Numerical simulation method of tunnel crossing active faults based on discrete element-finite difference coupling

Abstract

The present application relates to the technical field of underground tunnel engineering, and discloses a numerical simulation method for tunnel crossing active fault based on discrete element-finite difference coupling, which solves the problem that the existing numerical simulation method for tunnel crossing active fault cannot consider the simulation and calculation efficiency of the real block geometry of the rock mass in the active fault zone. The present application first generates an active fault block model conforming to the statistical distribution law of engineering practice by using Neper software, then imports it into 3DEC software and completes the whole process of modeling, mesh division, parameter assignment, excavation and support simulation and active fault creep / sliding movement simulation in the software, avoiding the cross-software data transmission of the traditional coupling method; at the same time, through fine block design, mesh division, contact setting and constitutive model matching, the real geology and mechanical properties of the rock mass in the active fault zone are fully restored, and high-precision simulation of the numerical simulation of the tunnel crossing the active fault is realized under the premise of considering the calculation efficiency.

Description

Technical Field

[0001] This invention relates to the field of underground tunnel engineering technology, specifically to a numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling. Background Technology

[0002] Currently, the world is entering a period of increased seismic activity. Research on anti-creep and anti-faulting of long tunnels crossing active faults has become a key focus in the field of underground engineering. Precise calculation and analysis of tunnels crossing active faults is the core foundation for carrying out related research.

[0003] Currently, the computational analysis methods for tunnels crossing active fractures are mainly divided into three categories: indoor physical model testing, analytical methods, and numerical simulation analysis methods, as detailed below:

[0004] (1) Indoor physical model test method:

[0005] It requires a lot of manpower, material resources and financial resources to prepare samples and develop and debug equipment, making it difficult to conduct multi-scheme tests; due to the size limitation of the equipment, the size effect cannot be avoided, and the mechanical properties of test objects such as rock mass, lining, and steel bars in scaled-down tests are difficult to be consistent with the prototype; it is impossible to realistically simulate loads such as initial ground stress, excavation support, internal and external water pressure, and existing equipment is difficult to realize the simulation of real motion modes of active fracture creep, especially instantaneous stick-slip faulting.

[0006] (2) Analytical method:

[0007] Because it employs numerous simplification assumptions, it can only provide exact solutions for simple working conditions and cannot be applied to complex tunnel crossing active fracture engineering projects. Therefore, it is rarely used in actual engineering.

[0008] (3) Numerical simulation analysis method:

[0009] These methods are categorized into two types: the finite element / finite difference method and the discrete element-finite difference coupled method. The finite element / finite difference method only simulates fractured rock masses in active fault zones using a continuous medium and constitutive model, making it difficult to consider the influence of actual factors such as the morphology of fractured rock mass blocks, large creep / stick-slip deformations, local fracturing, and cavities on the support structure. Existing discrete element-finite difference coupled methods often employ PFC3D+FLAC3D or 3DEC+FLAC3D joint solutions. On the one hand, this requires data transfer between different software, resulting in low computational efficiency and high resource consumption. On the other hand, it uses spherical or regular hexahedral blocks to simulate irregular rock masses in active fault zones, which differs significantly from reality and easily underestimates the adverse effects of rock mass movement on the support structure.

[0010] In summary, while existing numerical simulation analysis methods are the mainstream approach for calculating and analyzing tunnels crossing active faults, they still face technical challenges such as difficulty in reproducing the true geometric morphology of rock masses in active fault zones and low computational efficiency. These limitations prevent them from providing accurate numerical analysis data for the engineering design and safety control of tunnels crossing active faults. Therefore, there is an urgent need to develop a numerical simulation method for tunnels crossing active faults that balances computational efficiency with simulation realism. Summary of the Invention

[0011] The technical problem to be solved by this invention is to provide a numerical simulation method for tunnels crossing active faults based on discrete element-finite difference coupling, which solves the problem that existing numerical simulation methods for tunnels crossing active faults cannot simultaneously take into account the simulation of the real block geometry of rock mass in active fault zones and computational efficiency.

