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

Abstract

The invention discloses a true triaxial stress state teratology-physical energy ratio rockburst criterion and energy release calculation method, which comprises the following steps: step 1, when confining pressure sigma 2 and sigma 3 in two directions of a rock are equal and equal to conversion pressure sigma 3, t, the volume change energy density Ws, c of critical failure of the rock; 2, determining the volume change energy density Ws and the distortion energy density Wd of the rock in the actual stress state; 3, rock burst primary judgment is conducted, wherein the volume deformation energy density Ws'and the distortion energy density Wd 'of the rock are obtained; and step 6, rock burst re-judgment. According to the method, the stress tensor invariants are used for calculating the rockburst criterion and the rockburst energy release, the tedious calculation process that six stress tensor components are adopted for coordinate system transformation is avoided, and support is provided for tunnel rockburst prevention and control design.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel design, and in particular relates to a method for judging rockburst in a true triaxial stress state using a deformed-body energy ratio. Background Art

[0002] For high-in-situ stress hard rock tunnel projects, before tunnel excavation, the rock mass accumulates huge strain energy due to the initial in-situ stress. As the tunnel is excavated, the stress field and energy field of the surrounding rock near the excavation disturbance area undergo huge adjustments. After the adjustment, the stress or accumulated energy borne by the rock mass may increase several times, resulting in the destruction of the rock mass strength. Accompanied by the release of energy, rock bursts occur, which seriously threaten the safety of on-site workers, primary supports and workbenches, and operating machinery and equipment.

[0003] At present, there are many studies on rock burst, but most of them are empirical technical methods, lacking the support of rock mechanics theory, and the field application effect is poor. When studying rock burst in combination with rock mechanics theory, conventional triaxial compression test of rock is often used as the experimental basis. However, this test method makes the confining pressure in two directions approximately equal, and its results are suitable for projects where the second principal stress σ2 and the third principal stress σ3 of the rock mass are not much different. For rock masses with a large difference between σ2 and σ3, true triaxial compression test of rock needs to be used as the experimental basis to ensure that the error of engineering application is small. Summary of the invention

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

[0005] The present invention adopts the following technical solution: a true triaxial stress state deformity-body energy ratio rockburst criterion method, comprising the following steps:

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

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

[0008] Step 3: Preliminary judgment of rock burst:

[0009] When W s ≥W s,c When W, the rock failure mode is ductile deformation failure, no rock burst occurs, and the rock burst judgment ends; when W s <Ws,c When the rock is damaged, the failure mode is brittle fracture failure. When the rock reaches failure, rock burst occurs and the process goes to step 4.

[0010] Step 4: Find W s <W s,c Energy ratio coefficient λ′ of rock critical brittle fracture failure state at time:

[0011] Calculate the volume energy density W of the rock s ′ and distortion energy density W d ′, energy ratio coefficient of rock critical brittle fracture failure state

[0012]

[0013] Among them, I1′ and I2′ are respectively s <W s,c When the rock reaches the critical brittle fracture failure state, the first invariant of the stress tensor and the second invariant of the stress tensor correspond to;

[0014] E is the elastic modulus of rock;

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

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

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

[0018] Step 5: W s <W s,c Energy ratio coefficient λ of the actual stress state of rock at time:

[0019]

[0020] Step 6: Reassess the rockburst.

[0021] Furthermore, in step 6, when λ<0.8λ′, the actual stress state of the rock has not reached brittle fracture failure, and rock burst energy release does not occur. When λ≥0.8λ′, the actual stress state of the rock has reached brittle fracture failure, and rock burst energy release occurs.

[0022] Further, I1′=σ1′+σ2+σ3;

[0023] I2′=σ1′·σ2+σ2·σ3+σ3·σ1′.

[0024] The present invention also discloses a method for calculating the energy release of rockburst based on the true triaxial stress state distortion-volume energy ratio. Based on the above-mentioned true triaxial stress state distortion-volume energy ratio rockburst criterion method, the method includes the following steps:

[0025] When a rockburst is determined to have occurred, when the rock reaches the critical state of brittle fracture, the total strain energy density accumulated in the rock is W′: W′=W s ′+W d ′;

[0026] After the rock is brittlely fractured and rock burst occurs, the energy density released is ΔW: ΔW = W′-W s0 ;

[0027] The released energy density serves as a basis for rock burst prevention and control.

