Design method of active control support for deep tunnel considering rotation of stress principal axis of surrounding rock

Abstract

The application relates to a deep-buried tunnel active control support design method considering stress principal axis rotation of surrounding rock, which comprises the following steps: obtaining and dynamically updating in-situ mechanical parameters and engineering parameters of a tunnel excavation face rock mass, and determining rock mass strength parameters; establishing a three-dimensional numerical model, simulating excavation according to actual excavation footage of full-face or partial excavation on site, and recording displacement, stress variation and elastic-plastic state of a tunnel surrounding rock monitoring section key position; drawing a curve of principal stress state changing with excavation steps according to the three-dimensional numerical model, and determining the influence degree of stress principal axis rotation on rock mass strength, strength parameters and failure mode; proposing two stress control methods to improve the rock mass stress state; and according to the stress control method, positively analyzing and guiding support design, and realizing deep-buried tunnel surrounding rock stable stress control and active control by adopting active control measures. Compared with the prior art, the application has the advantages of improving the reliability and scientificity of support design and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tunnel numerical simulation analysis, and particularly relates to a deep-buried tunnel active control support design method considering rotation of stress principal axes of surrounding rock. BACKGROUND

[0002] With the increasing demand and construction intensity of traffic tunnels, deep-buried and super-deep-buried tunnel construction will usher in new development opportunities. A large number of long-term field stress monitoring results show that the excavation process of deep-buried rock mass tunnels is often in a true three-dimensional stress state, and the stress magnitude and direction will change significantly during the tunnel excavation process, further increasing the complexity of the surrounding rock stress. The engineering disaster problem caused by stress redistribution due to excavation unloading is particularly significant in deep-buried tunnels, and the fundamental reason is the nonlinear mechanical response of unloading rock mass under high ground stress and complex stress environment. Shallow rock mass engineering is mostly in the observation and empirical design stage, and deep engineering puts forward higher requirements for dynamic design to cope with deep rock mass with high concealment and strong uncertainty. The variation of calculation parameters is large, the three-dimensional spatial effect of excavation and the uncertainty of longitudinal influence range are large, and the best state of support opportunity and surrounding rock stability cannot be guaranteed. Compared with shallow tunnels, the three-dimensional spatial effect of deep-buried tunnel excavation and the longitudinal influence range of excavation are very wide, and if the surrounding rock stability support time design directly follows the experience of shallow tunnels, there will be more unreleased deformation after support, which will be acted on the support structure under the action of subsequent excavation, resulting in multiple replacement of steel arches to release the subsequent incremental deformation and stress, causing safety of tunnel surrounding rock, construction period, etc. In addition, shallow unloading rock mass is mainly in a low stress state, and two-dimensional excavation analysis theory (such as two-dimensional Hoek-Brown strength criterion) is sufficient. However, deep engineering is in a true three-dimensional high stress state, and is in a significant three-dimensional and nonlinear system, and accurate analysis must be based on a strength theory that can reflect the essential characteristics of rock mass, such as GZZ rock mass three-dimensional strength theory, to overcome the inapplicability of two-dimensional or linear strength criteria in deep engineering. At the same time, the longitudinal axial stress has a very important influence on the stress, strength, deformation and stability of the surrounding rock, and the existing analysis model mainly uses the plane strain model and does not consider the longitudinal axial stress (often the intermediate principal stress) of the tunnel, resulting in a large difference between the analysis results and the true situation.

[0003] With the development of rock theory and numerical simulation method, tunnel excavation is more and more studied and analyzed by numerical simulation. Generally, the rock mass is easily damaged during the tunnel excavation due to the influence of various natural stresses and construction methods and techniques. The stability problem of deep rock mass is mainly the engineering instability and disaster induced by high stress and complex stress, and the deformation control and back analysis idea cannot meet the high standard requirements of three-dimensional positive analysis and dynamic design of deep tunnel. Stress control becomes an important way to solve the accurate analysis and accurate control of deep rock mass tunnel engineering, and the core is to accurately and reliably analyze and master the stress distribution and evolution law during the tunnel excavation.

[0004] The deep tunnel excavation produces a wide distribution of plastic zone, showing a significant three-dimensional space effect, especially near the excavation face, which is the key to restrict the safety and stability of deep tunnel. The three-dimensional space effect mainly reflects the rotation of the principal stress of the surrounding rock near the excavation face, and the surrounding rock near the excavation face appears obvious stress principal axis rotation phenomenon. Although many studies have recognized the important influence of the extrusion effect of the excavation face and the complex stress path on the stability of the tunnel surrounding rock and the construction safety, the research mainly focuses on the qualitative evaluation of the change process of the principal stress size and direction of the rock element during the excavation, and rarely deeply analyzes the mechanical mechanism of the stress principal axis rotation of the surrounding rock near the excavation face of the deep tunnel and the influence on the rock mass strength, strength parameter and failure mode.

[0005] In summary, the existing numerical simulation method and support design method have the following problems: (1) the parameters of the three-dimensional numerical simulation model are mainly based on experience or geological exploration report, sometimes combined with the deformation of the surrounding rock to determine the simulation parameters by back analysis, without taking the actual rock mass parameters of the excavation face as the value; (2) the three-dimensional numerical simulation model does not use three-dimensional strength criterion for calculation; (3) the numerical model lacks research on the influence of the stress principal axis rotation of the surrounding rock near the excavation face on the rock mass strength, strength parameter and failure mode after calculation; (4) the support design is mostly based on engineering experience, lacks scientific basis and technical support, and no one has researched the stress control and active control of the surrounding rock stability of deep tunnel. SUMMARY

[0006] The purpose of the present application is to provide an active control support design method for deep tunnel considering the stress principal axis rotation of the surrounding rock, to reduce the subjectivity in support design, to quickly update the rock mass strength parameter according to the digital in-situ test of the excavation face, to intuitively and simply consider the three-dimensional strength effect of the intermediate principal stress of the rock mass, to quickly calculate the influence degree and range of the stress principal axis rotation of the surrounding rock of the tunnel excavation on the rock mass strength, strength parameter and rock mass failure mode, and to realize the stress control and active control support design of the surrounding rock stability of deep tunnel based on stress transfer and compensation.

