Tunnel excavation simulation method considering rock mass damage and surrounding rock stress release

Abstract

The invention discloses a tunnel excavation simulation method considering rock mass damage and surrounding rock stress release, which comprises the following steps: establishing a calculation model, and applying boundary conditions and initial ground stress to the model; excavating for the first time, and calculating and extracting a node unbalanced force at the free face; calculating the surrounding rock stress release rate of each point around the tunnel hole; applying a virtual acting force to each point; performing model calculation to obtain strength and deformation parameters after the surrounding rock is damaged; and adjusting the strength and deformation parameters of the surrounding rock to enable the current model to be in a balanced state, and ending the excavation cycle or repeating the operation. In the numerical simulation process of tunnel excavation, a surrounding rock damage degree evaluation method based on damage proximity and a Hook-Brown criterion and a surrounding rock stress release rate calculation method based on a surrounding rock initial stress release rate and an empirical formula are used; the problems of damage to the surrounding rock and stress release of the surrounding rock in the tunnel excavation process are solved respectively, so that the correctness and rationality of simulation are improved.

Description

Technical Field

[0001] The invention relates to the field of tunnel engineering, and in particular to a tunnel excavation simulation method taking into account rock mass damage and surrounding rock stress release. Background Art

[0002] Due to the complexity and diversity of the geological environment in which different tunnels are located, the stress and strain of the surrounding rock after tunnel excavation cannot be obtained by analytical methods. Therefore, numerical simulation is the most common and applicable way to obtain the stress and strain of the surrounding rock after tunnel excavation. For conventional tunnel excavation numerical simulation, the destructive behavior of the surrounding rock during the excavation process and the gradual release of stress are usually not considered, which to a certain extent leads to deviations between the results of the numerical simulation and the actual situation, thus affecting the correctness and rationality of the simulation.

[0003] In the actual tunnel excavation process, the surrounding rock will be damaged due to blasting load and unloading, resulting in surrounding rock deterioration and strength reduction. In conventional numerical simulations, the surrounding rock parameter values ​​are usually fixed, and the impact of surrounding rock damage is not considered, which is inconsistent with the actual situation. In addition, the stress in the surrounding rock is gradually released after excavation, while conventional numerical simulations usually assume that the surrounding rock stress is quickly released after excavation, which is also inconsistent with the actual situation. Summary of the invention

[0004] In order to solve the deficiencies in the above-mentioned prior art, the present invention provides a tunnel excavation simulation method taking into account rock damage and surrounding rock stress release, so as to solve the problems of surrounding rock destruction and surrounding rock stress release during tunnel excavation and improve the accuracy and rationality of the simulation.

[0005] In order to achieve the above technical purpose, the technical solution adopted by the present invention is:

[0006] A tunnel excavation simulation method considering rock mass damage and surrounding rock stress release, the steps are as follows:

[0007] S1. Establish a computational model, apply boundary conditions and initial geostress to the model, and assign Hawke-Brown model and initial complete rock mass parameters to the unit;

[0008] S2, perform the first excavation and calculation to extract the node unbalanced force at the free surface formed by the new excavation;

[0009] S3. Calculate the stress release rate of the surrounding rock at each point around the tunnel; the surrounding rock stress release rate is obtained by a calculation method based on the initial stress release rate of the surrounding rock and an empirical formula;

[0010] S4, applying virtual force at each point around the tunnel; by applying virtual force to a certain point, the stress release rate of the surrounding rock at the point is controlled;

[0011] S5. Perform model calculations using a surrounding rock damage evaluation method based on damage proximity and the Hawke-Brown criterion. First, calculate the damage proximity of the surrounding rock according to the current stress state of the surrounding rock. Then, obtain the disturbance coefficient in the Hawke-Brown criterion based on the damage proximity of the surrounding rock. Then, calculate the strength parameters and deformation parameters of the surrounding rock after damage based on the Hawke-Brown criterion.

[0012] S6. Adjust the strength parameters and deformation parameters of the surrounding rock to make the current model in a balanced state. This round of excavation cycle has ended and is about to enter the next cycle. If the model still needs to be excavated for the next step, repeat steps S1-S5.

