FDEM simulation method and system for hydraulic coupling fracture of tunnel fractured rock mass

Abstract

The invention discloses a tunnel fractured rock mass hydraulic coupling fracture FDEM simulation method and system, and relates to the technical field of rock mechanics and rock engineering. The method comprises the following steps: acquiring fracture information of a target area in a target tunnel and mechanical property parameters of a surrounding rock sample; according to the fracture occurrence and connectivity, the fracture type is determined; constructing an excavation numerical model of the target tunnel by utilizing an FDEM simulation program according to the mechanical property parameters and the fracture types; hydraulic coupling fracture simulation is executed based on the excavation numerical model; in the simulation process, normal stress and tangential stress generated by water flow on adjacent triangular units on the two sides of each target unit are calculated according to the fracture type; the target unit is a quadrilateral unit with a fracture path; the normal stress and the tangential stress are converted into corresponding nodal forces; and the node force is applied to the corresponding target unit, and the fracture opening degree is updated. According to the invention, the instability mechanism of the deep tunnel surrounding rock under the combined action of water pressure and ground stress can be accurately simulated.

Description

Technical Field

[0001] The present invention relates to the field of rock mechanics and rock engineering technology, and in particular to a FDEM simulation method and system for hydraulic coupling fracture of a tunnel fissured rock mass. Background Art

[0002] The surrounding rock of underground projects, such as deep transportation tunnels, water conservancy tunnels, and mining tunnels, is commonly characterized by networks of primary fractures. When these fractures connect to karst caves, faults, underground rivers, or surface water bodies, they are often filled with water or even saturated. As the depth of the project increases, the water pressure within these fractures increases significantly. During tunnel excavation, the exposure of these fractures can lead to high-pressure water inrush hazards, seriously threatening construction safety.

[0003] The stress state of the surrounding rock of a deep, water-bearing tunnel is extremely complex. On the one hand, it is subjected to high ground stress, and on the other hand, it is affected by the infiltration of high-pressure fissure water. After excavation and unloading, the redistribution of surrounding rock stress causes changes in the fracture aperture, which in turn changes the seepage path and pressure distribution. The changes in the seepage field, in turn, react on the rock stress field, forming a two-way water-mechanical coupling effect. This coupling process of mutual influence and interaction between the stress field and the seepage field is complex and continuous until a new equilibrium state is reached. In order to accurately understand the dynamic changes in the stress and seepage fields of the tunnel surrounding rock throughout the entire space and during the entire excavation process, numerical simulation is an important research tool.

[0004] However, neither single continuous nor discontinuous numerical methods can effectively simulate the complex bidirectional coupling between stress and seepage fields. While the finite element-discrete element method (FDEM) has been shown to be advantageous in simulating the fracture and expansion of surrounding rock in tunnels and has been applied, it still has significant shortcomings in simulating hydraulic coupling.

[0005] Existing finite element-discrete element coupling methods (FDEM) primarily focus on the surrounding rock fracture process under stress fields, but have yet to systematically integrate seepage field coupling models. Furthermore, existing FDEM hydraulic coupling simulations are mostly limited to simulating the splitting behavior of small-scale rock specimens under hydraulic pressure. This differs significantly from the engineering scale and mechanisms of the dynamic evolution of tunnel excavation unloading, progressive surrounding rock fracture, and seepage. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention provides a FDEM simulation method and system for hydraulically coupled fracture of tunnel fractured rock mass, which can accurately simulate the instability mechanism of deep tunnel surrounding rock under the combined action of water pressure and ground stress, and provide theoretical support for the prevention and control of hydraulic disasters.

[0007] To achieve the above objectives, the present invention provides a tunnel excavation FDEM simulation method, comprising:

[0008] Obtaining fracture information of a target area in a target tunnel and mechanical properties of surrounding rock samples; the fracture information includes fracture occurrence, connectivity, and initial opening;

[0009] Determine the fracture type based on the fracture occurrence and connectivity;

[0010] According to the mechanical performance parameters and the crack type, a numerical excavation model of the target tunnel is constructed using a FDEM simulation program; the numerical excavation model includes triangular elements and quadrilateral elements; the FDEM simulation program is embedded with calculation formulas for water pressure, water flow velocity, and water flow rate;

[0011] A hydraulic coupled fracturing simulation is performed based on the excavation numerical model. During the simulation, the following operations are iteratively performed until a termination condition is met:

[0012] According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is a quadrilateral element with a fracture path;

[0013] Converting the normal stress and tangential stress into corresponding nodal forces;

[0014] The nodal forces are applied to the corresponding target elements, and the crack opening is updated.