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

[0008] A deep-buried tunnel active control support design method considering stress principal axis rotation of surrounding rock, comprising the following steps:

[0009] Step 1) Based on tunnel engineering field geological exploration, in-situ testing and analysis of rock mass parameters of the excavation face, real-time acquisition and dynamic updating of in-situ mechanical parameters and engineering parameters of the tunnel excavation face rock mass, and determination of rock mass strength parameters based on the in-situ mechanical parameters of the rock mass;

[0010] Step 2) Based on the engineering parameters, in-situ mechanical parameters and rock mass strength parameters, a deep-buried tunnel excavation three-dimensional numerical model considering the three-dimensional strength and yield criterion of the rock mass is established, the excavation is simulated according to the actual excavation footage of full-face or partial excavation in the field, and the changes of displacement, stress and elastic-plastic state of the tunnel surrounding rock monitoring section key positions with the advancement of the excavation face are recorded;

[0011] Step 3) According to the deep-buried tunnel excavation three-dimensional numerical model, the stress components of the key rock elements around the monitoring section are extracted, the principal stress size and direction are calculated, the distribution evolution thereof with excavation is analyzed, the elastic-plastic state of the key rock elements is judged, the plasticity represents yielding, and the curve of the principal stress state with the change of the excavation step is drawn, so as to quickly analyze the three-dimensional space effect of deep-buried tunnel excavation, find out the change law of the principal stress size and direction and the influence on the rock mass strength, strength parameters and rock mass failure mode, and determine the influence degree of stress principal axis rotation on the rock mass strength, strength parameters and failure mode;

[0012] Step 4) According to the influence degree of stress principal axis rotation on the rock mass strength, strength parameters and failure mode from the analysis result of step 3), two stress control methods of "stress transfer by reducing the maximum principal stress" and "stress compensation by improving the minimum principal stress" are proposed to improve the stress state of the rock mass, so that the rock mass changes from an unstable state to a stable state;

[0013] Step 5) According to the two stress control methods of step 4), the support design is analyzed and guided, and active control measures are adopted to realize the stable stress control and active control of the deep-buried tunnel surrounding rock, wherein the active control measures include advanced grouting in front of the top of the excavation face, reinforcement of the advanced core rock mass of the excavation face, installation of steel arches after excavation, and setting of anchor rods.

[0014] The in-situ mechanical parameters of the rock mass include initial ground stress, strain softening coefficient, density, elastic modulus, Poisson's ratio, softness and hardness of the rock, determination of uniaxial compressive strength of the rock, geological strength index, and blasting disturbance coefficient.

[0015] The engineering parameters include tunnel radius and support force.

[0016] The calculation method for determining the rock mass strength parameters based on the in-situ mechanical parameters of the rock mass is:

[0017]

[0018] wherein m b , s, a are rock mass strength parameters, m i , GSI, D are rock mass in-situ mechanical parameters, m i is the degree of rock hardness, GSI is the geological strength index, and D is the blasting disturbance coefficient.

[0019] The step 2) comprises the following steps:

[0020] Step 2-1) a three-dimensional yield criterion GZZ is used to establish a three-dimensional numerical model of deep-buried tunnel excavation considering the three-dimensional strength and yield criterion of rock mass, and the GZZ criterion is as follows:

[0021]

[0022] wherein I1, J2 and J3 are the first stress invariant, the second invariant of deviatoric stress and the third invariant of deviatoric stress respectively, σ c is the uniaxial compressive strength of rock,

[0023] Step 2-2) based on the in-situ mechanical parameters of rock mass at the excavation face, the equivalent rock mass cohesion c and the equivalent rock mass internal friction angle

[0024]

[0025]

[0026] wherein σ 3max is the maximum confining pressure upper limit;

[0027] The maximum confining pressure upper limit σ 3max and the rock mass strength σ cm have the following relationship:

[0028]

[0029] wherein γ is the rock mass specific weight, H is the tunnel depth, γ i and h i are the overburden rock mass specific weight and rock thickness respectively;

[0030] Step 2-3) the boundary conditions of the three-dimensional numerical model are obtained by comprehensively analyzing the maximum principal stress and minimum principal stress direction side pressure coefficient λ Hv and λ hv of the tunnel site area through the in-situ micro-fracturing test and geological exploration data, and the following formula is used to convert the ground stress parameters into the model boundary conditions:

[0031]

[0032] where σ v is the vertical stress, σ H is the maximum horizontal stress, σ h is the minimum horizontal stress, θ Hy is the angle between the maximum principal stress direction and the tunnel axis.

[0033] Step 2-4) The tunnel excavation of the three-dimensional numerical model is divided into excavation steps and construction steps, and according to the actual excavation method and footage on site, full-face excavation or partial excavation simulation, cycle footage length, step distance parameters are selected, and the changes of displacement, stress and elastic-plastic state of the key position of the monitoring section of the tunnel surrounding rock with the advancement of the excavation face are recorded.

[0034] The step 3) comprises the following steps:

[0035] Step 3-1) According to the calculation results of the three-dimensional numerical model of deep-buried tunnel excavation considering the three-dimensional strength and yield criterion of rock mass, the stress components of the key rock elements around the monitoring section are extracted, and the principal stress size and direction are calculated:

[0036]

[0037] where σ is the first, second or third principal stress, σ x , σ y and σ z are the normal stresses in x, y and z directions of the key rock elements extracted from the model calculation results, τ xy , τ yx , τ xz , τ zx , τ yz , τ zy are the shear stresses in xy, yx, xz, zx, yz and zy directions of the key rock elements extracted in x, y and z directions, and l, m and n are the cosine values of the angles between the principal stress and x, y and z directions, respectively.

[0038] Step 3-2) According to the principal stress size and direction of the key rock elements, the distribution evolution of the stress state of the key rock elements with excavation is analyzed, and the elastic-plastic state of the rock elements is judged according to the three-dimensional strength criterion of rock mass, and the plasticity represents the yield.

[0039] Step 3-3) The curve of the principal stress state changing with the excavation step is drawn, so as to quickly analyze the three-dimensional spatial effect of deep-buried tunnel excavation, find the change law of the principal stress size and direction and the influence on the rock mass strength, strength parameters and rock mass failure mode, and determine the influence degree of the stress principal axis rotation on the rock mass strength, strength parameters and failure mode.

