Damping joint model modeling method based on PFC built-in model improvement

Abstract

The invention discloses an improved damping joint model modeling method based on a PFC built-in model, relates to the field of civil engineering technology numerical calculation, and solves the problems of stress concentration caused by particle interlocking during rock shearing in a discrete element model, lack of a damper in a smooth joint model, single energy dissipation mode and the like. The method comprises the steps that a normal damper parallel to the normal contact force direction and a tangential damper parallel to the tangential contact force direction are added on the basis of a smooth joint model to serve as a damping joint model; the normal contact force and the tangential contact force of the damping joint model are respectively divided into a linear part and a damping part; the linear part and the smooth joint model part are completely the same, the damping part provides the viscous behavior of a contact interface, and the damping force of the damping part is generated by a damper and is calculated according to the normal and tangential critical damping ratio; the problems that a smooth joint does not have a damping system and the energy dissipation mode is single are solved.

Description

Technical Field

[0001] The invention relates to the field of numerical calculation of civil engineering technology, and in particular to a damping joint modeling method based on an improved PFC built-in model. Background Art

[0002] Tunnel rock mass often has multiple groups of dominant joints and cracks, and these weak structural surfaces are interconnected and easily cause shear failure. In order to simulate the process of shear instability of rock mass, there are two ways to simulate weak structural surfaces in discrete elements.

[0003] One is to break the connecting bonds of the structural surface without considering the directionality of the structural surface, and weaken the contact micro-parameters through which the structural surface passes. Since the discrete element method discretizes rock materials into particles of different sizes, the structural surface of the rock mass is not a plane, but an irregular surface with unevenness and a certain degree of roughness, and its roughness is often greater than the real structural surface. When the weakening parameter method is used to simulate the structural surface, if a certain contact direction intersects with the sliding direction at a small angle, when the convex point of the upper rock mass contacts the convex point of the lower rock mass, the contact will be subjected to a huge shear load, and the upper dislocated rock mass cannot bypass the protruding particles, and the rock shear process is hindered.

[0004] The other is to consider the directionality of the structural surface and set the contact model that the structural surface passes through to a non-bonded model such as a joint model or a smooth joint model. When the smooth joint model is used to simulate the structural surface, although the smooth joint model can ensure that a certain particle passes through another particle it contacts along the sliding direction, the new contact formed during the sliding process is defaulted to linear contact, which still hinders the sliding of the rock mass. The basic composition of the discrete element is a rigid disk or a ball, which cannot be destroyed, so the rock mass can only continue to slide by bypassing the irregular protruding particles.

[0005] On the other hand, through the study of the constitutive structure of the smooth joint model, it was found that the smooth joint model dissipates shear dislocation energy only by relying on the friction coefficient, and the energy dissipation method is single, which is quite different from the real shear dislocation method. At present, the discrete element method can also simulate the effect of particle crushing, but it requires the development of complex algorithms, and parameters such as particle crushing intensity, number and size of particles after crushing are difficult to determine. Reducing the particle diameter can reduce the roughness of the simulated structural surface, but it will also increase the computational complexity of the discrete element simulation. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a modeling method of a damped joint model based on an improved PFC built-in model, which solves the problems of stress concentration caused by particle interlocking during rock shear in a discrete element model and the lack of dampers in the smooth joint model and a single energy dissipation method.

[0007] A damping joint modeling method based on an improved PFC built-in model, comprising:

[0008] On the basis of the smooth joint model, a normal damper parallel to the normal contact force direction and a tangential damper parallel to the tangential contact force direction are added as a damping joint model;

[0009] The normal contact force and tangential contact force of the damped joint model are divided into a linear part and a damping part. The linear part is exactly the same as the smooth joint model part. The damping part provides the viscous behavior of the contact interface. The damping force of the damping part is generated by the damper and calculated by the critical damping ratio of the normal and tangential directions.

[0010] The damping joint model is active if its bond is activated or the surface gap is negative.

[0011] Furthermore, the calculation formulas of the normal contact force and the tangential contact force are divided into a linear part and a damping part as follows:

[0012]

[0013] Where F n With F s are the normal contact force and the tangential contact force, and are the normal force of the linear part and the tangential force of the linear part, and are the normal force of the damping part and the tangential force of the damping part, β n With β s are the normal damping coefficient and the tangential damping coefficient, v n and v s are the relative normal velocity and relative tangential velocity, m c is the equivalent mass of the contact, m1 and m2 are the masses of the two contacting entities, k n and k s are the normal stiffness and tangential stiffness respectively, and A is the joint contact area.