[0012] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0013] A numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling includes the following steps:

[0014] S1. Based on the geological survey results, determine the zoning characteristics, geometric features, and occurrence of active faults; the geological survey results include geological survey reports and geological maps;

[0015] S2. Based on the tunnel design scheme, determine the tunnel's geometric characteristics and their relationship with active faults;

[0016] S3. Determine the components of the numerical simulation model and the geometric parameters of each component;

[0017] S4. Determine the partitions and locations of the active fracture using discontinuous medium simulation, set the block size and distribution pattern of the partitions and locations, and generate the corresponding block models in Neper software;

[0018] S5. Export the block model generated in Neper software in .3dec format;

[0019] S6. Import the exported block model file into 3DEC software to form a numerical model of the active fracture discontinuous medium simulation part;

[0020] S7. Generate numerical models of other components of the numerical simulation model in 3DEC software;

[0021] S8. In 3DEC software, the entire numerical simulation model is meshed with tetrahedral meshes to transform the rigid block into a deformable block;

[0022] S9. Assign matching constitutive models and corresponding calculation parameters to each component block of the numerical simulation model;

[0023] S10. Classify the contacts between different blocks and assign corresponding contact parameters;

[0024] S11. Apply boundary conditions to the numerical simulation model and complete the initial geostress equilibrium;

[0025] S12. Simulate the tunnel excavation and support process in 3DEC software;

[0026] S13. Simulate the creeping or stick-slipping motion of active fracture in 3DEC software.

[0027] This solution integrates Neper software block modeling with 3DEC software for unified computation, completing all subsequent simulation steps solely within 3DEC software. This avoids data transfer between different software in traditional coupled methods, significantly improving computational efficiency. Neper software generates discontinuous block models that conform to actual distribution patterns, restoring the true block geometry of rock masses in active fault zones. This solves the problem of inconsistencies between traditional methods using regular block simulations and reality, making simulation results more closely aligned with engineering practice. The entire process—modeling, mesh generation, parameter assignment, excavation and support simulation, and fault movement simulation—is completed within a single 3DEC software, ensuring the continuity and logical consistency of simulation steps and reducing data conversion errors.

[0028] Furthermore, in step S1, the zoning characteristics of the active fracture are in the form of a single zone, three zones, or five zones, the geometric characteristics are the width of each zone of the active fracture, and the orientation is the strike, dip, and dip angle of the active fracture.

[0029] This scheme clarifies the specific characterization forms of active fault zones, geometry, and attitude, providing standardized geological parameters for accurate modeling of active faults and avoiding modeling deviations caused by ambiguous parameter definitions.

[0030] Furthermore, in step S4, the block model is generated in the Neper software using the Voronoi method or the Graingrowth method. The distribution of the block size is normal, uniform, or log-normal, and the block size near the perimeter of the hole is smaller than the block size away from the perimeter of the hole.

[0031] This scheme limits the block generation method and block size distribution rules of Neper software, and sets smaller blocks according to the stress sensitivity characteristics around the tunnel, so as to improve the simulation accuracy of key areas around the tunnel and accurately capture the impact of the movement of the blocks around the tunnel on the support structure. At the same time, the standardized distribution rules make the block modeling more operable and repeatable.

[0032] Furthermore, in step S6, in the 3DEC software, partial blocks are deleted to simulate on-site cavities, or partial blocks are bonded to simulate on-site protruding rock blocks.

[0033] In this scheme, by deleting / bonding blocks to simulate on-site cavities / protruding rock blocks, the actual geological morphology of the active fault zone is further restored, and the influence of special geological structures such as cavities and protruding rock blocks on the stress of the tunnel is considered.

[0034] Furthermore, in step S7, the Block, Polyhedron, or Fish functions of 3DEC software are used to generate solid element models of the complete rock mass, lining, and active fracture sections that are not simulated using discontinuous media; the Cable and Beam structural elements of 3DEC software are used to simulate anchor bolts and steel arches, and the Cable elements are used to simulate the reinforcing bars in the concrete lining.

