Multi-factor rockburst prediction method considering tunnel construction process

Abstract

The invention discloses a multi-factor rockburst prediction method considering a tunnel construction process. The method comprises the following steps: deriving an underground cavern surrounding rock crack initiation criterion under a non-axisymmetric external load condition; deducing to obtain an elastic solution of the circular cavern under the non-axisymmetric external load condition in consideration of the construction process; according to the crack initiation criterion and the elastic solution, the crack initiation condition of the circular cavern under the non-axisymmetric external load condition in the construction process is deduced and obtained; according to the elastic solution, a surrounding rock detonation state theoretical analytical solution in the crack initiation and detonation development process considering the tunnel construction process is deduced; and establishing a multi-factor rockburst prediction model considering the average pressure stress of the quasi-explosion body in the construction process, and predicting the rockburst. According to the method, multiple rockburst influence factors can be considered, the rockburst occurrence position and the rockburst grade can be more accurately predicted, and the rockburst occurrence time or the construction stage and the distance from the tunnel face can be accurately predicted.

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 Technique

[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; on the contrary, 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, 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 shoot suddenly towards the free face direction, experiencing a progressive failure process of rapid "splitting - shear folding - ejection".

[0003] During the tunnel excavation process, part of the rock mass is excavated and the stress 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, and when it exceeds its own strength, it is crushed or fractured and ejected, forming a rockburst. And 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 fractures occur 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 arch shoulder part of the sidewall, 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 the publication date of July 22, 2022 and the 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 cannot 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, construction stage and 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: Step 1: Derive the crack initiation criterion for the surrounding rock of underground chambers under non-axisymmetric external loads. Step 2: Derive the elastic solution of a circular chamber under non-axisymmetric external loads considering the construction process. Step 3: According to the crack initiation criterion obtained in Step 1 and the elastic solution obtained in Step 2, derive the crack initiation condition of a circular chamber under non-axisymmetric external loads considering the construction process. Step 4: According to 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 the rockburst.

[0008] The characteristics of the present invention also lie in: 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 underground chambers under non-axisymmetric external loads is obtained as follows: When the criterion is: ; When the criterion is: ; where circumferential stress, radial stress, shear stress, is the tensile strength.

[0009] 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 chamber with internal loads acting on the chamber wall and under non-axisymmetric external loads, as follows:

[0010]

[0011]

[0012] where 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, Based on 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 follows:

[0013]

[0014]

[0015] 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 circular cavern under non-axisymmetric external loads, as follows:

[0016]

[0017] Step 2.4, Based on the orifice stress boundary conditions in Step 2.3, considering the stress release coefficient , obtain the stress boundary of the circular cavern under non-axisymmetric external loads considering the tunnel construction process, that is and , as follows:

[0018]

[0019] Step 2.5, Based on the fundamental solution of the stress field in Step 2.1 and the cavern stress boundary with the stress release coefficient in Step 2.4, obtain the secondary stress field of the surrounding rock of the circular cavern under non-axisymmetric external loads considering the tunnel construction process, as follows:

[0020]

[0021]

[0022] Let , then there is:

[0023]

[0024] 。

[0025] Step 3 is specifically as follows: Step 3.1: According to 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 tunnel under non-axisymmetric external load conditions considering the construction process, as shown in the following formula:

[0026]

[0027]

[0028]

[0029] Wherein, 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, ; Step 3.2: According to the crack initiation criterion obtained in Step 1, the elastic solution obtained in Step 2, and the combined expression of stress components obtained in Step 3.1, obtain the crack initiation condition of a circular tunnel under non-axisymmetric external load conditions considering the construction process, that is, the implicit crack initiation condition equation sets ① and ② about : Equation set ①: When , cracking occurs when the following two equations are satisfied simultaneously:

[0030]

[0031] Wherein, is the tensile strength, is the shear stress; Equation set ②: When 0, cracking occurs when the following two equations are satisfied simultaneously:

[0032]

[0033] Judge whether the surrounding rock will crack according to the implicit crack initiation condition equation sets ① and ②. If the surrounding rock cracks, the crack initiation radius at a specific position can be obtained according to the implicit crack initiation condition equation sets ① and ②.