[0014] Furthermore, it also includes: constructing a particle collision or shear model, assigning a damping joint model to a fixed particle, and verifying the effect of the damping joint model at the micro level by analyzing the relationship between the micro parameters of the damping joint model and the macroscopic mechanical properties when other particles collide or shear with the fixed particle;

[0015] Further, the constructing of the particle collision or shear model comprises:

[0016] Construct a collision between two spherical particles perpendicular to the damping joint direction and set the corresponding normal damping coefficient;

[0017] The ball particles are set to fall from a fixed height and hit the fixed ball particles. The rebound height is lower than the falling height, and the rebound speed is lower than the speed at the initial contact. The maximum contact force is smaller than the contact force of the smooth joint model, which proves that the damping model is effective and can reduce the energy in the normal direction of the particles.

[0018] The ball particles are set to move from a fixed distance to a fixed ball particle. The two balls come into contact. When the moving ball passes through the fixed ball, the corresponding normal damping coefficient is set and the speed decreases. This proves that the damping joint model is effective at this time and can reduce the energy in the tangential direction of the particle.

[0019] Furthermore, it is characterized in that the relationship between the microscopic parameters and macroscopic mechanical properties of the analytical damping joint model includes:

[0020] By changing the values ​​of the normal damping coefficient and the tangential damping coefficient of the damping joint model to change the rebound speed of the spherical particles, the relationship between the normal damping coefficient, the tangential damping coefficient and the macroscopic restitution coefficient is obtained as follows:

[0021]

[0022]

[0023] Where R n is the normal restitution coefficient, R t is the tangential restitution coefficient, β n With β s are the normal and tangential damping coefficients, respectively.

[0024] Furthermore, it also includes: constructing a discrete element joint rock model, wherein the discrete element joint rock model includes a damping joint model as a joint, simulating shear instability of rock at the joint under the action of gravity, and comparing and analyzing the difference between the rock shear force before and after using the damping joint model to verify the effect of the damping joint model at the macro level.

[0025] Furthermore, the construction of a discrete element joint rock model includes:

[0026] Construct a discrete element specimen consisting of a parallel bond contact model;

[0027] After the model is balanced, DFN joints (Discrete Fracture Network) are inserted into the discrete element specimen and given geometric parameters including length, width and inclination;

[0028] Assign the damping joint model to the DFN joint as the joint, and assign the damping joint micro parameters including the damping joint friction coefficient, damping coefficient, and joint stiffness;

[0029] Make DFN active (key command activate) to ensure that the subsequently generated contact is damped joint contact.

[0030] Furthermore, the simulated rock undergoes shear instability at the joints under the action of gravity, including:

[0031] Fix a row of particles at the bottom of the model to prevent the bottom rock from moving, then turn on gravity (key command gravity), set the gravity acceleration, the default direction of the gravity acceleration is the negative y direction, rebalance the model, start the calculation, the rock undergoes shear movement at the joints, and collect the shear force results.

[0032] Furthermore, the comparative analysis of the differences between rock shear forces before and after using the damping joint model includes:

[0033] The linear contact model replaces the damping joint model as the joint, and the linear contact parameters including the linear contact elastic modulus, stiffness ratio, and friction coefficient are set. The shear instability of the rock at the joint under the action of gravity is simulated, the shear motion of the rock at the joint is calculated, and the shear force data of the entire model are obtained. The shear force results when the damping joint model is used as the joint are compared and analyzed.

[0034] Furthermore, it also includes verifying the effect of the damping joint model at the micro and macro levels. If the effect does not meet the expectations, the damping joint model is reconstructed.

[0035] The beneficial effects of the present invention include:

[0036] The present invention redevelops the smooth joint model in the discrete element software into a damping joint model, thereby solving the problem that the smooth joint itself does not have a damping system and has a single energy dissipation mode.

[0037] The present invention proposes a simple two-particle collision or shear contact, and calibrates the relationship between the newly added microscopic parameters and macroscopic parameters of the damping joint model.

[0038] The present invention introduces the damping joint model and the DFN method into the shear motion of jointed rock, solving the problems of the existing simulation method in which the new contact becomes a linear contact and the shear is blocked. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a modeling method for a damping joint model based on an improved PFC built-in model and the correlation between microscopic parameters and macroscopic mechanical properties in an embodiment.