[0035] This scheme clarifies the generation methods of different model components in 3DEC software, adapts to the mechanical properties of different structures such as complete rock mass, lining, anchor bolts, and reinforcing bars, ensures the mechanical rationality of each component model, and makes the stress and deformation of each structure during the simulation process more in line with the actual engineering mechanics laws.

[0036] Furthermore, in step S8, the mesh size of each component of the numerical simulation model is set independently, and the mesh size of each block is also set independently.

[0037] In this scheme, the mesh size can be set independently for each component and block, realizing a combination of fine mesh subdivision and coarse mesh subdivision. Small meshes are used to improve accuracy in key areas such as around the tunnel and active faults, while large meshes are used to reduce the amount of computation in non-critical areas such as intact rock masses, thus balancing simulation accuracy and computational efficiency.

[0038] Furthermore, the constitutive model is a linear elastic constitutive model or an elastoplastic constitutive model, and each component block selects a matching constitutive model according to the actual engineering requirements.

[0039] This scheme provides two constitutive models to choose from: linear elastic and elastoplastic. The corresponding constitutive model can be matched according to the actual engineering conditions (such as the elastic deformation stage and the plastic failure stage), so that the mechanical response of the model is more in line with the actual deformation and failure characteristics of the rock mass and structure, thereby improving the mechanical accuracy of the simulation results.

[0040] Furthermore, in step S10, the Fish language of 3DEC software is used to identify and classify the contact between blocks. The contact includes contact between the same component and contact between different components. The blocks are set to an adhesive or detached state.

[0041] In this scheme, Fish language is used to realize the automated identification and classification of block contact, which improves the efficiency and accuracy of the contact parameter assignment; it allows for parameter differentiation for the same contact type and blocks to be set to bonded / detached state, restoring the heterogeneity of rock mass contact in active fault zones and the actual connection state between blocks, which can accurately simulate the process of block contact failure and detachment, and capture the dynamic impact of block movement on the support structure.

[0042] Furthermore, in step S11, the boundary conditions include displacement boundary conditions and stress boundary conditions. Normal displacement constraints are applied to the six surfaces of the numerical simulation model: upper, lower, left, right, front, and back. Before the calculation, the non-rock mass block is given an empty model. After the geostress equilibrium calculation is completed, the displacement field is cleared to zero. An initial stress field can be applied to the internal elements to improve the calculation efficiency.

[0043] In this scheme, the application of boundary conditions and the operation process of geostress balance are standardized. Operations such as emptying the non-rock mass block model and zeroing the displacement field eliminate the interference of irrelevant factors on the calculation results. Applying the initial stress field to the internal unit further improves the calculation efficiency of geostress balance and ensures the authenticity of the initial geostress field and the efficiency of the calculation.

[0044] Furthermore, in step S13, the creep or stick-slip displacement of the active fracture is simulated by the product of boundary velocity × time per step × total number of steps, and the displacement of the active fracture in different directions is simulated by adjusting the velocity direction, and the creep boundary velocity is at least two orders of magnitude lower than the stick-slip boundary velocity.

[0045] This scheme clarifies the simulation calculation method for creep / stick slip displacement, ensures calculation stability by controlling boundary velocity and step size, adjusts velocity direction to adapt to different fracture motion forms, and the quantitative requirements of creep and stick slip velocity restore the actual rate difference between the two motions.

[0046] The beneficial effects of this invention are:

[0047] (1) Effectively improves computational efficiency:

[0048] All simulation calculation steps after block modeling are completed in 3DEC software, avoiding data transfer between different software in the traditional discrete element-finite difference coupling method, reducing computational resource consumption and data conversion errors. At the same time, unnecessary processes can be simplified and initial stress fields can be applied to internal elements according to the analysis focus, further improving computational efficiency.

[0049] (2) Improve the realism of the model:

[0050] The Neper software generates complex-shaped blocks that conform to statistical distribution patterns, restoring the true block geometry of rock masses in active fault zones. Cavities / protruding rock blocks can be simulated by deleting / bonding blocks, taking into account the influence of special geological structures. Block contact can be set to bonded / detached states, which can accurately simulate the actual connection and movement of blocks, improving the matching degree between the numerical model and the actual geological conditions on site.