[0015] Optionally, the mechanical performance parameters include elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion and internal friction angle; the mechanical performance parameters are obtained by performing uniaxial compression, Brazilian splitting and triaxial compression tests on the surrounding rock specimens.

[0016] Optionally, the calculation formula of the normal contact stiffness of the triangular unit is:

[0017]

[0018] Where, P n is the normal stiffness of the triangular element contact, P b is the basic stiffness, and P b =0.1448P f , P f is the penalty value of the quadrilateral unit; assuming that triangle unit i and triangle unit j are adjacent triangle units on both sides of the target unit, Δh i is the height of triangular element i in the contact surface direction, Δh j is the height of triangular element j in the contact surface direction, Δl i is the length of the contact surface between triangle unit i and triangle unit j.

[0019] Optionally, the types of cracks include Class I, Class II, Class III, Class IV and Class V cracks; the Class I cracks contain a living water source, and the water flow remains constant; the Class II cracks are located on the tunnel floor, and remain in a static water-filled state after pressure release; the Class III cracks are connected to the Class I cracks and can retain water; the Class IV cracks are connected to the Class I cracks or the Class II cracks, and only partially retain water; the Class V cracks are connected to the Class I cracks, and are completely emptied after tunnel excavation and cannot retain water.

[0020] Optionally, during the simulation process, only the hydrostatic pressure is calculated for the Class II, Class III, and Class IV fractures; and the hydrostatic pressure and hydrodynamic pressure of the Class V fracture are both 0.

[0021] Optionally, the water pressure calculation formula is: ΔP = ρ w gH; the water flow rate calculation formula is: The water flow calculation formula is: Q = vu0W;

[0022] Where ΔP is the water pressure difference around the cave, ρ w is the water density, g is the acceleration of gravity, H is the water head height at the outlet of the crack around the cave; v is the water flow velocity at the outlet of the crack around the cave; Q is the water flow rate, u0 is the initial opening of the crack, and W is the crack width.

[0023] Optionally, the calculation formula for the normal stress is:

[0024]

[0025] The calculation formula of the tangential stress is:

[0026]

[0027] Where σ ni is the normal stress of crack i, H i is the hydraulic head height of fracture i, τ i is the tangential stress of crack i, μ i is the dynamic viscosity of water in crack i, ρ w is the water density, g is the acceleration due to gravity, v i is the water flow velocity in fracture i, u i is the crack opening of crack i.

[0028] Optionally, the calculation formula of the node force is:

[0029]

[0030] Where, f xi0 、f xi1 、f xi2 and f xi3represents the nodal forces of nodes i0, i1, i2 and i3 in the x-direction respectively; f yi0 、f yi1 、f yi2 and f yi3 Represent the nodal forces of nodes i0, i1, i2 and i3 in the y direction respectively; i0, i1, i2 and i3 are the four nodes of the quadrilateral unit arranged counterclockwise, Δx is the coordinate difference of the quadrilateral unit nodes in the x direction, and Δy is the coordinate difference of the quadrilateral unit nodes in the y direction.

[0031] The present invention also provides a tunnel fracture rock mass hydraulic coupling fracture FDEM simulation system, comprising:

[0032] A data acquisition unit is configured to acquire crack information of a target area in a target tunnel and mechanical property parameters of a surrounding rock sample; the crack information includes: crack occurrence, connectivity, and initial opening;

[0033] A type determination unit, configured to determine the fracture type according to the fracture occurrence and connectivity;

[0034] a model building unit, configured to build an excavation numerical model of the target tunnel using a FDEM simulation program according to the mechanical performance parameters and the fracture type; the excavation numerical model includes triangular elements and quadrilateral elements; the FDEM simulation program is embedded with calculation formulas for water pressure, water velocity, and water flow;

[0035] The simulation unit is configured to perform a hydraulic coupled fracturing simulation based on the excavation numerical model. During the simulation, the following operations are iteratively performed until a termination condition is satisfied:

[0036] According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is a quadrilateral element with a fracture path;

[0037] Converting the normal stress and tangential stress into corresponding nodal forces;

[0038] The nodal forces are applied to the corresponding target elements, and the crack opening is updated.