[0040] Figure 2 It is a schematic diagram of the mechanical behavior of the damping joint model involved in the present invention.

[0041] Figure 3The invention relates to the force and displacement laws of the damping joint bonding model.

[0042] Figure 4 The force and displacement laws for the non-bonded model to which the present invention relates.

[0043] Figure 5 The present invention relates to the force and displacement laws of the damping model.

[0044] Figure 6 (a) is a diagram showing displacement, force and velocity when simulating particle collision using a smooth joint model according to the present invention.

[0045] Figure 6 (b) is a diagram showing displacement, force and velocity when simulating particle collision using a damping joint model according to the present invention.

[0046] Figure 7 This is the relationship between the normal damping coefficient and the tangential restitution coefficient involved in the present invention.

[0047] Figure 8 This is the relationship between the tangential damping coefficient and the tangential restitution coefficient involved in the present invention.

[0048] Fig. 9 (a) is a schematic diagram of rock shear under gravity when a linear contact model is used in the present invention.

[0049] Fig. 9 (b) is a schematic diagram of rock shearing under gravity when the damping joint model is used in the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0051] A damping joint modeling method based on the improved PFC built-in model, such as Figure 1 As shown, including:

[0052] On the basis of the smooth joint model, a normal damper parallel to the normal contact force direction and a tangential damper parallel to the tangential contact force direction are added as a damping joint model;

[0053] The normal contact force and tangential contact force of the damped joint model are divided into a linear part and a damping part. The linear part is exactly the same as the smooth joint model part. The damping part provides the viscous behavior of the contact interface. The damping force of the damping part is generated by the damper and calculated by the critical damping ratio of the normal and tangential directions.

[0054] The damping joint model is active if its bond is activated or the surface gap is negative.

[0055] In this embodiment, normal and tangential dampers are added on the basis of the smooth joint model, and the damper action direction is parallel to the normal and tangential contact force directions. Figure 2 Specifically, Figure 2 The working calculation principle of the damping joint model; g s is the particle distance, σ c is the tensile strength, c is the viscosity coefficient, is the friction angle; Ks is the tangential stiffness, Kn is the normal stiffness; β n With β s are the normal and tangential damping coefficients; θ p is the joint inclination. The damped joint model provides the behavior of a planar joint that does not resist relative rotation, so the contact torque is equal to zero. The model contact force is divided into a linear part and a damped part. The linear part is exactly the same as the smooth joint model part and provides a linear elastic, with expansion of the bond (bond) or friction interface behavior. The linear force is composed of a constant normal stiffness k n and tangential stiffness k s The bond interface behavior is linear elastic until the tensile or shear strength limit is exceeded and the bond breaks, leaving the interface unbonded. The tensile strength is denoted by σ c , while the shear strength is determined by the friction angle in the Mohr-Coulomb criterion and viscosity coefficient c. The unbonded interface behavior is linear elastic and frictional dilatant, accommodating slip by imposing a Coulomb limit on the shear force using the friction coefficient. The damping part provides the viscous behavior of the contact interface, and the damping force is generated by the damper, which is determined by the critical damping ratio β in the normal and tangential directions. n and β s If the bond of the damping joint model is activated or the surface gap g s If it is a negative value, the damping joint model will take effect.

[0056] In another embodiment, the normal contact force and the tangential contact force are both divided into a linear part and a damping part, and the calculation formula is as follows:

[0057]

[0058] Where Fn With F s are the normal contact force and the tangential contact force, and are the normal force of the linear part and the tangential force of the linear part, and are the normal force of the damping part and the tangential force of the damping part, β n With β s are the normal damping coefficient and the tangential damping coefficient, v n and v s are the relative normal velocity and relative tangential velocity, m c is the equivalent mass of the contact, m1 and m2 are the masses of the two contacting entities, k n and k s are the normal stiffness and tangential stiffness respectively, and A is the joint contact area.

[0059] In this embodiment, according to different mechanical behavior characteristics, the force and displacement laws of the damped joint model are presented from the following three parts: linear bond model, linear non-bonded model, and damped model.

[0060] (1) Force and displacement laws for the linear bonding model

[0061] Before the forces exceed the tensile or shear strength limit, the force and displacement laws for linear bonds are linear elastic. If the damped joint model is bonded, the normal force criterion for the linear part is Figure 3 As shown, the calculation formula is as follows:

[0062]

[0063] The calculation formula of the linear part tangential force is expressed as:

[0064]

[0065] Where τ s is the tangential strength determined by the Mohr-Coulomb criterion.