[0034] Step 4 is specifically as follows: Step 4.1: Obtain the expression of the crack tip stress or the force on the quasi-explosion body considering the tunnel construction process when the surrounding rock starts to crack, based on the elastic solution obtained in Step 2; After the excavation of the cavity, the circumferential stress of the surrounding rock at the cavity wall is:

[0035] When the surrounding rock starts to crack, the crack tip stress is the circumferential stress of the cavity wall at the crack initiation position , that is:

[0036] Among them, , are the circumferential stresses before and after the surrounding rock starts to crack 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 crack initiation radius and ; Step 4.2: Derive the expression of the average compressive stress on the quasi-explosion body considering the tunnel construction process, based on the circumferential stress obtained in Step 4.1:

[0037] When the compressive stress exceeds the compressive strength of the rock mass, that is , the surrounding rock detonates.

[0038] Step 5 is specifically as follows: Step 5.1: Based on the stress intensity ratio criterion, establish the relationship between the rockburst grade, stress intensity ratio , compressive stress , and compressive strength as ; Step 5.2: Based on the expression of the average compressive stress of the multi-factor quasi-explosion body considering the stress release coefficient obtained in Step 4, establish a multi-factor rockburst prediction model and judge the rockburst grade.

[0039] The relationship between the stress intensity ratio and the rockburst grade is: K < 0.3, no rockburst; 0.3 ≤ K < 0.5, mild rockburst; 0.5 ≤ K < 0.7, medium rockburst; 0.7 ≤ K < 0.9, strong rockburst; 0.9 ≤ K, extremely strong rockburst.

[0040] The beneficial effects of the present invention are as follows: Based on the basic theory of tunnel mechanics, considering the construction process of the tunnel, and following Griffith's brittle fracture strength theory, the present invention method deduces an elastic-brittle solution for stress release - surrounding rock stress redistribution - initiation and detonation of the surrounding rock of 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, burial depth, lateral pressure coefficient, the strength and deformation characteristic parameters of the surrounding rock, etc., and can more accurately predict the specific location on the tunnel wall where the rockburst occurs, the range of the quasi-explosion body at the location, the grade of the rockburst, as well as the time of the rockburst and the distance of the rockburst from the tunnel face. Description of the Drawings

[0041] Figure 1 is a schematic diagram of the prediction method of the present invention; Figure 2 is a flow chart of the prediction method of the present invention. Detailed Embodiments

[0042] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0043] The multi-factor rockburst prediction method of the present invention considering the tunnel construction process, as Figure 1 and Figure 2 shown, is specifically implemented according to the following steps: Step 1: Deduce the crack initiation criterion for the surrounding rock of an underground cavity under non-axisymmetric external loads, specifically: Step 1.1: Reveal the internal mechanism of the fracture of brittle materials such as rocks from the energy perspective; ① There are many randomly distributed microcracks or microfractures inside brittle materials such as rocks. 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.

[0044] 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 semi-major axis length of the crack, is the elastic modulus.

[0045] 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 complete splitting failure, revealing that splitting tensile failure is the essence of rock failure under uniaxial compression conditions.

[0046] Step 1.2: Analyze the crack initiation criterion of rock-like brittle materials based on Griffith strength theory; In coordinate system, the Griffith strength criterion is a piecewise function: ① When , , that is, as long as is satisfied, the microcracks in the rock will start to initiate and expand.

[0047] ② When , , at this time, the microcracks will initiate and fail along the angle, and it satisfies .

[0048] Among them, is the first principal stress, is the third principal stress, is the tensile strength.

[0049] Step 1.3: Derive the crack initiation criterion of the surrounding rock of underground caverns under non-axisymmetric external loads based on the stress circle theory; The relationships between the principal stress and the circumferential stress , radial stress , and shear stress in the stress circle are: (1a) (1b) Substitute the above formula (1) into the crack initiation criterion of rock-like brittle materials in Step 1.2, and the crack initiation criterion of the surrounding rock of underground caverns under non-axisymmetric external loads can be obtained: ① When ,

[0050] ② When ,

[0051] Step 2: Derive the elastic solution of a circular cavern under non-axisymmetric external loads considering the construction process, specifically: 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 : (2a) (2b) (2c) Wherein, is the hole diameter, is the vertical load, is the lateral pressure coefficient, is the radial stress of the inner boundary of the hole wall, is the tangential stress of the inner boundary of the hole wall, is the polar radius, is the position angle.

