the specimen, , and It is obtained by conducting true triaxial loading and unloading tests on specimens to simulate the true stress path of the surrounding rock after the excavation of a deeply buried tunnel.

[0146] Furthermore, the strain increment of the rock in the plastic zone conforms to the non-associated flow rule and satisfies the plastic potential function ;

[0147] The plastic potential function has the following expression:

[0148] ;

[0149] where is the plastic radial strain increment, is the plastic circumferential strain increment, is the dilatancy coefficient of the rock.

[0150] Furthermore, due to the strain-softening behavior of the surrounding rock in the plastic stage, the geological strength index of the rock linearly decays with the increase of its plastic deviatoric strain. Therefore, a strain-softening model of the surrounding rock in the plastic stage is established;

[0151] The strain-softening model of the surrounding rock in the plastic stage has the following expression:

[0152] ;

[0153] ;

[0154] where is the plastic deviatoric strain of the rock, which is the difference between the plastic circumferential strain and the plastic radial strain ; is the critical plastic deviatoric strain of the rock; is the peak value of the geological strength index of the rock, which is also its initial value; is the residual value of the geological strength index of the rock.

[0155] S4.2. Solve the stress evolution path of the surrounding rock of the deep tunnel under the combined action of the surrounding rock and bolts after tunnel excavation based on the deep tunnel calculation model (i.e., solve the radial deformation of the th layer of the surrounding rock at the th unloading);

[0156] Specifically as follows:

[0157] S4.2.1. Assume that the stress in the anchored area of the surrounding rock needs to satisfy the following equilibrium equation:

[0158] ;

[0159] in, is the anchor geometry coefficient, ; is the distance from any position of the surrounding rock to the center of the circle, is the radial stress of the surrounding rock.

[0160] The stress in the non-anchored area of the surrounding rock must satisfy the following equilibrium equation:

[0161] ;

[0162] The stress in the elastic zone of the surrounding rock must satisfy the following quantitative relationship:

[0163] ;

[0164] The stress in the plastic zone of the surrounding rock must meet the three-dimensional HB strength criterion.

[0165] S4.2.2. Calculate the surrounding rock stress. The specific process is as follows:

[0166] As shown in Figures 3(a) to 3(c), the surrounding rock is divided into an elastic zone with anchor, an elastic zone without anchor, a plastic zone with anchor, and a plastic zone without anchor according to the relationship between the radius of the anchoring zone and the radius of the plastic zone.

[0167] Among them, the stress in the elastic zone with anchor is calculated by combining the stress balance equation of the surrounding rock anchoring zone and the stress quantitative relationship formula of the elastic zone of the surrounding rock; the stress in the elastic zone without anchor is calculated by combining the stress balance equation of the surrounding rock non-anchoring zone and the stress quantitative relationship formula of the elastic zone of the surrounding rock; the stress in the plastic zone with anchor is calculated by combining the stress balance equation of the rock anchoring zone and the three-dimensional HB strength criterion expression; the stress in the plastic zone without anchor is calculated by combining the stress balance equation of the surrounding rock non-anchoring zone and the three-dimensional HB strength criterion expression.

[0168] Furthermore, when calculating the stresses in the elastic zone with anchors, the elastic zone without anchors, the plastic zone with anchors, and the plastic zone without anchors, the finite difference method is used to solve the stress evolution path of the surrounding rock during the tunnel excavation unloading process. The specific calculation method is as follows: Assume that the virtual support reaction force acting on the tunnel wall is The original rock stress of the tunnel Gradually uninstall to 0 required The number of the step and surrounding rock layer is , then the finite difference method is used to obtain the The surrounding rock mass at the time of first unloading The stress of the layer is ,in, is the number of unloading steps for support reaction unloading, is the number for the stratification of surrounding rock, ;

[0169] S4.2.3. According to the calculation results of the surrounding rock stress, solve for the elastic strain of the th layer of the surrounding rock ;

[0170] The specific process is as follows:

[0171] Solve for the elastic strain increment of the th layer of the surrounding rock relative to the th layer according to Hooke's law , and then obtain the elastic strain of the th layer of the surrounding rock ;

[0172] The elastic strain increment of the th layer of the surrounding rock relative to the th layer is expressed as follows:

[0173] ;;

[0174] The elastic strain of the th layer of the surrounding rock is expressed as follows:

[0175] ;

[0176] ;

[0177] Among them, is the stress increment of the th layer relative to the th layer;

[0178] S4.2.4. Simultaneously solve the deformation compatibility equation and the plastic potential function to obtain the total strain of the surrounding rock;

[0179] The total strain of the surrounding rock is expressed as follows:

[0180] ;

[0181] ;

[0182] .