[0028] Furthermore, when the energy state of the rock reaches brittle fracture and rock burst energy release occurs, the rock is destroyed and the residual volume variable energy density W in the rock is s0 as follows:

[0029] Among them: I1″ is the first invariant value of the rock stress tensor after rock burst energy release and destruction; I1″=3σ3.

[0030] The present invention also discloses a rockburst area in a tunnel excavation process, and a rockburst criterion method based on the above-mentioned true triaxial stress state distortion-body energy ratio is as follows:

[0031] For W s ≥W s,c The rock surrounding the site is initially judged to be in a ductile deformation failure mode, and no rock burst occurs. The surrounding rock of the site is a non-rock burst area;

[0032] For W s <W s,c And λ≤0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and rock burst may occur. The rock is re-judged not to be destroyed, and rock burst will not occur. The surrounding rock of the field is a potential rock burst area;

[0033] For W s <W s,c And λ≥0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and at the same time, it is re-judged that the rock has reached failure and rock burst energy release has occurred, and the surrounding rock in the field is the rock burst occurrence zone.

[0034] The beneficial effects of the present invention are: 1. Based on the true triaxial compression test of rock, it reflects the actual stress state of rock in actual engineering. 2. The stress tensor invariant is used to calculate the rock burst criterion and the amount of rock burst energy release, avoiding the tedious calculation process of using six stress tensor components for coordinate system transformation. 3. Based on the rock mechanics theory, the rock failure mode when a rock burst occurs is considered and the energy release is calculated, which has better quantitativeness and accuracy, and can promote the development of rock burst damage and rock burst prevention and control parameter design from empirical to scientific. 4. The surrounding rock around the tunnel is divided into different areas, and rock burst prevention and control design is carried out in a targeted manner. Under the premise of ensuring construction safety, excessive support and reinforcement are avoided, and the economic benefits of the project are significant. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Figure 2 This is the rockburst criterion zoning map. DETAILED DESCRIPTION

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

[0038] The present invention proposes a rockburst criterion and a rockburst energy release calculation method for a deformed-volume energy ratio in a true triaxial stress state. The current rockburst criterion method is highly empirical and has poor accuracy, and accidents of rockbursts causing casualties, harming equipment and support structures during construction are frequent. Based on the stress state of rock under true triaxial compression test conditions, a deformed-volume energy ratio rockburst criterion and a rockburst energy release calculation method characterized by stress tensor invariants are proposed. The method can provide support for tunnel rockburst prevention and control design, reduce rockburst disasters, improve engineering construction safety, and has certain economy.

[0039] The true triaxial stress state deformed-body energy ratio rockburst criterion and rockburst energy release calculation method of the present invention are applicable to the rockburst judgment and prediction of high-in-situ stress, extremely high-in-situ stress hard surrounding rock drilling and blasting tunnels, TBM tunnels and deep-buried large-span cavern engineering. 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 rock under any complex stress state. In addition, the method is applicable to the situation where the surrounding rock integrity of the tunnel or underground cavern engineering is good. For the surrounding rock with poor integrity, weak fracture or ductile deformation, the surrounding rock energy release during the excavation process of the tunnel or cavern engineering is mainly ductile deformation energy consumption or collapse and block falling, and it is difficult to accumulate a lot of strain energy, and the possibility of rockburst is small. High in-situ stress refers to the maximum in-situ stress of 30MPa to 60MPa, and extremely high in-situ stress refers to the maximum in-situ stress of not less than 60MPa. Hard surrounding rock refers to the saturated uniaxial compressive strength of rock not less than 30MPa.