[0051] (3) Improve the accuracy of simulation results:

[0052] By setting smaller blocks and refining the mesh in key areas such as the tunnel perimeter, the rock mass movement and stress deformation of the support structure in key areas can be accurately captured. Each component can be matched with a linear elastic or elastoplastic constitutive model, and different parameters can be assigned to different blocks, making the mechanical response of the model more realistic. The simulation results can provide a precise basis for the design of engineering measures for tunnels crossing active fractures.

[0053] (4) It can capture the adverse effects of local blocks on the support structure:

[0054] The contact model between active fracture blocks allows for bonding failure and detachment, accurately simulating the abnormal movement of individual blocks and capturing the adverse effects of local block creep / stick slip on the support structure. This overcomes the shortcomings of traditional continuous medium models that cannot consider local rock mass movement, providing a more comprehensive analytical basis for the anti-fracture design of support structures. Attached Figure Description

[0055] Figure 1 The flowchart shows the numerical simulation method for tunnel crossing active fracture based on discrete element-finite difference coupling in the embodiment.

[0056] Figure 2 A numerical simulation model (half) of the active fracture discontinuous medium (block).

[0057] Figure 3 This is a block model (half) of the numerical simulation model.

[0058] Figure 4 This is a mesh model (half) of the numerical simulation model.

[0059] Figure 5 These are the boundary conditions for the numerical simulation model.

[0060] Figure 6 This is a cloud map showing the horizontal displacement of the surrounding rock after the calculation is completed.

[0061] Figure 7 This is a contour plot of the horizontal displacement of the active fracture in fault_1 after the calculation is completed.

[0062] Figure 8This is a contour plot of the maximum tensile stress in the lining structure after the calculation is completed.

[0063] Figure 9 This is a cloud diagram showing the maximum compressive stress of the lining structure after the calculation.

[0064] Figure 10 This is a displacement contour map of the lining structure after the calculation is completed. Detailed Implementation

[0065] This invention aims to provide a numerical simulation method for tunnels crossing active faults based on discrete element-finite difference (DEM) coupling, addressing the problem that existing numerical simulation methods for tunnels crossing active faults cannot simultaneously simulate the realistic block geometry of rock masses in active fault zones and improve computational efficiency. The core idea of ​​this invention is to combine the advantages of Neper software in modeling complex discontinuous blocks with the advantages of 3DEC software in DEM coupling computation. First, an active fault block model that conforms to the statistical distribution laws of actual engineering is generated using Neper software. Then, this model is imported into 3DEC software, where the entire process of modeling, mesh generation, parameter assignment, excavation and support simulation, and active fault creep / stick-slip motion simulation is completed, avoiding cross-software data transfer issues common in traditional coupling methods. Simultaneously, through refined block design, mesh generation, contact settings, and constitutive model matching, the true geological and mechanical properties of the rock masses in active fault zones are fully reproduced. This achieves high-precision numerical simulation of tunnels crossing active faults while maintaining computational efficiency, providing accurate numerical analysis data for engineering design and safety control.

[0066] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0067] Example:

[0068] The core and affected areas of an active fault zone are approximately 10m wide, trending north-south with a dip angle of 90° and a creep rate of 2mm / a, primarily composed of fractured rock. A deep-buried tunnel with a 10m diameter, approximately orthogonally traversing this active fault, has a design life of 50 years. The stress-displacement analysis of the tunnel under 10cm creep deformation conditions on the active fault is required. For detailed implementation procedures, please refer to [link to implementation details]. Figure 1 This includes the following steps:

[0069] S1. Analysis of Active Fracture Characteristics:

[0070] The purpose of this step is to obtain the basic geological parameters of active faults, provide a geological basis for accurate modeling of active faults, and ensure the geological conformity of the model.

