Multi-factor rockburst prediction method considering the tunnel construction process

Abstract

The present invention discloses a multi-factor rockburst prediction method considering the tunnel construction process, including: deriving the crack initiation criterion for the surrounding rock of an underground cavity under non-axisymmetric external loads; deriving the elastic solution of a circular cavity under non-axisymmetric external loads considering the construction process; deriving the crack initiation condition of a circular cavity under non-axisymmetric external loads considering the construction process according to the crack initiation criterion and the elastic solution; deriving the theoretical analytical solution of the surrounding rock detonation state during the crack initiation and detonation development process considering the tunnel construction process according to the elastic solution; establishing a multi-factor rockburst prediction model considering the average compressive stress of the quasi-explosion body during the construction process, and predicting rockburst. The method of the present invention can consider various rockburst influencing factors, more accurately predict the occurrence location and rockburst grade of rockburst, and can also accurately predict the occurrence time or construction stage of rockburst and the distance from the tunnel face.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering and relates to a multi-factor rockburst prediction method considering the tunnel construction process. Background Art

[0002] After the tunnel is excavated, the surrounding rock stress is redistributed. If the surrounding rock stress is everywhere less than the rock mass strength, the surrounding rock remains in an elastic state; conversely, when the stress in some areas of the surrounding rock exceeds the rock mass strength, the surrounding rock enters a plastic or failure state. Rockburst occurs during the tunnel excavation process in hard and intact or relatively intact high in-situ stress areas. It is a rock failure phenomenon caused by the sudden release of the energy accumulated in the rock mass when the rock is compressed to the elastic limit. Its essence is the brittle failure of the rock. The sudden brittle failure of rockburst causes rock flakes (blocks) to break away from the parent body and suddenly eject in the direction of the free face, experiencing a progressive failure process of rapid "splitting-shearing-ejecting".

[0003] During the tunnel excavation process, the stress of the excavated part of the rock mass is released, and the surrounding rock stress is redistributed again. The stress gradually concentrates on the tunnel wall, and the surrounding rock starts to crack at a certain position inside the tunnel wall. During the further stress release process, the cracks gradually expand, accompanied by the re-cracking of the internal surrounding rock, and gradually form pancake-shaped or slab-cracked surrounding rock. After splitting, each rock slab bears the circumferential pressure. When it exceeds its own strength, it is crushed or fractured and ejected, forming rockburst. Rockburst occurs due to the fracture on the basis of slab cracking, so it can be considered that at the beginning of the rockburst incubation, it is circumferential slab cracking, and then the slab cracks and breaks on the basis of stress adjustment. And the stress adjustment changes with the construction progress, and the most core manifestation is the stress release coefficient.

[0004] When the tunnel surrounding rock is in high in-situ stress and the lateral pressure coefficient is greater than 1, the circumferential stress is the smallest at the sidewall part and the largest at the crown part. Rockburst generally occurs at the sidewall arch shoulder part, but the stress intensity ratio criterion shows that rockburst is more likely to occur at the crown, which is contradictory to the actual situation. Therefore, the rockburst grade cannot be simply predicted and judged by the stress intensity ratio. Therefore, the influence of the construction effect of the tunnel or the stress release of the surrounding rock during the construction process on rockburst should be considered.

[0005] A Chinese patent with a publication date of July 22, 2022 and a publication number of CN114778800A discloses a multi-factor rockburst prediction method based on an analytical method. This method can more accurately predict the specific location of the tunnel rockburst on the tunnel wall, the range of the quasi-explosion body at the location, and the grade of the rockburst, but it cannot predict the occurrence time of the rockburst or the distance of the rockburst from the tunnel face or perform four-dimensional positioning of the rockburst prediction. Summary of the Invention

[0006] The object of the present invention is to provide a multi-factor rockburst prediction method considering the tunnel construction process, which can consider various rockburst influencing factors, more accurately predict the occurrence location and grade of rockburst, and can also accurately predict the occurrence time of rockburst, the construction stage, and the distance from the tunnel face.

[0007] The technical solution adopted by the present invention is a multi-factor rockburst prediction method considering the tunnel construction process, which is specifically implemented according to the following steps:

[0008] Step 1: Derive the cracking criterion of the surrounding rock of an underground chamber under non-axisymmetric external loads.

[0009] Step 2: Derive the elastic solution of a circular chamber under non-axisymmetric external loads considering the construction process.

[0010] Step 3: According to the cracking criterion obtained in Step 1 and the elastic solution obtained in Step 2, derive the cracking condition of a circular chamber under non-axisymmetric external loads considering the construction process.

[0011] Step 4: According to the elastic solution obtained in Step 2, derive the theoretical analytical solution of the initiation state of the surrounding rock during the initiation and development process considering the tunnel construction process.

[0012] Step 5: Establish a multi-factor rockburst prediction model considering the average compressive stress of the quasi-explosion body during the construction process and predict the rockburst.

[0013] The present invention is further characterized in that:

[0014] Specifically, Step 1 is as follows: According to the internal mechanism of the fracture of rock-like brittle materials, Griffith strength theory, and stress circle theory, the cracking criterion of the surrounding rock of an underground chamber under non-axisymmetric external loads is obtained as follows:

[0015] When the criterion is: ;

[0016] When the criterion is: ;

[0017] where circumferential stress, radial stress, shear stress, is the tensile strength.

[0018] Specifically, Step 2 is as follows:

[0019] Step 2.1: According to the basic theory of elasticity, derive the basic solution of the elastic secondary stress field of a circular chamber with internal loads on the chamber wall and under non-axisymmetric external loads, as follows:

[0020]

[0021]

[0022]

[0023] Among them, circumferential stress, radial stress, shearing stress, is the polar radius, is the position angle, is the hole diameter, vertical load, is the coefficient of lateral pressure, radial stress at the inner boundary of the hole wall, is the tangential stress at the inner boundary of the hole wall;

[0024] Step 2.2: Based on the analysis of the secondary stress field in Step 2.1, obtain the analysis of the initial stress field of a circular chamber under non-axisymmetric external loads as follows:

[0025]

[0026]

[0027]

[0028] Step 2.3: Based on the analysis of the initial stress field in Step 2.2, obtain the stress boundary conditions at the orifice of the hole wall of a circular chamber under non-axisymmetric external loads as follows:

[0029]

[0030]

[0031] Step 2.4: Based on the orifice stress boundary conditions in Step 2.3, considering the stress release coefficient , obtain the stress boundary of a circular chamber under non-axisymmetric external loads considering the tunnel construction process, that is and as follows:

[0032]

[0033]

[0034] Step 2.5: Based on the basic solution of the stress field in Step 2.1 and the chamber stress boundary with the stress release coefficient in Step 2.4, obtain the secondary stress field of the surrounding rock of a circular chamber under non-axisymmetric external loads considering the tunnel construction process as follows:

[0035]

[0036]

[0037]

[0038] Let , then there are:

[0039]

[0040]

[0041] .