[0040] The method of the present invention is based on the true triaxial compression test of rock, in which the confining pressure is set as follows: σ2>σ3, σ2 and σ3 are two surrounding rocks represented by principal stresses, i.e., surrounding rocks in two directions; Figure 1 As shown in the figure. Through the theoretical derivation of rock mechanics, the rock burst criterion and the calculation method of rock burst release energy value are obtained. Therefore, it is suitable for rock burst prediction and energy release calculation of high ground stress hard rock tunnel engineering or cavern engineering.

[0041] When the confining pressures σ2 and σ3 are small, the axial compressive failure mode of hard rock is mostly brittle fracture failure. At the moment when the axial stress σ1 reaches the failure point, the strain energy accumulated in the rock is converted into kinetic energy and released instantly because the rock can no longer bear the pressure, which is called rock burst. There are two forms of energy release of rock burst. The first is that it is manifested as stress waves propagating into space in the deep surrounding rock. The rock burst energy release at the construction site can be monitored by microseismic monitoring technology. The second form is that rock burst occurs in the shallow surface surrounding rock around the tunnel, and huge rock blocks are ejected into the tunnel clearance, threatening the safety of construction personnel, support structures and mechanical equipment. As the confining pressures σ2 and σ3 increase, the axial compressive strength of the rock also increases. 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 will weaken the trend of brittle failure of the rock and strengthen the trend of ductile failure, which is manifested as weakened rock burst energy release and enhanced ductile deformation energy consumption.

[0042] Rock transformation pressure σ 3,t It is the critical confining pressure at which rock changes from brittle fracture failure to ductile deformation failure, and is an indicator of the mechanical properties of rock. When the confining pressure of rock is greater than the rock conversion pressure σ 3,t When the rock is axially compressed, it is in the ductile deformation failure mode. The strain energy accumulated in the rock is dissipated in the form of ductile deformation, and rock burst will not occur. When the confining pressure of the rock is less than the rock conversion pressure σ 3,t When the rock is subjected to axial compression, it is in a brittle fracture failure mode, and the strain energy accumulated in the rock is released outward in the form of kinetic energy, which manifests as rock burst energy release.

[0043] Whether a rock has rockburst destruction 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 using stress state to characterize rockburst are: there are many tensor components of the stress state, the direction of the principal stress is uncertain, and the magnitude of the energy released by the rockburst cannot be calculated. However, using energy state to characterize rockburst can avoid these problems, because the energy state of the rock is a scalar, and only one state quantity is involved when making a rockburst criterion, and this state quantity is independent of the direction of the coordinate axis. At the same time, using energy state to characterize rockburst can also quickly calculate the magnitude of the energy released by the rockburst, which can be used as the basis for the design of rockburst prevention and control parameters. Therefore, using energy state to characterize rockburst has stronger engineering practicality. The present invention uses energy state to characterize the rockburst criterion and calculates the amount of rockburst energy released. The energy state of rockburst can be derived through the stress state tensor of the rock.

[0044] The true triaxial stress state deformity-body energy ratio rockburst criterion method of the present invention comprises the following steps:

[0045] Step 1: Determine when the confining pressure of the rock is equal to the conversion pressure σ 3,t When the volume variable energy density of rock critical failure is W s,c .

[0046] The conversion pressure σ of rock is obtained by conventional triaxial test method of rock or empirical method of table lookup. 3,t .

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

[0048] The stress state tensor of the rock cube specimen in this critical brittle fracture failure state is:

[0049]

[0050] Under this critical brittle fracture failure state, the average stress of the rock is obtained by formula (1):

[0051]

[0052] Under this critical brittle fracture failure state, the spherical stress tensor of the rock is obtained by formula (2):

[0053]

[0054] Under this critical brittle fracture failure state, the volume variable energy density is calculated from the rock sphere stress tensor according to formula (3):

[0055]

[0056] In the formula, E and μ represent the elastic modulus and Poisson's ratio of rock, which reflect the deformation and strain energy storage capacity of rock, respectively. 3,t and Δσ c They are the rock conversion pressure and confining pressure σ2 and σ3, which are equal to the axial compressive strength stress deviator of the rock under the conversion pressure condition, and characterize the strength index of the rock. These four parameters are all mechanical property indicators of the rock. Therefore, under this critical brittle fracture failure state, the volume variable energy density W of the rock s,c It is also an index of the mechanical properties of rock, and a mechanical index that characterizes the critical state of ductile deformation and brittle fracture of rock.

