True triaxial stress state distortion-body energy ratio rockburst criterion and energy release calculation method

Abstract

The present invention discloses a true triaxial stress state distortion - volume energy ratio rockburst criterion and an energy release calculation method, including the following: Step 1, when the confining pressures σ2 and σ3 in two directions of the rock are equal and equal to the conversion pressure σ 3,t , the volumetric strain energy density W s,c of the critical failure of the rock; Step 2, determine the volumetric strain energy density W s and the distortion energy density W d of the actual stress state of the rock; Step 3, preliminary rockburst judgment: obtain the volumetric strain energy density W s ′ and the distortion energy density W d ′ of the rock; Step 6, re - judgment of rockburst. This method calculates the rockburst criterion and the magnitude of rockburst energy release using stress tensor invariants, avoiding the cumbersome calculation process of coordinate system transformation using six stress tensor components, and providing support for the prevention and control design of tunnel rockburst.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel design, and particularly relates to a rockburst criterion method based on the distortion-body energy ratio under the true triaxial stress state. Background Art

[0002] For high in-situ stress hard rock tunnel engineering, before tunnel excavation, the rock mass accumulates a large amount of strain energy due to the action of the initial in-situ stress. With the excavation of the tunnel, the stress field and energy field of the surrounding rock near the excavation disturbed area are greatly adjusted. After adjustment, the stress borne by the rock mass or the accumulated energy may increase several times, resulting in the strength failure of the rock mass. Along with the energy release, rockburst occurs, seriously threatening the safety of on-site operators, primary support and working platforms, and working machinery and equipment.

[0003] At present, there are many studies on rockburst, but more are empirical technical methods, lacking the support of rock mechanics theory, and the on-site application effect is poor. When studying rockburst in combination with rock mechanics theory, the conventional triaxial compression test of rock is mostly used as the experimental basis. However, in this test method, the confining pressures in two directions are approximately equal, and its results are applicable to projects where the difference between the second principal stress σ2 and the third principal stress σ3 of the rock mass is not large. For rock masses with a large difference between σ2 and σ3, the true triaxial compression test of rock needs to be used as the experimental basis to ensure a small error in engineering application. Summary of the Invention

[0004] The purpose of the present invention is to provide a rockburst criterion and energy release calculation method based on the distortion-body energy ratio under the true triaxial stress state, and calculate the rockburst criterion and the magnitude of rockburst energy release using stress tensor invariants, avoiding the cumbersome calculation process of coordinate transformation using six stress tensor components, and providing support for tunnel rockburst prevention and control design.

[0005] The present invention adopts the following technical solutions: A rockburst criterion method based on the distortion-body energy ratio under the true triaxial stress state, including the following steps:

[0006] Step 1: When the confining pressures σ2 and σ3 in two directions of the rock are equal and equal to the conversion pressure σ 3,t the volumetric strain energy density W s,c of the critical failure of the rock;

[0007] Step 2: Determine the volumetric strain energy density W s and the distortion energy density W d of the actual stress state of the rock;

[0008] Step 3: Preliminary rockburst judgment:

[0009] When W s ≥W s,c the failure mode of the rock is ductile deformation failure, and no rockburst occurs, and the rockburst judgment ends; when W s <Ws,c When it is, the failure mode of the rock is brittle fracture failure. When the rock reaches failure, rock burst occurs and it enters Step Four.

[0010] Step Four: Obtain W s <W s,c The energy ratio coefficient λ′ of the critical brittle fracture failure state of the rock at this time:

[0011] Obtain the volumetric strain energy density W s ′ and the distortional energy density W d ′, the energy ratio coefficient of the critical brittle fracture failure state of the rock

[0012]

[0013] wherein, I1′ and I2′ are respectively the first invariant of the stress tensor and the second invariant of the stress tensor corresponding to the condition that the rock reaches the critical brittle fracture failure state at W s <W s,c at this time;

[0014] E is the elastic modulus of the rock;

[0015] μ is the Poisson's ratio of the rock;

[0016] σ1′ is the axial compression failure strength value of the rock under the confining pressures σ2 and σ3;

[0017] σ2 and σ3 are two confining pressure values of the rock.

[0018] Step Five: The energy ratio coefficient λ of the actual stress state of the rock at W s <W s,c at this time:

[0019]

[0020] Step Six: Rejudgment of rock burst.