[0013] Furthermore, in step S3, the surrounding rock stress release rate is calculated as follows:

[0014] Assuming that the stress release rate of the tunnel surrounding rock is the same as the displacement release rate around the tunnel, the displacement release rate around the tunnel in the longitudinal direction can be determined by formula (1):

[0015]

[0016] Where λ0 is the displacement release rate at the tunnel face, x is the distance from the tunnel face, which is positive behind the tunnel face, and X is a constant;

[0017] If the displacement release rate at the tunnel face is known, and it is assumed that the displacement has been released by b% at a meter behind the tunnel face, the constant X can be calculated; then the displacement release rate at any point in the tunnel can be calculated by formula (1), that is, the stress release rate of the surrounding rock at that point.

[0018] Furthermore, in step S4, the magnitude of the applied virtual force is determined by the initial unbalanced force at the point and the stress release rate, and the calculation method is shown in formula (2):

[0019] F=(1-λ)F0 (2)

[0020] Where λ is the stress release rate at that point, and F0 is the initial unbalanced force at that point, which is the unbalanced force at the moment of tunnel excavation.

[0021] Further, in step S5, the surrounding rock damage degree evaluation method based on damage proximity and Hawke-Brown criterion has the following specific steps:

[0022] S51. Calculate the surrounding rock failure proximity FAI based on the current surrounding rock stress state:

[0023]

[0024] Where, ω-stress hazard coefficient, ω=1-YAI, YAI-rock yield proximity; FD-rock failure degree;

[0025] The rock yield proximity YAI is calculated by equations (4) to (5):

[0026]

[0027]

[0028] In the formula, C and is the cohesion and internal friction angle, I1 is the first invariant of the stress tensor, J2 is the second invariant of the stress deviator, θ σ is the stress Rhodes angle, σ t is the tensile strength of rock, σ1 and σ3 are the first and third principal stresses respectively;

[0029] The rock failure degree FD is calculated by equations (6) to (8):

[0030]

[0031]

[0032] FD=max(FD s , F.D. t ) (8)

[0033] Where, FD s is the shear failure degree, FD t is the tensile failure rate, is the equivalent plastic shear strain, is the equivalent limiting plastic shear strain, is the equivalent plastic tensile strain, is the equivalent ultimate plastic tensile strain;

[0034] S52. Calculate the rock disturbance coefficient D according to the damage proximity:

[0035] The rock disturbance coefficient D is calculated by the function of the destruction proximity, as shown in formula (9):

[0036] D=f(FAI) (9)

[0037] S53. Calculate the strength parameters and deformation parameters of rock after failure according to the Hawke-Brown criterion:

[0038]

[0039]

[0040]

[0041]

[0042] In the formula, m b , s is the rock strength parameter in the Hawke-Brown criterion, E is the elastic modulus of the rock, m i , a is a constant related to the properties of the surrounding rock, GSI is the geological strength index, which can be converted through the BQ index. The calculation of the BQ index can be determined by referring to relevant specifications.

[0043] Further, in step S52, the association between the destruction proximity and the disturbance coefficient includes but is not limited to: the destruction proximity is linearly correlated with the disturbance coefficient, the destruction proximity is quadratically correlated with the disturbance coefficient, the destruction index in the destruction proximity is linearly correlated with the disturbance coefficient, and the destruction index in the destruction proximity is quadratically correlated with the disturbance coefficient.

[0044] The tunnel excavation simulation method considering rock damage and surrounding rock stress release of the present invention adopts a surrounding rock stress release rate calculation method based on the initial stress release rate of the surrounding rock and an empirical formula and a surrounding rock damage degree evaluation method based on damage proximity and the Hawke-Brown criterion, respectively solving the problem of surrounding rock stress release size and surrounding rock damage during tunnel excavation, thereby improving the accuracy and rationality of the simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 It is a flow chart of a tunnel excavation simulation method considering rock mass damage and surrounding rock stress release;

[0047] Figure 2 Schematic diagram of the relationship between destruction proximity FAI and disturbance degree D. DETAILED DESCRIPTION

[0048] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians of the art without making creative work are within the scope of protection of the present application.