[0039] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0040] The proposed FDEM simulation method for hydraulically coupled fractures in tunnel fractured rock masses incorporates fracture type classification and an iterative mechanism for hydraulic-mechanical coupling calculations into the FDEM framework. This method, for the first time, systematically implements dynamic bidirectional coupling between stress and seepage fields during unloading during deep tunnel excavation in numerical simulations. This method meticulously classifies fractures based on their occurrence and connectivity, and differentiates the calculation formulas for water pressure, flow velocity, and flow for different fracture types. This addresses the lack of seepage field integration in existing FDEM methods and overcomes the limitations of single-stress field simulation.

[0041] By iteratively executing the closed-loop process of "stress calculation-node force conversion-opening degree update", the normal stress and tangential stress generated by water flow on the fracture wall rock mass (adjacent triangular units) are dynamically converted into the node load of the target quadrilateral unit, and the fracture opening is updated in real time and fed back to the hydraulic calculation. This mechanism accurately reproduces the interaction between the progressive fracture of the surrounding rock and the evolution of the seepage path in actual engineering, and overcomes the defect that the existing method can only simulate the hydraulic splitting of small-sized specimens and is out of touch with the engineering scale. The present invention realizes high-precision simulation of the fracture expansion, dynamic reconstruction of seepage and evolution of sudden water inrush risk of the fracture network under the action of water-mechanical coupling throughout the deep tunnel excavation process, providing reliable data support for the spatiotemporal prediction and prevention and control strategy formulation of high-pressure sudden water inrush disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0043] Figure 1 A schematic diagram of a method flow of a FDEM simulation method for hydraulically coupled fracture of a tunnel fractured rock mass according to an embodiment of the present invention;

[0044] Figure 2 A schematic diagram of crack types shown in an embodiment of the present invention;

[0045] Figure 3 A schematic diagram of a FDEM triangle element normal contact stiffness calculation model according to an embodiment of the present invention;

[0046] Figure 4 A schematic diagram of normal stress of a quadrilateral element shown in an embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the tangential stress of a quadrilateral unit shown in an embodiment of the present invention;

[0048] Figure 6 This is a schematic diagram of quadrilateral unit node sorting according to an embodiment of the present invention;

[0049] Figure 7 A schematic diagram of crack opening according to an embodiment of the present invention;

[0050] Figure 8 This is a schematic diagram of the failure morphology of a tunnel fractured rock mass under hydraulic coupling according to an embodiment of the present invention;

[0051] Figure 9 This is a schematic diagram of the module structure of the FDEM simulation system for hydraulic coupling fracture of tunnel fractured rock mass shown in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] See also Figure 1 , Figure 1 The figure is a flow chart of the FDEM simulation method for hydraulically coupled fracture of a tunnel fractured rock mass. The FDEM simulation method for hydraulically coupled fracture of a tunnel fractured rock mass includes the following steps:

[0054] S101: Obtain crack information of a target area in a target tunnel and mechanical property parameters of a surrounding rock sample.

[0055] Among them, fracture information includes: fracture occurrence, connectivity and initial opening. Fracture occurrence refers to the spatial orientation and geometric characteristics of fractures, such as strike and dip, which are used to describe the spatial distribution pattern of fractures; connectivity refers to the hydraulic connection or connection state between fractures, such as whether the fractures are connected to water sources or other fractures, which directly affects the formation of seepage paths; initial opening refers to the initial width of the fracture, reflecting the physical state of the fracture when it is undisturbed. This information can be obtained through on-site surveys of the project, such as geological exploration, drilling sampling, and three-dimensional scanning, to ensure that the data can truly reflect the actual geological conditions of the tunnel surrounding rock. By accurately obtaining fracture information, it can provide key input for subsequent fracture classification and seepage field simulation, avoiding simulation distortion due to data deviation.