[0042] Step 3 is specifically as follows:

[0043] Step 3.1: According to the cracking criterion obtained in Step 1 and the elastic solution obtained in Step 2, obtain the combined expression of the elastic stress components of a circular tunnel under the condition of non-axisymmetric external loads considering the construction process, as shown in the following formula:

[0044]

[0045]

[0046]

[0047]

[0048] Among them, circumferential stress, radial stress, stress release coefficient, vertical load, is the lateral pressure coefficient, is the position angle, is the polar radius, is the tunnel diameter, ;

[0049] Step 3.2: According to the cracking criterion obtained in Step 1, the elastic solution obtained in Step 2, and the combined expression of the stress components obtained in Step 3.1, obtain the cracking condition of a circular tunnel under the condition of non-axisymmetric external loads considering the construction process, that is, the implicit cracking condition equation groups ① and ② about :

[0050] Equation group ①: When , cracking occurs when the following two formulas are satisfied simultaneously:

[0051]

[0052]

[0053] Among them, is the tensile strength, is the shear stress;

[0054] Equation set ②: When is 0, cracking occurs when the following two equations are satisfied simultaneously:

[0055]

[0056]

[0057] Judge whether the surrounding rock will crack according to implicit cracking condition equation sets ① and ②. If the surrounding rock cracks, the cracking radius at a specific position can be obtained according to implicit cracking condition equation sets ① and ②. .

[0058] Step 4 is specifically as follows:

[0059] Step 4.1: According to the elastic solution obtained in step 2, obtain the stress expression at the crack tip considering the tunnel construction process or the force expression of the quasi-explosion body when the surrounding rock cracks;

[0060] After the excavation of the cavity, the circumferential stress of the surrounding rock at the is:

[0061]

[0062] When the surrounding rock cracks, the stress at the crack tip is the circumferential stress of the cavity wall at the cracking position , that is:

[0063]

[0064] Among them, , are the circumferential stresses before and after the cracking of the surrounding rock respectively, is the polar radius, is the cavity diameter, is the stress release coefficient, is the vertical load, is the lateral pressure coefficient, is the position angle, is the cracking radius and ;

[0065] Step 4.2: According to the circumferential stress obtained in step 4.1, derive the expression of the average compressive stress received by the quasi-explosion body considering the tunnel construction process:

[0066]

[0067] When the compressive stress Exceeding the rock mass compressive strength When, that is When, the surrounding rock detonates.

[0068] Step 5 is specifically as follows:

[0069] Step 5.1: According to the stress intensity ratio criterion, establish the relationship between the rockburst grade, stress intensity ratio , compressive stress , compressive strength as ;

[0070] Step 5.2: Based on the multi-factor quasi-explosion body average compressive stress expression obtained in Step 4, establish a multi-factor rockburst prediction model and judge the rockburst grade.

[0071] Stress intensity ratio The relationship with the rockburst grade is as follows:

[0072] K < 0.3, no rockburst;

[0073] 0.3 ≤ K < 0.5, slight rockburst;

[0074] 0.5 ≤ K < 0.7, moderate rockburst;

[0075] 0.7 ≤ K < 0.9, strong rockburst;

[0076] 0.9 ≤ K, extremely strong rockburst.

[0077] The beneficial effects of the present invention are as follows:

[0078] The method of the present invention starts from the basic theory of tunnel mechanics, considers the tunnel construction process, follows the Griffith brittle fracture strength theory, deduces the elastic-brittle solution of stress release in chamber excavation - stress redistribution of surrounding rock - initiation and detonation of surrounding rock on the tunnel wall considering the stress release coefficient, and proposes a multi-factor rockburst prediction method considering the tunnel construction process. This method can simultaneously consider various rockburst influencing factors, such as the tunnel diameter, buried depth, lateral pressure coefficient, the strength and deformation characteristic parameters of the surrounding rock, etc., and can more accurately predict the specific location of tunnel rockburst on the tunnel wall, the range of the quasi-explosion body at the location, the rockburst grade, as well as the time of rockburst occurrence and the distance of the rockburst from the tunnel face. Description of the Drawings

[0079] Figure 1 is a schematic diagram of the prediction method of the present invention;

[0080] Figure 2 is a flowchart of the prediction method of the present invention. Detailed Embodiments

[0081] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0082] The multi-factor rockburst prediction method for the tunnel construction process of the present invention, such as Figure 1 and Figure 2 shown, is specifically implemented according to the following steps:

[0083] Step 1: Deduce the crack initiation criterion for the surrounding rock of underground caverns under non-axisymmetric external loads, specifically:

[0084] Step 1.1: Reveal the internal mechanism of the fracture of brittle rock-like materials from the energy perspective;

[0085] ① There are many randomly distributed microcracks or microfissures inside brittle rock-like materials. Under the action of external forces, stress concentration occurs at the tips of the microcracks. When the energy accumulated at the tips of the microcracks reaches a certain value, the microcracks begin to expand.

[0086] ② In the case of uniaxial compression, the maximum tensile stress is at the crack tip. When the stress acting at the crack tip reaches the energy required to form a new crack, there is , and the crack begins to expand. Among them, represents the maximum tensile stress at the crack tip, represents the specific surface energy of the crack, the length of the long semi-axis of the crack, is the elastic modulus.