[0021] Furthermore, in this Step Six, when λ < 0.8λ′, the actual stress state of the rock does not reach brittle fracture failure and no rock burst energy release occurs. When λ ≥ 0.8λ′, the actual stress state of the rock reaches brittle fracture failure and rock burst energy release occurs.

[0022] Furthermore, I1′ = σ1′ + σ2 + σ3;

[0023] I2′ = σ1′·σ2 + σ2·σ3 + σ3·σ1′.

[0024] The present invention also discloses a calculation method for rock burst energy release based on the distortion - volume energy ratio in the true triaxial stress state, based on the above - mentioned rock burst criterion method of the distortion - volume energy ratio in the true triaxial stress state, including the following:

[0025] When it is determined that rockburst occurs and the rock reaches the critical state of brittle fracture failure, the total strain energy density W' accumulated in the rock: W' = W s '+W d ';

[0026] After the rock undergoes brittle fracture failure and rockburst occurs, the released energy density is ΔW: ΔW = W' - W s0 ;

[0027] The released energy density is used as the basis for rockburst prevention and control.

[0028] Furthermore, when the energy state of the rock reaches brittle fracture failure and energy is released during rockburst, the rock is damaged, and the remaining volumetric strain energy density W in the rock s0 is as follows:

[0029] where: I1″ is the value of the first invariant of the rock stress tensor after energy release during rockburst failure; I1″ = 3σ3.

[0030] The present invention also discloses the rockburst area during tunnel excavation. Based on the above true triaxial stress state distortion - body energy ratio rockburst criterion method, it is as follows:

[0031] For the surrounding rock in the field where W s ≥W s,c the initial judgment of the rock failure mode is ductile deformation failure, and rockburst does not occur. The surrounding rock in this field is a non - rockburst area;

[0032] For the surrounding rock in the field where W s <W s,c and λ ≤ 0.8λ', the initial judgment of the rock failure mode is brittle fracture failure, and there may be rockburst. After re - judgment, the rock has not reached failure, and rockburst does not occur. The surrounding rock in this field is a potential rockburst area;

[0033] For the surrounding rock in the field where W s <W s,c and λ ≥ 0.8λ', the initial judgment of the rock failure mode is brittle fracture failure. At the same time, after re - judgment, the rock reaches failure and energy is released during rockburst. The surrounding rock in this field is a rockburst occurrence area.

[0034] The beneficial effects of the present invention are as follows: 1. Based on the true triaxial compression test of rock, it reflects the true stress state of rock in engineering practice. 2. The stress tensor invariant is used to calculate the rockburst criterion and the magnitude of rockburst energy release, avoiding the cumbersome calculation process of coordinate system transformation using six stress tensor components. 3. Based on rock mechanics theory, the failure mode of rock during rockburst is considered and the energy release is calculated, with better quantification and accuracy, which can promote the development of rockburst damage and rockburst prevention and control parameter design from empiricism to science. 4. The surrounding rock of the tunnel is divided into different regions, and targeted rockburst prevention and control design is carried out. On the premise of ensuring construction safety, over-support and reinforcement are avoided, and the engineering economic benefit is remarkable. Description of the Drawings

[0035] Figure 1 It is a true triaxial compression stress state diagram of rock;

[0036] Figure 2 It is a zoning diagram of rockburst criterion. Detailed Embodiment

[0037] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0038] For the true triaxial stress state distortion-body energy ratio rockburst criterion and rockburst energy release calculation method of the present invention, for the current rockburst criterion methods with strong empiricism and poor accuracy, and frequent accidents of rockburst causing casualties, damaging equipment and support structures during construction, based on the stress state under the true triaxial compression test conditions of rock, a distortion-body energy ratio rockburst criterion and rockburst energy release calculation method characterized by stress tensor invariant is proposed. This method can provide support for tunnel rockburst prevention and control design, reduce rockburst disaster accidents, improve the safety of engineering construction, and has certain economy.

