A tunnel excavation simulation method considering rock mass damage and surrounding rock stress release

Abstract

The application discloses a tunnel excavation simulation method considering rock mass damage and surrounding rock stress release, and steps are as follows: a calculation model is established, and boundary conditions and initial ground stress are applied to the model; first excavation and calculation are carried out, and node unbalanced force at a free surface is extracted; stress release rates of surrounding rocks at each point around a tunnel hole are calculated; virtual acting forces are applied to each point; model calculation is carried out, and strength and deformation parameters of the surrounding rocks after damage are obtained; the strength and deformation parameters of the surrounding rocks are adjusted, so that the current model is in a balanced state, and the current excavation cycle is ended or the above operation is repeated. In the numerical simulation process of the tunnel excavation, the application uses a surrounding rock damage degree evaluation method based on damage proximity and the Hoek-Brown criterion and a surrounding rock stress release rate calculation method based on the initial stress release rate of the surrounding rock and an empirical formula, respectively solves the damage problem and the stress release size problem of the surrounding rock in the tunnel excavation process, and thus the correctness and rationality of simulation are improved.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering, and in particular to a tunnel excavation simulation method that considers rock mass damage and surrounding rock stress release. Background Technology

[0002] Due to the complexity and diversity of geological environments in which different tunnels are located, the stress and strain of the surrounding rock after tunnel excavation cannot be obtained analytically. Therefore, numerical simulation is the most common and applicable method for obtaining these results. However, conventional numerical simulations of tunnel excavation typically do not consider the destructive behavior of the surrounding rock and the gradual stress release process during excavation. This can lead to discrepancies between the simulation results and actual conditions, thus affecting the accuracy and rationality of the simulation.

[0003] During actual tunnel excavation, the surrounding rock is damaged by blasting loads and unloading, leading to rock deterioration and reduced strength. Conventional numerical simulations typically use fixed values ​​for surrounding rock parameters, failing to consider the impact of rock failure, which is inconsistent with reality. Furthermore, the stress in the surrounding rock gradually releases after excavation, while conventional numerical simulations usually assume that the stress is rapidly released after excavation, which also contradicts actual conditions. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a tunnel excavation simulation method that considers rock mass damage and surrounding rock stress release, thereby solving the problems of surrounding rock damage and stress release magnitude during tunnel excavation and improving the accuracy and rationality of the simulation.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

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

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

[0008] S2. Perform the first excavation and calculation, and extract the unbalanced forces at the nodes of the newly excavated free face;

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

[0010] S4. Apply virtual forces at various points around the tunnel; control the stress release rate of the surrounding rock at a certain point by applying virtual forces to that point.

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

[0012] S6. Adjust the strength and deformation parameters of the surrounding rock to bring the current model to a balanced state. This round of excavation has ended and the next cycle is about to begin. If further excavation calculations are required, repeat steps S1-S5.

[0013] Furthermore, in step S3, the method for calculating the surrounding rock stress release rate is 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 longitudinal displacement release rate around the tunnel can be determined by equation (1):

[0015]

[0016] In the formula, λ0 is the displacement release rate at the tunnel face, x is the distance from the tunnel face (positive when 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, then the constant X can be calculated; then the displacement release rate at any point in the tunnel, i.e. the stress release rate of the surrounding rock at that point, can be calculated by formula (1).

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

[0019] F=(1-λ)F0 (2)

[0020] In the formula, λ is the stress release rate at that point, and F0 is the initial unbalanced force at that point, the magnitude of which is the unbalanced force at the instant of tunnel excavation.