[0052] Step 2.2: Derive the initial stress field of a circular cavity under non-axisymmetric external loads according to the secondary stress field in Step 2.1: When the hole diameter in Equation (2) and the load on the hole wall is 0, the initial stress field can be obtained: (3a) (3b) (3c) Step 2.3: Derive the stress boundary conditions at the orifice of the circular cavity under non-axisymmetric external loads according to the analysis of the initial stress field in Step 2.2: After the cavity is excavated, the stress at the cavity edge is in a zero state. Due to the existence of the initial in-situ stress, in order to satisfy the zero-stress state at the cavity 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 hole wall can be obtained: (4a) (4b) Step 2.4: Derive the stress boundary of a circular cavity considering the stress release coefficient under non-axisymmetric external loads, that is and : 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 changes from the initial boundary to 0. The stress release coefficient represents the ratio of the stress released due to cavity excavation to the original stress. Then represents the ratio of the remaining stress to the original stress due to cavity excavation. Then, as the cavity excavation process progresses, the equivalent inner boundary stress load acting on the cavity wall is If it is times, the load on the tunnel wall during the excavation of the tunnel wall is: (5b) Step 2.5: Based on the basic solution of the stress field in Step 2.1 and the tunnel stress boundary with the stress release coefficient in Step 2.4, derive the secondary stress field of the surrounding rock of the circular tunnel considering the stress release coefficient under the action of non-axisymmetric external loads: Substitute the tunnel 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: (6a) (6b) (6c) Let , then there is: (7a) (7b) (7c) Step 3: Derive the cracking condition of the circular tunnel under non-axisymmetric external loads considering the construction process, specifically: Step 3.1: Based on the tunnel cracking criterion in Step 1.3 and the secondary stress field components of the surrounding rock of the circular tunnel considering the tunnel construction process in Step 2.5, derive the combined expression of the elastic stress components of the circular tunnel under non-axisymmetric external loads considering the construction process.

[0053] According to the stress field components, the stress field combined expression is: (8a) (8b) (8c) (8d) Step 3.2: Substitute the secondary stress field in Step 2.5 and the stress component combined expression in Step 3.1 into the tunnel cracking criterion in Step 1.3, and derive the cracking condition of the circular tunnel under non-axisymmetric external loads considering the construction process.

[0054] ① When , 0, then cracking occurs. Substitute the stress field components and combined expressions into the above formula, that is, cracking occurs when the following formulas (9a) and (9b) are satisfied simultaneously: (9a) (9b) ② When is 0, is 0, then cracking occurs. Substitute the stress field components and the combined expressions into the above equation. That is, cracking occurs when the following equations (10b) and (10b) are satisfied simultaneously: (10a) (10b) Equations (9 - 10) are all implicit functions of , which are the implicit cracking condition equation sets ① and ② respectively. Among them, 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, which are unknown. During the actual construction process, for a specific tunnel position (side wall , arch shoulder , crown ), the stress release coefficient during a specific construction process (through two - and three - dimensional numerical tests of tunnel excavation analysis, 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.

[0055] Step 4: Derive the theoretical analytical solution of the initiation and detonation development process of the surrounding rock considering the tunnel construction process, specifically: Step 4.1: After the tunnel is excavated, the surrounding rock cracks. Derive the expression of the stress at the crack tip or the force on the quasi - detonation body considering the tunnel construction process; After the tunnel is excavated, the circumferential stress of the surrounding rock at the tunnel wall is: (11) When the surrounding rock cracks, the stress at the crack tip is the circumferential stress of the tunnel wall at the cracking position , that is: (12) Step 4.2: Derive the expression of the average compressive stress on the quasi - detonation body considering the tunnel construction process.

[0056] The average compressive stress on the quasi - detonation body is: (13) When the compressive stress Exceeding the rock mass compressive strength When, that is When, the surrounding rock will detonate.

[0057] Step 5: Establish a multi-factor rockburst prediction model considering the average compressive stress of the quasi-explosion body during the construction process, specifically as follows: Step 5.1: Analyze the relationship between the rockburst grade, stress intensity ratio compressive stress , and compressive strength in the stress intensity ratio criterion; 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: K < 0.3, no rockburst; 0.3 ≤ K < 0.5, slight rockburst; 0.5 ≤ K < 0.7, medium rockburst; 0.7 ≤ K < 0.9, strong rockburst; 0.9 ≤ K, extremely strong rockburst.

[0058] Step 5.2: Based on the multi-factor average compressive stress of the quasi-explosion body considering the stress release coefficient expression, establish a multi-factor rockburst prediction model.

[0059] According to the formula for the average compressive stress received by 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 can be calculated. When the compressive strength of the surrounding rock is known, according to the relationship between the stress intensity ratio and the rockburst grade, the rockburst grade can be judged.