[0056] The mechanical properties of surrounding rock samples can be obtained through indoor tests. Mechanical properties parameters include core indicators such as elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion and internal friction angle. Specifically, the elastic modulus, Poisson's ratio and uniaxial compressive strength of the surrounding rock sample can be determined by conducting uniaxial compression tests; the tensile strength can be determined by conducting Brazilian splitting tests; and the cohesion and internal friction angle can be determined by conducting triaxial compression tests. As the core input for constructing numerical models, mechanical properties parameters can directly affect the accuracy of rock mass fracture behavior; it is understandable that the test process must strictly follow the rock mechanics testing specifications to ensure that the samples are taken from the in-situ surrounding rock in the target area of ​​the tunnel to ensure the accuracy of the parameters.

[0057] Fracture information describes the rock mass structure from a macroscopic geological perspective, while mechanical property parameters quantify the rock mass's mechanical response from a microscopic material perspective. Combining these two allows for a comprehensive characterization of the hydraulic coupling characteristics of the tunnel surrounding rock. For example, initial opening and mechanical parameters jointly determine the deformation behavior of fractures under hydraulic pressure; parameters such as connectivity and cohesion synergistically influence the bidirectional coupling between seepage and stress.

[0058] S102: Determine the fracture type based on fracture occurrence and connectivity.

[0059] In practice, fracture type classification can be achieved by combining geological mapping and borehole exploration data with analysis of fracture network connectivity and water recharge relationships. Fracture occurrence determines the spatial distribution of fractures and the direction of potential hydraulic gradients, while connectivity directly determines the recharge, runoff, and drainage paths of water within the fracture network. Together, these two factors influence the hydraulic behavior of fractures.

[0060] See also Figure 2 , Figure 2 Schematic diagram of fracture types. By comprehensively analyzing the fracture occurrence and connectivity of the rock mass in the target area, fractures can be divided into five types with different hydraulic characteristics: Class I, Class II, Class III, Class IV and Class V fractures. Specifically, Class I fractures refer to fractures with a constant active water source inside (such as connected to an underground river). Their water flow remains constant during the simulation process and are the main water supply channels. Class II fractures specifically refer to fractures located at the bottom of the tunnel that can still maintain a static water-filled state after excavation and pressure relief. They are usually connected to closed water bodies or local saturated areas. Class III fractures refer to fractures that are connected to Class I fractures (active water sources) and can effectively retain water. They can maintain a certain water pressure and water volume under excavation disturbances. Class IV fractures refer to fractures that are connected to Class I or Class II fractures but can only partially retain water. Their water conductivity and water storage capacity are relatively limited. Class V fissures refer to fissures that are connected to Class I fissures, but after tunnel excavation, they are directly exposed or connected to drainage channels, resulting in the complete drainage of water and the inability to retain water.

[0061] By classifying fractures, the dynamic responses of different fractures during hydraulic coupling can be distinguished. Class I fractures dominate flow as the source; Class II, III, and IV fractures involve water storage and seepage, but with different water pressure states (Class II is static, Class III is pressure-maintaining, and Class IV is partially pressure-depleted); and Class V fractures lose their hydraulic effect due to emptying. The classification results directly determine the method and calculation intensity of applying hydraulic loads (hydrostatic pressure and hydrodynamic pressure) to each type of fracture in subsequent simulations. For example, Class II, III, and IV only need to calculate hydrostatic pressure, Class V ignores hydraulic loads, and Class I requires a complete hydrodynamic calculation.

[0062] S103: Based on the mechanical performance parameters and crack types, a numerical model of the target tunnel excavation is constructed using the FDEM simulation program.

[0063] In the application, the calculation formulas for water pressure, water flow velocity and water flow can be embedded in the FDEM simulation program; on this basis, the corresponding three-dimensional excavation numerical model is established using FDEM according to the actual geological profile and engineering dimensions of the target tunnel; the surrounding rock units in the excavation numerical model are also called grid units, including triangular units and quadrilateral units, among which the triangular units represent continuous rock masses, and the quadrilateral units connecting these triangular units represent potential fracture interfaces.

[0064] When calibrating the Mode II fracture energy corresponding to different cohesions and the Mode I fracture energy corresponding to different tensile strengths in the excavation numerical model, the calibration method adopted can refer to the standard process described in the invention patent "A Precise Fracture Energy Calibration Method to Eliminate Loading Rate Effects" (Patent No.: ZL202211201119.6). The viscous damping, joint penalty, and tangential contact stiffness can be calculated using the following method:

[0065]

[0066] Where: μ is the viscous damping, h is the grid size, that is, the side length of the triangular unit, E is the elastic modulus, ρ is the rock density, P f is the joint penalty, P t is the tangential contact stiffness.