[0039] The true triaxial stress state distortion-body energy ratio rockburst criterion and rockburst energy release calculation method of the present invention is applicable to the rockburst judgment and prediction of drill and blast tunnels, TBM tunnels and deep-buried large-span underground cavern projects with hard surrounding rocks under high in-situ stress and extremely high in-situ stress. Since the present invention is based on the true triaxial compression test of rock, it is applicable to the rockburst prediction and rockburst energy release calculation of tunnel surrounding rocks under any complex stress state. In addition, this method is applicable to the situation where the surrounding rock of the tunnel or underground cavern project is relatively intact. For the surrounding rock with poor integrity, soft and broken or mainly ductile deformation, during the excavation of the tunnel or cavern project, the energy release of the surrounding rock is mainly ductile deformation energy consumption or collapse and block falling, and it is difficult to accumulate a large amount of strain energy, so the possibility of rockburst is small. High in-situ stress means that the maximum in-situ stress is between 30 MPa and 60 MPa, and extremely high in-situ stress means that the maximum in-situ stress is not less than 60 MPa. Hard surrounding rock means that the saturated uniaxial compressive strength of the rock is not less than 30 MPa.

[0040] The method in the present invention is based on the true triaxial compression test of rocks. The confining pressures are set as: σ2>σ3, where σ2 and σ3 are the two surrounding rocks expressed in terms of principal stresses, that is, the surrounding rocks in two directions; as Figure 1 shown. Through the theoretical derivation of rock mechanics, the rockburst criterion and the calculation method of the rockburst energy release value are obtained. Therefore, it is applicable to the rockburst prediction and energy release calculation of high in-situ stress hard rock tunnel engineering or cavern engineering.

[0041] When the confining pressures σ2 and σ3 of hard rocks are small, the axial compression failure mode is mostly brittle fracture failure. At the moment when the axial stress σ1 reaches failure, since the rock cannot bear the pressure any more, the strain energy accumulated in the rock is instantaneously released as kinetic energy, which is the rockburst. There are two forms of energy release of rockburst. The first is the stress wave propagating into space in the deep part of the surrounding rock, and the rockburst energy release at the construction site can be monitored by microseismic monitoring technology; the second form is that rockburst occurs in the shallow surface surrounding rock of the tunnel perimeter, and huge rock blocks are ejected into the tunnel clearance, threatening the safety of construction workers, support structures and mechanical equipment. As the confining pressures σ2 and σ3 increase, the axial compressive strength of the rock also increases, and at the same time, the failure mode of the rock gradually transitions from brittle fracture failure to ductile deformation failure, that is, the increase in confining pressure weakens the tendency of brittle failure of the rock and strengthens the tendency of ductile failure, manifested as the weakening of rockburst energy release and the strengthening of ductile deformation energy consumption.

[0042] The rock transformation pressure σ 3,t is the critical confining pressure for the rock to transition from brittle fracture failure to ductile deformation failure, and it is a mechanical property index of the rock. When the confining pressure of the rock is greater than the rock transformation pressure σ 3,t , the axial compression of the rock is in the ductile deformation failure mode, and the strain energy accumulated in the rock is dissipated in the form of ductile deformation, and no rockburst will occur; when the confining pressure of the rock is less than the rock transformation pressure σ 3,t , the axial compression of the rock is in the brittle fracture failure mode, and the strain energy accumulated in the rock is released outward in the form of kinetic energy, manifested as rockburst energy release.

[0043] Whether rock undergoes rockburst failure can be characterized not only by the stress state of the rock, but also by the energy state accumulated in the rock. The problems with characterizing rockburst using the stress state are as follows: there are many tensor components in the stress state, the directions of the principal stresses are uncertain, and it is impossible to calculate the magnitude of the energy released by rockburst, etc. Characterizing rockburst using the energy state can avoid these problems because the energy state of the rock is a scalar. When conducting the rockburst criterion, only one state variable is involved, and this state variable is independent of the coordinate axis direction. At the same time, using the energy state to characterize rockburst can also quickly calculate the magnitude of the energy released by rockburst, which can be used as the basis for designing rockburst prevention and control parameters. Therefore, using the energy state to characterize rockburst has stronger engineering practicability. The present invention uses the energy state to characterize the rockburst criterion and calculates the amount of energy released by rockburst. The energy state of rockburst can be derived from the stress state tensor of the rock.

[0044] The true triaxial stress state distortion-volume energy ratio rockburst criterion method of the present invention includes the following steps:

[0045] Step 1: Determine that when the confining pressure of the rock is equal to the conversion pressure σ 3,t at this time, the volumetric strain energy density W s,c of the critical failure of the rock.