[0021] Furthermore, in step S5, the specific steps of the method for evaluating the degree of surrounding rock damage based on the proximity of damage and the Hawke-Brown criterion are as follows:

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

[0023]

[0024] In the formula, ω is the stress hazard factor, ω = 1 - YAI, YAI is the rock yield proximity; FD is the rock failure degree;

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

[0026]

[0027]

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

[0029] Rock damage degree FD is calculated using equations (6) to (8):

[0030]

[0031]

[0032] FD = max(FD) s FD t (8)

[0033] In the formula, FD s It is the shear failure degree, FD t It is the tensile stress. It is the equivalent plastic shear strain. It is the equivalent limit plastic shear strain. It is the equivalent plastic tensile strain. It is the equivalent ultimate plastic tensile strain;

[0034] S52. Calculate the rock disturbance coefficient D based on the proximity of the damage:

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

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

[0037] S53. Calculate the strength and deformation parameters of the 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, and m is the rock strength parameter. i α and β are constants related to the properties of the surrounding rock. GSI is a geological strength index, which can be obtained by converting it from the BQ index. The calculation of the BQ index can be determined with reference to relevant specifications.

[0043] Furthermore, in step S52, the correlation between the destruction proximity and the disturbance coefficient includes, but is not limited to: the destruction proximity and the disturbance coefficient are linearly correlated; the destruction proximity and the disturbance coefficient are quadratically correlated; the destruction index in the destruction proximity and the disturbance coefficient are linearly correlated; and the destruction index in the destruction proximity and the disturbance coefficient are quadratically correlated.

[0044] The present invention provides a tunnel excavation simulation method that considers rock mass damage and surrounding rock stress release. It employs a method for calculating the surrounding rock stress release rate based on the initial stress release rate and empirical formulas, and a method for evaluating the degree of surrounding rock damage based on the proximity of damage and the Hawke-Brown criterion. These methods address the issues of the magnitude of surrounding rock stress release and the damage of surrounding rock during tunnel excavation, thereby improving the accuracy and rationality of the simulation. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating a tunnel excavation simulation method that considers rock mass damage and surrounding rock stress release.

[0047] Figure 2 This diagram illustrates the relationship between proximity FAI and disturbance degree D. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0049] A tunnel excavation simulation method considering rock mass damage and surrounding rock stress release is proposed. 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 calculation model, apply boundary conditions and initial geostress to the model, and assign the Hawke-Brown model and initial complete rock mass parameters to the elements.

[0051] S2. Perform the first excavation, then perform a calculation to determine the unbalanced forces at the nodes of the free face formed by this excavation. Record the unbalanced forces at the nodes of the free face formed by this excavation under the current state.

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

[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 around the tunnel. The longitudinal displacement release rate around the tunnel can be determined by equation (1):

[0054]

[0055] In the formula, λ0 is the displacement release rate at the working face, x is the distance from the working face (positive when behind the working 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, then the constant X can be calculated. With the constant X obtained, the displacement release rate at any point in the tunnel can be calculated by equation (1), which is also the stress release rate at that point.

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

[0058] F=(1-λ)F0 (2)

[0059] In the formula, λ is the stress release rate at that point, and F0 is the initial unbalanced force at that point, the magnitude of which is the unbalanced force at the instant of tunnel excavation.

[0060] S5. Perform model calculations using a method for evaluating the degree of surrounding rock failure based on the proximity of failure and the Hawke-Brown criterion. First, calculate the proximity of failure of the surrounding rock based on its current stress state. Then, obtain the disturbance coefficient in the Hawke-Brown criterion based on the proximity of failure. Finally, calculate the strength and deformation parameters of the surrounding rock after failure using the Hawke-Brown criterion. This process should be executed multiple times during the numerical simulation 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 index (FAI) based on the current surrounding rock stress state:

[0062]

[0063] In the formula, ω is the stress hazard factor, ω = 1 - YAI, YAI is the rock yield proximity, and FD is the rock failure degree.