[0040] The main stress size and direction change rule and the influence on rock mass strength, strength parameter and rock mass failure mode include:

[0041] A, there is almost no secondary crack in the rock unit under the original rock stress level, with the excavation face continuously advancing to the rock unit, the stress size and direction are changed, when the stress size exceeds the damage threshold or the rock mass yield strength, micro cracks with a certain angle with the stress direction appear in the rock mass, and each excavation causes the stress principal axis to rotate, new micro cracks are continuously produced, the crack density gradually increases and finally causes the intersection and penetration of new and old cracks, and the mutual penetration between new and old micro cracks will produce more obvious macro cracks; when the excavation face approaches the rock unit, a large number of crack systems have been produced in the rock mass due to the rotation of the stress principal axis, which greatly weakens the rock mass mechanics and strength parameters, the large stress difference and the shift of the stress principal axis make the rock unit yield or fail rapidly; the change of stress size controls the depth of crack, the change of stress direction controls the density of crack, and the rock mass failure is the result of the comprehensive action of the stress size change and direction rotation, and once the initial crack appears, the stress rotation will have an important influence on the crack extension direction and extension depth, and the rock mass parameters gradually weaken;

[0042] B, during the excavation of deep tunnel, the stress principal axis rotates, the potential rock failure surface also rotates accordingly during the excavation process, the stress principal axis shift also causes additional plastic deformation increment, and finally the rotation of the stress principal axis changes the rock failure mode and failure mode;

[0043] C, during the excavation of deep tunnel, the stress principal axis of the key rock unit rotates, mainly concentrated near the excavation face, the stress state of the key rock unit along the longitudinal axis and the cross section near the excavation face is calculated and counted, and the specific influence range of the stress principal axis rotation of the key rock unit on the rock mass strength, strength parameter and failure mode is obtained.

[0044] The core of the two stress control methods in step 4) to improve the stress state of rock mass and make the rock mass change from unstable state to stable state is to make the stress state of the key rock unit within the triaxial rock compression strength plastic failure control line obtained based on GZZ strength criterion, so that the rock enters the plastic yield state but is not damaged.

[0045] Step 5) is specifically: according to the two stress control methods of step 4), the active analysis guides the support design, according to the specific influence range of the stress principal axis rotation of the key rock unit on the rock mass strength, strength parameter and failure mode, active control measures are adopted to inhibit the stress unloading effect caused by excavation, and the stress state of the key rock unit is within the triaxial rock compression strength plastic failure control line obtained based on GZZ strength criterion.

[0046] The control parameters of the active control measure include the size of the reserved core rock mass, the range of the advanced core rock mass reinforcement, the I-beam type of the steel arch, the steel arch spacing, the steel arch layer number, the shotcrete strength type and thickness, and the length, diameter, spacing and prestress size of the anchor rod.

[0047] Compared with the prior art, the present application has the following beneficial effects:

[0048] (1) The present application can quickly and accurately obtain and update the rock mass strength parameters in real time through digital in-situ testing, and directly use the parameters as the model input parameters, so that the actual rock mass parameters of the excavation face can be quickly and accurately selected in real time.

[0049] (2) The present application establishes a three-dimensional numerical model of deep-buried tunnel excavation using the three-dimensional strength / yield criterion of rock mass, calculates and analyzes the stress state of the key rock elements around the monitoring section of the tunnel according to the numerical results, and draws the curve of the principal stress state changing with the excavation step.

[0050] (3) The present application quickly analyzes the three-dimensional spatial effect of deep-buried tunnel excavation according to the numerical results, finds the variation law of the principal stress size and direction and the influence on the rock mass strength, strength parameters and rock mass failure mode, and determines the influence degree and range.

[0051] (4) The present application improves the stress state of the rock mass by proposing two stress control methods of “reducing the maximum principal stress” and “increasing the minimum principal stress”, so that the rock mass can be changed from an unstable state to a stable state.

[0052] (5) The present application truly considers the nonlinear mechanical characteristics and engineering response of deep true three-dimensional high-stress unloading rock mass, can effectively avoid the excessive dependence on the shallow tunnel engineering experience and the blind use of the shallow tunnel engineering experience in the support design of deep-buried tunnel, improves the reliability and scientificity of the support design calculation and analysis of deep-buried tunnel, and realizes the stress control and active control of the surrounding rock stability of deep-buried tunnel based on stress transfer and compensation. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The flowchart of the method of the present application is shown in the figure;

[0054] Figure 2 The three-dimensional finite element numerical model of the Grand Canyon deep-buried tunnel of the embodiment of the present application is shown in the figure;

[0055] Figure 3 The stress states of the tunnel crown and haunch before and after excavation under the GZZ criterion of the embodiment of the present application are shown in the figure;

[0056] Figure 4 The main stress transfer law of a vault characteristic rock unit of the embodiment of the present application;

[0057] Figure 5 The main stress transfer law of a haunch characteristic rock unit of the embodiment of the present application;

[0058] Figure 6 The schematic diagram of the weakening of the strength parameters of a rock mass caused by the rotation of the principal stress axis of the embodiment of the present application;

[0059] Figure 7 The π plane schematic diagram of the reduction of the strength of a rock mass and the weakening of the strength parameters caused by the rotation of the principal stress axis of the embodiment of the present application. DETAILED DESCRIPTION

[0060] The present application will be described in detail below in combination with the drawings and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present application, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following embodiments.

[0061] The present embodiment provides a deep-buried tunnel active control support design method considering the rotation of the stress principal axis of surrounding rock, as shown in Figure 1 , including the following steps:

[0062] Step 1) Based on the in-situ geological exploration of the tunnel engineering, the digital in-situ test and analysis of the rock mass parameters of the excavation face, the in-situ mechanical parameters and engineering parameters of the rock mass of the tunnel excavation face are obtained and dynamically updated in real time, and the rock mass strength parameters are determined based on the in-situ mechanical parameters of the rock mass.

[0063] In the present embodiment, the in-situ mechanical parameters of the rock mass include the initial ground stress, the strain softening coefficient, the density ρ, the elastic modulus E, the Poisson's ratio ν, the hardness m i of the rock, the uniaxial compressive strength σ c of the rock, the geological strength index GSI, and the blasting disturbance coefficient D; the engineering parameters include the tunnel radius and the support force.

[0064] Specifically, for each excavation surface, the three-dimensional laser scanning is used to extract the geometric information of the structural surface of the tunnel excavation surface joint fissure (three-dimensional trace occurrence, group number and distribution form, etc.), through the cross-section information and the corresponding digital processing flow, the joint fissure distribution characteristics of the excavation surface rock mass are obtained, and the H-B strength parameters GSI and D are obtained by using the parameter value method recommended by Hoek et al. See: Hoek E, Marinos P. Predicting Tunnel Squeezing Problems in Weak Heterogeneous Rock Masses [J]. Tunnels and Tunnelling International. 2000, 32(11): 45-51, which will not be repeated here. Since GZZ can completely degrade H-B, H-B and GZZ parameters are shared.