[0049] A tunnel excavation simulation method considering rock mass damage and surrounding rock stress release. To simulate the tunnel excavation process, this process uses the finite difference calculation software FLAC 3D To perform numerical calculations, the process is as follows Figure 1 As shown, the steps are as follows:

[0050] S1. Establish a computational model, apply boundary conditions and initial geostress to the model, and assign the Hawke-Brown model and initial complete rock mass parameters to the unit.

[0051] S2. Perform the first excavation, and then perform a step of calculation to calculate the unbalanced force of the nodes at the free surface formed by this excavation. Record the unbalanced force of the nodes at the free surface formed by this excavation under the current state.

[0052] S3. Calculate the stress release rate of each point around the tunnel; the surrounding rock stress release rate is obtained by a calculation method based on the initial stress release rate of the surrounding rock and an empirical formula;

[0053] In this method, it is assumed that the stress release rate of the tunnel surrounding rock is the same as the displacement release rate of the tunnel perimeter. The longitudinal displacement release rate of the tunnel perimeter can be determined by formula (1):

[0054]

[0055] Where λ0 is the displacement release rate at the tunnel face, x is the distance from the tunnel face, which is positive behind the tunnel face, and X is a constant.

[0056] If the displacement release rate at the tunnel face is known, and it is assumed that the displacement has been released by b% at a meter behind the tunnel face, the constant X can be calculated. When the constant X is obtained, the displacement release rate at any point in the tunnel can be calculated by formula (1), which is also the stress release rate at that point.

[0057] S4. Apply virtual force to each point around the tunnel. In numerical simulation, the stress release rate at a certain point is controlled by applying virtual force to the point. The magnitude of the virtual force is determined by the initial unbalanced force and the stress release rate at the point. The calculation method is shown in formula (2):

[0058] F=(1-λ)F0 (2)

[0059] Where λ is the stress release rate at that point, and F0 is the initial unbalanced force at that point, which is the unbalanced force at the moment of tunnel excavation.

[0060] S5. Carry out model calculation, and use the surrounding rock damage degree evaluation method based on damage proximity and Hawke-Brown criterion to calculate. First, calculate the damage proximity of the surrounding rock according to the current stress state of the surrounding rock, and obtain the disturbance coefficient in the Hawke-Brown criterion according to the damage proximity of the surrounding rock. Calculate the strength and deformation parameters of the surrounding rock after damage according to the Hawke-Brown criterion; This process should be executed multiple times during the numerical simulation process to obtain the rock parameters of the tunnel surrounding rock at different damage stages; the specific steps are as follows:

[0061] S51. Calculate the surrounding rock failure proximity FAI based on the current surrounding rock stress state:

[0062]

[0063] Wherein, ω is stress hazard coefficient, ω=1-YAI, YAI is rock yield proximity, and FD is rock failure degree.

[0064] The rock yield proximity YAI is calculated by equations (4) to (5):

[0065]

[0066]

[0067] In the formula, C and is the cohesion and internal friction angle, I1 is the first invariant of the stress tensor, J2 is the second invariant of the stress deviator, θ σ is the stress Rhodes angle, σ t is the tensile strength of rock, σ1 and σ3 are the first and third principal stresses respectively;

[0068] The rock failure degree FD is calculated by equations (6) to (8):

[0069]

[0070]

[0071] FD=max(FD s , F.D.t ) (8)

[0072] Where, FD s is the shear failure degree, FD t is the tensile failure rate, is the equivalent plastic shear strain, is the equivalent limiting plastic shear strain, is the equivalent plastic tensile strain, is the equivalent ultimate plastic tensile strain; the ultimate plastic shear strain and ultimate plastic tensile strain can be obtained through indoor rock tests or numerical simulation methods.

[0073] S52. Calculate the rock disturbance coefficient D according to the damage proximity:

[0074] The rock disturbance coefficient is an important parameter in the Hawke-Brown criterion. In this method, it is calculated by the function of the destruction proximity, as shown in formula (9):

[0075] D=f(FAI) (9)

[0076] The correlation between the destruction proximity and the disturbance coefficient includes but is not limited to: the destruction proximity is linearly correlated with the disturbance coefficient, the destruction proximity is quadratically correlated with the disturbance coefficient, the destruction index in the destruction proximity is linearly correlated with the disturbance coefficient, and the destruction index in the destruction proximity is quadratically correlated with the disturbance coefficient.