[0060] In the prediction method of the present invention: The function of Step 1 is to analyze the crack initiation criterion of the rock from the perspective of the internal mechanism of brittle crack initiation and failure after the rock is loaded, and then propose the crack initiation criterion for rockburst occurrence in the surrounding rock of underground caverns under non-axisymmetric external load conditions.

[0061] After the tunnel is excavated, the essence of rockburst occurrence 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. It is a hard and 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 a sudden brittle failure, causing rock fragments 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".

[0062] There are many fine (potential) cracks or fissures inside any material. Under the action of external forces, large stress concentrations will occur 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. Rock is such a brittle material containing a large number of microcracks and pores. Under uniaxial compression conditions, splitting tensile failure is the essence of rock failure. Griffith's strength theory interprets the splitting tensile failure mechanism from the energy perspective and extends the crack initiation criterion for rocks under loading.

[0063] Adopting the crack initiation criterion for rock bursts in underground chambers based on the essence of rock splitting failure has the following advantages: Griffith's strength theory well reveals the internal mechanism of splitting failure of brittle materials such as rocks under loading and the energy required for failure. Griffith's strength theory can well describe the brittle failure characteristics of rocks in rock bursts. By cleverly using the stress circle theory, the crack initiation criterion for rocks under loading can be further extended to the crack initiation criterion after excavation unloading of the surrounding rock of underground chambers under non-axisymmetric external loads.

[0064] 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 chamber under non-axisymmetric external loads considering the construction process.

[0065] After the tunnel excavation is unloaded, the stress of the surrounding rock is redistributed, forming a 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 a plastic or failure state. If the tensile stress in a local area of the surrounding rock reaches the ultimate tensile strength, local tensile brittle failure will occur.

[0066] Adopting the elastic analytical solution of a circular chamber under non-axisymmetric external loads considering the construction effect has the following advantages: Rock bursts occur under high in-situ stress conditions, in hard and intact or relatively intact rock masses, and occur after the excavation unloading of the tunnel. It is a sudden release of energy after a certain period of energy accumulation. The elastic solution of a circular chamber under non-axisymmetric external loads considering the construction process is a basic elastic mechanics equation, and the elastic theoretical solution of the chamber considering various influencing factors (such as: tunnel diameter , vertical load , lateral pressure coefficient , stress release coefficient etc.) can be derived.

[0067] 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 chamber under non-axisymmetric external loads considering the construction process.

[0068] Using the theoretical analysis of the rock mass cracking condition, the principle is as follows: The essence of rockburst is the brittle failure of rocks. Rockburst is the product of high in-situ stress. Due to the unloading of the cavern excavation, under the action of circumferential concentrated stress, sudden brittle failure occurs, causing rock flakes (blocks) to break away from the parent body and shoot suddenly towards the free face direction, experiencing a progressive failure process of rapid "splitting - shear folding - ejection". That is to say, rockbursts mostly occur after initial cracking and then ejection.

[0069] According to the form of the cracking criterion expression of the surrounding rock of underground caverns, the combined expression of elastic stress components of a circular cavern considering the construction process under non-axisymmetric external loads is derived, and then the implicit function group of the cracking condition of a circular cavern considering the construction process under non-axisymmetric external loads is derived. When the implicit function group of the cracking condition holds or has a solution, microcracks will initiate in the surrounding rock of the cavern.

[0070] Using the theoretical analysis of the rock mass cracking condition considering the construction process, its advantages are as follows: Given the basic parameters of the tunnel (vertical load , lateral pressure coefficient , tensile strength , cavern diameter ), the implicit function of cracking 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 cracking radius .

[0071] 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.

[0072] Using the theoretical analysis of the rock mass initiation state, the principle is as follows: There are many random microcracks inside brittle materials. Under the action of external forces, large stress concentrations are generated near the tips of the microcracks. 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 the product of high in-situ stress. It is a hard brittle rock mass with a large reserve of elastic strain energy. Due to the excavation of the cavern, the radial constraint is removed, the circumferential stress suddenly increases, and the energy is further concentrated. Under the action of the concentrated stress, sudden brittle failure occurs.

[0073] Using the theoretical analysis of the rock mass initiation state considering the construction process, 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 initiation. After the initiation of the surrounding rock inside the rock mass, a quasi-explosion body is generated. The quasi-explosion body is stressed and adjusted. When the average compressive stress of the quasi-explosion body exceeds the compressive strength of the rock mass When this occurs, the quasi-explosion body detonates, i.e., a rockburst disaster occurs.