[0065] In this embodiment, for each tunnel excavation surface, at least 6 photos of different angles are collected by using three-dimensional laser scanning or intelligent mobile terminal to obtain and improve the three-dimensional point cloud data, so as to ensure the accuracy of analysis. Then, the three-dimensional reconstruction method is used to obtain the geometric information of the excavation surface, such as joint fissure occurrence, spacing, trace, roughness, opening degree, etc., and then the rock mass strength parameters (such as GSI and D) are obtained according to the method recommended by Hoek et al. The rock σ c , the in-situ stress test is carried out by the micro-fracture test, and at the same time, the field observation and recording method is used to identify the underground water and filler information.

[0066] The calculation method of the rock mass strength parameter based on the in-situ mechanical parameters of the rock mass is as follows:

[0067]

[0068] Wherein, m b , s, a are rock mass strength parameters, m i , GSI, D are in-situ mechanical parameters of the rock mass, m i is the hardness of the rock, GSI is the geological strength index, and D is the blasting disturbance coefficient.

[0069] The above process is a back analysis process different from the geotechnical parameters, and belongs to the positive analysis category. This process can realize the rapid in-situ detection and positive analysis of the rock mass parameters, and update the rock mass strength parameters of the excavation surface in real time.

[0070] Step 2) Based on the engineering parameters, in-situ mechanical parameters and rock mass strength parameters, a deep-buried tunnel excavation three-dimensional numerical model considering the three-dimensional strength and yield criterion of rock mass is established, the excavation is simulated according to the actual excavation footage of full-face or partial excavation in the field, and the changes of displacement, stress and elastic-plastic state of the key positions of the monitoring section of the tunnel surrounding rock with the advancement of the excavation face are recorded.

[0071] Step 2-1) A deep-buried tunnel excavation three-dimensional numerical model considering the three-dimensional strength and yield criterion of rock mass is established by using the three-dimensional yield criterion GZZ, and the GZZ criterion is as follows:

[0072]

[0073] In the formula, I1, J2 and J3 are the first stress invariant, the second invariant of deviatoric stress and the third invariant of deviatoric stress, respectively, σ c is the uniaxial compressive strength of rock,

[0074] Step 2-2) Based on the in-situ mechanical parameters of the rock mass at the excavation face, the equivalent rock mass cohesion c and the equivalent rock mass internal friction angle

[0075]

[0076]

[0077] In the formula, σ 3max is the maximum confining pressure upper limit;

[0078] The maximum confining pressure upper limit σ 3max and the rock mass strength σ cm have the following relationship:

[0079]

[0080] In the formula, γ is the unit weight of rock mass, H is the depth of the tunnel, γ i and h i are the unit weight and thickness of the overlying rock mass, respectively;

[0081] Step 2-3) The boundary conditions of the three-dimensional numerical model are obtained by comprehensively analyzing the maximum principal stress and minimum principal stress directions of the lateral pressure coefficient λ Hv and λ hv of the tunnel site area through the in-situ micro-fracture test and geological exploration data, and the following formula is used to convert the ground stress parameters into the model boundary conditions:

[0082]

[0083] In the formula, σ v is the vertical stress, σ H is the horizontal maximum stress, and σh For the minimum horizontal stress, θ Hy The angle between the direction of the maximum principal stress and the tunnel axis;

[0084] Steps 2-4) Divide the tunnel excavation of the three-dimensional numerical model into excavation steps and construction steps. Select full-section excavation or partial excavation simulation, cycle advance length, and step distance parameters according to the actual excavation method and advance on site. Record the displacement, stress changes, and elastoplastic state of the key positions of the tunnel surrounding rock monitoring section as the excavation face advances.

[0085] Step 3) Based on the three-dimensional numerical model of deep-buried tunnel excavation, extract the stress components of key rock units around the tunnel at the monitoring section, calculate the magnitude and direction of principal stress, analyze its distribution evolution with excavation, determine the elastoplastic state of key rock units (plasticity represents yielding), and plot the curve of principal stress state changing with excavation step. This allows for rapid analysis of the three-dimensional spatial effects of deep-buried tunnel excavation, finding the variation law of principal stress magnitude and direction and its influence on rock mass strength, strength parameters, and rock mass failure mode, and clarifying the degree of influence of stress principal axis rotation on rock mass strength, strength parameters, and failure mode.

[0086] Step 3-1) Based on the calculation results of the three-dimensional numerical model for deep-buried tunnel excavation considering the three-dimensional strength and yield criterion of the rock mass, extract the stress components of the key rock elements surrounding the tunnel at the monitoring section, and calculate the magnitude and direction of the principal stresses:

[0087]

[0088] In the formula, σ is the first, second, or third principal stress. x σ y and σ z These are the normal stresses in the x, y, and z directions extracted from the key rock elements in the model calculation results, τ. xy τ yx τ xz τ zx τ yz τ zy , respectively, are the shear stresses in the xy, yx, xz, zx, yz, and zy directions extracted from the key rock units, and l, m, and n are the cosine values ​​of the angles between the principal stresses and the x, y, and z directions, respectively;

[0089] Step 3-2) Based on the magnitude and direction of the principal stress of the key rock unit, analyze the distribution evolution of the stress state of the key rock unit with excavation, and determine the elastic-plastic state of the rock unit according to the three-dimensional strength criterion of the rock mass. Plasticity indicates that it has yielded.

[0090] Step 3-3) draw the curve of the principal stress state with the change of the excavation step, so as to quickly analyze the three-dimensional space effect of the deep-buried tunnel excavation, find the change law of the principal stress size and direction and the influence on the rock mass strength, strength parameter and rock mass failure mode, and determine the influence degree of the stress principal axis rotation on the rock mass strength, strength parameter and failure mode.

[0091] The change law of the principal stress size and direction and the influence on the rock mass strength, strength parameter and rock mass failure mode include:

[0092] A. The rock unit almost does not have secondary cracks at the original rock stress level. With the continuous advancement of the excavation face to the rock unit, the stress size and direction are changed. When the stress size exceeds the damage threshold or the rock mass yield strength, micro cracks with a certain angle to the stress direction appear in the rock mass, and each excavation causes the stress principal axis to rotate, continuously generates new micro cracks, gradually increases the crack density and eventually causes the intersection and penetration of new and old cracks, and the mutual penetration between new and old micro cracks will produce more obvious macro cracks. When the excavation face approaches the rock unit, a large number of crack systems have been generated in the rock mass due to the rotation of the stress principal axis, which greatly weakens the rock mass mechanics and strength parameters, and the large stress difference and the shift of the stress principal axis make the rock unit quickly yield or fail. The change of the stress size controls the depth of the crack, the change of the stress direction controls the density of the crack, and the rock mass failure is the result of the comprehensive action of the stress size change and direction rotation. Once the initial crack appears, the stress rotation will have an important influence on the crack propagation direction and propagation depth, and the rock mass parameters gradually weaken.