[0071] Specifically, based on geological survey results (including geological survey reports and geological maps), the zoning characteristics, geometric features, and attitude of active faults are analyzed and determined. The zoning characteristics of active faults refer to considering them as one zone, three zones (core zone + lateral damage zones), or five zones (slip surface + lateral core zones + lateral damage zones), etc. The geometric features of active faults refer to the width of each zone. The attitude of active faults refers to their strike, dip, and dip angle.

[0072] To simplify calculations, this embodiment divides the active fault into single-zone features; the geometric features are a bandwidth of 10m and an attitude of north-south with a dip angle of 90°.

[0073] S2. Tunnel Feature Analysis:

[0074] The purpose of this step is to clarify the structural parameters of the tunnel and the spatial relationship between the tunnel and the active fracture, so as to provide a basis for the overall layout design of the numerical simulation model.

[0075] Specifically, based on the tunnel design scheme, the geometric characteristics of the tunnel and its relationship with the active fracture are analyzed. The geometric characteristics of the tunnel refer to its cross-sectional shape and dimensions. The relationship between the tunnel and the active fracture refers to the angle between the tunnel's axial direction and the active fracture.

[0076] In this embodiment, the tunnel has a circular cross-section, an excavation diameter of 10m, and is to be lined with C30 concrete with a lining thickness of 1m, resulting in a tunnel diameter of 8m after lining. The tunnel and the active fault are orthogonally crossed.

[0077] S3. Numerical Model Feature Analysis:

[0078] The purpose of this step is to define the overall structure and spatial dimensions of the numerical simulation model, ensuring that the model can cover the study area of ​​the tunnel crossing the active fracture, while avoiding the waste of computation caused by an excessively large model size.

[0079] Specifically, the components of the numerical simulation model and the geometric parameters of each component are determined. The components of the numerical simulation model include intact rock mass (non-faulted rock mass), active fractures (including different zones), lining, anchor bolts, steel arches, etc. The geometric parameters of each component refer to its specific dimensions, such as length, width, height, and diameter.

[0080] In this embodiment, the components of the numerical simulation model include intact rock mass, active fracture, and concrete lining; the geometric parameters are set as follows: model length 110m (active fracture length 10m, intact rock mass on both sides 50m each), width 60m, height 60m, and the support structure only considers the lining structure with a thickness of 1m.

[0081] S4.Neper generates active fracture models:

[0082] The purpose of this step is to recreate the true discontinuous block morphology of the fractured rock mass in the active fault zone, accurately capture the movement characteristics of the rock mass in the fault zone, and improve the simulation accuracy of key areas through differentiated block size design.

[0083] Specifically, the active fracture is identified by using discontinuous media (i.e., block simulation) to determine the zones and locations, and then the block size and distribution patterns of these zones or locations are determined. Corresponding block models are generated in the Neper software. Each zone of the active fracture can be simulated using either continuous media or block simulation. Different locations within the same zone of the active fracture can also be simulated using either continuous media or block simulation. The block sizes of zones or locations of the active fracture simulated using block simulation can be consistent or inconsistent. Furthermore, blocks closer to the tunnel perimeter can be smaller, while blocks farther from the tunnel perimeter can be larger. The block size distribution follows statistical patterns, such as normal, uniform, or log-normal distributions. Blocks can be generated in Neper software using either the Voronoi method or the Graingrowth method.

[0084] In this embodiment, it is assumed that the active fracture within 15m of the tunnel axis is simulated using block volume, while the remaining parts are simulated using continuous medium. The equivalent diameter of the block volume is 1.5m, conforms to a log-normal distribution, and has a standard deviation of 0.05. The active fracture block volume model is generated using the Graingrowth method in Neper software.

[0085] S5. Export the Neper model:

[0086] The purpose of this step is to ensure that the block model can be recognized and read by the 3DEC software, and to achieve model data compatibility between the Neper software and the 3DEC software.

[0087] Specifically, the partition blocks generated in the Neper software are exported in ".3dec" format. The .3dec format is the standard format used by 3DEC software to recognize discontinuous block models. Using this format avoids errors in model data conversion and ensures the integrity of the block model. In this embodiment, the generated active fracture block model is exported as a "fault_1.3dec" file.