[0046] Through the conventional triaxial test method of rock or the empirical method of looking up tables, obtain the conversion pressure σ 3,t of the rock.

[0047] For the cubic specimen of the true triaxial compression test of the rock, during the test, adjust the confining pressures σ2 and σ3 so that the confining pressures in the two directions are equal and both are equal to the conversion pressure σ 3,t , that is, σ2 = σ3 = σ 3,t . In this stress state, when the axial stress σ1 of the rock reaches the critical failure state, its magnitude is σ1 = Δσ c + σ 3,t , where Δσ c is the axial stress deviator at the critical failure of the rock. At this time, the stress state makes the rock in a critical brittle fracture failure state, and the index of this state is represented by the subscript c for "critical state".

[0048] When the rock cubic specimen is in this critical brittle fracture failure state, the stress state tensor is:

[0049]

[0050] In this critical brittle fracture failure state, the magnitude of the mean stress of the rock obtained from Equation (1) is:

[0051]

[0052] In this critical brittle fracture failure state, the spherical stress tensor of the rock obtained from Equation (2) is:

[0053]

[0054] Under this critical brittle fracture failure state, according to Equation (3), the volumetric strain energy density is calculated from the spherical stress tensor of the rock:

[0055]

[0056] In the formula, E and μ represent the elastic modulus and Poisson's ratio of the rock, respectively reflecting the rock's deformation and strain energy storage capacity, σ 3,t and Δσ c are the transformed pressure of the rock and the deviatoric stress of the axial compressive strength of the rock under the condition that the confining pressures σ2 and σ3 are equal to the transformed pressure, respectively, characterizing the strength index of the rock. These four parameters are all mechanical property indexes of the rock. Therefore, under this critical brittle fracture failure state, the volumetric strain energy density W s,c of the rock is also a mechanical property index of the rock, characterizing the mechanical index of the critical state of ductile deformation failure and brittle fracture failure of the rock.

[0057] In Equation (4), W s,c is calculated using σ 3,t , Δσ c , and does not use the stress tensor invariant for calculation. The reason is that: through the conventional triaxial compression test of the rock, the empirical method of looking up tables, or the strength theory calculation method, σ 3,t , Δσ c these two quantities can be directly obtained. Therefore, there is no need to convert them into stress tensor invariants to calculate W s,c .

[0058] Step 2. Determine the volumetric strain energy density W s and the distortional energy density W d :

[0059] The principal stress state tensor of the rock under the actual stress state is as follows:

[0060]

[0061] Among them, σ1, σ2, and σ3 are the three principal stress values of the rock under the actual stress state. The invariants of the principal stress state tensor are calculated by Equation (5), specifically as follows:

[0062] I1 = σ1 + σ2 + σ3 (6);

[0063] I2 = σ1·σ2 + σ2·σ3 + σ3·σ1 (7);

[0064] I1 and I2 are the first invariant and the second invariant of the principal stress tensor under the actual stress state of the rock, respectively. Both are scalar values and are independent of the coordinate system direction. Therefore, I1 and I2 reflect the actual state variables of the rock, rather than the mechanical property indexes of the rock.

[0065] The volumetric strain energy density W of the rock under the actual stress state s and the distortional energy density W d are respectively as follows:

[0066]

[0067] Through numerical calculation or on-site mechanical measurement in tunnel engineering, the actual stress state of the surrounding rock can be obtained, and the volumetric strain energy density W of the rock under the actual stress state can be calculated according to Equations (8) and (9). s and the distortional energy density W d .

[0068] In Equations (8) and (9), I1 and I2 are used to characterize W s and W d . The advantages are that the physical meanings of W s and W d become clearer, because I1 and I2 are scalar values that reflect state variables, which exactly correspond to the scalar characteristics of the energy states of W s and W d . This avoids the cumbersome process of calculating W s and W d using six stress state components and does not involve the process of coordinate system direction transformation of the stress state tensor matrix.

[0069] Step 3: Preliminary judgment of rockburst - mainly judge the failure mode of the rock.

[0070] Judge the failure mode of the rock according to Equations (4) and (8):

[0071] When W s ≥W s,c , the failure mode of the rock is ductile deformation failure. If the rock fails, the energy dissipates in the form of ductile deformation and no rockburst occurs, and the rockburst judgment ends.