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

[0065]

[0066]

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

[0068] Rock damage degree FD is calculated using equations (6) to (8):

[0069]

[0070]

[0071] FD = max(FD) s FDt (8)

[0072] In the formula, FD s It is the shear failure degree, FD t It is the tensile stress. It is the equivalent plastic shear strain. It is the equivalent limit plastic shear strain. It is the equivalent plastic tensile strain. It is the equivalent ultimate plastic tensile strain; the ultimate plastic shear strain and ultimate plastic tensile strain can be obtained through laboratory rock tests or numerical simulations.

[0073] S52. Calculate the rock disturbance coefficient D based on the proximity of the damage:

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

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

[0076] The correlation between destruction proximity and disturbance coefficient includes, but is not limited to: linear correlation between destruction proximity and disturbance coefficient, quadratic correlation between destruction proximity and disturbance coefficient, linear correlation between destruction degree index in destruction proximity and disturbance coefficient, and quadratic correlation between destruction degree index in destruction proximity and disturbance coefficient.

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

[0078]

[0079]

[0080]

[0081]

[0082] In the formula, M b s is the rock strength parameter in the Hawke-Brown criterion, E is the elastic modulus of the rock, and m is the rock strength parameter. i α and β are constants related to the properties of the surrounding rock. GSI is a geological strength index, which can be obtained by converting it from the BQ index. The calculation of the BQ index can be determined with reference 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 failure. If the Mohr-Coulomb index is used, the above parameters can be converted into c and φ through the following formulas.

[0084]

[0085]

[0086]

[0087]

[0088] S6. Adjust the strength and deformation parameters of the surrounding rock to bring the current model to a basic equilibrium state. This signifies that the current tunnel excavation cycle has ended and the next cycle is about to begin. If further excavation calculations are needed, simply repeat 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 elements the Hawke-Brown model and initial complete rock mass parameters.

[0092] Step 2: Perform the first excavation, followed by a calculation. This step calculates the unbalanced forces at the nodes of the free face formed by the excavation. Record the unbalanced forces at the nodes of the free face formed by the excavation under the current conditions.

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

[0094] Therefore, the stress relief rate at any point can be calculated using equation (18):

[0095]

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

[0097]

[0098] If the tunnel is excavated using the bench method or other sectional excavation methods, different initial stress release rates (displacement release rates at the tunnel face) can be used to calculate the constant X for different parts, and then substituted into equation (18) to obtain the stress release rate for different parts.

[0099] Step 4: Apply virtual forces at various points around the tunnel face. If a point is 2 meters behind the tunnel face, the applied virtual force 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 applied again.

[0102] Step 5: Perform model calculations. During the calculation process, the proximity of the surrounding rock failure is calculated every 100 steps, and the degree of disturbance is calculated based on the proximity of failure. In this example, the relationship between the proximity of failure (FAI) and the degree of disturbance (D) is as follows: Figure 2 As shown. After obtaining the degree of disturbance of the unit, 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 while the calculation of the proximity of surrounding rock failure can be performed in each step, this leads to excessively low model computational efficiency, and since the stress state of the surrounding rock does not change significantly within a single calculation step, this approach is largely meaningless. However, it is also not advisable to set the interval for calculating the proximity of surrounding rock failure too large, as this may result in a reduced degree of disturbance to the surrounding rock. Furthermore, the current degree of disturbance to the surrounding rock must not be less than the previous degree of disturbance. If the currently calculated degree of disturbance is less than the previous degree of disturbance, then the degree of disturbance to the surrounding rock remains equal to the previous degree of disturbance.

[0104] Step 6: The current model is basically in equilibrium, which means that the current tunnel excavation cycle has ended and the next cycle is about to begin. If further excavation calculations are needed, simply repeat steps 1 to 5 in this example.