[0087] ③ When the external force increases, the crack will expand along the direction perpendicular to the maximum tensile stress and gradually develop into the direction parallel to the maximum principal stress until it is completely split and damaged, revealing that splitting tensile failure is the essence of rock failure under uniaxial compression conditions.

[0088] Step 1.2: Analyze the crack initiation criterion for brittle rock-like materials based on Griffith strength theory;

[0089] In coordinate system, the Griffith strength criterion is a piecewise function:

[0090] ① When , , that is, as long as is satisfied, the microcracks of the rock begin to initiate and expand.

[0091] ② When , , at this time, the microcracks will initiate and damage along the angle, and it satisfies .

[0092] Among them, is the first principal stress, is the third principal stress, is the tensile strength.

[0093] Step 1.3: Derive the crack initiation criterion for the surrounding rock of underground caverns under non-axisymmetric external loads based on the stress circle theory;

[0094] The relationship between the principal stress and the circumferential stress , the radial stress , and the shear stress in the stress circle is:

[0095] (1a)

[0096] (1b)

[0097] Substitute the above formula (1) into the crack initiation criterion for rock-like brittle materials in Step 1.2 to obtain the crack initiation criterion for the surrounding rock of underground caverns under non-axisymmetric external loads:

[0098] ① When is true,

[0099] ② When is true,

[0100] Step 2: Derive the elastic solution of a circular cavern under non-axisymmetric external loads considering the construction process, specifically:

[0101] Step 2.1: Derive the elastic secondary stress field of a circular cavern under the action of internal loads and on the cavern wall, and under the action of non-axisymmetric external loads and :

[0102] (2a)

[0103] (2b)

[0104] (2c)

[0105] where, is the cavern diameter, is the vertical load, is the lateral pressure coefficient, is the radial stress at the inner boundary of the cavern wall, is the tangential stress at the inner boundary of the cavern wall, is the polar radius, is the position angle.

[0106] Step 2.2: Based on the secondary stress field in Step 2.1, deduce the initial stress field of a circular cavern under non-axisymmetric external loads:

[0107] When the cavern diameter in Equation (2) , and the load on the cavern wall is 0, the initial stress field can be obtained:

[0108] (3a)

[0109] (3b)

[0110] (3c)

[0111] Step 2.3: Based on the analysis of the initial stress field in Step 2.2, deduce the stress boundary conditions at the orifice of the circular cavern under non-axisymmetric external loads:

[0112] After the cavern is excavated, the stress at the cavern edge is in a zero state. Due to the existence of the initial in-situ stress, to satisfy the zero-stress state at the cavern edge, a load opposite to the initial in-situ stress must be applied along the orifice edge. Thus, the stress boundary conditions at the orifice of the cavern wall can be obtained:

[0113] (4a)

[0114] (4b)

[0115] Step 2.4: Based on the orifice stress boundary conditions in Step 2.3, deduce the stress boundary of the circular cavern under non-axisymmetric external loads considering the stress release coefficient , that is and :

[0116] When the excavation process is represented by the secondary stress field in Equation (2), the inner boundary conditions in Equation (4) correspond to and in Equation (2), which gradually change from the initial boundary to 0. The stress release coefficient represents the ratio of the stress released due to cavern excavation to the original stress. Then represents the ratio of the remaining stress to the original stress due to cavern excavation. As the cavern excavation process progresses, the equivalent inner boundary stress load acting on the cavern wall is times the boundary stress after excavation is completed. Then the load on the cavern wall during the excavation process is:

[0117] (5a)

[0118] (5b)

[0119] Step 2.5: Based on the basic solution of the stress field in Step 2.1 and the cavity stress boundary with the stress release coefficient in Step 2.4, derive the secondary stress field of the surrounding rock of a circular cavity considering the stress release coefficient under non-axisymmetric external loads:

[0120] Substitute the cavity wall load obtained in Step 2.4 into the secondary stress field of Equation (2), and the secondary stress field of the surrounding rock considering the construction effect or stress release coefficient under non-axisymmetric external loads can be derived:

[0121] (6a)

[0122] (6b)

[0123] (6c)

[0124] Let , then we have:

[0125] (7a)

[0126] (7b)

[0127] (7c)

[0128] Step 3: Derive the cracking condition of a circular cavity under non-axisymmetric external loads considering the construction process, specifically:

[0129] Step 3.1: Based on the cavity cracking criterion in Step 1.3 and the components of the secondary stress field of the surrounding rock of a circular cavity considering the tunnel construction process in Step 2.5, derive the combined expression of the elastic stress components of a circular cavity under non-axisymmetric external loads considering the construction process.

[0130] According to the stress field components, the combined expression of the stress field is:

[0131] (8a)

[0132] (8b)

[0133] (8c)

[0134] (8d)

[0135] Step 3.2: Substitute the secondary stress field in Step 2.5 and the combined expression of the stress components in Step 3.1 into the cavity cracking criterion in Step 1.3 to derive the cracking condition of a circular cavity under non-axisymmetric external loads considering the construction process.

[0136] ① When When is 0, cracking occurs. Substituting the stress field components and combined expressions into the above equation, cracking occurs when the following equations (9a) and (9b) are satisfied simultaneously:

[0137] (9a)

[0138] (9b)

[0139] ② When is 0, is 0, cracking occurs. Substituting the stress field components and combined expressions into the above equation, cracking occurs when the following equations (10b) and (10b) are satisfied simultaneously:

[0140] (10a)

[0141] (10b)

[0142] Equations (9 - 10) are all implicit functions of , which are the implicit cracking condition equation systems ① and ② respectively, where the hole diameter is , the vertical load is , the lateral pressure coefficient , and the tensile strength of the surrounding rock are all known; while corresponds to the cracking radius, corresponds to the angle of the cracking position of the tunnel surrounding rock, corresponds to the stress release coefficient and is unknown. During the actual construction process, for a specific tunnel position (side wall , spandrel , crown ), the stress release coefficient of a specific construction process (through the analysis of 2D and 3D tunnel excavation numerical tests, the relationship between the stress release coefficient and the distance from the analysis section to the tunnel face can be easily obtained), and then can be uniquely determined, and then the cracking radius can be determined.