[0072] When W s <W s,c , the failure mode of the rock is brittle fracture failure. If the rock fails, the energy is released in the form of rockburst and rockburst occurs, then go to the next step.

[0073] Step 4: The energy ratio coefficient λ′ of the rock at the critical brittle failure state when W s <W s,c ;

[0074] When the initial rockburst judgment result W in Step 3 s <W s,c is less than s,c , there is a possibility of rockburst, and this step continues to be executed.

[0075] Under the actual stress state of the rock, under certain confining pressures σ2 and σ3, as the axial stress σ increases and reaches σ1' at the critical failure of the rock, the rock will undergo brittle fracture failure and release energy due to rockburst. The physical quantities corresponding to the critical failure stress state of the rock at this time are represented by "′"; when the axial stress σ1 is less than σ1' in the critical failure state of the rock, the rock will not undergo brittle fracture failure and rockburst energy release, but only accumulate strain energy inside the rock.

[0076] Under certain confining pressure levels σ2 and σ3, as the axial stress σ1 increases and reaches σ1' in the critical failure state of the rock, in this critical brittle fracture failure state, the stress state tensor of the rock at this time is:

[0077]

[0078] where: σ2 and σ3 are the confining pressure values of the rock; σ1' is the axial compression failure strength value of the rock under the confining pressures σ2 and σ3, which is a mechanical property index of the rock, and this index is related to the confining pressure.

[0079] Calculate the invariants of the stress state tensor in this critical brittle fracture failure state from Equation (10) as follows:

[0080] I1′ = σ1′ + σ2 + σ3 (11);

[0081] I2′ = σ1′·σ2 + σ2·σ3 + σ3·σ1′ (12);

[0082] where: I1′ and I2′ are respectively the first invariant and the second invariant of the stress tensor of the rock in this critical brittle fracture failure state, both of which are scalar values and are independent of the coordinate system direction. I1′ and I2′ both represent mechanical property indexes related to the confining pressure of the rock.

[0083] In this critical brittle fracture failure state, the volumetric strain energy density W s ′ and the distortional strain energy density W d ′ are:

[0084]

[0085] In Equations (13) and (14), W s ′ and W dThe influencing parameters of ′ are E, μ, I1′, and I2′. Among them, E and μ are the mechanical property indexes of the rock, and I1′ and I2′ are the mechanical property indexes related to the confining pressures σ2 and σ3 of the rock. Therefore, under the confining pressures σ2 and σ3, the critical state calculation of W for the rock to be axially compressed to brittle fracture failure and rockburst energy release s ′ and W d ′ are both rock mechanical property indexes related to the confining pressures σ2 and σ3.

[0086] Under the conditions of confining pressures σ2 and σ3, as the axial stress σ1 of the rock gradually increases to the critical state of brittle fracture failure, the volumetric strain energy density W s ′ and the distortional strain energy density W d ′ also increase accordingly. Among them, the result of the increase in the volumetric strain energy density W s ′ is that the axial compressive strength of the rock increases, that is, the ability of the rock to accumulate strain energy without failure increases, and at the same time, it will promote the transformation of the failure mode of the rock from brittle fracture failure to ductile deformation failure, weakening the potential of the rock to release energy by rockburst; the result of the increase in the distortional strain energy density W d ′ is that it promotes the rock to undergo brittle fracture failure and release energy by rockburst. When the distortional strain energy density increases to the critical brittle fracture failure of the rock, rockburst energy release occurs. Therefore, the distortional strain energy density promotes the rock to tend to failure. When W s <W s,c , the failure of the rock is brittle fracture failure and rockburst energy release, while the volumetric strain energy density enhances the anti-failure ability of the rock, that is, inhibits the rock from failing. When the total strain energy density is constant, the effects of the two on the brittle fracture failure of the rock and the occurrence of rockburst energy release are opposite.

[0087] When the rock reaches the critical state of brittle failure, define the energy ratio coefficient λ′ of the distortional-volumetric strain energy density at this time:

[0088]

[0089] Since W s ′ and W d ′ are rock mechanical property indexes related to the confining pressures σ2 and σ3, the energy ratio coefficient λ′ is also a rock mechanical property index related to the confining pressures σ2 and σ3. The physical meaning of λ′ is: when W s <W s,c and the confining pressures are σ2 and σ3, the critical energy ratio of the distortional strain energy density to the volumetric strain energy density when the rock reaches brittle fracture failure.