[0105] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

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 calculation model, apply boundary conditions and initial geostress to the model, and assign Hawke-Brown model and initial complete rock mass parameters to the elements; S2. Perform the first excavation and calculation, and extract the unbalanced forces at the nodes of the newly excavated free face; S3. Calculate the stress release rate of the surrounding rock at various points around the tunnel; The stress release rate of the surrounding rock was obtained by calculation based on the initial stress release rate of the surrounding rock and an empirical formula. S4. Apply virtual forces at various points around the tunnel; The stress release rate of the surrounding rock at a certain point is controlled by applying a virtual force to that point. S5. Perform model calculations using the surrounding rock failure assessment method based on failure proximity and the Hawke-Brown criterion. First, calculate the failure proximity of the surrounding rock based on its current stress state. Then, obtain the disturbance coefficient in the Hawke-Brown criterion based on the failure proximity. Finally, calculate the strength and deformation parameters of the surrounding rock after failure based on the Hawke-Brown criterion. The specific steps of the surrounding rock failure assessment method based on failure proximity and the Hawke-Brown criterion are as follows: S51 、 Calculate the probability of surrounding rock failure based on the current stress state of the surrounding rock. FAI : （3） In the formula, -Stress hazard factor, , YAI- Rock yield proximity; FD - Rock damage degree; Rock yield proximity YAI Calculate using equations (4) to (5): (4) (5) In the formula, and It is cohesion and internal friction angle. It is the first invariant of the stress tensor. It is the second invariant of the stress deviatoric tensor. It is the stress Rhodes angle. It is the tensile strength of the rock. These are the first principal stress and the third principal stress, respectively. Rock damage FD Calculate using equations (6) to (8): (6) (7) (8) In the formula, It is the degree of shear failure. It is the tensile stress. It is the equivalent plastic shear strain. It is the equivalent limit plastic shear strain. It is the equivalent plastic tensile strain. It is the equivalent ultimate plastic tensile strain; S52、 Calculate the rock disturbance coefficient based on the proximity of the damage. D : Rock disturbance coefficient D It is calculated by a function that destroys proximity, as shown in equation (9): (9) S53、 Calculate the strength and deformation parameters of the rock after failure according to the Hawke-Brown criterion: (10) (11) (12) (13) In the formula, , s It is the rock strength parameter in the Hawke-Brown criterion. It is the elastic modulus of the rock. , a These are constants related to the properties of the surrounding rock. GSI It is a geological strength indicator, which can be obtained through... BQ The indicators were converted to obtain, BQ The calculation of the indicators can be determined with reference to relevant standards; S6、 Adjust the strength and deformation parameters of the surrounding rock to bring the current model to a state of equilibrium. This round of excavation has ended and the next round is about to begin. If further excavation calculations are still required for the model, repeat steps S1-S5.

2. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 1, characterized in that: In step S3, the method for calculating the surrounding rock stress release rate is as follows: Assuming the stress release rate of the tunnel surrounding rock is the same as the displacement release rate around the tunnel, the longitudinal displacement release rate around the tunnel can be determined by equation (1): (1) In the formula, It is the displacement release rate at the working face. It is the distance from the tunnel face, with the value behind the tunnel face being positive. It is a constant; If the displacement release rate at the tunnel face is known, and it is assumed that b% of the displacement has been released at a distance a meters behind the tunnel face, then the constant can be calculated. X Then, the displacement release rate at any point in the tunnel, i.e. the stress release rate of the surrounding rock at that point, is calculated by formula (1).

3. The tunnel excavation simulation method considering rock mass damage and surrounding rock stress release according to claim 2, characterized in that: In step S4, the magnitude of the applied virtual force is determined by the initial unbalanced force and stress release rate at that point, and the calculation method is shown in equation (2): (2) In the formula, The stress relief rate at that point. This is the initial unbalanced force at that point, and its magnitude is the unbalanced force at the instant 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 S52, the correlation between the destruction proximity and the disturbance coefficient includes, but is not limited to: the destruction proximity and the disturbance coefficient are linearly correlated; the destruction proximity and the disturbance coefficient are quadratically correlated; the destruction index in the destruction proximity and the disturbance coefficient are linearly correlated; and the destruction index in the destruction proximity and the disturbance coefficient are quadratically correlated.

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