[0077] S53. Calculate the strength parameters and deformation parameters of rock after failure according to the Hawke-Brown criterion:

[0078]

[0079]

[0080]

[0081]

[0082] Where M b , s is the rock strength parameter in the Hawke-Brown criterion, E is the elastic modulus of the rock, m i , a is a constant related to the properties of the surrounding rock, GSI is the geological strength index, which can be converted through the BQ index. The calculation of the BQ index can be determined by referring to relevant specifications.

[0083] If the Hawke-Brown criterion is used in the calculation, the above parameters can be directly used for the calculation of the rock mass after destruction. If the Moore-Coulomb index is used, the above parameters can be converted into c, φ through the following formula.

[0084]

[0085]

[0086]

[0087]

[0088] S6. Adjust the strength parameters and deformation parameters of the surrounding rock to make the current model basically in a balanced state. The corresponding practical meaning is that the current round of tunnel excavation cycle has ended and is about to enter the next cycle. If the model still needs to be excavated for the next step, just repeat the operations of steps S1-S5.

[0089] Experimental example:

[0090] To simulate the tunnel excavation process, this process uses the finite difference calculation software FLAC 3D to perform numerical calculations.

[0091] Step 1: Establish a computational model, apply boundary conditions and initial geostress to the model, and assign the Hawke-Brown model and initial complete rock mass parameters to the unit.

[0092] Step 2: Carry out the first excavation, and then perform a calculation step. This calculation step can calculate the unbalanced force of the nodes at the free surface formed by this excavation. Record the unbalanced force of the nodes at the free surface formed by this excavation under the current state.

[0093] Step 3: Calculate the stress release rate at each point. If the stress release rate at the tunnel face is 30%, and 95% of the stress release is completed 20 meters behind the tunnel face, the constant X can be obtained as 7.578.

[0094] Therefore, the stress release rate at any point can be calculated by formula (18):

[0095]

[0096] If a point is 2 meters behind the tunnel face, its stress release rate is:

[0097]

[0098] If the tunnel is excavated using the step method or other partial excavation methods, different initial stress release rates (displacement release rates at the tunnel face) can be used at different locations to calculate the constant X, which can be substituted into formula (18) to obtain the stress release rates at different locations.

[0099] Step 4: Apply virtual force to each point around the hole. If a point is 2 meters behind the face, the virtual force applied is:

[0100] F=(1-λ)F0=(1-0.46)F0=0.54F0

[0101] If a virtual force has been applied to a point in a previous calculation, the original force needs to be deleted and the newly calculated force needs to be reapplied.

[0102] Step 5: Carry out model calculation. During the calculation process, it is set to calculate the surrounding rock failure proximity every 100 steps, and calculate the disturbance degree through the failure proximity. In this example, the relationship between the failure proximity FAI and the disturbance degree D is as follows: Figure 2 After obtaining the unit disturbance degree, the deformation parameters and strength parameters of the rock after failure can be calculated by equations (10) to (13).

[0103] It is worth noting that the calculation of the proximity of surrounding rock damage can be performed once in each step, but this will lead to low calculation efficiency of the model, and because the stress state of the surrounding rock will not change significantly within one calculation step, this is of little significance; but it is not advisable to set the interval of calculating the proximity of surrounding rock damage too large, which may lead to a smaller degree of disturbance of the surrounding rock. In addition, the current degree of disturbance of the surrounding rock cannot be less than the previous degree of disturbance. If the current calculated degree of disturbance of the surrounding rock is less than the previous degree of disturbance, the degree of disturbance of the surrounding rock is still equal to the previous degree of disturbance.

[0104] Step 6: The current model is basically in a balanced state, which means that the tunnel excavation cycle has ended and is about to enter the next cycle. If the model still needs to be excavated, just repeat the operations from the first to the fifth steps in this example.