[0143] Step 4: Derive the theoretical analytical solution of the surrounding rock detonation state during the cracking and detonation development process considering the tunnel construction process, specifically:

[0144] Step 4.1: After the tunnel is excavated, the surrounding rock cracks, and derive the expression of the stress at the crack tip or the force on the quasi-explosion body considering the tunnel construction process;

[0145] After the tunnel is excavated, the circumferential stress of the surrounding rock at the tunnel wall is:

[0146] (11)

[0147] When the surrounding rock starts to crack, the stress at the crack tip is the circumferential stress of the tunnel wall at the crack initiation position, i.e.: at the crack initiation position, i.e.:

[0148] (12)

[0149] Step 4.2: Derive the expression for the average compressive stress on the quasi-explosion body considering the tunnel construction process.

[0150] The average compressive stress on the quasi-explosion body is:[[]]END]]

[0151] (13)

[0152] When the compressive stress exceeds the compressive strength of the rock mass , i.e. when, the surrounding rock will detonate.

[0153] Step 5: Establish a multi-factor rockburst prediction model for the average compressive stress of the quasi-explosion body considering the construction process, specifically as follows:

[0154] Step 5.1: Analyze the relationship between the rockburst grade, stress intensity ratio compressive stress , and compressive strength in the stress intensity ratio criterion;

[0155] According to the commonly used stress intensity ratio criterion, the relationship between the rockburst grade, stress intensity ratio , compressive stress , and compressive strength is , and there is:

[0156] K < 0.3, no rockburst;

[0157] 0.3 ≤ K < 0.5, slight rockburst;

[0158] 0.5 ≤ K < 0.7, moderate rockburst;

[0159] 0.7 ≤ K < 0.9, intense rockburst;

[0160] 0.9 ≤ K, extremely intense rockburst.

[0161] Step 5.2: Based on the expression of the average compressive stress of the multi-factor quasi-explosion body considering the stress release coefficient , establish a multi-factor rockburst prediction model.

[0162] According to the formula for the average compressive stress on the quasi-explosion body in the theoretical analysis of the initiation and detonation state of the surrounding rock, the average compressive stress of the quasi-explosion body When the uniaxial compressive strength of the surrounding rock is known According to the relationship between the stress strength ratio and the rockburst grade, the rockburst grade can be judged.

[0163] In the prediction method of the present invention: the function of step 1 is to analyze the crack initiation criterion of rocks from the perspective of the internal mechanism of brittle crack initiation and failure after the rocks are loaded, and then propose the crack initiation criterion for rockburst in the surrounding rock of underground caverns under non-axisymmetric external load conditions.

[0164] After the tunnel is excavated, the essence of rockburst in the surrounding rock of the tunnel wall is that after the excavation unloading of the cavern, the surrounding rock of the tunnel wall is suddenly brittlely damaged due to the sudden increase in circumferential stress and radial unloading. Rockburst is the product of high in-situ stress and is a hard brittle rock mass with a large amount of elastic strain energy reserve. Due to the radial unloading during the excavation of the cavern and the sudden increase in circumferential stress, the concentrated energy generates sudden brittle failure, causing rock flakes to break away from the parent body and suddenly eject towards the free face direction, experiencing a progressive failure process of rapid "splitting - shear folding - ejection".

[0165] There are many micro (potential) cracks or fissures inside any material. Under the action of external forces, large stress concentrations will be generated around these fissures. The failure of materials often starts from the ends of the fissures and leads to complete failure through the expansion of the fissures. And rocks are this kind of brittle material containing a large number of microcracks and pores. Under uniaxial compression conditions, splitting tensile failure is the essence of rock failure. Griffith strength theory interprets the splitting tensile failure mechanism from the energy perspective and extends the crack initiation criterion for rocks under load.

[0166] The advantage of adopting the crack initiation criterion for rockburst in caverns based on the essence of rock splitting failure is that Griffith strength theory well reveals the internal mechanism of splitting fracture of rock-like brittle materials under load and the energy required for fracture. Griffith strength theory can well describe the brittle failure characteristics of rocks in rockburst. By cleverly using the stress circle theory, the crack initiation criterion for rocks under load can be further extended to the crack initiation criterion after the excavation unloading of the surrounding rock of underground caverns under non-axisymmetric external load conditions.

[0167] In the prediction method of the present invention: the function of step 2 is to accurately derive the elastic theoretical analytical solution of a circular cavern under non-axisymmetric external load conditions considering the construction process.

[0168] After the tunnel excavation unloading, the stress of the surrounding rock is redistributed to form the secondary stress field of the surrounding rock. If the stress of the surrounding rock is everywhere less than the strength of the rock mass, the surrounding rock remains in an elastic state; on the contrary, when the stress in some areas of the surrounding rock exceeds the strength of the rock mass, the surrounding rock enters the plastic or failure state. If the tensile stress in the local area of the surrounding rock reaches the ultimate tensile strength, local tensile brittle failure will occur.

[0169] Adopt the elastic analytical solution of a circular cavern under non-axisymmetric external loads considering construction effects. Its advantages are as follows: Rockburst occurs under high in-situ stress conditions in hard and intact or relatively intact rock masses after tunnel excavation unloading. It is a sudden release after a certain period of energy accumulation. The elastic solution of a circular cavern under non-axisymmetric external loads considering the construction process is a basic elastic mechanics equation, and the derived elastic theoretical solution of the cavern can consider various influencing factors (such as: tunnel diameter , vertical load , lateral pressure coefficient , stress release coefficient , etc.).

[0170] In the prediction method of the present invention: The function of step 3 is to derive the crack initiation condition of the surrounding rock of a circular cavern under non-axisymmetric external loads considering the construction process.

[0171] Adopt the theoretical analysis of the crack initiation condition of the surrounding rock. The principle is: The essence of rockburst is the brittle failure of rock. Rockburst is the product of high in-situ stress. Due to tunnel excavation unloading, under the action of circumferential concentrated stress, sudden brittle failure occurs, causing rock flakes (blocks) to break away from the matrix and suddenly eject towards the free face direction, experiencing a progressive failure process of rapid "splitting - shear folding - ejection". That is to say, rockburst mostly occurs after crack initiation and then explosion.