[0067] See also Figure 3 , Figure 3 Figure 2 is a schematic diagram of the FDEM triangular element normal contact stiffness calculation model. Assuming that triangular element i and triangular element j are adjacent triangular elements on both sides of the target element, the normal contact stiffness of triangular element i or j can be calculated using the following formula:

[0068]

[0069] Where, P n is the normal stiffness of the triangular element contact, Pb is the basic stiffness, and P b =0.1448P f , P f is the penalty value for quadrilateral elements; Δh i is the height of triangular element i in the contact surface direction, Δh j is the height of triangular element j in the contact surface direction, Δl i is the length of the contact surface between triangle unit i and triangle unit j.

[0070] S104: Execute hydraulic coupled fracturing simulation based on the excavation numerical model.

[0071] During the simulation, the following operations are performed iteratively until the termination condition is met:

[0072] According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is the quadrilateral element with a fracture path;

[0073] Convert normal stress and tangential stress into corresponding nodal forces;

[0074] The nodal forces are applied to the corresponding target elements and the crack openings are updated.

[0075] Among them, the termination condition can be set as follows: during the simulation process, no new cracks are generated within N consecutive calculation time steps, and the rate of change of the stress (normal stress and tangential stress) generated by the water flow on the triangular unit is less than or equal to the first preset value, and the rate of change of the seepage field parameters (water pressure, flow velocity, flow) is less than or equal to the second preset value.

[0076] The values ​​of the first preset value, the second preset value, and N can be flexibly set according to actual conditions. For example, the first preset value and the second preset value are both set to 0, and N is set to 3. It can be understood that a stress change rate less than the first preset value means that the change rate of both the normal stress and the tangential stress must be less than the first preset value; the same applies to the seepage field parameters.

[0077] During the simulation, only the hydrostatic pressure is calculated for Type II, Type III, and Type IV fractures; both the hydrostatic and hydrodynamic pressures for Type V fractures are 0.

[0078] For Type I fractures, the calculation process of water pressure, water velocity and water flow is as follows.

[0079] After the tunnel is excavated and unloaded, the water pressure around the tunnel drops to 0, and the water pressure difference is:

[0080] ΔP=ρ w gH;

[0081] Where ΔP is the water pressure difference around the cave, ρ wis the water density, g is the acceleration of gravity, and H is the water head height at the water outlet of the cracks around the cave.

[0082] Furthermore, the water flow velocity at the outlet of the crack around the cave can be obtained based on the water pressure difference:

[0083]

[0084] Where v is the water flow velocity at the outlet of the crack around the cave.

[0085] According to the flow rate, the water flow rate can be calculated as:

[0086] Q = vu0W;

[0087] Where Q is the flow rate, u0 is the initial opening of the crack, and W is the crack width.

[0088] During the simulation, it is assumed that the flow rate in the same fracture is equal and constant. In this way, the flow velocity at any position in the same fracture can be obtained as:

[0089]

[0090] Where, v i is the water flow velocity in fracture i, u i is the crack opening of crack i, W i is the crack width of crack i.

[0091] See also Figure 4 and Figure 5 , the calculation formulas for the normal stress and tangential stress of the triangular elements on both sides are:

[0092]

[0093] Where, σ ni is the normal stress of crack i, H i is the hydraulic head height of fracture i, τ i is the tangential stress of crack i, μ i is the dynamic viscosity of water.

[0094] Furthermore, the normal stress and tangential stress are converted into the nodal force of the quadrilateral element to calculate the influence of water flow on the fracture opening and flow velocity, and the fracture opening and flow velocity are updated again in the next calculation step to realize the simulation of hydraulic coupling.

[0095] See also Figure 6 , Figure 6 This is a schematic diagram of the node arrangement of quadrilateral elements. The calculation formula for the node force is:

[0096]

[0097] Where, fxi0 、f xi1 、f xi2 and f xi3 represents the nodal forces of nodes i0, i1, i2 and i3 in the x-direction respectively; f yi0 、f yi1 、f yi2 and f yi3 Represent the nodal forces of nodes i0, i1, i2 and i3 in the y direction respectively; i0, i1, i2 and i3 are the four nodes of the quadrilateral unit arranged counterclockwise, Δx is the coordinate difference of the quadrilateral unit nodes in the x direction, and Δy is the coordinate difference of the quadrilateral unit nodes in the y direction.