[0066]

[0067] After bond fracture, the linear bond model is transformed into a linear unbonded model, and the normal and tangential forces are updated according to the force and displacement laws of the unbonded model.

[0068] (2) Force and displacement laws for linear unbonded models

[0069] The force and displacement laws for the linear unbonded model are linear elastic and frictional dilatant. If the damped joint model is unbonded, the normal force of the linear component is expressed as:

[0070]

[0071] The linear part tangential force calculation formula is as follows:

[0072]

[0073] In the formula Express the tangential force subject to the Mohr-Coulomb criterion:

[0074]

[0075] when Exceed When , the slip state is activated, the shear displacement causes the normal force to increase due to the expansion, and μ is the friction force.

[0076]

[0077] Where ψ is the expansion angle.

[0078] The force and displacement laws for the linear unbonded model are as follows: Figure 4 shown.

[0079] (3) Force and displacement laws of the damping model

[0080] The force-displacement law of the damping model is given according to the normal and shear critical damping ratios, such as Figure 5 The normal force and shear force of the damping model are expressed as:

[0081]

[0082] Where v n and v s are the relative normal velocity and tangential velocity, m c is the equivalent mass of the contact.

[0083]

[0084] Where m1 and m2 are the masses of the two contacting entities respectively;

[0085] The relative normal velocity and tangential velocity expressions are as follows:

[0086]

[0087] Where Δt is the time step calculated by the discrete element software, and U n and U s They represent the displacement increments in the normal and tangential directions respectively.

[0088] In another embodiment, the method further comprises: constructing a particle collision or shear model, assigning a damping joint model to a fixed particle, and verifying the effect of the damping joint model at the microscopic level by analyzing the relationship between the microscopic parameters of the damping joint model and the macroscopic mechanical properties when other particles collide or shear with the fixed particle;

[0089] In another embodiment, constructing the particle collision or shear model comprises:

[0090] Construct a collision between two spherical particles perpendicular to the damping joint direction and set the corresponding normal damping coefficient;

[0091] The ball particles are set to fall from a fixed height and hit the fixed ball particles. The rebound height is lower than the falling height, and the rebound speed is lower than the speed at the initial contact. The maximum contact force is smaller than the contact force of the smooth joint model, which proves that the damping model is effective and can reduce the energy in the normal direction of the particles.

[0092] The ball particles are set to move from a fixed distance to a fixed ball particle. The two balls come into contact. When the moving ball passes through the fixed ball, the corresponding normal damping coefficient is set and the speed decreases. This proves that the damping joint model is effective at this time and can reduce the energy in the tangential direction of the particle.

[0093] Specifically, in this embodiment, two discrete element spherical particles are constructed to collide vertically with each other in the direction of smooth joints. The ball falls from a certain height and hits the fixed spherical particles below, rebounding, and the collision time, contact force and speed change during the collision process are obtained, such as Figure 6 Similarly, two discrete element sphere particles are constructed to collide perpendicular to the damping joint direction, and the normal damping coefficient is set to 0.8. The results are shown in Figure 6 As shown in (b), Figure 6 It can be seen from the figure that the damper added in this embodiment is effective and usable.

[0094] When moving parallel to the joint direction, the ability of two particles to shift relative to each other without rotating around the particles is also crucial to the damped joint model. Fix one particle and give the other particle a speed of 1m / s parallel to the joint surface and the fixed particle. The two particles cover each other and slide relative to each other, and no movement around the particle surface occurs. At this time, the damped joint model is proven to be valid.

[0095] In another embodiment, the relationship between the microscopic parameters and macroscopic mechanical properties of the analyzed damping joint model includes:

[0096] By changing the values ​​of the normal damping coefficient and the tangential damping coefficient of the damping joint model to change the rebound speed of the spherical particles, the relationship between the normal damping coefficient, the tangential damping coefficient and the macroscopic restitution coefficient is obtained as follows:

[0097]

[0098]

[0099] Where R n is the normal restitution coefficient, R t is the tangential restitution coefficient, β n With β s are the normal and tangential damping coefficients, respectively.