[0172] According to the form of the crack initiation criterion expression of the underground cavern surrounding rock, derive the combined expression of the elastic stress components of a circular cavern considering the construction process under non-axisymmetric external loads, and then derive the implicit function group of the crack initiation condition of a circular cavern considering the construction process under non-axisymmetric external loads. When the implicit function group of the crack initiation condition holds or has a solution, microcrack initiation will occur in the surrounding rock of the cavern.

[0173] Adopt the theoretical analysis of the crack initiation condition of the surrounding rock considering the construction process. Its advantages are as follows: Given the basic parameters of the tunnel (vertical load , lateral pressure coefficient , tensile strength , tunnel diameter ), the implicit function of crack initiation at any position of the cavern can be determined. The stress release coefficient is equivalent to the distance from the tunnel face. The position angle determines the rockburst direction of the cavern section, and the polar radius determines the crack initiation radius .

[0174] In the prediction method of the present invention: The function of step 4 is to accurately derive the theoretical analysis of the initiation state of the surrounding rock during the development process of rockburst considering the tunnel construction process.

[0175] Using the theory of the initiation state of surrounding rock for analysis, its principle is as follows: There are many random micro-cracks inside brittle materials. Under the action of external forces, a large stress concentration is generated near the tip of the micro-cracks. When the accumulated energy reaches a certain value, the cracks will start to expand and gradually transition towards the direction of the major principal stress. Rockburst is a product of high in-situ stress. It is a hard and brittle rock mass with a large reserve of elastic strain energy. Due to the excavation of the cavern, the radial constraint is removed, and the circumferential stress suddenly increases, further concentrating the energy. Under the action of the concentrated stress, sudden brittle failure occurs.

[0176] Using the theory of the initiation state of surrounding rock considering the construction process for analysis, its advantages are as follows: It takes into account the stress release mechanism during the tunnel construction process and the characteristics of the gestation, formation, development, and evolution of tunnel rockburst. The rockburst of the surrounding rock follows the gestation and development mechanism of initial cracking first and then detonation. After initial cracking occurs inside the surrounding rock, a quasi-explosion body is generated. The quasi-explosion body is stressed and adjusted. When the average compressive stress exceeds the compressive strength of the rock mass then the quasi-explosion body detonates, that is, a rockburst disaster occurs.

[0177] In the prediction method of the present invention: The function of step 5 is to accurately establish a multi-factor rockburst prediction model considering the tunnel construction process.

[0178] Using the multi-factor rockburst prediction model, its principle is as follows: By combining the elastic solution of a circular cavern considering stress release during the construction process under non-axisymmetric external loads and the Griffith initial cracking criterion of the surrounding rock, an elastic-brittle implicit solution of the surrounding rock can be obtained, and further, the circumferential stress of the surrounding rock under elastic-brittle conditions and the average compressive stress received by the quasi-explosion body can be obtained. Based on the commonly used stress intensity ratio criterion, according to the stress intensity ratio the grade of rockburst can be judged.

[0179] Using the multi-factor rockburst prediction model considering the tunnel construction process, its advantages are as follows: For actual tunnel projects, the lateral pressure coefficient , compressive strength , tensile strength , unit weight , elastic modulus , the diameter of the cavern , position angle , burial depth , etc. parameters can be conveniently obtained. The relationship between the vertical load and the burial depth and the unit weight is . And there is an empirical relationship between the deformation modulus and the compressive strength , tensile strength . That is to say, as long as the deformation modulus of the rock mass is known, the compressive strength and the tensile strength can be obtained Given the basic parameters of a known tunnel, the implicit function of crack initiation at any position in the chamber can be determined, and the stress release coefficient is equivalent to the distance from the tunnel face, and the position angle determines the rockburst direction of the chamber section and the polar radius to determine the crack initiation radius. During the actual construction of the chamber, for a specific chamber position (such as the side wall , the shoulder , the crown ), at a specific construction progress, distance from the tunnel face or stress release coefficient , it can be uniquely determined , and then the crack initiation radius can be determined. When the average compressive stress of the quasi-explosion body exceeds the compressive strength of the rock mass, detonation occurs. At the same time, according to the stress intensity ratio criterion, the grade of rockburst occurrence is judged. Rockburst is a brittle failure of rocks caused by the sudden release of energy from the chamber wall after tunnel excavation under high in-situ stress conditions in hard and intact or relatively intact rock masses. Griffith's strength theory essentially reveals the internal mechanism of the fracture of brittle materials such as rocks. Therefore, it is completely consistent theoretically to study the crack initiation and detonation after chamber excavation through Griffith's strength theory. Moreover, there are many factors affecting the crack initiation and detonation of the surrounding rock of the tunnel chamber wall, and the method of the present invention exactly considers various influencing factors of chamber excavation construction theoretically, which meets the engineering practice in terms of the formation conditions of rockburst gestation.

[0180] In actual engineering, high in-situ stress chamber rockbursts mostly occur in the side wall parts of tunnels. For example, in the diversion tunnel of Jinping II Hydropower Station, the number of rockbursts occurring in the side wall, shoulder, crown, and invert are 348, 147, 138, and 11 times respectively. The method of the present invention can prove theoretically that when the lateral pressure coefficient is greater than 1, rockbursts mainly occur in the side wall parts, and the rockburst grade of the side wall parts is greater than that of the crown parts, which meets the engineering requirements in terms of the accuracy of rockburst prediction.

[0181]

[0182] ​After the excavation of the cavern, the radial constraint is removed and the circumferential stress increases suddenly. Microcracks in the surrounding rock initiate and propagate, which in turn causes rock flakes on the cavern wall to eject towards the free face, resulting in rockburst disasters and affecting the safety of tunnel construction. Therefore, the prediction of rockburst should have a certain practicality and effectiveness. At least, on the premise of meeting the construction progress and safety of the tunnel, it should be able to predict and judge in advance the possible distance, location, and grade of rockburst, so as to optimize the construction plan or support plan in a timely manner, and then ensure the safety of tunnel construction. The new multi-factor rockburst prediction method of the present invention is simple, fast, and intelligent, and can predict the distance of the rockburst occurrence location from the tunnel face. In terms of the practicality and effectiveness of rockburst prediction, it fully meets the requirements of engineering construction.