[0098] The calculation formulas for Δx and Δy are as follows:

[0099]

[0100] like Figure 6 As shown, where x i0 、x i1 、x i2 and x i3 The corresponding coordinate values ​​of nodes i0, i1, i2 and i3 in the x direction, y i0 、y i1 、y i2 and y i3 They correspond to the coordinate values ​​of nodes i0, i1, i2 and i3 in the y direction.

[0101] See also Figure 7 , Figure 7 Figure 2 is a schematic diagram of fracture opening. The total fracture opening is the sum of the new opening caused by water flow after tunnel excavation and the initial opening. The new opening is calculated using the FDEM numerical program, while the initial opening is obtained based on on-site surveys, as shown in the following formula:

[0102] u=u0+Δu;

[0103] Where u is the total crack opening, u0 is the initial crack opening, and Δu is the new crack opening.

[0104] like Figure 8 As shown, Figure 8 The figure is a schematic diagram of the failure morphology of the tunnel fractured rock mass under the hydraulic coupling action obtained by the method of the present invention.

[0105] Corresponding to the aforementioned embodiment of the method for realizing the application function, the present invention also provides a tunnel fracture rock mass hydraulic coupling fracture FDEM simulation system and corresponding embodiments.

[0106] See Figure 9 , Figure 9The following is a schematic diagram of the module structure of the FDEM simulation system for hydraulic coupling fracture of tunnel fractured rock mass. The system includes:

[0107] The data acquisition unit 91 acquires the crack information of the target area in the target tunnel and the mechanical properties of the surrounding rock sample; the crack information includes: crack occurrence, connectivity and initial opening;

[0108] A type determination unit 92 is used to determine the fracture type based on the fracture occurrence and connectivity;

[0109] a model building unit 93 for building a numerical excavation model of the target tunnel using a FDEM simulation program based on the mechanical property parameters and the fracture type; the numerical excavation model includes triangular elements and quadrilateral elements; the FDEM simulation program is embedded with calculation formulas for water pressure, water velocity, and water flow;

[0110] The simulation unit 94 is configured to perform a hydraulic coupled fracturing simulation based on the excavation numerical model. During the simulation, the following operations are iteratively performed until a termination condition is satisfied:

[0111] According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is the quadrilateral element with a fracture path;

[0112] Convert normal stress and tangential stress into corresponding nodal forces;

[0113] The nodal forces are applied to the corresponding target elements and the crack openings are updated.

[0114] Regarding the system in the above embodiment, the specific manner in which each unit module performs operations has been described in detail in the embodiment of the method, and will not be elaborated again here.

[0115] While various embodiments of the present invention have been described above, the above descriptions are intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A FDEM simulation method for hydraulic coupling fracture of tunnel fractured rock mass, characterized by: include: Obtain crack information of the target area in the target tunnel and mechanical properties parameters of the surrounding rock samples; The fracture information includes: fracture occurrence, connectivity and initial opening; Determine the fracture type based on the fracture occurrence and connectivity; According to the mechanical performance parameters and the crack type, a numerical excavation model of the target tunnel is constructed using a FDEM simulation program; the numerical excavation model includes triangular elements and quadrilateral elements; the FDEM simulation program is embedded with calculation formulas for water pressure, water flow velocity, and water flow rate; A hydraulic coupled fracturing simulation is performed based on the excavation numerical model. During the simulation, the following operations are iteratively performed until a termination condition is met: According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is a quadrilateral element with a fracture path; Converting the normal stress and tangential stress into corresponding nodal forces; The nodal forces are applied to the corresponding target elements, and the crack opening is updated.

2. The FDEM simulation method for hydraulic coupling fracture of tunnel fractured rock mass according to claim 1 is characterized in that: The mechanical performance parameters include elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion and internal friction angle; the mechanical performance parameters are obtained by conducting uniaxial compression, Brazilian splitting and triaxial compression tests on the surrounding rock samples.