[0074] 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.

[0075] Using the multi-factor rockburst prediction model, its principle is: by combining the elastic solution of a circular tunnel considering stress release during construction under non-axisymmetric external loads and the Griffith crack initiation criterion of the surrounding rock, an elastic-brittle implicit solution of the surrounding rock can be obtained, and then 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.

[0076] Using the multi-factor rockburst prediction model considering the tunnel construction process, its advantages are: for actual tunnel projects, the lateral pressure coefficient of the surrounding rock , compressive strength , tensile strength , unit weight , elastic modulus , the diameter of the tunnel chamber , position angle , burial depth and other parameters can be conveniently obtained. The relationship between the vertical load and the burial depth and the unit weight is . There is an empirical relationship between the deformation modulus and the compressive strength , tensile strength , that is, as long as the deformation modulus of the rock mass is known, the compressive strength and the tensile strength can be obtained. On the premise of knowing the basic parameters of the tunnel, the crack initiation implicit function at any position of the tunnel chamber 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 tunnel chamber section, and the polar radius determines the crack initiation radius. During the actual construction process of the tunnel chamber, for a specific tunnel chamber position (such as the side wall , the arch 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 When detonation occurs. Meanwhile, according to the stress intensity ratio criterion, the level of rockburst occurrence is judged.

[0077] Rockburst is a brittle failure of rocks caused by the sudden release of energy on the tunnel wall after tunnel excavation and unloading in hard and intact or relatively intact rock masses under high in-situ stress conditions. Griffith strength theory essentially reveals the internal mechanism of the fracture of brittle materials such as rocks. Therefore, it is theoretically fully consistent to study the initial cracking and detonation after chamber excavation through Griffith strength theory. Moreover, there are many factors affecting the initial cracking and detonation of the surrounding rock of the tunnel 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 incubation.

[0078] In actual engineering, high in-situ stress chamber rockbursts mostly occur in the sidewall parts of tunnels. For example, in the diversion tunnel of Jinping II Hydropower Station, the number of rockbursts occurring in the sidewall, arch shoulder, arch crown, and arch bottom 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 sidewall parts, and the rockburst level in the sidewall parts is greater than that in the arch crown part, which meets the engineering requirements in terms of the accuracy of rockburst prediction.

[0079] After chamber excavation, the radial constraint is removed and the circumferential stress increases suddenly. Microcracks in the surrounding rock initiate and expand, and then rock flakes on the tunnel wall are ejected towards the free face, forming a rockburst disaster, which affects 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 can predict and judge in advance the possible distance, location, and level of rockburst occurrence, so as to optimize the construction plan or support plan in time, and then ensure the safety of tunnel construction. The new multi-factor rockburst prediction method of the present invention has the characteristics of simplicity, rapidity, and intelligence, and can predict the distance of the rockburst occurrence position from the tunnel face, which fully meets the engineering construction requirements in terms of the practicality and effectiveness of rockburst prediction.

[0080] There is the following basic relationship between the stress release process of tunnel excavation and the occurrence of rockburst: ① During the stress release process of tunnel excavation, the stress release coefficient increases from 0 to 1, increases from 0 to 1, and the initial cracking radius decreases from the initial state.

[0081] ② When the stress release coefficient is, that is, in the unexcavated state, the in-situ stress state can be obtained at this time.

[0082] ③ During the process of the stress release coefficient increasing from 0 to 1, the initial cracking radius Gradually decrease, the average stress of the quasi-explosion body gradually increases. Once the average stress of the quasi-explosion body within this section is greater than the compressive strength, rockburst occurs.

[0083] ④ During the process that the stress release coefficient increases from 0 to 1, it just makes , then there exists a critical stress release coefficient . At this time, the average stress of the quasi-explosion body within the crack initiation radius tends to infinity, and rockburst occurs at this time.

[0084] ⑤ During the process that the stress release coefficient increases from 0 to 1, if there is no critical stress release coefficient , then the average stress of the quasi-explosion body is still used to judge whether there is rockburst.

[0085] ⑥ When continues to increase and tends to 1, the minimum crack 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, there will be no rockburst during the whole excavation process.

[0086] Therefore, the core idea of the crack initiation and detonation of surrounding rock considering the construction effect of underground caverns is as follows: ① When , that is, the initial stress field before excavation, the maximum crack initiation radius can be calculated at this time; ② Let , and see if the critical stress release coefficient can be obtained.