[0090] Since W s ′ and W dσ1′ is a rock mechanical property index related to confining pressures σ2 and σ3, and the determination method is as follows: E and μ are obtained by conducting uniaxial compression tests on rocks, and the axial compressive strength σ1′ of rocks under different confining pressures σ2 and σ3 is obtained by conducting true triaxial compression tests on rocks, and then it is calculated according to Equations (13) and (14).

[0091] Step Five, W s <W s,c The energy ratio coefficient λ of the actual stress state of the rock at time <W

[0092] Under the actual stress state of the rock, the confining pressures are σ2 and σ3, and σ1′ when the axial stress σ1 has not reached the critical failure. Since the rock has not reached brittle fracture failure, the rock is safely stressed and accumulates strain energy internally in this state.

[0093] The volumetric strain energy density W of the rock under this actual stress state s is calculated according to Equation (8); the distortional strain energy density W of the rock under this actual stress state d is calculated according to Equation (9).

[0094] The energy ratio coefficient λ of the distortional - volumetric strain energy density of the rock under this actual stress state

[0095]

[0096] W s 、W d and λ are related to the current stress state variables of the rock, so they are stress state indices of the rock.

[0097] Step Six, Rockburst re - judgment - mainly judge whether a rockburst occurs.

[0098] Due to the certain discreteness of the stress state of the tunnel engineering and the test results of rock mechanical property indices, when using this invention patent for rockburst re - judgment, a 20% safety reserve is retained. According to Equations (15) and (16):

[0099] When λ < 0.8λ′, the actual stress state of the rock has not reached brittle fracture failure, the rock is still in a state of safe stress and accumulates strain energy, and no rockburst energy release occurs. When λ ≥ 0.8λ′, the actual stress state of the rock reaches brittle fracture failure, rockburst energy release occurs, and enter the next step to calculate the rockburst energy release value. A 20% safety reserve is generally adopted in engineering, so 0.8 is selected.

[0100] Step Seven, Calculation of rockburst energy release value.

[0101] When the rock reaches the critical state of brittle fracture failure, the total strain energy density W′ accumulated in the rock can be calculated by Equations (13) and (14):

[0102] W′ = W s ′ + W d ′ (17);

[0103] Where W s ′ can be calculated by Equation (13), and W d ′ can be calculated by Equation (14).

[0104] When the rock energy state reaches brittle fracture failure and rockburst energy release occurs, the rock is damaged. The damaged rock cannot bear shear stress. Therefore, it is considered that the stress state of the rock at this time is a hydrostatic pressure state, and its stress value is σ3, which is on the safe side in engineering applications. The stress state tensor of the rock at this time is as follows:

[0105]

[0106] The first invariant I1′ in this stress state calculated from Equation (18) is:

[0107] I1″ = 3σ3 (19);

[0108] At this time, only the volumetric strain energy W s0 density remains in the rock, and the calculation is as follows:

[0109]

[0110] After the rock brittle fracture failure and rockburst occur, the released energy density is ΔW: the total energy density W′ before the rockburst minus the remaining energy density W s0 . The calculation is as follows:

[0111] ΔW = W′ - W s0 (21);

[0112] Equation (21) does not consider the surface energy consumed during the internal crack propagation of the rock and the cracking of the rock fracture surface. Therefore, the calculated value of the rockburst energy release is on the high side, which is on the safe side for engineering.

[0113] Step Eight: Classification of the Rockburst Area during Tunnel Excavation;

[0114] During the tunnel excavation construction process, the distortion energy density field W d , volumetric strain energy density field W s and total energy density field W of the surrounding rock in the tunnel perimeter field are calculated by numerical simulation methods.

[0115] For the surrounding rock in the field where W s ≥ W s,c , the initial judgment of the rock failure mode is ductile deformation failure, and no rockburst occurs. Evaluate the surrounding rock in this field as a non-rockburst area and name it Area Ⅰ;

[0116] For W s <W s,c And λ ≤ 0.8λ′, initially judge that the rock failure mode is brittle fracture failure, and there may be rockburst. After re-judgment, the rock has not reached failure and there is no rockburst. Evaluate the surrounding rock of this field as a potential rockburst area, named Area II;

[0117] For W s <W s,c And λ ≥ 0.8λ′, initially judge that the rock failure mode is brittle fracture failure, and there may be rockburst. At the same time, after re-judgment, the rock reaches failure and rockburst energy is released. Evaluate the surrounding rock of this field as a rockburst occurrence area, named Area III. At the same time, according to Equation (21), calculate the energy released by rockburst failure and use it as the basis for the design of rockburst prevention and control parameters.