[0105] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A tunnel excavation simulation method considering rock mass damage and surrounding rock stress release, characterized in that: The steps are as follows: S1. Establish a computational model, apply boundary conditions and initial geostress to the model, and assign Hawke-Brown model and initial complete rock mass parameters to the unit; S2, perform the first excavation and calculation to extract the node unbalanced force at the free surface formed by the new excavation; S3. Calculate the stress release rate of the surrounding rock at each point around the tunnel; The surrounding rock stress release rate is obtained by using a calculation method based on the initial stress release rate of the surrounding rock and an empirical formula; S4, applying virtual forces at various points around the tunnel; By applying a virtual force to a certain point, the stress release rate of the surrounding rock at that point can be controlled; S5. Perform model calculations using a surrounding rock damage evaluation method based on damage proximity and the Hawke-Brown criterion. First, calculate the damage proximity of the surrounding rock according to the current stress state of the surrounding rock. Then, obtain the disturbance coefficient in the Hawke-Brown criterion based on the damage proximity of the surrounding rock. Then, calculate the strength parameters and deformation parameters of the surrounding rock after damage based on the Hawke-Brown criterion. S6. Adjust the strength parameters and deformation parameters of the surrounding rock to make the current model in a balanced state. This round of excavation cycle has ended and is about to enter the next cycle. If the model still needs to be subjected to the next step of excavation calculation, the operations of steps S1 to S5 are repeated.

2. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 1 is characterized in that: In step S3, the calculation method of surrounding rock stress release rate is: Assuming that the stress release rate of the tunnel surrounding rock is the same as the displacement release rate around the tunnel, the displacement release rate around the tunnel in the longitudinal direction can be determined by formula (1): Where λ0 is the displacement release rate at the tunnel face, x is the distance from the tunnel face, which is positive behind the tunnel face, and X is a constant; If the displacement release rate at the tunnel face is known, and it is assumed that the displacement has been released by b% at a meter behind the tunnel face, the constant X can be calculated; then the displacement release rate at any point in the tunnel can be calculated by formula (1), that is, the stress release rate of the surrounding rock at that point.

3. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 2 is characterized in that: In step S4, the magnitude of the applied virtual force is determined by the initial unbalanced force at the point and the stress release rate. The calculation method is shown in formula (2): F=(1-λ)F0 (2) Where λ is the stress release rate at that point, and F0 is the initial unbalanced force at that point, which is the unbalanced force at the moment of tunnel excavation.

4. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 1, characterized in that: In step S5, the surrounding rock damage degree evaluation method based on damage proximity and Hawke-Brown criterion has the following specific steps: S51. Calculate the surrounding rock failure proximity FAI based on the current surrounding rock stress state: Where, ω-stress hazard coefficient, ω=1-YAI, YAI-rock yield proximity; FD-rock failure degree; The rock yield proximity YAI is calculated by equations (4) to (5): In the formula, C and is the cohesion and internal friction angle, i1 is the first invariant of the stress tensor, j2 is the second invariant of the stress deviator, θ σ is the stress Rhodes angle, σ t is the tensile strength of rock, σ1 and σ3 are the first and third principal stresses respectively; The rock failure degree FD is calculated by equations (6) to (8): Where, FD s is the shear failure degree, FD t is the tensile failure rate, is the equivalent plastic shear strain, is the equivalent limiting plastic shear strain, is the equivalent plastic tensile strain, is the equivalent ultimate plastic tensile strain; S52. Calculate the rock disturbance coefficient D according to the damage proximity: The rock disturbance coefficient D is calculated by the function of the destruction proximity, as shown in formula (9): D=f(FAI) (9) S53. Calculate the strength parameters and deformation parameters of rock after failure according to the Hawke-Brown criterion: In the formula, m b , s is the rock strength parameter in the Hawke-Brown criterion, E is the elastic modulus of the rock, m i , a is a constant related to the properties of the surrounding rock, GSI is the geological strength index, which can be converted through the BQ index. The calculation of the BQ index can be determined by referring to relevant specifications.

5. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 4 is characterized in that: In step S52, the association between the destruction proximity and the disturbance coefficient includes but is not limited to: the destruction proximity is linearly correlated with the disturbance coefficient, the destruction proximity is quadratically correlated with the disturbance coefficient, the destruction index in the destruction proximity is linearly correlated with the disturbance coefficient, and the destruction index in the destruction proximity is quadratically correlated with the disturbance coefficient.

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