[0183] S4.2.5. From the total strain and the elastic strain increment of the surrounding rock, solve for the plastic strain increment of the th layer of the surrounding rock relative to the th layer , and then the plastic strain of the th layer of the surrounding rock is obtained ;

[0184] The plastic strain increment of the th layer of the surrounding rock relative to the th layer is as follows: ;

[0185] ;

[0186] The plastic strain of the th layer of the surrounding rock is as follows: ;

[0187] ;

[0188] From the strain and physical equations of the surrounding rock, the radial deformation of the th layer of the surrounding rock during the th unloading can be solved;

[0189] ;

[0190] where is the radius of the th layer of the surrounding rock.

[0191] S4.3. Based on the radial deformation of the th layer of the surrounding rock during the th unloading, solve the stress evolution path of the deep tunnel bolt under the combined action of the surrounding rock and the bolt after tunnel excavation;

[0192] The specific process is as follows:

[0193] S4.3.1. Solve the relative displacement between any point in the bolt and the surrounding rock during the th unloading, as well as the shear stress of the bolt;

[0194] The relative displacement between any point in the bolt and the surrounding rock during the th unloading is as follows:

[0195] ;

[0196] where is the node number of the neutral point of the bolt; is the deformation of the th layer of the surrounding rock corresponding to the neutral point of the bolt after the bolt is installed during the th unloading; After the anchor bolt is installed, the deformation of the surrounding rock corresponding to the nd layer during the th unloading is considered.

[0197] Furthermore, as shown in Figure 4 , the method for determining the position of the neutral point of the anchor bolt is as follows:

[0198] The position of the neutral point is determined according to the self - balance equation of the anchor bolt;

[0199] The self - balance equation of the anchor bolt is as follows:

[0200] ;

[0201] Where, is the distance between the neutral point of the anchor bolt and the anchor head, is the distance between any point on the anchor bolt and the anchor bolt.

[0202] Even further, when specifically solving for the position of the neutral point of the anchor bolt, the specific process is as follows:

[0203] (i) Assume the position of the neutral point is ;

[0204] (ii) According to the expression of and the expression of , successively trial - calculate the relative displacements and shear stresses of each node of the anchor bolt;

[0205] (iii) Substitute the trial - calculation results of the shear stress into the self - balance equation of the anchor bolt and determine whether the shear stress satisfies the self - balance equation;

[0206] (iv) If not satisfied, adjust the position of the neutral point to , and return to step (ii) to recalculate the relative displacements and shear stresses of each node of the anchor bolt until the calculation converges to find a suitable position of the neutral point , and confirm this position of the neutral point as the final position.

[0207] If satisfied, directly determine the position of the neutral point of the anchor bolt as the final position.

[0208] S4.3.2. Calculate the axial force of the th layer of the anchor bolt during the th unloading based on the shear stress of the anchor bolt;

[0209] The axial force of the th layer of the anchor bolt during the th unloading is expressed as follows:

[0210] ;

[0211] S4.3.3. Calculate the tensile strain of the bolt based on the linear hardening elastoplastic mechanical model of the bolt ;

[0212] The tensile strain of the bolt is expressed as follows:

[0213] ;

[0214] where is the cross-sectional area of the bolt.

[0215] S4.4. Calculate the energy density and total energy of the surrounding rock according to the stress path of the surrounding rock;

[0216] The specific process is as follows:

[0217] S4.4.1. According to the calculation results of the stress path of the surrounding rock, obtain the elastic energy density of the th layer of the surrounding rock after times of unloading, the plastic dissipation energy density and the plastic release energy density ;

[0218] The elastic energy density , the plastic dissipation energy density and the plastic release energy density are expressed as follows:

[0219] ;

[0220] ;

[0221] ;

[0222] where is the plastic dissipation strain, is the plastic release strain, is the natural constant;

[0223] S4.4.2. Integrate the energy density components within the plastic zone to obtain the elastic strain energy increment , the plastic dissipation energy and the plastic release energy of the plastic zone of the surrounding rock during the plastic deformation stage;

[0224] The elastic strain energy increment , the plastic dissipation energy and the plastic release energy of the plastic zone of the surrounding rock during the plastic deformation stage are expressed as follows:

[0225] ;

[0226] ;

[0227] Among them, is the initial elastic strain energy density of the surrounding rock before tunnel excavation, is the Poisson's ratio of the surrounding rock, is the elastic modulus of the surrounding rock.