[0093] B. During the deep-buried tunnel excavation process, the stress principal axis rotates, and the potential rock fracture surface also rotates accordingly. The stress principal axis shift also causes additional plastic deformation increment, and the rotation of the stress principal axis finally changes the rock failure mode and failure form.

[0094] C. During the deep-buried tunnel excavation process, the stress principal axis of the key rock unit rotates, mainly concentrating near the excavation face. The stress state of the key rock unit near the excavation face is calculated along the longitudinal axis and the cross section respectively, and the specific influence range of the stress principal axis rotation of the key rock unit on the rock mass strength, strength parameter and failure mode is obtained.

[0095] Step 4) Based on the analysis results of Step 3), and according to the degree of influence of the rotation of the principal stress axis on the rock mass strength, strength parameters and failure mode, two stress control methods are proposed: "reducing the stress transfer of the maximum principal stress" and "increasing the stress compensation of the minimum principal stress" to improve the stress state of the rock mass, so that the rock mass can be transformed from an unstable state to a stable state. The core is to keep the stress state of the key rock units within the triaxial rock compressive strength plastic failure control line obtained based on the GZZ strength criterion, so that the rock enters the plastic yield state but is not destroyed.

[0096] Step 5) Based on the two stress control methods in Step 4), positive analysis guides the support design. Targeting the specific impact range of the rotation of the principal stress axis of the key rock unit on the rock mass strength, strength parameters, and failure mode, active control measures are adopted, such as pre-grouting in front of the top of the excavation face, pre-reinforcement of the core rock mass of the excavation face, installation of steel arches after excavation, and installation of anchor bolts, to suppress the stress unloading effect caused by excavation. The stress state of the key rock unit is kept within the triaxial rock compressive strength plastic failure control line obtained based on the GZZ strength criterion, thereby achieving stable stress control and active control of the surrounding rock of the deep-buried tunnel.

[0097] Specifically, the control parameters of the active control measures are determined based on the specific impact range of the rotation of the principal stress axis of the key rock unit on the rock mass strength, strength parameters and failure mode. In this embodiment, the control parameters of the active control measures include the size of the reserved core rock mass, the range of advanced core rock mass reinforcement, the type of I-beam of the steel arch frame, the spacing of the steel arch frames, the number of layers of the steel arch frames, the strength and thickness of the shotcrete, and the length, diameter, spacing and prestress of the anchor bolts.

[0098] This embodiment uses the Grand Canyon deep-buried tunnel (1672m) as an example to illustrate the modeling process. Figure 2 As shown, the three-dimensional numerical model takes into account the actual terrain and geological characteristics of the tunnel site in order to simulate the real excavation process as much as possible. Figure 2 Contour lines and topographic maps of the computational domain are provided. The model dimensions are 380m (length) × (150m + 150m) (width) × 2822.5m (depth), where 2822.5m is the highest elevation point in the computational domain. In the numerical calculation, a fixed displacement constraint is applied to the bottom of the model, and the complex geostress field in the tunnel site area is simulated through stress boundaries in the lateral and forward directions. The upper boundary of the model is a free boundary. Based on field micro-fracturing tests and geological survey data, the lateral pressure coefficients (λ) in the directions of the maximum and minimum principal stresses in the tunnel site area are obtained as follows: λ Hv =1.32 and λ hv= 0.874; wherein, the maximum horizontal principal stress direction is N18°W, the tunnel excavation direction is N70°W, and there is a 52° angle between the tunnel axis and the tunnel excavation direction. The overall error of the in-situ stress parameters with the given values of the regional in-situ stress map of western China (Sichuan) is less than 10%, and thus has a certain reliability. Meanwhile, the in-situ stress parameters are converted into the model boundary conditions according to equation (5).

[0099] To ensure the calculation accuracy, the tunnel grid size is divided into three levels, and the tunnel size, the 40m diameter transition circle domain outside the tunnel, and the size outside the circle domain are 0.6m, 2m and 10m respectively. The number of units of the deep-buried tunnel is 1046938. After several trial calculations, the grid size and the tunnel model can meet the requirements of calculation accuracy and convergence. The other parameters of the numerical model are mainly given according to the design data and the actual situation on site. The calculation length of the tunnel excavation is 100m, and each cycle is 2.0m, which is divided into excavation steps and construction steps.

[0100] To minimize the influence of the model boundary effect on the numerical calculation and analysis results, the surrounding rock characteristic elements around the tunnel are analyzed, and the stress distribution and transfer law of the key rock elements of the surrounding rock around the tunnel during the excavation process are studied. The key rock elements of the surrounding rock around the tunnel in the embodiment are taken as examples, which are the key rock elements at the arch top and the arch waist of the middle section (y=50m) of the model.

[0101] Figure 3 The stress time-history curves of the surrounding rock characteristic elements under the GZZ criterion are given. The unexcavated stress is inside the π plane strength envelope, and is very close to the hydrostatic stress axis (coordinate origin), which is an extremely stable stress state; but the surrounding rock after excavation is in an unstable stress state, which is in a yield or even failure state. The stress flow changes very slowly far from the excavation face, but changes very dramatically near the excavation face, accompanied by the rotation of the stress principal axis. With the continuous advancement of the excavation face, the σ1 and σ2 of the surrounding rock characteristic elements around the tunnel increase rapidly, the stress increment is 30-50MPa, and then decreases rapidly, the stress drop is more than 50MPa. While the radial stress σ r (σ3) shows a gradually decreasing trend during the excavation unloading process. The stress change law near the excavation face is greatly different from the stress distribution law of the section position far from the excavation face (plane strain tunnel), which shows the significant three-dimensional spatial effect of the deep-buried tunnel excavation process. The surrounding rock characteristic elements of the arch top and the arch waist under the GZZ criterion have a large σ1-σ2 difference and a small σ2-σ3, which are near the triaxial compression stress state on the π plane (θ σ = -π / 6), and the main failure mode is shear failure.

[0102] The stress state and deformation characteristics near the excavation face are significantly different from those in the stable section far from the excavation face (which can be considered as a plane strain tunnel). To find the complex stress path and principal stress axis rotation law of a certain rock unit at the arch crown and arch waist during the 10m advance before and after the excavation face, two characteristic rock units, the arch crown point and the right arch waist point of the Y=50 tunnel section, were analyzed. Table 1 shows the distribution of the principal stress axis direction at characteristic points of a 2000m deep buried tunnel, obtained from equation (6). Figure 4 and Figure 5 These are the stress principal axis transfer patterns of key rock units around the tunnel caused by excavation and unloading.