[0088] Importing the Neper model into S6.3DEC:

[0089] The purpose of this step is to construct a discontinuous block model of the active fault core region in the 3DEC software, laying the foundation for subsequent integrated calculations, and at the same time, it can recreate the special geological structures on site.

[0090] Specifically, the exported files are imported into 3DEC software to form a numerical model of the active fracture using block simulation. Furthermore, within 3DEC software, partial blocks can be deleted to simulate in-situ cavities, or partial blocks can be bonded to simulate in-situ protruding rock blocks.

[0091] In this embodiment, the file "fault_1.3dec" is read into the 3DEC software, and the generated active fracture block model is as follows: Figure 2 As shown.

[0092] S7.3DEC generates other parts of the model:

[0093] The purpose of this step is to complete the overall construction of the numerical simulation model in the 3DEC software, realize the model unification of all components, and provide a complete model foundation for subsequent integrated calculations.

[0094] Specifically, numerical models of other components are directly generated in the 3DEC software. These other components refer to the intact rock mass, lining, anchor bolts, etc., from step S3, as well as other parts of the active fracture not generated in the Neper software from step S4. The intact rock mass, lining, and ungenerated active fractures, etc., are simulated using solid elements, which can be generated using Block, Polyhedron, or Fish elements in 3DEC; the anchor bolts, steel arches, etc., are simulated using structural elements, which can be simulated using Cable, Beam, or other structural elements in 3DEC; and the reinforcing steel in the concrete lining can be simulated using Cable elements.

[0095] In this embodiment, using 3DEC software, direct command statements are used to generate the remaining part of the active fracture (fault_2) and the complete rock mass on both sides of the active fracture. The Fish language is then used to generate the ring-shaped lining structure, such as... Figure 3 As shown.

[0096] S8. Mesh Generation:

[0097] The purpose of this step is to transform rigid blocks into deformable mechanical calculation units, realize the stress and deformation calculation of rock masses and structures through mesh generation, and balance simulation accuracy and calculation efficiency through differentiated mesh design.

[0098] Specifically, tetrahedral meshes are a general mesh form in 3DEC software suitable for complex block models, and can adapt to the irregular shapes of discontinuous blocks; rigid blocks are divided into deformable mesh elements so that their stress deformation can be calculated by the finite difference method; regular small meshes are used in critical areas to improve accuracy, while regular large meshes are used in non-critical areas to reduce the amount of computation.

[0099] In this embodiment, the entire model is meshed using tetrahedral meshes. The discontinuous medium portion of the active fracture fault_1 uses an irregular mesh to fit the block shape, while the remaining continuous medium portions use regular meshes. The generated mesh model is as follows: Figure 4 As shown.

[0100] S9. Assignment unit calculates parameters:

[0101] The purpose of this step is to assign constitutive models and calculation parameters that conform to actual mechanical properties to each component of the model, so as to ensure that the mechanical response of the model can truly reflect the actual deformation and failure laws of the rock mass and structure.

[0102] Specifically, the mechanical properties of different geological bodies and structures vary significantly, requiring the selection of a suitable constitutive model, while combining engineering geological tests and material tests to determine the calculation parameters.

[0103] In this embodiment, except for the active fracture fault_1 part which adopts the linear elastic constitutive model, the remaining continuous medium part adopts the Mohr-Coulomb model. The specific calculation parameters are shown in Table 1.

[0104] Table 1 Calculation parameters for each component block

[0105]

[0106] S10. Assign contact parameters:

[0107] The purpose of this step is to reproduce the actual contact characteristics between different blocks, ensure that the force transmission between blocks conforms to the laws of actual engineering mechanics, and accurately simulate the bonding, sliding, and detachment processes of block contact.

[0108] Specifically, the contact between blocks is the core of force transmission in the discrete element model. The contact characteristics of blocks with different components are significantly different, and differentiated parameters need to be assigned through identification and classification. The Fish language can be used to realize the automatic identification and classification of contact, improving efficiency and accuracy.