[0228] S4.5. Calculate the energy density and total absorbed energy of the bolt according to the stress path of the bolt.

[0229] The specific process is as follows:

[0230] S4.5.1. According to the calculation results of the bolt stress path, the distribution density of the absorbed energy of the bolt along the length direction ;

[0231] The distribution density of the absorbed energy of the bolt along the length direction is expressed as follows:

[0232] ;

[0233] S4.5.2. Integrate the energy density of any point of the bolt along the length direction to solve the absorbed energy of a single bolt during the th unloading. Further, according to the number of bolts included in the unit length of the tunnel along the longitudinal direction, the total absorbed energy of the bolts per unit cross-section of the tunnel under plane strain conditions can be obtained ;

[0234] The total absorbed energy of the bolts per unit cross-section of the tunnel under plane strain conditions is expressed as follows:

[0235] ;

[0236] Where: is the differential.

[0237] Step Five: Calculate the instability energy judgment basis of the surrounding rock based on the dissipated energy density of the surrounding rock and the absorbed energy of the support structure and the instability energy judgment basis of the bolt ;

[0238] Judge the stability of the surrounding rock according to the instability energy judgment basis of the surrounding rock and judge according to the instability energy judgment basis Judge the stability of the bolt. If the stability of the surrounding rock and the bolt both meet the requirements, output the design scheme of the tunnel bolt support structure. If the stability of the surrounding rock and the bolt both do not meet the requirements, adjust the relevant parameters of the tunnel support structure determined in Step 3 and return to Step 4.

[0239] Further, the judgment basis for the instability energy of the surrounding rock The expression is:

[0240] ;

[0241] Wherein, is the maximum plastic strain energy density of the surrounding rock, is the energy consumption limit value of the surrounding rock.

[0242] When the judgment basis for the instability energy of the surrounding rock , it is determined that the surrounding rock has no risk of instability failure; when the judgment basis for the instability energy of the surrounding rock , it is determined that the surrounding rock will have the risk of instability, and the greater the judgment basis for the instability energy of the surrounding rock , the higher the risk of instability.

[0243] Further, the judgment basis for the instability energy of the bolt The expression is:

[0244] ;

[0245] ;

[0246] Wherein: is the maximum absorbed energy density of the bolt, is the energy storage limit value of the bolt, is the yield strength of the bolt, is the ultimate tensile strength of the bolt, is the yield strain of the bolt, is the failure strain of the bolt.

[0247] When the judgment basis for the instability energy of the bolt , it is determined that the bolt is in the normal working stage (that is, the bolt is in a state where it will not be pulled off); when the judgment basis for the instability energy of the bolt , it is determined that the bolt will be pulled off.

[0248] Example:

[0249] Taking the major principal stress as 10.20 MPa, the intermediate principal stress as 10.10 MPa, and the minor principal stress Taking 9.80 MPa as an example, a design method for a deep-buried soft rock tunnel support structure based on energy regulation involved in this application is specifically described as follows:

[0250] Step 1: Select a complete and relatively large rock mass from the engineering site in the tunnel site area, and prepare the rock mass into cylindrical specimens with a size of 50 mm × 100 mm (diameter × height) and cubic specimens with a size of 100 mm × 100 mm × 100 mm (length × width × height). The surface flatness error of the cylindrical specimens and cubic specimens is ±0.05 mm, and the verticality error is ±0.25°.

[0251] Step 2: According to the results of uniaxial compression tests, obtain the following strength parameters of the formation: rock elastic modulus , Poisson's ratio , uniaxial compressive strength , peak geological strength index , rock mass quality characteristic parameter , disturbance coefficient ;

[0252] According to the test results of in-situ stress in the tunnel site area, conduct true triaxial loading and unloading tests on the cubic specimens, and based on the established determination method for the energy dissipation limit of surrounding rock in deep-buried soft rock tunnels under high in-situ stress, obtain the energy dissipation limit of the surrounding rock.