[0057] In formula (4), W s,c Using σ 3,t , Δσ c The stress tensor invariant is not used for calculation because the σ can be directly obtained through conventional triaxial compression test of rock, empirical method of table lookup or strength theory calculation method. 3,t , Δσ c These two quantities do not need to be converted into stress tensor invariants to calculate W s,c .

[0058] Step 2: Determine the volumetric energy density W of the rock under actual stress s and the distortion energy density W d :

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

[0060]

[0061] Among them, σ1, σ2, and σ3 are the three principal stress values ​​of the actual stress state of the rock. The invariant of the principal stress state tensor is calculated by formula (5), 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 direction of the coordinate system. Therefore, I1 and I2 reflect the actual state quantity of the rock rather than the mechanical properties index of the rock.

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

[0066]

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

[0068] In formula (8) and formula (9), I1 and I2 are used to represent W s and W d The advantage is that W s and W d The physical meaning of is clearer, because I1 and I2 are scalar values, reflecting the state quantity, which is exactly the same as W s and W d The energy state scalar characteristics of W are corresponding, which avoids the use of 6 stress state components to calculate W s and W d It is a tedious process and does not involve the direction transformation process of the stress state tensor matrix coordinate system.

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

[0070] The rock failure mode is determined according to equations (4) and (8):

[0071] When W s ≥W s,c When the rock is damaged, the energy is dissipated in the form of ductile deformation, and no rock burst occurs, and the rock burst judgment ends.

[0072] When W s <W s,c When the rock is broken, the failure mode is brittle fracture failure. If the rock is broken, the energy is released in the form of rock burst, and rock burst occurs, and the next step is entered.

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

[0074] When the total rockburst preliminary judgment result W in step 3 is s <W s,c There is a possibility of rock burst, so continue with this step.

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

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

[0077]

[0078] Among them: σ2, σ3 are the confining pressure values ​​of the rock; σ1′ is the axial compressive failure strength value of the rock under confining pressures σ2 and σ3, which is an index of the mechanical properties of the rock, and this index is related to the confining pressure.

[0079] The invariant of the stress state tensor under the critical brittle fracture failure state is calculated by formula (10), as follows:

[0080] I1′=σ1′+σ2+σ3 (11);

[0081] I2′=σ1′·σ2+σ2·σ3+σ3·σ1′ (12);

[0082] Among them: I1′ and I2′ are the first invariant and the second invariant of the stress tensor of the rock under the critical brittle fracture failure state, both of which are scalar values ​​and have nothing to do with the direction of the coordinate system. I1′ and I2′ both represent the mechanical performance indicators related to the confining pressure of the rock.

[0083] Under this critical brittle fracture failure state, the volume variable energy density of the rock is W s ′ and distortion energy density W d 'for:

[0084]

[0085] In formula (13) and formula (14), W s ′ and W dThe influencing parameters of ′ are E, μ, I1′, and I2′. Among them, E and μ are the mechanical properties of rock, and I1′ and I2′ are the mechanical properties related to the confining pressure σ2 and σ3 of rock. Therefore, under the confining pressure σ2 and σ3, the W of the critical state calculated when the rock is axially compressed to reach brittle fracture failure and rock burst energy release occurs is s ′ and W d ′, are all rock mechanical property indicators related to confining pressures σ2 and σ3.

[0086] Under the conditions of confining pressure σ2 and σ3, as the axial stress σ1 gradually increases to the critical state of brittle fracture failure, the volume energy density W s ′ and distortion energy density W d ' also increases accordingly. Among them, the volume change energy density W s The result of the increase is: the axial compressive strength of the rock increases, that is, the ability of the rock to accumulate strain energy without being damaged increases, and at the same time, it will promote the transformation of the rock failure mode from brittle fracture failure to ductile deformation failure, weakening the potential of the rock to release energy in rock burst; the distortion energy density W d The result of the increase of ′ is that the rock is forced to undergo brittle fracture and rock burst energy release occurs. When the distortion energy density increases to the critical brittle fracture of the rock, rock burst energy release occurs. Therefore, the distortion energy density promotes the rock to be destroyed. s <W s,c When the total strain energy density is constant, the influence of the two on the brittle fracture of rock and the release of rock burst is opposite.