[0109] In this embodiment, the Fish language is used to identify the contacts between the blocks, including contacts within host_1, contacts within host_2, contacts within the active fracture fault_1, contacts within fault_2, contacts within the lining, contacts between host_1 and fault_2, contacts between host_1 and fault_1, contacts between host_1 and the lining, contacts between host_2 and fault_2, contacts between host_2 and fault_1, contacts between host_2 and the lining, and contacts between fault_1 and fault_2. For simplicity, the contacts between the blocks of the active fracture fault_1 are considered contact type one, using the Coulomb slip contact model; the contacts between the remaining blocks are considered contact type two, using the elastic contact model. The contact parameters for the two types are shown in Table 2.

[0110] Table 2 Contact parameters for different contact types

[0111]

[0112] S11. Geostress balance:

[0113] The purpose of this step is to simulate the actual geostress environment and boundary constraints of the engineering project, ensuring that the initial conditions of the numerical simulation are consistent with the actual engineering situation.

[0114] Specifically, boundary conditions are applied to achieve initial stress equilibrium. These boundary conditions include displacement boundary conditions and stress boundary conditions. It should be noted that this step can be omitted or simplified depending on the actual situation.

[0115] S12. Tunnel Excavation and Support Simulation:

[0116] The purpose of this step is to recreate the actual construction process of the tunnel project, so that the stress and deformation of the model can reflect the impact of excavation and support on the surrounding rock and structure.

[0117] Specifically, tunnel excavation essentially involves removing the surrounding rock mass, while support provides mechanical support to the surrounding rock and structure. In 3DEC software, rock mass removal is simulated using a voided model, and the construction of the support structure is simulated using a constitutive model. It should be noted that this step can be omitted or simplified depending on the actual situation.

[0118] S13. Simulation of active fracture creep / stick slip:

[0119] The purpose of this step is to simulate the actual movement of active fractures, capture the stress and displacement response of the surrounding rock and support structure during the fracture movement, and provide a basis for engineering safety evaluation and design optimization.

[0120] In this embodiment, a horizontal creep displacement of 10cm is assumed, while vertical creep displacement is not considered. Therefore, normal constraints are applied to the left, right, bottom, and top surfaces of the entire numerical model; normal constraints are also applied to the front and rear surfaces of the host_1 rock mass; a linear displacement is applied to the front surface of the active fracture, gradually increasing from 0cm to 10cm from left to right; a 10cm displacement is applied to the front surface of the host_2 rock mass. The boundary conditions of the numerical model are as follows: Figure 5 As shown. In 3DEC software, displacement is represented by the product of the velocity boundary and the calculation step. To ensure calculation stability, the calculation time for each step is set to 1×10^6 seconds in this calculation. -4 The boundary velocity is 0.01 m / s, and the calculation steps are 100,000 steps to simulate a 50-year creep displacement of 10 cm in an active fracture.

[0121] By setting the boundary conditions and calculation parameters as described above, numerical simulation calculations were completed in 3DEC software, and the calculation results were analyzed.

[0122] Figures 6-7 These are the overall displacement contour plot of the model and the displacement contour plot of the fault_1 active fracture, respectively. Figure 6 and Figure 7 It can be seen that, due to the influence of the lining structure, the deformation of the internal active fracture fault_1 is smaller than the externally applied creep displacement. In addition, since the contact between the fault_1 blocks can be disrupted, its deformation is non-uniform, and the deformation of individual blocks may be larger or smaller.

[0123] Figures 8-9 These are the contour maps of the maximum tensile stress and maximum compressive stress of the lining structure, respectively. Figure 10 This is a displacement contour map of the lining structure. Figure 8 , Figure 9 and Figure 10 It can be seen that the deformation of the lining structure is basically the same as the overall deformation. The maximum tensile stress has not yet exceeded the uniaxial compressive strength of C30 concrete, but the maximum compressive stress has exceeded the maximum compressive strength of C30 concrete. This indicates that the tunnel engineering treatment plan cannot meet the safe operation requirements of this project, and the design plan needs to be further modified.