[0103] Table 1. Distribution of principal characteristic stress axes near the excavation face of a 2000m deep buried tunnel.

[0104]

[0105] The initial stress inside the unit is relatively small. As the excavation face gradually approaches the characteristic rock unit under investigation, σ1 and σ2 at the crown A and waist B both increase rapidly, while σ3 gradually decreases, indicating an increase in differential stress. Whether the rock unit is in a yielding state can be determined by the smooth GZZ strength criterion, or by whether the maximum principal differential stress reaches 1 / 3σ. ci An approximate assessment is made. The area extending 2m ahead of the tunnel excavation face to the already excavated surrounding rock is in a plastic yielding state, exhibiting poor rock mass stability. Within a 2m radius (-2m) before and after the tunnel, the principal stress axis undergoes a significant shift, demonstrating a clear transfer of the principal stress axis. For the arch apex, σ1 only exhibits principal stress axis rotation within ±2m of the excavation face advancement; beyond ±2m, σ1 remains constant. x Within ±2m, σ1 rotates from the x-axis to the yz-plane, forming a certain angle with both the y-axis and z-axis; σ2 lies in the yz-plane within ±2m, and suddenly shifts towards the x-direction within this range (σ... x ); σ2 also underwent a 90° directional shift before and after excavation. For the arch waist point, σ1 changed from σ before excavation. x Transferred to σ after excavation z The transfer rule is opposite to that of σ2; σ2 transfers from σ... z Transform into σ x σ3 underwent a 90° directional shift before and after excavation.

[0106] like Figure 4 and Figure 5 As shown, as the excavation face gradually approaches the characteristic unit (crown point A and waist point B), σ1 and σ2 at the crown and waist are under stress loading, while σ3 gradually decreases, representing stress unloading. The differential stress increases, and the rock stability decreases. For the crown point A, within a 2m range (±2m) before and after the excavation face reaches the point, σ1 and σ2 exhibit a 90° stress direction rotation; beyond ±2m, σ1 and σ2... xThe direction is consistent, and σ1 in the range of ±2m rotates from the x-axis to the yz plane and has a certain angle with the y-axis and z-axis; σ2 is in the yz plane in the range of ±2m and suddenly shifts to the x direction (σ x ) in the range of ±2m. For the arch waist point, σ1 shifts from σ x before excavation to σ z after excavation, and the shift rule is opposite to that of σ2, which changes from σ z to σ x , and σ3 has a 90° directional shift before and after excavation. The maximum differential stress near the excavation face (arch crown 68MPa, arch waist 61MPa) is very small compared with the maximum differential stress of the surrounding rock after excavation (plane strain tunnel) (arch crown 51MPa, arch waist 63MPa), but there is a big difference in the direction of the principal stress. The tunnel diseases (rock burst, large deformation, steel arch distortion, etc.) in this project mainly occur at the excavation face section, indicating that the three-dimensional space effect of the excavation face and the rotation of the principal stress direction are the main reasons for the instability of the deep tunnel.

[0107] As shown in Figure 6 , there are almost no secondary cracks in the rock element at the original rock stress level. With the continuous advancement of the excavation face to the rock element, the stress magnitude and direction change. When the stress magnitude exceeds the damage threshold or the rock mass yield strength, microcracks with a certain angle to the stress direction appear in the rock mass (rock), and each excavation causes the stress principal axis to rotate, continuously generating new microcracks, gradually increasing the crack density, and eventually causing the intersection and penetration of new and old cracks. As shown in Figure 6 , assume that a certain unexcavated rock in front of the excavation face is subjected to σ1 and is in a stable state. The deep compressive rock produces microcracks distributed along the failure angle direction under slight disturbance (crack 1 Figure 6 in # ); with the continuous advancement of the excavation face to the rock, the change in the direction of the principal stress causes the rock to continuously generate new cracks with a certain angle to the direction of σ1 (cracks 1 Figure 6 , 2 # , 3 # , i # , … in # ), and the mutual penetration between new and old microcracks will produce more obvious macrocracks; when the excavation face approaches the rock element, a large number of crack systems have been generated in the rock mass due to the rotation of the stress principal axis, greatly weakening the rock mass mechanics and strength parameters. The large stress difference and the shift of the stress principal axis cause the rock element to rapidly yield or fail. The change in stress magnitude controls the depth of the crack, and the change in stress direction controls the density of the crack. Rock mass failure is the result of the combined action of stress magnitude change and direction rotation, and once the initial crack appears, stress rotation will have an important influence on the crack propagation direction and propagation depth, and the rock mass parameters will gradually weaken.

[0108] As Figure 7 shown, in the π plane, I1, J2 reflect the stress level and stress deviator of rock mass, respectively, and θ σ reflects the principal stress direction. During excavation, the change of stress level can reduce the rock strength, making the rock stress state migrate from within the π plane to outside the π plane; while the change of direction can weaken the rock strength parameters (m b , s, a) Figure 7 ), making the strength envelope gradually shrink (radius reduction) on the π plane, from the solid line envelope to the dashed line envelope. Figure 7

[0109] Figure 4 The dashed line with triangular marks in Figure 5 is the triaxial rock compressive strength (TCS) obtained based on the GZZ strength criterion. When σ1 is higher than TCS, it can be judged that the rock enters the plastic yield state, and the difference between σ1 and TCS can be used for the support design of surrounding rock, such as reducing σ1 to below TCS through the design of anchor rods and steel arches. At the same time, it should be recognized that the support measures to reduce the peak stress σ1 can be identified as passive support. Figure 4 Figure 5 The dashed line in Figure 5 is the rock failure confining pressure line (FCP), which can be obtained by fixing σ1 and σ2 and solving by the GZZ strength criterion. When the σ3 unloading caused by excavation is below the control line (i.e. σ3 < FCP), the rock enters the plastic yield state. In engineering design, the relative relationship between σ3 and FCP can be used for the active support design of surrounding rock stability, such as controlling the deformation of surrounding rock and inhibiting the stress unloading effect caused by excavation through the method of reserving core rock mass (New Austrian Tunneling Method) or reinforcing the core rock mass in advance (New Idea Method), so as to keep σ3 inside the rock mass and control σ3 above the confining pressure control line.