[0087] When the rock reaches the critical state of brittle failure, the energy ratio coefficient λ′ of the deformed-to-body strain energy density is defined as:

[0088]

[0089] Because W s ′ and W d ′ is a rock mechanical property index related to the confining pressure σ2 and σ3, so the energy ratio coefficient λ′ is also a rock mechanical property index related to the confining pressure σ2 and σ3. The physical meaning of λ′ is: s <W s,c When the confining pressure is σ2 or σ3, the critical energy ratio of the distortion energy density to the volume energy density when the rock reaches brittle fracture failure.

[0090] Because W s ′ and W d′ is a rock mechanical property index related to the confining pressures σ2 and σ3. The determination method is as follows: E and μ are obtained by using the uniaxial compression test of rock, and the axial compressive strength σ1′ of rock under different confining pressures σ2 and σ3 is obtained by using the true triaxial compression test of rock. Then, it is calculated according to formula (13) and formula (14).

[0091] Step 5: W s <W s,c The energy ratio coefficient λ of the actual stress state of the rock at that time.

[0092] When the rock is under actual stress, the confining pressure is σ2 and σ3, and the axial stress σ1 does not reach σ1′ at critical failure. Since the rock has not reached brittle fracture failure, the rock is safely stressed in this state and strain energy is accumulated inside.

[0093] The volume variable energy density W of the rock under this actual stress state s According to formula (8), the distortion energy density W of the rock under this actual stress state is calculated as d Calculated according to formula (9).

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

[0095]

[0096] W s , W d and λ, which are related to the current stress state of the rock, are therefore indicators of the stress state of the rock.

[0097] Step 6: Rockburst reassessment - mainly to determine whether rockburst occurs.

[0098] Since the stress state of the tunnel project and the test results of the rock mechanical performance index have a certain degree of discreteness, a 20% safety reserve is reserved when the rock burst re-judgment is performed using the patent of the present invention. According to formula (15) and formula (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 safe stress state and accumulates strain energy, and no rock burst energy release occurs. When λ≥0.8λ′, the actual stress state of the rock reaches brittle fracture failure, rock burst energy release occurs, and the next step is to calculate the rock burst energy release value. A 20% safety reserve is generally used in engineering, so 0.8 is selected.

[0100] Step 7: Calculation of rock burst 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 formula (13), W d ′ can be calculated by formula (14).

[0104] When the energy state of the rock reaches brittle fracture failure and rock burst energy release occurs, the rock is destroyed. The destroyed rock cannot withstand 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 relatively safe in engineering applications. The stress state tensor of the rock at this time is as follows:

[0105]

[0106] The first invariant I1′ under this stress state is calculated by formula (18):

[0107] I1″=3σ3 (19);

[0108] At this time, only the volume strain energy W remains in the rock s0 Density, calculated as:

[0109]

[0110] After the rock is brittlely fractured and rockburst occurs, the energy density released is ΔW: the total energy density W′ before the rockburst minus the residual energy density W after the rockburst s0 . The calculation is as follows:

[0111] ΔW=W′-W s0 (twenty one);

[0112] Formula (21) does not take into account the surface energy consumed when the cracks inside the rock expand and the rock fracture surface cracks. Therefore, the calculated rockburst energy release value is too large, which is too safe for engineering.

[0113] Step 8: Classification of rockburst areas during tunnel excavation;

[0114] During the tunnel excavation process, the numerical simulation method is used to calculate the distortion energy density field W of the surrounding rock in the tunnel area. d , volume variable energy density field W s and the total energy density field W.