[0124] In this example, the present invention can simulate the actual morphology (shape, size and distribution pattern) of rock blocks in the key focus area and the influence of individual rock blocks on the lining structure, making the calculation results more consistent with the actual situation; it also avoids the coupling calculation between different calculation software, effectively reducing computing resources and improving computing efficiency.

[0125] Although embodiments of the present invention have been described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, and all such changes and alterations shall not depart from the protection scope of the present invention.

Claims

1. A numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling, characterized in that, Includes the following steps: S1. Based on the geological survey results, determine the zoning characteristics, geometric features, and occurrence of active faults; the geological survey results include geological survey reports and geological maps; S2. Based on the tunnel design scheme, determine the tunnel's geometric characteristics and their relationship with active faults; S3. Determine the components of the numerical simulation model and the geometric parameters of each component; S4. Determine the partitions and locations of the active fracture using discontinuous medium simulation, set the block size and distribution pattern of the partitions and locations, and generate the corresponding block models in Neper software; S5. Export the block model generated in Neper software in .3dec format; S6. Import the exported block model file into 3DEC software to form a numerical model of the active fracture discontinuous medium simulation part; S7. Generate numerical models of other components of the numerical simulation model in 3DEC software; S8. In 3DEC software, the entire numerical simulation model is meshed with tetrahedral meshes to transform the rigid block into a deformable block; S9. Assign matching constitutive models and corresponding calculation parameters to each component block of the numerical simulation model; S10. Classify the contacts between different blocks and assign corresponding contact parameters; S11. Apply boundary conditions to the numerical simulation model and complete the initial geostress equilibrium; S12. Simulate the tunnel excavation and support process in 3DEC software; S13. Simulate the creeping or stick-slipping motion of active fracture in 3DEC software.

2. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S1, the zoning characteristics of the active fracture are in the form of a single zone, three zones, or five zones, the geometric characteristics are the width of each zone of the active fracture, and the attitude is the strike, dip, and dip angle of the active fracture.

3. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S4, the block model is generated in Neper software using the Voronoi method or the Graingrowth method. The distribution of the block size is normal, uniform, or log-normal, and the block size near the perimeter of the hole is smaller than the block size away from the perimeter of the hole.

4. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S6, in the 3DEC software, partial blocks are deleted to simulate on-site cavities, or partial blocks are bonded to simulate on-site protruding rock blocks.

5. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S7, the Block, Polyhedron, or Fish functions of 3DEC software are used to generate solid element models of the complete rock mass, lining, and active fracture sections that are not simulated using discontinuous media; the Cable and Beam structural elements of 3DEC software are used to simulate anchor bolts and steel arches, and the Cable elements are used to simulate the reinforcing bars in the concrete lining.

6. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S8, the mesh size of each component of the numerical simulation model is set independently, and the mesh size of each block is also set independently.

7. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, The constitutive model is either a linear elastic constitutive model or an elastoplastic constitutive model, and the constitutive model of each component block is selected according to the actual engineering requirements.

8. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S10, the Fish language of 3DEC software is used to identify and classify the contact between blocks. The contact includes contact between the same component and contact between different components. The blocks are set to an adhesive or detached state.

9. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S11, the boundary conditions include displacement boundary conditions and stress boundary conditions. Normal displacement constraints are applied to the six surfaces of the numerical simulation model: top, bottom, left, right, front, and back. Before the calculation, the non-rock mass block is given an empty model. After the geostress equilibrium calculation is completed, the displacement field is cleared to zero.

10. The numerical simulation method for tunnel crossing active fractures based on discrete element-finite difference coupling as described in claim 1, characterized in that, In step S13, the creep or stick-slip displacement of the active fracture is simulated by multiplying the boundary velocity by the time of each step by the total number of steps. The displacement in different directions of the active fracture is simulated by adjusting the velocity direction, and the creep boundary velocity is at least two orders of magnitude lower than the stick-slip boundary velocity.

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