[0253] Step 3: Select mortar bolts with a length of 5.0 m, which are evenly distributed along the longitudinal and circumferential directions of the tunnel. The layout spacing of adjacent bolts along the longitudinal direction of the tunnel is , and a total of 30 bolts are arranged along the circumferential direction of the tunnel perimeter. Establish a calculation model for deep-buried soft rock tunnels considering the interaction between the surrounding rock and bolts according to the preliminary design parameters of the bolts, and calculate the dissipated energy density of the surrounding rock and the absorbed energy of the support structure.

[0254] Step 4: According to the calculation results of the energy density of the surrounding rock and the support structure, obtain the maximum dissipated energy density Figure 5 of the surrounding rock and the maximum absorbed energy density Figure 6 of the bolts under the interaction between the surrounding rock and the support as shown in and .

[0255] According to the test results of the energy dissipation limit of the surrounding rock and the calculation results of the maximum dissipated energy density of the surrounding rock, obtain the instability energy judgment criterion of the surrounding rock;

[0256] According to the strength parameters of the bolts and the calculation results of the maximum absorbed energy density of the bolts, obtain the instability energy judgment criterion of the bolts;

[0257] The instability energy judgment criterion of the surrounding rock and the instability energy judgment basis of the anchor bolt Both are less than 1, meeting the design requirements, and the design is completed.

[0258] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A design method for the support structure of a deep-buried soft rock tunnel based on energy regulation, characterized in that, It includes the following steps: Step 1: Test the in-situ stress in the tunnel site area to obtain the components of the in-situ stress in the directions of the major principal stress, intermediate principal stress, and minor principal stress respectively; Based on the rock masses at the engineering site in the tunnel site area, specimens in the shape of cylinders and cubes are respectively made; Step 2: Conduct a conventional uniaxial compression test on the cylindrical specimens to obtain the basic strength parameters of the surrounding rock; Conduct a true triaxial loading and unloading test on the cubic specimens to obtain the ultimate dissipated energy of the surrounding rock; Step 3. Taking the energy consumption limit value U of the surrounding rock p,lim as the evaluation index for the bearing capacity of the surrounding rock of the deep-buried soft rock tunnel under high geostress, and formulating the design scheme of the tunnel bolt support structure. Mortar bolts are evenly distributed along the longitudinal and circumferential directions of the tunnel to form the tunnel support structure, and then the relevant parameters of the tunnel support structure are formulated; Step 4: Based on the relevant parameters of the proposed tunnel support structure, establish a calculation model of a deep-buried soft rock tunnel considering the cooperative action of the surrounding rock and bolts, and calculate the dissipated energy density of the surrounding rock and the absorbed energy of the support structure; Step 5: Calculate the instability energy judgment basis C of the surrounding rock based on the dissipation energy density of the surrounding rock and the absorbed energy of the support structure r and the instability energy judgment basis C of the bolt b ; Criterion C for judging the instability energy of surrounding rock r The expression is as follows: Among them, U p,max is the maximum plastic strain energy density of the surrounding rock, and U p,lim is the energy consumption limit value of the surrounding rock; The instability energy judgment basis C of the bolt b The expression is as follows: Where: U b,max is the maximum absorption energy density of the bolt, U b,lim is the energy storage limit value of the bolt, σ by is the yield strength of the bolt, σ bmax is the ultimate tensile strength of the bolt, ε by is the yield strain of the bolt, ε bmax is the failure strain of the bolt; Judgment basis C for instability energy of surrounding rock r The specific process for judging the stability of surrounding rock is as follows: When the instability energy judgment basis C of the surrounding rock r <1, it is determined that there is no risk of instability failure of the surrounding rock; when the instability energy judgment basis C of the surrounding rock r ≥1, it is determined that the surrounding rock will have the risk of instability, and the greater the instability energy judgment basis C of the surrounding rock r is, the higher the risk of instability; Judgment basis C for the instability energy of the bolt b The specific process for judging the stability of the bolt is as follows: When the instability energy judgment basis C of the anchor bolt b <1, it is determined that the anchor bolt is in the normal working stage; when the instability energy judgment basis C of the anchor bolt b ≥1, it is determined that the anchor bolt will be pulled off; When the instability energy judgment basis C of the surrounding rock r and the instability energy judgment basis C of the bolt b are both less than 1, it means that the design requirements of the support structure for deep-buried soft rock tunnels are met; when the instability energy judgment basis C of the surrounding rock r and the instability energy judgment basis C of the bolt b are both greater than or equal to 1, it means that the design requirements of the support structure for deep-buried soft rock tunnels are not met; Step 6: Determine the stability of the surrounding rock according to the instability energy judgment criterion C of the surrounding rock r Determine the stability of the surrounding rock and determine the stability of the bolt according to the instability energy judgment criterion C of the bolt b Judge the stability of the bolt; if the stability of the surrounding rock and the bolt both meet the requirements, output the design scheme of the tunnel bolt support structure. If the stability of the surrounding rock and the bolt do not meet the requirements, adjust the relevant parameters of the tunnel support structure proposed in Step 3, such as increasing the number of bolts, reducing the bolt spacing, increasing the bolt length, or selecting bolts with greater strength, and return to Step 4.

2. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 1, characterized in that The basic strength parameters of the surrounding rock include: elastic modulus E, Poisson's ratio v, uniaxial compressive strength σ c , dilation coefficient K ψ , peak geological strength index GSI p , surrounding rock mass quality characteristic parameter m i and disturbance coefficient D; The specific process of obtaining the ultimate dissipated energy of the surrounding rock is as follows: S2.1: According to the in-situ stress test results, set the required initial values of the stresses on the six surfaces of the specimen respectively to simulate the stress state of the surrounding rock before tunnel excavation; among them, the initial value of the axial stress acting surfaces on the upper and lower parts of the specimen is set as the major principal stress σ1, the initial value of the lateral stress on two mutually parallel side surfaces of the specimen is set as the intermediate principal stress σ2, and the initial value of the lateral stress on the other two mutually parallel side surfaces of the specimen is set as the minor principal stress σ3; Keep the intermediate principal stress σ2 unchanged, continuously increase the axial major principal stress σ1 at a constant loading rate by means of displacement loading, and continuously unload the minor principal stress σ3 at a constant unloading rate by means of stress unloading. When the minor principal stress σ3 is unloaded to zero, the test ends, and the stress-strain curves of the specimen in the directions of the major principal stress, intermediate principal stress, and minor principal stress at different time periods during the true triaxial loading and unloading process are obtained; S2.

2. Obtain the elastic strain energy U of the specimen based on the stress-strain and each energy component of the specimen in the directions of the major principal stress σ1, the intermediate principal stress σ2, and the minor principal stress σ3 during the elastic deformation stage of the true triaxial loading and unloading process e and the plastic dissipation energy U p ; S2.

3. Calculate the energy dissipation rate of the specimen based on the elastic strain energy \(U\) e and the plastic dissipation energy \(U\) p of the specimen. The elastic strain energy U of the test piece e is expressed as follows: where E is the elastic modulus of the specimen and v is the Poisson's ratio of the specimen, is the elastic strain in the direction of the major principal stress, is the elastic strain in the direction of the intermediate principal stress, is the elastic strain in the direction of the minor principal stress; Plastic dissipation energy U of rock p The expression is as follows: U p = U - U e ; U = ∫σ1dε1 + ∫σ2dε2 + ∫σ3dε3; Among them, U is the total energy input into the rock, and its value is equal to the integral of the principal stress in each direction with respect to the strain; ε1 is the total strain in the direction of the major principal stress, ε2 is the total strain in the direction of the intermediate principal stress, and ε3 is the total strain in the direction of the minor principal stress; specifically, ε1, ε2, and ε3 are measured by LVDT displacement sensors installed in the true triaxial test equipment; Energy dissipation rate of the specimen The expression is as follows: Among them, ε1 is the total strain in the direction of the major principal stress; S2.

4. Take the energy dissipation rate of the specimen when it reaches its maximum value and use the corresponding plastic dissipation energy as the energy consumption limit value U of the surrounding rock p,lim . Take the energy consumption limit value U of the surrounding rock p,lim as the evaluation index for the bearing capacity of the surrounding rock of deep buried soft rock tunnels under high in-situ stress.