[0115] For W s ≥W s,c The rock failure mode of the surrounding rock in the field was initially judged to be ductile deformation failure, and no rock burst occurred. The surrounding rock of the field was evaluated as a non-rock burst area and named as Area I;

[0116] For W s <W s,c And λ≤0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and rock burst may occur. The rock is re-judged not to be destroyed, and rock burst will not occur. The surrounding rock of the site is evaluated as a potential rock burst area, named as Area II;

[0117] For W s <W s,c And λ≥0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and rock burst may occur. At the same time, the rock is judged to be destroyed and rock burst energy is released. The surrounding rock of the field is evaluated as the rock burst occurrence zone, named as Zone III. At the same time, according to formula (21), the energy released by rock burst is calculated and used as the basis for the design of rock burst prevention and control parameters.

[0118] Specific implementation steps:

[0119] 1. Preliminary judgment of rock burst

[0120] Determine the transformation pressure σ of the rock 3,t At confining pressure σ2=σ3=σ 3,t When the rock axial stress σ1 reaches the critical failure state, the volume variable energy density W of the rock under this stress state s,c It is calculated using formula (4).

[0121] Under the actual stress state, the confining pressure of rock is σ2, σ3, and the axial stress is σ1. The volume variable energy density W of rock under this stress state is s Calculated using formula (8).

[0122] Initial assessment of rock burst:

[0123] When W s ≥W s,c When the rock failure mode is ductile deformation failure, Figure 2 Zone I in the rock. If the rock is damaged, the energy in the rock is dissipated in the form of ductile deformation, and no rock burst occurs, and the rock burst judgment ends;

[0124] When W s <W s,c When the rock is broken, the failure mode is brittle fracture failure. If the rock is broken, the energy in the rock is released in the form of rock burst, and rock burst occurs, and the next step of rock burst re-judgment is entered.

[0125] 2. Rockburst review:

[0126] When the conditions for the initial rockburst judgment are met, a rockburst rejudgment is carried out.

[0127] Under the actual stress state of the rock, the confining pressure is σ2, σ3. When the axial stress σ1 reaches σ1′ of the critical failure of the rock, the volume variable energy density W of the rock under this stress state iss ' Calculated using formula (13), the distortion energy density W under this stress state d ′ is calculated using formula (14), and the deformity-body energy ratio λ′ under this stress state is calculated using formula (15).

[0128] Under the actual stress state of rock, the confining pressure is σ2, σ3. When the axial stress σ1 does not reach the critical failure σ1′ of rock, the volume variable energy density W of rock under this stress state is s Using formula (8), the distortion energy density W under this stress state is calculated as d The calculation is performed using formula (9), and the deformation-body energy ratio λ under this stress state is calculated using formula (16).

[0129] Rockburst re-judgment: When λ≥0.8λ′, Figure 2 In zone III, 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, the actual stress state of the rock has not reached brittle fracture failure, the rock is still in a safe bearing state, and no rock burst occurs.

[0130] 3. Calculation of rock burst energy release:

[0131] Under the condition of meeting the second rockburst re-judgment condition, calculate the rockburst energy release size.

[0132] When the critical state of brittle fracture failure is reached, the total strain energy density W′ accumulated in the rock is calculated using formula (17).

[0133] When the energy state of the rock reaches brittle fracture failure and rock burst release occurs, the remaining volume variable energy density of the rock is W s0 Calculated using formula (20).

[0134] The energy value released by rock burst is calculated using formula (21).

[0135] 4. Classification of rock burst areas during tunnel excavation:

[0136] Adopting the first rock burst judgment: W s ≥W s,c In the field, the rock failure mode was initially judged to be ductile deformation failure, and no rock burst occurred. The surrounding rock of the field was evaluated as a non-rock burst area and named as Area I;

[0137] Adopting the first rockburst preliminary judgment and the second rockburst re-judgment: for W s <W s,c And λ≤0.8λ′, the initial judgment is that the rock failure mode is brittle fracture failure, and rock burst may occur. The re-judgment shows that the rock has not reached the point of failure and rock burst will not occur. The surrounding rock of the site is evaluated as a potential rock burst area; it is named Area II.