[0110] Therefore, through the two ways of reducing σ1 or increasing σ3, the stability of surrounding rock can be ensured, as shown in Figure 4 and Figure 5 . When the surrounding rock is in the yield state (the excavation face passes through the rock element), the difference between σ1 and TCS is large, and the effect of active control needs to reduce σ1 by 10 MPa, while σ3 is very close to FCP, and increasing σ3 by 2 MPa can control the rock stress state within the elastic range, indicating that the effect of active control is good. This property is mainly determined by the nonlinearity of rock mass strength with confining pressure. When the confining pressure is small, the rock mass strength is very sensitive to the change of confining pressure, and a small increase in confining pressure can greatly increase the rock mass strength; while the confining pressure is large, the effect of increasing confining pressure on improving strength is very limited, therefore, the active control method of increasing σ3 is better under the condition of low σ3.

[0111] It should be noted that before the excavation face reaches the rock unit, although the stress principal axis of the rock has shifted, the stress principal axis shift has not caused the weakening of the rock mass parameters due to the elastic stress state of the rock, and after the excavation face passes through the rock unit, the stress principal axis rotation will cause the weakening of the rock strength parameters, so the stability of the surrounding rock within the range of 2m behind the excavation face needs to be focused on. When the rock yields or fails, the failure surface trend and tendency are often similar to the directions of σ2 and σ3, respectively, and the support design such as the direction of the anchor rod can be carried out according to the directions of σ2 and σ3 in the and Figure 4 and Figure 5 σ2 and σ3, and the appropriate support method (active support and passive support) and support timing are selected according to the local conditions.

[0112] The stress magnitude change caused by tunnel excavation exceeds the rock strength to only produce plastic deformation, and the shift of the principal stress direction near the excavation face will greatly reduce the rock strength and weaken the rock physical and mechanical parameters, and even cause the change of the rock failure mode. In the design and construction of shallow tunnel, the complex stress path and stress principal axis rotation problem have not been paid enough attention to, and the reason is that the lower stress level has not reached the damage threshold, and the stress principal axis shift has not caused the obvious rock mass strength reduction or rock parameter weakening, and in the deep buried high ground stress environment, the excavation unloading makes the surrounding rock appear a large area of plastic zone, and the stress principal axis rotation will cause the weakening of the rock mass strength and physical and mechanical parameters. Therefore, the problems of three-dimensional space effect and complex stress path at the excavation face are the reasons for restricting the safe and efficient construction of the deep tunnel, and the influence degree of the principal stress direction on the surrounding rock stability and construction safety is even greater than that of the stress level.

[0113] The theoretical model (three-dimensional strength theory, post-peak dilatancy angle model) suitable for deep rock mass, numerical calculation method (non-associated plastic flow rule, three-dimensional elastoplastic constitutive numerical implementation) and parameter selection (real-time, rapid and accurate selection of rock mass parameters based on digital in-situ test) established and proposed by the present application provide a reliable theoretical basis for the accurate simulation and stress accurate analysis of deep tunnel engineering excavation, specifically:

[0114] The application utilizes digital in-situ test technology to quickly obtain mechanical parameters, fully considers the influence of three-dimensional strength of deep unloading rock mass and tunnel longitudinal axial stress (intermediate principal stress) on tunnel three-dimensional space effect and surrounding rock stress state (LDP curve characteristics), and can reflect the action of deep rock mass shear dilatancy characteristics, strain softening, residual strength and geological joint fracture development, more truly considers the nonlinear mechanical characteristics and engineering response of deep true three-dimensional high stress unloading rock mass, can be applied to deep rock mass with high concealment and spatial variability, effectively avoids the over-reliance on shallow tunnel engineering experience and the blind use of deep buried tunnel in support design, improves the reliability and scientificity of deep buried tunnel support design calculation and analysis, realizes the stress transfer and compensation based deep buried tunnel surrounding rock stability stress control and active control, meanwhile, the method can quickly calculate the surrounding rock stress state of excavation face and analyze the tunnel excavation three-dimensional space effect and rock mass plastic influence range, can provide scientific basis and technical support for deep buried / ultra-deep buried tunnel dynamic design, and can be directly used for engineering construction site.

[0115] The foregoing describes in detail the preferred embodiments of the application. It should be understood that those skilled in the art can make many modifications and changes without creative labor based on the concept of the application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the prior art according to the concept of the application shall be within the protection scope determined by the claims.

Claims

1. A method for designing an active control support of a deep-buried tunnel considering rotation of a stress principal axis of surrounding rock, characterized in that, The method comprises the following steps: Step 1) based on the tunnel engineering site geological exploration, the digital in-situ test and analysis of the rock mass parameters of the excavation face, the in-situ mechanical parameters and engineering parameters of the tunnel excavation face are obtained and dynamically updated in real time, and the rock mass strength parameters are determined based on the in-situ mechanical parameters of the rock mass; Step 2) based on the engineering parameters, the in-situ mechanical parameters and the rock mass strength parameters, a three-dimensional numerical model of deep-buried tunnel excavation considering the three-dimensional strength and yield criterion of the rock mass is established, the excavation is simulated according to the actual excavation footage of the full-face or partial excavation of the site, and the changes of the displacement, stress and elastic-plastic state of the key positions of the monitoring section of the tunnel surrounding rock with the advancement of the excavation face are recorded; Step 3) according to the three-dimensional numerical model of deep-buried tunnel excavation, the stress components of the key rock elements around the monitoring section are extracted, the principal stress size and direction are calculated, the distribution evolution thereof with the excavation is analyzed, the elastic-plastic state of the key rock elements is judged, the plasticity represents the yield, and the curve of the principal stress state with the change of the excavation step is drawn, so as to quickly analyze the three-dimensional space effect of deep-buried tunnel excavation, find out the change law of the principal stress size and direction and the influence on the rock mass strength, strength parameters and rock mass failure mode, and determine the influence degree of the stress principal axis rotation on the rock mass strength, strength parameters and failure mode; Step 4) according to the influence degree of the stress principal axis rotation on the rock mass strength, strength parameters and failure mode from the analysis result of step 3), two stress control methods of "reducing the maximum principal stress" and "increasing the minimum principal stress" are proposed to improve the stress state of the rock mass, so that the rock mass is changed from an unstable state to a stable state; Step 5) according to the two stress control methods of step 4), the support design is analyzed and guided, and active control measures are adopted to realize the stable stress control and active control of the deep-buried tunnel surrounding rock, wherein the active control measures comprise advanced grouting in front of the top of the excavation face, advanced core rock mass reinforcement of the excavation face, installation of steel arches after excavation, and setting of anchor rods.

2. The method according to claim 1, wherein, The in-situ mechanical parameters of the rock mass comprise initial ground stress, strain softening coefficient, density, elastic modulus, Poisson's ratio, softness and hardness of the rock, uniaxial compressive strength of the rock, geological strength index and blasting disturbance coefficient.