[0183] There is the following basic relationship between the stress release process of tunnel excavation and the occurrence of rockburst:

[0184] ① During the stress release process of tunnel excavation, the stress release coefficient increases from 0 to 1, and the initiation radius decreases from the initial state.

[0185] ② When the stress release coefficient is, that is, in the unexcavated state, the original in-situ stress state can be obtained at this time.

[0186] ③ During the process when the stress release coefficient increases from 0 to 1, the initiation radius gradually decreases, and the average stress of the quasi-explosion body gradually increases. Once the average stress of the quasi-explosion body in this section is greater than the compressive strength, rockburst occurs.

[0187] ④ During the process when the stress release coefficient increases from 0 to 1, it just makes , then there is a critical stress release coefficient . At this time, the average stress of the quasi-explosion body within the initiation radius tends to infinity, and rockburst occurs at this time.

[0188] ⑤ During the process when the stress release coefficient increases from 0 to 1, if there is no critical stress release coefficient , the average stress of the quasi-explosion body is still used to judge whether there is rockburst.

[0189] ⑥ When continues to increase and approaches 1, the minimum initiation radius can be obtained at this time. If the average stress of the quasi-explosion body is still less than the compressive strength at this time, no rockburst will occur during the entire excavation process.

[0190] Therefore, the core idea of the initiation and detonation of the surrounding rock considering the construction effect of underground caverns is as follows:

[0191] ①When , that is, the initial stress field before excavation, the maximum crack initiation radius can be calculated at this time;

[0192] ②Let , and see if the critical stress release coefficient can be obtained.

[0193] ③If there exists , the corresponding crack initiation radius at this time must be very small, and rockburst will definitely occur at this time.

[0194] ④If there does not exist , let , there exists a minimum crack initiation radius at this time. If it does not detonate at this time, no rockburst will occur during the entire excavation process.

[0195] Through the multi-factor rockburst prediction method considering the tunnel construction process of the present invention, the detailed process of implementing rockburst prediction is as follows:

[0196] Step a: Obtain the basic characteristic parameters of the surrounding rock and the tunnel, including the tunnel diameter , buried depth , lateral pressure coefficient , the compressive strength , tensile strength , unit weight , etc.

[0197] Step b: Obtain the elastic stress component solution and stress combination result considering the construction process of the chamber, such as in Equations (7 - 8).

[0198] Step c: Substitute the stress components and combination results into the Griffith crack initiation criterion selection condition and criterion expression of the tunnel surrounding rock, and establish an implicit function of the surrounding rock crack initiation about , such as in Equations (9 - 10).

[0199] Step d: Judge whether the implicit function has a solution, and further judge whether the surrounding rock will crack under specific conditions. If the surrounding rock cracks, the crack initiation radius at a specific position can be obtained according to the crack initiation implicit function. According to the crack initiation radius, calculate the average compressive stress of the quasi-explosion body, such as in Equations (11 - 13).

[0200] Step e: Obtain the stress release coefficient curve during the chamber excavation process, and make a detailed and accurate prediction of the rockburst grade according to the strength-stress ratio of the quasi-explosion body.

[0201] Example 1:

[0202] For a certain tunnel section of the Sangzhuling Tunnel on the Lalin Railway, the buried depth is 427 m, and the unit weight is 26 kN / m 3, the deformation modulus is 34 GPa, the compressive strength is 130 MPa, the tensile strength is 3.9 MPa, the lateral pressure coefficient is 2.41, the tunnel diameter is 8.0 m, and it is actually a weak rockburst. Substitute the above parameters into the implicit function group (9 - 10) of the circular tunnel under the non-axisymmetric external load condition considering the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed, and the construction speed is considered as 1 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.88 (i.e., 14.4 m away from the tunnel face or after 7.2 days of excavation), a slight weak rockburst occurs at the sidewall (initiation radius 8.16 m, stress intensity ratio 0.39), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium rockburst finally. When the stress release coefficient is 0.92 (i.e., 17.6 m away from the tunnel face or after 8.8 days of excavation), a slight weak rockburst occurs at the arch shoulder (initiation radius 8.94 m, stress intensity ratio 0.30), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium rockburst finally. During the entire construction process, there is no possibility of rockburst in the surrounding rock within 60° of the crown. Considering the implicit function group (9 - 10) of the circular tunnel under the non-axisymmetric external load condition during the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed, and the construction speed is considered as 1 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.88 (i.e., 14.4 m away from the tunnel face or after 7.2 days of excavation), a slight weak rockburst occurs at the sidewall (initiation radius 8.16 m, stress intensity ratio 0.39), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium rockburst finally. When the stress release coefficient is 0.92 (i.e., 17.6 m away from the tunnel face or after 8.8 days of excavation), a slight weak rockburst occurs at the arch shoulder (initiation radius 8.94 m, stress intensity ratio 0.30), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium rockburst finally. During the entire construction process, there is no possibility of rockburst in the surrounding rock within 60° of the crown.

[0203] Example 2:

[0204] For a certain section of the Sangzhuling Tunnel on the Lalin Railway, the buried depth is 340 m, the unit weight is 26 kN / m 3 , the deformation modulus is 34 GPa, the compressive strength is 130 MPa, the tensile strength is 3.9 MPa, the lateral pressure coefficient is 1.48, the tunnel diameter is 8.0 m, and it is actually a weak rockburst. Substitute the above parameters into the implicit function group (9 - 10) of the circular tunnel under the non-axisymmetric external load condition considering the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed, and the construction speed is considered as 2 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.66 (i.e., 5.1 m away from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the sidewall (initiation radius 8.39 m, stress intensity ratio 0.32), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally. When the stress release coefficient is 0.62 (i.e., 5.1 m away from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the arch shoulder (initiation radius 8.63 m, stress intensity ratio 0.31), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally. When the stress release coefficient is 0.59 (i.e., 4.6 m away from the tunnel face or after 2.3 days of excavation), a slight weak rockburst occurs at the arch top (initiation radius 8.83 m, stress intensity ratio 0.31), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally. Considering the implicit function group (9 - 10) of the circular tunnel under the non-axisymmetric external load condition during the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed, and the construction speed is considered as 2 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.66 (i.e., 5.1 m away from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the sidewall (initiation radius 8.39 m, stress intensity ratio 0.32), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally. When the stress release coefficient is 0.62 (i.e., 5.1 m away from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the arch shoulder (initiation radius 8.63 m, stress intensity ratio 0.31), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally. When the stress release coefficient is 0.59 (i.e., 4.6 m away from the tunnel face or after 2.3 days of excavation), a slight weak rockburst occurs at the arch top (initiation radius 8.83 m, stress intensity ratio 0.31), which is in good agreement with the actual situation. If timely support is not provided, there is a possibility of medium - strong rockburst finally.