[0100] Specifically, in this embodiment, the rebound height and rebound speed of the ball particles are changed by the damping coefficient. Figure 7 As shown in the figure, by changing the tangential damping coefficient, the tangential velocity of the particle is reduced. The relationship between the tangential collision recovery coefficient and the damping coefficient is as follows: Figure 8 shown.

[0101] In another embodiment, it also includes: constructing a discrete element joint rock model, wherein the discrete element joint rock model includes a damping joint model as a joint, simulating shear instability of rock at the joint under the action of gravity, and comparing and analyzing the difference between the rock shear force before and after using the damping joint model to verify the effect of the damping joint model at the macro level.

[0102] In another embodiment, constructing a discrete element jointed rock model comprises:

[0103] Construct a discrete element specimen consisting of a parallel bond contact model;

[0104] After the model is balanced, DFN joints (Discrete Fracture Network, a built-in joint method in discrete element software) are inserted into the discrete element specimen, and geometric parameters including length, width and inclination are assigned;

[0105] Assign the damping joint model to the DFN joint as the joint, and assign the damping joint micro parameters including the damping joint friction coefficient, damping coefficient, and joint stiffness;

[0106] Make DFN active (key command activate) to ensure that the subsequently generated contact is damped joint contact.

[0107] Specifically, in this embodiment, a discrete element rock sample is constructed according to the particle parameters and the parallel bond parameters. Parallel bond contact parameters. After the model is balanced, a DFN joint is inserted into the discrete element sample, and geometric parameters including length, width and inclination are assigned. The DFN joint is assigned its damping joint model. DFN is activated (key command activate) to ensure that the new contact generated subsequently is a damping joint contact.

[0108] The particle parameters include particle elastic modulus, stiffness ratio, particle density, minimum radius, and radius ratio. The parallel bonding parameters include parallel bonding contact elastic modulus, stiffness ratio, tensile strength, cohesion, and friction angle. The damped joint model parameters include joint normal stiffness, tangential stiffness, normal damping coefficient, tangential damping coefficient, tensile strength, cohesion, friction angle, and friction coefficient. The specific parameter values ​​are shown in Table 1.

[0109] Table 1 Parameter value table

[0110]

[0111]

[0112] In another embodiment, the simulated rock undergoes shear instability at the joints under the action of gravity, comprising:

[0113] Fix a row of particles at the bottom of the model to prevent the bottom rock from moving, then turn on gravity (key command gravity), set the gravity acceleration, the default direction of the gravity acceleration is the negative y direction, rebalance the model, start the calculation, the rock undergoes shear movement at the joints, and collect the shear force results.

[0114] In another embodiment, the comparative analysis of the difference between rock shear force before and after using the damping joint model includes:

[0115] The linear contact model replaces the damping joint model as the joint, and the linear contact parameters including the linear contact elastic modulus, stiffness ratio, and friction coefficient are set. Then, the shear instability of the rock at the joint under the action of gravity is simulated, and the shear motion of the rock at the joint is calculated. The shear force data of the entire model are obtained, and the shear force results when the damping joint model is used as the joint are compared and analyzed. The comparison results are shown in Fig. 9 As shown in Figure 2, the damping joint model can simulate the rock shear process well, and the shear process can produce a blocking effect without being affected by the particle stiffness. The specific values ​​of the linear contact (Linear-Bond) parameters are shown in Table 2.

[0116] Table 2 Linear parameter value table

[0117] Linear parameters Elastic modulus 20 GPa Stiffness ratio 2.0 Friction coefficient 0.2

[0118] After verifying the effect of the damping joint model at the micro and macro levels, if the effect does not meet expectations, the damping joint model will be reconstructed.

[0119] The above-mentioned embodiments only express the specific implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the protection scope of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A damping joint modeling method based on an improved PFC built-in model, characterized in that: include: On the basis of the smooth joint model, a normal damper parallel to the normal contact force direction and a tangential damper parallel to the tangential contact force direction are added as a damping joint model; The normal contact force and tangential contact force of the damped joint model are divided into a linear part and a damping part. The linear part is exactly the same as the smooth joint model part. The damping part provides the viscous behavior of the contact interface. The damping force of the damping part is generated by the damper and calculated by the critical damping ratio of the normal and tangential directions. The damping joint model is active if its bond is activated or the surface gap is negative.