3. The method according to claim 1, wherein, The engineering parameters comprise tunnel radius and support force.

4. The method according to claim 1, wherein, The calculation method of the rock mass strength parameters based on the in-situ mechanical parameters of the rock mass is as follows: wherein m b , s, a are rock mass strength parameters, m i , GSI, D are rock mass in-situ mechanical parameters, m i is the degree of rock hardness, GSI is the geological strength index, and D is the blasting disturbance coefficient.

5. The method according to claim 4, wherein, Step 2) comprises the following steps: Step 2-1) a three-dimensional yield criterion GZZ is used to establish a three-dimensional numerical model of deep-buried tunnel excavation considering the three-dimensional strength and yield criterion of the rock mass, and the GZZ criterion is as follows: wherein I1, J2 and J3 are the first, second and third deviatoric invariants, respectively, and σ c is the uniaxial compressive strength of the rock, Step 2-2) based on the in-situ mechanical parameters of the rock mass at the excavation face, the equivalent rock mass cohesion c and the equivalent rock mass internal friction angle are determined wherein σ 3max upper limit of maximum confining pressure; Maximum confining pressure upper limit σ 3max The relationship between the rock mass strength σ cm and the confining pressure σ is as follows: In the formula, γ is the rock mass specific weight, H is the tunnel buried depth, γ i and h i are the overlying rock mass specific weight and rock thickness, respectively. Step 2-3) The lateral pressure coefficient λ of the maximum principal stress and the minimum principal stress direction of the tunnel site is obtained by combining the field micro-fracturing test and geological exploration data Hv and λ hv The in-situ stress parameters are converted into the model boundary conditions by using the following formula: where σ v is the vertical stress, σ H is the maximum horizontal stress, σ h is the minimum horizontal stress, θ Hy is the angle between the maximum principal stress direction and the tunnel axis. Step 2-4) the tunnel excavation of the three-dimensional numerical model is divided into excavation steps and construction steps, the full-face excavation or partial excavation simulation is selected according to the actual excavation method and footage of the site, the cycle footage length and step distance parameters are selected, and the changes of the displacement, stress and elastic-plastic state of the key positions of the monitoring section of the tunnel surrounding rock with the advancement of the excavation face are recorded.

6. The method according to claim 1, wherein, Step 3) comprises the following steps: Step 3-1) According to the calculation results of the deep-buried tunnel excavation three-dimensional numerical model considering the three-dimensional strength and yield criterion of rock mass, the stress components of the key rock element around the monitoring section are extracted, and the principal stress size and direction are calculated: where σ is the first, second or third principal stress, σ x , σ y and σ z are the normal stresses in the x, y and z directions extracted from the model calculation results for the key rock element, τ xy , τ yx , τ xz , τ zx , τ yz , τ zy are the shear stresses in the xy, yx, xz, zx, yz and zy directions extracted from the key rock element, and l, m and n are the cosine values of the angles between the principal stresses and the x, y and z directions, respectively. Step 3-2) According to the principal stress size and direction of the key rock element, the distribution evolution of the stress state of the key rock element with excavation is analyzed, and the elastic-plastic state of the rock element is judged according to the three-dimensional strength criterion of the rock mass. The plasticity represents the yield; Step 3-3) Draw the curve of the principal stress state with the change of the excavation step, so as to quickly analyze the three-dimensional space effect of the deep-buried tunnel excavation, find out the change rule of the principal stress size and direction and the influence on the rock mass strength, strength parameter and rock mass failure mode, and clarify the influence degree of the stress principal axis rotation on the rock mass strength, strength parameter and failure mode.

7. The method according to claim 6, wherein, The change rule of the principal stress size and direction and the influence on the rock mass strength, strength parameter and rock mass failure mode include: A. The rock element almost does not exist secondary cracks under the original rock stress level. With the continuous advancement of the excavation surface to the rock element, the stress size and direction are changed. When the stress size exceeds the damage threshold or the yield strength of the rock mass, micro cracks with a certain angle to the stress direction appear in the rock mass, and the stress principal axis rotates every time the excavation is carried out, which continuously produces new micro cracks, makes the crack density gradually increase and finally causes the intersection and penetration of new and old cracks, and the mutual penetration between new and old micro cracks will produce more obvious macro cracks; When the excavation surface approaches the rock element, a large number of crack systems have been produced in the rock mass due to the rotation of the stress principal axis, which causes great weakening of the rock mass mechanics and strength parameters, and the large stress difference and the transfer of the stress principal axis make the rock element produce rapid yield or failure; The change of stress size controls the depth of crack, the change of stress direction controls the density of crack, and the rock mass failure is the result of the comprehensive action of the stress size change and direction rotation, and once the initial crack appears, the stress rotation will have an important influence on the crack propagation direction and propagation depth, and the rock mass parameters will gradually weaken; B. During the deep-buried tunnel excavation process, the stress principal axis rotates, and the potential rock fracture surface also rotates accordingly with the excavation process. The stress principal axis transfer will also cause additional plastic deformation increment, and the rotation of the stress principal axis will change the rock failure mode and failure form; C. During the deep-buried tunnel excavation process, the stress principal axis of the key rock element rotates mainly near the excavation surface, and the stress state of the key rock element near the excavation surface is calculated and counted along the longitudinal axis and the transverse section respectively, and the specific influence range of the stress principal axis rotation of the key rock element on the rock mass strength, strength parameter and failure mode is obtained.

8. The method according to claim 1, wherein, The core of the two stress control methods used in step 4) to improve the stress state of the rock mass and make the rock mass change from unstable state to stable state is to make the stress state of the key rock element within the triaxial rock compressive strength plastic failure control line obtained based on the GZZ strength criterion, so that the rock enters the plastic yield state but is not damaged.

9. The method according to claim 1, wherein the method is characterized by, The step 5) is specifically: according to the two stress control methods of step 4), the specific influence range of the stress principal axis rotation of the key rock element on the rock mass strength, strength parameters and failure mode, active control measures are adopted, the stress unloading effect caused by excavation is inhibited, and the stress state of the key rock element is controlled within the triaxial rock compressive strength plastic failure control line obtained based on the GZZ strength criterion.

10. The method according to claim 9, wherein the method is characterized by, The control parameters of the active control measures are determined according to the specific influence range of the stress principal axis rotation of the key rock element on the rock mass strength, strength parameters and failure mode, and the control parameters of the active control measures include the size of the reserved core rock mass, the range of the advanced core rock mass reinforcement, the I-shaped steel type of the steel arch, the steel arch spacing, the steel arch layer number, the shotcrete strength type and thickness, and the length, diameter, spacing and prestress size of the anchor rod.

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