[0205] Example 3:

[0206] A section of the Sangzhuling Tunnel of the Lhasa-Nyingchi Railway, with a burial depth of 806m and a bulk density of 25.5kN / m 3 , deformation modulus 33GPa, compressive strength 130MPa, tensile strength 4.0MPa, lateral pressure coefficient 1.06, cave diameter 8.0m, and no rock burst in practice. Substitute the above parameters into Considering the implicit function group (9-10) of the circular cavern under the non-axisymmetric external load conditions during the construction process, and the stress release coefficient at the face is considered to be 0.3, the deformation stress release is completed at the 3D tunnel diameter, and the construction speed is considered to be 2m / d, the rockburst prediction results are as follows: when the stress release coefficient is 0.89 (i.e. 15.2m away from the face or 7.6d after excavation), a slight weak rockburst occurs at the side wall (initiation radius 9.00m, stress intensity ratio is 0.31), a slight weak rockburst occurs at the arch shoulder (initiation radius 9.06m, stress intensity ratio is 0.31), and a slight weak rockburst occurs at the arch top (initiation radius 9.12m, stress intensity ratio is 0.30). The rockburst level gradually increases with the increase of the stress release coefficient, that is, after the excavation of the cavern, the later the support is, the higher the level of rockburst occurs. If support is provided in time, no rock burst will occur. During construction, if support is provided before the stress release coefficient is 0.89 (i.e. 15.2m away from the face or 7.6d before excavation), no rock burst will occur, which is consistent with the actual situation.

[0207] Embodiment 4:

[0208] A section of the Qinling Tunnel of the Han-Wei River Diversion Project, with a burial depth of 800m and a bulk density of 27.2kN / m 3 , deformation modulus 35GPa, compressive strength 60MPa, tensile strength 3.2MPa, lateral pressure coefficient 1.19, hole diameter 3.4m, it is actually a medium rock burst. Substitute the above parameters into Considering the implicit function group (9-10) of the circular cavern under the non-axisymmetric external load conditions during the construction process, the stress release coefficient at the tunnel face is considered to be 0.3, the deformation stress release is completed at the 3D tunnel diameter, and the construction speed is considered to be 2m / d. The rockburst prediction results are as follows: when the stress release coefficient is 0.3 (i.e., at the tunnel face), a slight weak rockburst occurs at the side wall (initiation radius 5.01m, stress intensity ratio 0.4), a slight weak rockburst occurs at the arch shoulder (initiation radius 4.96m, stress intensity ratio 0.47), and a moderate rockburst occurs at the arch top (initiation radius 4.91m, stress intensity ratio 0.55), which is consistent with the actual situation. If not supported in time, there is a possibility of strong rockburst in the end.

[0209] Embodiment 5:

[0210] A section of the Qinling Tunnel of the Han-Wei Diversion Project, with a burial depth of 1070m and a bulk density of 28kN / m 3, with a deformation modulus of 33 GPa, a compressive strength of 80 MPa, a tensile strength of 3.3 MPa, a lateral pressure coefficient of 1.13, a tunnel diameter of 3.4 m, and it is actually medium rockburst. Substitute the above parameters into the In the implicit function group (9 - 10) of the circular tunnel under the condition of non-axisymmetric external load considering the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed. The construction speed is considered as 2 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.3 (i.e., at the tunnel face), slight weak rockburst occurs at the sidewall (initiation radius 5.59 m, stress intensity ratio 0.36), slight weak rockburst occurs at the arch shoulder (initiation radius 5.59 m, stress intensity ratio 0.39), and slight weak rockburst occurs at the crown (initiation radius 5.59 m, stress intensity ratio 0.42). The rockburst grade gradually increases with the increase of the stress release coefficient, that is, after the tunnel is excavated, the later the support is, the higher the rockburst grade. If the support is not timely, medium-strong rockburst will occur. If the support is carried out after the stress release coefficient reaches 0.68 (i.e., 2.6 m away from the tunnel face or 1.3 d after excavation), medium rockburst will occur, which is in good agreement with the actual situation.

[0211] Example 6:

[0212] For a certain section of the Qinling Tunnel of the Han River to Wei River Diversion Project, the buried depth is 660 m, the unit weight is 28.6 kN / m 3 , with a deformation modulus of 38 GPa, a compressive strength of 80 MPa, a tensile strength of 3.1 MPa, a lateral pressure coefficient of 1.25, a tunnel diameter of 3.4 m, and it is actually strong rockburst. Substitute the above parameters into the In the implicit function group (9 - 10) of the circular tunnel under the condition of non-axisymmetric external load considering the construction process, and the stress release coefficient at the tunnel face is considered as 0.3. When the 3D tunnel diameter is reached, the deformation stress release is completed. The construction speed is considered as 2 m / d. The rockburst prediction results are as follows: When the stress release coefficient is 0.36 (i.e., 0.4 m away from the tunnel face or 0.2 d after excavation), slight weak rockburst occurs at the sidewall (initiation radius 5.01 m, stress intensity ratio 0.30). When the stress release coefficient is 0.3 (i.e., at the tunnel face), slight weak rockburst occurs at the arch shoulder (initiation radius 5.13 m, stress intensity ratio 0.34). When the stress release coefficient is 0.3 (i.e., at the tunnel face), slight weak rockburst occurs at the crown (initiation radius 5.07 m, stress intensity ratio 0.41). The rockburst grade gradually increases with the increase of the stress release coefficient, that is, after the tunnel is excavated, the later the support is, the higher the rockburst grade. If the support is not timely, strong rockburst will occur. If the support is carried out after the stress release coefficient reaches 0.88 (i.e., 6.2 m away from the tunnel face or 3.1 d after excavation), strong rockburst will occur, which is in good agreement with the actual situation.