[0087] ③ If there exists , then the corresponding crack initiation radius must be very small at this time, and rockburst will definitely occur at this time.

[0088] ④ If there is no , let . There exists a minimum crack initiation radius at this time. If there is no detonation at this time, there will be no rockburst during the whole excavation process.

[0089] 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: 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.

[0090] Step b: Obtain the elastic stress component solution and stress combination result considering the construction process of the cavern, such as in Equations (7 - 8).

[0091] Step c: Substitute the stress components and combination results into the Griffith cracking criterion selection conditions and criterion expressions of the tunnel surrounding rock to establish The implicit function of surrounding rock cracking is as shown in Equations (9-10).

[0092] Step d: Determine whether the implicit function has a solution, and then determine whether the surrounding rock will crack under specific conditions. If the surrounding rock cracks, the cracking radius at a specific location can be obtained according to the cracking implicit function. According to the cracking radius, calculate the average compressive stress of the quasi-explosion body, as shown in formulas (11-13).

[0093] Step e: Obtain the stress release coefficient curve during the cavern excavation process, and make a detailed and accurate prediction of the rockburst level based on the strength-stress ratio of the quasi-explosion body.

[0094] Embodiment 1: A tunnel section of Sangzhuling in Lalin Railway, with a burial depth of 427m and a bulk density of 26kN / m 3 , deformation modulus 34GPa, compressive strength 130MPa, tensile strength 3.9MPa, lateral pressure coefficient 2.41, cave diameter 8.0m, actually a weak rockburst. 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 face is considered to be 0.3, the deformation stress release is completed at the 3D hole diameter, and the construction speed is considered to be 1m / d. The rockburst prediction results are as follows: when the stress release coefficient is 0.88 (i.e. 14.4m away from the face or 7.2d after excavation), a slight weak rockburst occurs at the side wall (initiation radius 8.16m, stress intensity ratio 0.39), which is consistent with the actual situation. If it is not supported in time, there is a possibility of medium rockburst in the end. When the stress release coefficient is 0.92 (i.e. 17.6m away from the face or 8.8d after excavation), a slight weak rockburst occurs at the spandrel (initiation radius 8.94m, stress intensity ratio 0.30), which is consistent with the actual situation. If it is not supported in time, there is a possibility of medium rockburst in the end. During the entire construction process, there is no possibility of rockburst in the surrounding rock within 60° of the arch.

[0095] Embodiment 2: A section of Sangzhuling Tunnel of Lhasa-Nyingchi Railway, with a burial depth of 340m and a bulk density of 26kN / m 3 , deformation modulus 34GPa, compressive strength 130MPa, tensile strength 3.9MPa, lateral pressure coefficient 1.48, cave diameter 8.0m, actually a weak rockburst. Substitute the above parameters into For the implicit function group of the initial crack of a circular tunnel (9 - 10) under the condition of non-axisymmetric external loads during the construction process, with the stress release coefficient at the tunnel face considered as 0.3, the deformation stress release completed at 3D tunnel diameter, and the construction speed considered as 2 m / d, the rockburst prediction results are as follows: When the stress release coefficient is 0.66 (i.e., at a distance of 5.1 m from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the side wall (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 may be medium to strong rockbursts eventually. When the stress release coefficient is 0.62 (i.e., at a distance of 5.1 m from the tunnel face or after 2.5 days of excavation), a slight weak rockburst occurs at the 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 may be medium to strong rockbursts eventually. When the stress release coefficient is 0.59 (i.e., at a distance of 4.6 m from the tunnel face or after 2.3 days of excavation), a slight weak rockburst occurs at the crown (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 may be medium to strong rockbursts eventually.

[0096] Example 3: For a certain section of the Sangzhuling Tunnel on the Lalin Railway, the buried depth is 806 m, the unit weight is 25.5 kN / m 3 , the deformation modulus is 33 GPa, the compressive strength is 130 MPa, the tensile strength is 4.0 MPa, the lateral pressure coefficient is 1.06, the tunnel diameter is 8.0 m, and actually there is no rockburst. Substitute the above parameters into the For the implicit function group of the initial crack of a circular tunnel (9 - 10) under the condition of non-axisymmetric external loads during the construction process, with the stress release coefficient at the tunnel face considered as 0.3, the deformation stress release completed at 3D tunnel diameter, and the construction speed considered as 2 m / d, the rockburst prediction results are as follows: When the stress release coefficient is 0.89 (i.e., at a distance of 15.2 m from the tunnel face or after 7.6 days of excavation), a slight weak rockburst occurs at the side wall (initiation radius 9.00 m, stress intensity ratio 0.31), a slight weak rockburst occurs at the shoulder (initiation radius 9.06 m, stress intensity ratio 0.31), and a slight weak rockburst occurs at the crown (initiation radius 9.12 m, stress intensity ratio 0.30). 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 timely support is provided, no rockburst will occur. During construction, if support is carried out before the stress release coefficient reaches 0.89 (i.e., before a distance of 15.2 m from the tunnel face or after 7.6 days of excavation), no rockburst will occur, which is in good agreement with the actual situation.