2. The damping joint modeling method based on the improved PFC built-in model according to claim 1 is characterized in that: The calculation formulas of the normal contact force and the tangential contact force are divided into the linear part and the damping part as follows: Where F n With F s are the normal contact force and the tangential contact force, and are the normal force of the linear part and the tangential force of the linear part, and are the normal force of the damping part and the tangential force of the damping part, β n With β s are the normal damping coefficient and the tangential damping coefficient, v n and v s are the relative normal velocity and relative tangential velocity, m c is the equivalent mass of the contact, m1 and m2 are the masses of the two contacting entities, k n and k s are the normal stiffness and tangential stiffness respectively, and A is the joint contact area.

3. The damping joint modeling method based on the improved PFC built-in model according to claim 1 is characterized in that: Also includes: A particle collision or shear model is constructed, and a damping joint model is assigned to the fixed particles. When other particles collide or shear with the fixed particles, the effect of the damping joint model at the microscopic level is verified by analyzing the relationship between the microscopic parameters of the damping joint model and the macroscopic mechanical properties.

4. The damping joint modeling method based on the improved PFC built-in model according to claim 3 is characterized in that: The constructing of the particle collision or shear model comprises: Construct a collision between two spherical particles perpendicular to the damping joint direction and set the corresponding normal damping coefficient; The ball particles are set to fall from a fixed height and hit the fixed ball particles. The rebound height is lower than the falling height, and the rebound speed is lower than the speed at the initial contact. The maximum contact force is smaller than the contact force of the smooth joint model, which proves that the damping model is effective and can reduce the energy in the normal direction of the particles. The ball particles are set to move from a fixed distance to a fixed ball particle. The two balls come into contact. When the moving ball passes through the fixed ball, the corresponding normal damping coefficient is set and the speed decreases. This proves that the damping joint model is effective at this time and can reduce the energy in the tangential direction of the particle.

5. A damping joint modeling method based on an improved PFC built-in model according to any one of claims 3-4, characterized in that: The relationship between the microscopic parameters and macroscopic mechanical properties of the analytical damping joint model includes: By changing the values ​​of the normal damping coefficient and the tangential damping coefficient of the damping joint model to change the rebound speed of the spherical particles, the relationship between the normal damping coefficient, the tangential damping coefficient and the macroscopic restitution coefficient is obtained as follows: Where R n is the normal restitution coefficient, R t is the tangential restitution coefficient, β n With β s are the normal and tangential damping coefficients, respectively.

6. The damping joint modeling method based on the improved PFC built-in model according to claim 1 is characterized in that: Also includes: A discrete element joint rock model is constructed, wherein the discrete element joint rock model includes a damping joint model as a joint, simulating shear instability of rock at the joint under the action of gravity, and a comparative analysis of the difference between the rock shear force before and after using the damping joint model is performed to verify the effect of the damping joint model at the macro level.

7. The damping joint modeling method based on the improved PFC built-in model according to claim 6 is characterized in that: The construction of the discrete element joint rock model comprises: Construct a discrete element specimen consisting of a parallel bond contact model; After the model is balanced, DFN joints are inserted into the discrete element specimens and given geometric parameters including length, width and inclination; Assign the damping joint model to the DFN joint as the joint, and assign the damping joint micro parameters including the damping joint friction coefficient, damping coefficient, and joint stiffness; Make DFN active to ensure that the subsequently generated contact is damped joint contact.

8. The damping joint modeling method based on the improved PFC built-in model according to claim 6 is characterized in that: The simulated rock undergoes shear instability at the joints under the action of gravity, including: Fix a row of particles at the bottom of the model to prevent the bottom rock from moving, then turn on gravity and set the gravity acceleration. The default direction of the gravity acceleration is the negative y direction. Rebalance the model and start the calculation. The rock undergoes shear movement at the joints and collects the shear force results.

9. A damping joint modeling method based on an improved PFC built-in model according to any one of claims 6 to 8, characterized in that: The comparative analysis of the differences between rock shear stress before and after using the damping joint model includes: The linear contact model replaces the damping joint model as the joint, and the linear contact parameters including the linear contact elastic modulus, stiffness ratio, and friction coefficient are set. The shear instability of the rock at the joint under the action of gravity is simulated, the shear motion of the rock at the joint is calculated, and the shear force data of the entire model are obtained. The shear force results when the damping joint model is used as the joint are compared and analyzed.

10. The damping joint modeling method based on the improved PFC built-in model according to claim 1 is characterized in that: It also includes verifying the effect of the damping joint model at the micro and macro levels. If the effect does not meet expectations, the damping joint model will be rebuilt.

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