[0213] In summary, the prediction method of the present invention can consider various factors affecting rockburst and can accurately predict the occurrence location, depth, and grade of rockburst in the surrounding rock of the cavern under a certain stress release coefficient, time, or distance from the tunnel face. The rockburst prediction result is accurate, meeting the engineering requirements and can provide services for tunnel rockburst prediction.

Claims

1. A multi-factor rockburst prediction method considering the tunnel construction process, characterized in that, The implementation is carried out according to the following steps: Step 1: Derive the crack initiation criterion for the surrounding rock of an underground cavern under non-axisymmetric external loads; Step 2: Derive the elastic solution of a circular cavern under non-axisymmetric external loads considering the construction process; Step 3: Based on the crack initiation criterion obtained in Step 1 and the elastic solution obtained in Step 2, derive the crack initiation condition of a circular cavern under non-axisymmetric external loads considering the construction process; Step 4: Based on the elastic solution obtained in Step 2, derive the theoretical analytical solution of the surrounding rock detonation state during the crack initiation and detonation development process considering the tunnel construction process; Step 5: Establish a multi-factor rockburst prediction model considering the average compressive stress of the quasi-explosion body during the construction process and predict rockburst; Specifically, Step 3 is as follows: Step 3.1: Based on the crack initiation criterion obtained in Step 1 and the elastic solution obtained in Step 2, obtain the combined expression of elastic stress components of a circular cavern under non-axisymmetric external loads considering the construction process, as shown in the following formula: Among them, circumferential stress, radial stress, stress release coefficient, vertical load, is the lateral pressure coefficient, is the position angle, is the polar radius, is the hole diameter, ; Step 3.

2. Based on the crack initiation criterion obtained in Step 1, the elastic solution obtained in Step 2, and the stress component combination expression obtained in Step 3.1, the crack initiation condition of a circular tunnel under non-axisymmetric external loads considering the construction process is obtained, that is, the implicit crack initiation condition equation sets ① and ② with respect to : Equation set ①: When occurs, cracking occurs when the following two equations are satisfied simultaneously: Among them, is the tensile strength, is the shear stress; Equation set ②: When is 0, cracking occurs when the following two expressions are satisfied simultaneously: ； Specifically, Step 4 is as follows: Step 4.1: Based on the elastic solution obtained in Step 2, obtain the stress expression at the crack tip or the force expression of the quasi-explosion body considering the tunnel construction process when the surrounding rock cracks; After the excavation of the cavern, the circumferential stress of the surrounding rock at the is as follows: When the surrounding rock starts to crack, the stress at the crack tip is the circumferential stress of the tunnel wall at the crack initiation position, that is: ​ Among them, , are the circumferential stresses before and after the rock mass cracking respectively, is the polar radius, is the tunnel diameter, is the stress release coefficient, is the vertical load, is the lateral pressure coefficient, is the position angle, is the cracking radius and ; Step 4.2: Based on the circumferential stress obtained in Step 4.1, derive the average compressive stress on the quasi-explosion body considering the tunnel construction process Expression: When the compressive stress exceeds the compressive strength of the rock mass , that is , the surrounding rock detonates.

2. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1, characterized in that Specifically, Step 1 is as follows: According to the internal mechanism of the fracture of rock-like brittle materials, Griffith strength theory, and stress circle theory, the crack initiation criterion for the surrounding rock of an underground cavern under non-axisymmetric external loads is obtained as follows: When the criterion is: ; When the criterion is: ; Among them, circumferential stress, radial stress, shear stress, is the tensile strength.

3. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1, characterized in that, Specifically, Step 2 is as follows: Step 2.1: According to the basic theory of elasticity, derive the basic solution of the elastic secondary stress field of a circular cavern with internal loads acting on the cavern wall and under non-axisymmetric external loads, as shown in the following formula: Among them, circumferential stress, radial stress, shearing stress, is the polar radius, is the position angle, is the hole diameter, vertical load, is the coefficient of lateral pressure, radial stress at the inner boundary of the hole wall, is the tangential stress at the inner boundary of the hole wall; Step 2.2: According to the analysis of the secondary stress field in Step 2.1, obtain the analysis of the initial stress field of a circular cavern under non-axisymmetric external loads, as shown in the following formula: Step 2.3: According to the analysis of the initial stress field in Step 2.2, obtain the stress boundary condition at the orifice of the circular cavern under non-axisymmetric external loads, as shown in the following formula: Step 2.

4. According to the orifice stress boundary conditions in Step 2.3, considering the stress release coefficient , the stress boundary of a circular opening under non-axisymmetric external loads considering the tunnel construction process is obtained, that is and , as shown in the following formula: Step 2.5: According to the basic stress field solution in Step 2.1 and the cavern stress boundary containing the stress release coefficient in Step 2.4, obtain the secondary stress field of the surrounding rock of a circular cavern considering the tunnel construction process under non-axisymmetric external loads, as shown in the following formula: Let , then we have: 。 4. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1, characterized in that, Judge whether the surrounding rock will crack according to the implicit cracking condition equations ① and ②. If the surrounding rock cracks, the cracking radius at a specific position can be obtained according to the implicit cracking condition equations ① and ② .

5. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1, characterized in that Specifically, Step 5 is as follows: Step 5.

1. Based on the stress intensity ratio criterion, establish the relationship among rockburst grade, stress intensity ratio , compressive stress , and compressive strength , for ; Step 5.

2. Based on the average compressive stress of the multi-factor quasi-burst body considering the stress release coefficient obtained in Step 4 expression, establish a multi-factor rockburst prediction model and judge the rockburst grade.

6. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 5, characterized in that Stress intensity ratio The relationship with the rockburst grade is as follows: When K < 0.3, there is no rockburst; When 0.3 ≤ K < 0.5, there is slight rockburst; When 0.5 ≤ K < 0.7, there is moderate rockburst; When 0.7 ≤ K < 0.9, there is strong rockburst; When 0.9 ≤ K, there is extremely strong rockburst.

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