[0097] Example 4: For a certain section of the Qinling Tunnel of the Project of Drawing the Han River to Aid the Wei River, the buried depth is 800 m, the unit weight is 27.2 kN / m 3, the deformation modulus is 35 GPa, the compressive strength is 60 MPa, the tensile strength is 3.2 MPa, the lateral pressure coefficient is 1.19, the tunnel diameter is 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 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 0.3 (i.e., at the tunnel face), slight weak rockburst occurs at the side wall (initiation radius 5.01 m, stress intensity ratio 0.4), slight weak rockburst occurs at the arch shoulder (initiation radius 4.96 m, stress intensity ratio 0.47), and medium rockburst occurs at the crown (initiation radius 4.91 m, stress intensity ratio 0.55), which is in good agreement with the actual situation. If the support is not timely, there is a possibility of strong rockburst finally.

[0098] Example 5: For a certain section of the Qinling Tunnel of the Han River to Wei River Diversion Project, the buried depth is 1070 m, the unit weight is 28 kN / m 3 , the deformation modulus is 33 GPa, the compressive strength is 80 MPa, the tensile strength is 3.3 MPa, the lateral pressure coefficient is 1.13, the tunnel diameter is 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 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 0.3 (i.e., at the tunnel face), slight weak rockburst occurs at the side wall (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.

[0099] Example 6: 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 , the deformation modulus is 38 GPa, the compressive strength is 80 MPa, the tensile strength is 3.1 MPa, the lateral pressure coefficient is 1.25, the tunnel diameter is 3.4 m, and it is actually strong rockburst. Substitute the above parameters into the For the implicit function group of crack initiation of circular tunnels (9 - 10) under non-axisymmetric external loads during the construction process, with the stress release coefficient at the tunnel face considered as 0.3, the deformation and stress release completed at a 3D tunnel diameter, and the construction speed considered as 2 m / d, the results of rockburst prediction 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), a 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), a slight weak rockburst occurs at the shoulder of the arch (initiation radius 5.13 m, stress intensity ratio 0.34). When the stress release coefficient is 0.3 (i.e., at the tunnel face), a slight weak rockburst occurs at the crown of the arch (initiation radius 5.07 m, stress intensity ratio 0.41). The level of rockburst gradually increases with the increase of the stress release coefficient, that is, after the tunnel is excavated, the later the support is provided, the higher the level of rockburst. If the support is not provided in time, a strong rockburst will occur. If the support is provided after the stress release coefficient reaches 0.88 (i.e., 6.2 m away from the tunnel face or 3.1 d after excavation) during construction, a strong rockburst will occur, which is in good agreement with the actual situation.

[0100] In summary, the prediction method of the present invention can consider various factors affecting rockburst and accurately predict the location, depth, and level of rockburst in the surrounding rock of the tunnel under a certain stress release coefficient, time, or distance from the tunnel face. The rockburst prediction results are accurate, meeting the engineering requirements, and can serve for tunnel rockburst prediction.

Claims

1. A multi-factor rockburst prediction method considering the tunnel construction process, characterized in that: Follow the steps below to implement it: Step 1, derive the criterion for the cracking of surrounding rock of underground caverns under non-axisymmetric external load conditions; Step 2: derive the elastic solution of the circular cavern under the non-axisymmetric external load condition considering the construction process; Step 3, based on the cracking criterion obtained in step 1 and the elastic solution obtained in step 2, the cracking condition of the circular cavern under the non-axisymmetric external load condition considering the construction process is derived; Step 4: Based on the elastic solution obtained in step 2, a theoretical analytical solution of the surrounding rock detonation state in the process of cracking and detonation development during the tunnel construction process is derived; Step 5: Establish a multi-factor rockburst prediction model that takes into account the average compressive stress of the quasi-explosion body during the construction process, and predict the rockburst.

2. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1 is characterized in that: Step 1 is as follows: Based on the inherent mechanism of fracture of rock brittle materials, Griffith strength theory, and stress circle theory, the cracking criterion of the surrounding rock of underground caverns under non-axisymmetric external load conditions is obtained as follows: when When , the judgment is: ; when When , the judgment is: ; in, Hoop stress, Radial stress, Shear stress, For tensile strength.

3. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1 is characterized in that: Step 2 is as follows: Step 2.1, according to the basic theory of elastic mechanics, the basic solution of the elastic secondary stress field of a circular cavern with internal loads on the cavern wall and non-axisymmetric external loads is derived as follows: in, Hoop stress, Radial stress, Shear stress, is the polar diameter, is the position angle, is the hole diameter, Vertical load, is the lateral pressure coefficient, The radial stress at the inner boundary of the cave wall, is the tangential stress at the inner boundary of the cave wall; Step 2.2: Based on the secondary stress field analysis of step 2.1, the initial stress field analysis of the circular cavern under the non-axisymmetric external load is obtained as follows: Step 2.3: Based on the initial stress field analysis of step 2.2, the stress boundary condition of the circular cavern wall opening under the action of non-axisymmetric external load is obtained as follows: Step 2.4: Based on the orifice stress boundary condition of step 2.3, consider the stress release coefficient , the stress boundary of the circular cavern under the non-axisymmetric external load considering the tunnel construction process is obtained, that is, and , as follows: Step 2.5: Based on the basic solution of the stress field in step 2.1 and the cavern stress boundary with stress release coefficient in step 2.4, the secondary stress field of the circular cavern surrounding rock under the action of non-axisymmetric external load considering the tunnel construction process is obtained as follows: make , then: 。 4. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1 is characterized in that: 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, the combined expression of elastic stress components of the circular cavern under the non-axisymmetric external load condition considering the construction process is obtained as follows: in, Hoop stress, Radial stress, Stress relief factor, Vertical load, is the lateral pressure coefficient, is the position angle, is the polar diameter, is the hole diameter, ; Step 3.2: Based on the cracking criterion obtained in step 1, the elastic solution obtained in step 2, and the stress component combination expression obtained in step 3.1, the cracking condition of the circular cavern under the non-axisymmetric external load condition considering the construction process is obtained, that is, Implicit crack initiation condition equations ① and ②: Equation ①: When When the following two equations are satisfied at the same time, cracking occurs: in, is the tensile strength, is the shear stress; Equation group ②: When 0, cracking occurs when the following two equations are satisfied at the same time: 。 5. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 4 is characterized in that: According to the implicit cracking condition equations ① and ②, it is judged whether the surrounding rock will crack. 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. .

6. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1 is characterized in that: Step 4 is as follows: Step 4.1, based on the elastic solution obtained in step 2, obtain the crack tip stress or quasi-explosion body stress expression when the surrounding rock cracks initiation and considering the tunnel construction process; After the cavern is excavated, the cave wall The hoop stress of surrounding rock at is: When the surrounding rock cracks, the stress at the crack tip is the crack initiation position. The hoop stress of the cave wall at is: in, , are the hoop stresses before and after the cracking of the surrounding rock, is the polar diameter, is the hole diameter, Stress relief factor, Vertical load, is the lateral pressure coefficient, is the position angle, is the crack initiation radius and ; Step 4.2: Based on the hoop stress obtained in step 4.1, derive the average compressive stress on the quasi-explosion body considering the tunnel construction process. expression: When compressive stress Exceeding the rock mass compressive strength When The surrounding rock exploded.

7. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 1 is characterized in that: Step 5 is as follows: Step 5.1: Establish rockburst grade and stress intensity ratio according to stress intensity ratio criterion , compressive stress , compressive strength The relationship between ; Step 5.2: The average compressive stress of the multi-factor quasi-explosion body considering the stress release coefficient obtained in step 4 Expression, establish a multi-factor rockburst prediction model, and judge the rockburst grade.

8. The multi-factor rockburst prediction method considering the tunnel construction process according to claim 7 is characterized in that: Stress intensity ratio The relationship between it and the rockburst level is: K<0.3, no rock burst; 0.3≤K<0.5, slight rock burst; 0.5≤K<0.7, medium rock burst; 0.7≤K<0.9, severe rock burst; 0.9≤K, extremely strong rock burst.

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