3. The FDEM simulation method for hydraulic coupling fracture of tunnel fractured rock mass according to claim 1 is characterized in that: The calculation formula of the normal contact stiffness of the triangular element is: Where, P n is the normal stiffness of the triangular element contact, P b is the basic stiffness, and P b =0.1448P f , P f is the penalty value of the quadrilateral unit; assuming that triangle unit i and triangle unit j are adjacent triangle units on both sides of the target unit, Δh i is the height of triangular element i in the contact surface direction, Δh j is the height of triangular element j in the contact surface direction, Δl i is the length of the contact surface between triangle unit i and triangle unit j.

4. The FDEM simulation method for hydraulic coupled fracture of tunnel fractured rock mass according to claim 1, characterized in that: The types of cracks include Class I, Class II, Class III, Class IV and Class V cracks; the Class I cracks contain a source of living water, and the water flow remains constant; the Class II cracks are located on the tunnel floor and remain in a static water-filled state after pressure release; the Class III cracks are connected to the Class I cracks and can retain water; the Class IV cracks are connected to the Class I cracks or the Class II cracks and only partially retain water; the Class V cracks are connected to the Class I cracks and are completely emptied after tunnel excavation and cannot retain water.

5. The FDEM simulation method for hydraulic coupled fracture of tunnel fractured rock mass according to claim 4 is characterized in that: During the simulation, only the hydrostatic pressure is calculated for the Class II, Class III, and Class IV fractures; the hydrostatic pressure and hydrodynamic pressure for the Class V fracture are both 0.

6. The FDEM simulation method for hydraulic coupled fracture of tunnel fractured rock mass according to claim 1, characterized in that: The water pressure calculation formula is: ΔP=ρ w gH; the water flow rate calculation formula is: The water flow calculation formula is: Q = vu0W; Where ΔP is the water pressure difference around the cave, ρ w is the water density, g is the acceleration of gravity, H is the water head height at the outlet of the crack around the cave; v is the water flow velocity at the outlet of the crack around the cave; Q is the water flow rate, u0 is the initial opening of the crack, and W is the crack width.

7. The FDEM simulation method for hydraulic coupled fracture of tunnel fractured rock mass according to claim 1, characterized in that: The calculation formula of the normal stress is: The calculation formula of the tangential stress is: Where, σ ni is the normal stress of crack i, H i is the hydraulic head height of fracture i, τ i is the tangential stress of crack i, μ i is the dynamic viscosity of water in crack i, ρ w is the water density, g is the acceleration due to gravity, v i is the water flow velocity in fracture i, u i is the crack opening of crack i.

8. The FDEM simulation method for hydraulic coupled fracture of tunnel fractured rock mass according to claim 1, characterized in that: The calculation formula of the node force is: Where, f xi0 、f xi1 、f xi2 and f xi3 represents the nodal forces of nodes i0, i1, i2 and i3 in the x-direction respectively; f yi0 、f yi1 、f yi2 and f yi3 Represent the nodal forces of nodes i0, i1, i2 and i3 in the y direction respectively; i0, i1, i2 and i3 are the four nodes of the quadrilateral unit arranged counterclockwise, Δx is the coordinate difference of the quadrilateral unit nodes in the x direction, and Δy is the coordinate difference of the quadrilateral unit nodes in the y direction.

9. A FDEM simulation system for hydraulic coupling fracture of tunnel fractured rock mass, characterized by: include: A data acquisition unit, which acquires the crack information of the target area in the target tunnel and the mechanical properties parameters of the surrounding rock sample; The fracture information includes: fracture occurrence, connectivity and initial opening; A type determination unit, configured to determine the fracture type according to the fracture occurrence and connectivity; a model building unit, configured to build an excavation numerical model of the target tunnel using a FDEM simulation program according to the mechanical performance parameters and the fracture type; the excavation numerical model includes triangular elements and quadrilateral elements; the FDEM simulation program is embedded with calculation formulas for water pressure, water velocity, and water flow; The simulation unit is configured to perform a hydraulic coupled fracturing simulation based on the excavation numerical model. During the simulation, the following operations are iteratively performed until a termination condition is satisfied: According to the fracture type, the normal stress and tangential stress generated by the water flow on the adjacent triangular elements on both sides of each target element are calculated; the target element is a quadrilateral element with a fracture path; Converting the normal stress and tangential stress into corresponding nodal forces; The nodal forces are applied to the corresponding target elements, and the crack opening is updated.

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