3. The design method of the support structure for deeply buried soft rock tunnels based on energy regulation according to claim 1, characterized in that, The relevant parameters of the preliminarily determined tunnel support structure include: the layout spacing of adjacent bolts along the tunnel axis is L Z , the included angle between adjacent bolts along the circumferential direction of the tunnel is ω, and the length of the bolt is L b , the diameter of the anchorage area is D b , the elastic modulus E of the bolt b1 , the hardening modulus E of the bolt b2 , the yield strength σ of the bolt by , the ultimate tensile strength σ of the bolt bmax , the yield strain ε of the bolt by and the failure strain ε of the bolt bmax .

4. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 1, characterized in that The specific process of calculating the dissipated energy density of the surrounding rock and the absorbed energy of the support structure is as follows: S4.1: Establish a calculation model of a deep tunnel considering the cooperative action of the surrounding rock and bolts, and input the basic parameters of the tunnel model, the strength parameters of the surrounding rock, and the material parameters of the bolts; The basic parameters of the tunnel model include: the excavation radius of the tunnel is R0, the virtual support reaction force acting on the tunnel wall is P i , the initial rock stress where the tunnel is located is P0, the layout spacing of adjacent bolts along the tunnel axis is L Z , the angle between adjacent bolts along the circumferential direction of the tunnel perimeter is ω, the length of the bolt is L b and the radius of the anchorage zone is R b ; The surrounding rock strength parameters include: elastic modulus E, Poisson's ratio v, uniaxial compressive strength σ c , peak geological strength index GSI p , rock mass quality characteristic parameter m i and disturbance coefficient D; The bolt material parameters include: the shear stiffness K between the bolt and the grout interface b , the bond strength c between the bolt and the grout interface or between the surrounding rock and the grout interface s , the friction angle of the failure surface of the grouting body the elastic modulus E of the bolt b1 , the hardening modulus E of the bolt b2 , the yield strength σ of the bolt by , the ultimate tensile strength σ of the bolt bmax , the yield strain ε of the bolt by and the failure strain ε of the bolt bmax ; S4.

2. Based on the deep tunnel calculation model, solve the stress evolution path of the surrounding rock of the deep tunnel under the synergistic effect of the surrounding rock and anchor after tunnel excavation, and obtain the radial deformation of the jth layer of the surrounding rock during the i-th unloading. S4.

3. Radial deformation of the j-th layer of surrounding rock during the i-th unloading Solve the stress evolution path of the deep tunnel bolts under the combined action of the surrounding rock and bolts after tunnel excavation; S4.4: Calculate the energy density and total energy of the surrounding rock according to the stress evolution path of the surrounding rock; S4.5: Calculate the energy density and total absorbed energy of the bolts according to the stress evolution path of the bolts.

5. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 4, characterized in that, The deep tunnel calculation model established satisfies the following conditions: (Ⅰ): Assume that the tunnel burial depth is greater than 500m, and the in-situ stress before excavation is a hydrostatic pressure environment with uniform distribution; (Ⅱ): The surrounding rock is a homogeneous and isotropic elastic material, and the stress state in the plastic stage satisfies the three-dimensional H-B strength criterion and the strain increment conforms to the non-associated flow rule; (Ⅲ): The mechanical behavior of the interaction between the bolts and the surrounding rock satisfies the bond-slip model, and the relationship between the shear stress per unit length of the bolt and the relative displacement between the bolt and the surrounding rock satisfies the following formula: where τ b is the shear stress per unit length of the bolt; u rb is the relative displacement between a certain point on the bolt and the surrounding rock at this position; K b is the shear stiffness between the bolt and the grout interface or between the surrounding rock and the grout interface; c s is the bond strength between the bolt and the grout interface or between the surrounding rock and the grout interface; is the friction angle of the failure surface of the grouting body; D s is the effective diameter of the interface between the bolt and the grouting layer; σ t is the confining pressure per unit length of the bolt. For a bolt embedded in the surrounding rock, the confining pressure on the bolt is equal to the radial stress σ θ ; (Ⅳ) The relationship between the axial force and tensile deformation of the bolt satisfies the linear hardening elastoplastic mechanical model shown in the following formula: Among them, σ b is the axial stress of the bolt, and ε b is the tensile strain of the bolt.

6. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 5, characterized in that, Solve the radial deformation of the j-th layer of surrounding rock during the i-th unloading The specific process is as follows: S4.2.1 Assume that the stress in the bolted area of the surrounding rock satisfies the following equilibrium equation: where N0 is the bolt geometric coefficient, and N0 = πD s / ωL Z ; r is the distance from any position of the surrounding rock to the center of the circle, and σ r is the radial stress of the surrounding rock; The stress in the unbolted area of the surrounding rock satisfies the following equilibrium equation: The stress in the elastic area of the surrounding rock satisfies the following quantitative relationship; σ r +σ θ =2P0; The stress in the plastic area of the surrounding rock satisfies the three-dimensional H-B strength criterion; S4.2.2 Calculate the stress of the surrounding rock; Let the virtual support reaction force P acting on the tunnel wall i If it takes I steps for the in-situ rock stress P0 of the tunnel to be gradually unloaded to 0 and the number of the surrounding rock layers is j, then the stress of the j-th layer of the surrounding rock at the i-th unloading is obtained by the finite difference method as where I is the number of unloading steps of the support reaction force unloading, j is the number of the surrounding rock layers, and i = (1, 2,..., I); S4.2.

3. Solve the elastic strain increment of the j-th layer of surrounding rock relative to the (j + 1)-th layer according to the calculation results of the surrounding rock stress S4.2.

4. Simultaneously establish the deformation compatibility equation and the plastic potential function to solve the total strain of the surrounding rock S4.2.

5. Total strain based on surrounding rock Solve for the radial deformation of the j-th layer of the surrounding rock during the i-th unloading 7. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 6, characterized in that, The specific process of solving the stress evolution path of the deep tunnel bolt under the combined action of the surrounding rock and the bolt after tunnel excavation is as follows: S4.3.

1. Radial deformation of the j-th layer of surrounding rock during the i-th unloading Solve the relative displacement between any point on the bolt and the surrounding rock during the i-th unloading And the shear stress of the bolt; S4.3.

2. Calculate the axial force of the j-th layer of the anchor rod during the i-th unloading based on the shear stress of the anchor rod. S4.3.

3. Calculate the tensile strain of the anchor bolt based on the linear hardening elastoplastic mechanical model of the anchor bolt 8. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 7, characterized in that, The judgment method of the neutral point position of the bolt is as follows: The position of the neutral point is determined according to the self-balanced equation of the bolt; The self-balanced equation of the bolt is as follows: Among them, L ρ is the distance between the neutral point of the anchor rod and the anchor head, and L is the distance between any point on the anchor rod and the anchor rod; When specifically solving the neutral point position of the bolt, the specific process is as follows: (ⅰ) Assume that the position of the neutral point is ρ″; (ⅱ), According to 's expression and τ b 's expression, calculate the relative displacement and shear stress of each node of the bolt in turn; substitute the trial calculation results of the shear stress into the self - equilibrium equation of the bolt; (ⅲ) Judge whether the shear stress satisfies the self-balanced equation; (ⅳ) If not, adjust the position of the neutral point to ρ′ and return to (ⅱ); if satisfied, directly determine the neutral point position of the bolt as the final position.

9. The design method of the support structure for deep-buried soft rock tunnels based on energy regulation according to claim 8, characterized in that, The specific process of calculating the energy density and total energy of the surrounding rock according to the stress path of the surrounding rock is as follows: S4.4.

1. Obtain the elastic energy density of the j-th layer of surrounding rock after i times of unloading according to the calculation results of the surrounding rock stress path Plastic dissipation energy density And plastic release energy density S4.4.

2. Integrate the energy density component within the plastic zone range to obtain the elastic strain energy increment $E$ of the surrounding rock plastic zone in the plastic deformation stage. e(i) The plastic dissipation energy $E$ pd(i) and the plastic release energy $E$ pr(i) ; The specific process of calculating the energy density and absorbed total energy of the bolt according to the stress path of the bolt is as follows: S4.5.

1. Distribution density of the energy absorbed by the anchor bolt along the length direction according to the calculation results of the stress path of the anchor bolt S4.5.2 Integrate the energy density of any point on the bolt along the length direction to solve the absorbed energy of a single bolt during the i-th unloading; According to the number of rock bolts contained in a unit length along the longitudinal direction of the tunnel, the total absorbed energy E of the rock bolts in the unit cross-section of the tunnel under plane strain conditions is obtained b (i) 。

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