[0138] Adopting the first rockburst preliminary judgment and the second rockburst re-judgment: for W s <W s,c And λ≥0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and rock burst may occur. The rock is re-judged to be destroyed and rock burst energy is released. The surrounding rock of the field is evaluated as the rock burst occurrence zone, named as Zone III. At the same time, according to formula (20), the energy released by rock burst is calculated, which is used as the basis for the design of rock burst prevention and control parameters.

Claims

1. True triaxial stress state distortion-volume energy ratio rockburst criterion method, characterized by: The steps include: Step 1: The confining pressures σ2 and σ3 in both directions of the rock are equal and equal to the conversion pressure σ 3,t When the volume variable energy density of rock critical failure is W s,c ; Step 2: Determine the volumetric energy density W of the rock under actual stress s and the distortion energy density W d ; Step 3: Preliminary judgment of rock burst: When W s ≥W s,c When W, the rock failure mode is ductile deformation failure, no rock burst occurs, and the rock burst judgment ends; when W s <W s,c When the rock is damaged, the failure mode is brittle fracture failure. When the rock reaches failure, rock burst occurs and the process goes to step 4. Step 4: Find W s <W s,c Energy ratio coefficient λ′ of rock critical brittle fracture failure state at time: Calculate the volume energy density W of the rock s ′ and distortion energy density W d ′, energy ratio coefficient of rock critical brittle fracture failure state Among them, I1′ and I2′ are respectively s <W s,c When the rock reaches the critical brittle fracture failure state, the first invariant of the stress tensor and the second invariant of the stress tensor correspond to; E is the elastic modulus of rock; μ is the Poisson’s ratio of the rock; σ1′ is the axial compressive failure strength of rock under confining pressures σ2 and σ3; σ2 and σ3 are two confining pressure values ​​of rock. Step 5: W s <W s,c Energy ratio coefficient λ of the actual stress state of rock at time: Step 6: Reassess the rockburst.

2. The true triaxial stress state deformity-body energy ratio rockburst criterion method according to claim 1, characterized in that: In step 6, when λ<0.8λ′, the actual stress state of the rock has not reached brittle fracture failure, and rock burst energy release does not occur. When λ≥0.8λ′, the actual stress state of the rock has reached brittle fracture failure, and rock burst energy release occurs.

3. The true triaxial stress state deformity-body energy ratio rockburst criterion method according to claim 2, characterized in that: I1′=σ1′+σ2+σ3; ″′ I2=σ1·σ2+σ2σ3+σ3·σ1.

4. A method for calculating the energy release of rockburst based on the true triaxial stress state deformed-volume energy ratio, based on the true triaxial stress state deformed-volume energy ratio rockburst criterion method described in any one of claims 1 to 3, characterized in that: These include: When a rockburst is determined to have occurred, when the rock reaches the critical state of brittle fracture, the total strain energy density accumulated in the rock is W′: W′=W s ′+W d ′; After the rock is brittlely fractured and rockburst occurs, the energy density released is ΔW: ΔW = W′-W s0 ; The released energy density serves as a basis for rock burst prevention and control.

5. The method for calculating rockburst energy release under true triaxial stress state deformity-body energy ratio 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 destroyed and the residual volume variable energy density W in the rock is s0 as follows: Among them: I1″ is the first invariant value of the rock stress tensor after rock burst energy release and destruction; I1″=3σ3.

6. In the rockburst area during tunnel excavation, the method for determining the rockburst criterion of the true triaxial stress state deformed-body energy ratio according to any one of claims 1 to 3 is characterized in that: For W s ≥W s,c The rock surrounding the site is initially judged to be in a ductile deformation failure mode, and no rock burst occurs. The surrounding rock of the site is a non-rock burst area; For W s <W s,c And λ≤0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and rock burst may occur. The rock is re-judged not to be destroyed, and rock burst will not occur. The surrounding rock of the field is a potential rock burst area; For W s <W s,c And λ≥0.8λ′, the rock failure mode is initially judged to be brittle fracture failure, and at the same time, it is re-judged that the rock has reached failure and rock burst energy release has occurred, and the surrounding rock in the field is the rock burst occurrence zone.

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