[0118] Specific implementation steps:

[0119] I. Initial judgment of rockburst

[0120] Determine the transformed pressure σ of the rock 3,t . When the confining pressure σ2 = σ3 = σ 3,t , the axial stress σ1 of the rock reaches the critical failure state, and the volumetric strain energy density W of the rock under this stress state s,c Is calculated using Equation (4).

[0121] Under the actual stress state of the rock, the confining pressures are σ2 and σ3, and the axial stress is σ1. The volumetric strain energy density W of the rock under this stress state s Is calculated using Equation (8).

[0122] Initial judgment of rockburst:

[0123] When W s ≥ W s,c , the rock failure mode is ductile deformation failure, Figure 2 In Area I of . If the rock fails, the energy in the rock dissipates in the form of ductile deformation and there is no rockburst, and the rockburst judgment ends;

[0124] When W s <W s,c , the rock failure mode is brittle fracture failure. If the rock fails, the energy in the rock is released in the form of rockburst and there is rockburst, and enter the next step of rockburst re-judgment.

[0125] II. Rockburst re-judgment:

[0126] Under the condition of meeting the initial judgment of rockburst in I, conduct rockburst re-judgment.

[0127] Under the actual stress state conditions of the rock, the confining pressures are σ2 and σ3. When the axial stress σ1 reaches σ1′ of the rock critical failure, the volumetric strain energy density W of the rock under this stress states It is calculated by Equation (13), and the distortion energy density W under this stress state d It is calculated by Equation (14), and the distortion - volume energy ratio λ' under this stress state is calculated by Equation (15).

[0128] Under the actual stress state of the rock, the confining pressures are σ2 and σ3. When the axial stress σ1 has not reached σ1' at which the rock critically fails, the volumetric strain energy density W of the rock under this stress state s is calculated by Equation (8), and the distortion energy density W under this stress state d is calculated by Equation (9), and the distortion - volume energy ratio λ under this stress state is calculated by Equation (16).

[0129] Rock burst re - judgment: When λ≥0.8λ', Figure 2 in Zone III of, the actual stress state of the rock reaches brittle fracture failure, and rock burst energy release occurs; when λ < 0.8λ', Figure 2 in Zone II of, the actual stress state of the rock does not reach brittle fracture failure, the rock is still in a safe bearing state, and no rock burst occurs.

[0130] III. Rock burst energy release calculation:

[0131] Under the condition of meeting the rock burst re - judgment conditions in II, calculate the magnitude of the rock burst energy release.

[0132] When reaching the critical state of brittle fracture failure, the total strain energy density W' accumulated in the rock is calculated by Equation (17).

[0133] When the rock energy state reaches brittle fracture failure and rock burst energy release occurs, the remaining volumetric strain energy density W of the rock s0 is calculated by Equation (20).

[0134] The energy value released by the rock during rock burst is calculated by Equation (21).

[0135] IV. Rock burst area classification during tunnel excavation:

[0136] Adopt the rock burst preliminary judgment in I: W s ≥W s,c In the field, the preliminary judgment of the rock failure mode is ductile deformation failure, no rock burst occurs, and the surrounding rock of this field is evaluated as a non - rock burst area, named Zone I;

[0137] Adopt the rock burst preliminary judgment in I and the rock burst re - judgment in II: For W s <W s,c and λ≤0.8λ', the preliminary judgment of the rock failure mode is brittle fracture failure, and rock burst may occur. After re - judgment, the rock has not reached failure and no rock burst occurs. The surrounding rock of this field is evaluated as a potential rock burst area; named Zone II.

[0138] Adopt a primary judgment of rockburst and a secondary judgment of rockburst: For W s <W s,c And when λ≥0.8λ′, the primary judgment of the rock failure mode is brittle fracture failure, and there may be rockburst. The secondary judgment shows that the rock reaches failure and rockburst energy is released. It is evaluated that the surrounding rock of this field is a rockburst occurrence area, named Area III. At the same time, according to Equation (20), calculate the energy released by rockburst failure, which is used as the basis for the design of rockburst prevention and control parameters.

Claims

1. True triaxial stress state distortion - body energy ratio rockburst criterion method, characterized in that, It includes the following steps: Step 1. When the confining pressures σ2 and σ3 in two directions of the rock are equal and equal to the transformation pressure σ 3,t , the volumetric strain energy density W of critical failure of the rock s,c ; Step 2. Determine the volumetric strain energy density \(W\) of the actual stress state of the rock s and the deviatoric strain energy density \(W\) d ; Step 3. Initial judgment of rockburst: When W s ≥ W s,c , the failure mode of the rock is ductile deformation failure, and rockburst does not occur, and the rockburst judgment ends; when W s < W s,c , the failure mode of the rock is brittle fracture failure. When the rock reaches failure, rockburst occurs, and step four is entered; Step 4. Obtain W s <W s,c and the energy ratio coefficient λ′ of the critical brittle fracture failure state of the rock at this time: Obtain the volumetric strain energy density \(W\) of the rock s ′ and the deviatoric strain energy density \(W\) d ′, the energy ratio coefficient of the critical brittle fracture failure state of the rock where I1′ and I2′ are respectively the first invariant of the stress tensor and the second invariant of the stress tensor corresponding to the condition that the rock reaches the critical brittle fracture failure state at W s <W s,c ; E is the elastic modulus of the rock; μ is the Poisson's ratio of the rock; σ1′ is the axial compression failure strength value of the rock under the confining pressures σ2 and σ3; σ2 and σ3 are two confining pressure values of the rock; Step Five, W s <W s,c Energy ratio coefficient λ of the actual stress state of the rock when: Step 6. Rejudgment of rockburst.

2. The true triaxial stress state distortion-body energy ratio rockburst criterion method according to claim 1, characterized in that, In the said Step 6, when λ < 0.8λ′, the actual stress state of the rock does not reach brittle fracture failure and no rockburst energy release occurs; when λ ≥ 0.8λ′, the actual stress state of the rock reaches brittle fracture failure and rockburst energy release occurs.

3. The true triaxial stress state distortion-body energy ratio rockburst criterion method according to claim 2, characterized in that I1′ = σ1′ + σ2 + σ3; I2′ = σ1′·σ2 + σ2·σ3 + σ3·σ1′.

4. True triaxial stress state distortion - body energy ratio rockburst energy release calculation method, based on the true triaxial stress state distortion - body energy ratio rockburst criterion method described in any one of claims 1 - 3, characterized in that, It includes the following: When it is determined that rockburst occurs and the rock reaches the critical state of brittle fracture failure, the total strain energy density W′ accumulated in the rock: W′ = W s ′ + W d ′; After brittle fracture failure of the rock and occurrence of rock burst, the released energy density is ΔW: ΔW = W′ - W s0 ; The released energy density is used as the basis for rockburst prevention and control.

5. The true triaxial stress state distortion-body energy ratio rock burst energy release calculation method according to claim 4, characterized in that, When the energy state of the rock reaches brittle fracture failure and rock burst energy release occurs, the rock is damaged, and the remaining strain energy density W in the rock s0 is as follows: Where: I1″ is the value of the first invariant of the rock stress tensor after rockburst energy release damage; I1″ = 3σ3.

6. For the rockburst area during tunnel excavation, based on the true triaxial stress state distortion - volume energy ratio rockburst criterion method according to any one of claims 1 - 3, it is characterized in that For W s ≥W s,c For the surrounding rock of the field, the initial judgment of the rock failure mode is ductile deformation failure, and rockburst does not occur. The surrounding rock of the field is a non-rockburst area; For W s <W s,c And when λ ≤ 0.8λ′, the initial judgment of the rock failure mode is brittle fracture failure, and there may be rock bursts. After re-judgment, the rock has not reached failure and there is no rock burst. The surrounding rock of the field area is a potential rock burst area; For W s <W s,c And when λ≥0.8λ′, the initial judgment of the rock failure mode is brittle fracture failure. At the same time, it is rejudged that the rock reaches failure and rockburst energy release occurs, and the surrounding rock of the field is the rockburst occurrence area.

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