Near-field dynamics simulation method and system for tunnel rockfall impact protection

Abstract

The invention is suitable for the technical field of civil engineering, and relates to a near-field dynamics simulation method and system for tunnel rockfall impact protection, and the simulation method comprises the steps: determining a constitutive model and a micro-elastic modulus of a buffer layer material; establishing a falling rock impact near-field kinetic model of the buffer layer protection tunnel; setting rockfall impact conditions; performing near-field force theoretical calculation, and calculating impact force according to a key-based near-field dynamics theory; correcting the position of the tunnel material point; and evaluating the buffer effect of the buffer layer material to guide the construction design. The simulation system comprises a material parameter input module, a model construction module, an impact parameter input module, a near-field force calculation module, a collision detection and position correction module, a buffer effect evaluation module and a data storage and output module, and is used for storing simulation process data and visually outputting a result. The method is simple in process and convenient to operate, and the convenience of the buffer layer protection tunnel rockfall impact near-field dynamics simulation process and the accuracy of the simulation result are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of civil engineering, and particularly relates to a near-field dynamics simulation method for tunnel rockfall impact protection. BACKGROUND

[0002] A large number of tunnels in China are constructed in mountainous areas, and rockfall disasters are frequent disasters in mountainous areas, which seriously threaten traffic facilities and the safety of people and vehicles. Tunnel portal sections under steep and high slopes in dangerous mountainous areas are often provided with reinforced concrete shed tunnel structures with overlying buffer layers for rockfall protection. The protective shed tunnel with an overlying buffer layer has the characteristics of excellent energy absorption, rebound and impact resistance compared with the reinforced concrete shed tunnel. When designing the structure, the impact resistance of the shed tunnel with an overlying buffer layer of different materials and different thicknesses needs to be evaluated to guide the design of the buffer layer thickness and structural parameters. Considering that the cost of making a physical model test to explore the impact resistance is too high and the experimental process is relatively dangerous, it is of great engineering significance to develop a computer numerical simulation method and software suitable for the rockfall impact resistance of the shed tunnel.

[0003] At present, the simulation of rockfall impact is mostly based on the finite element method, such as Anasys and Aabaqus software. However, the finite element method is based on the classical continuum theory, and there are singularity problems in the solution of discontinuous places. Although the extended finite element method developed later makes further disposal of the problem, it needs to continuously divide the grid to simulate the generation, expansion and evolution of cracks, thereby affecting the efficiency of the simulation process. The near-field dynamics theory is based on the idea of non-local action, and can simulate the random generation, expansion and evolution of cracks, and has natural advantages in the simulation of impact damage of structures. Developing an overlying buffer layer shed tunnel rockfall impact resistance method based on the near-field dynamics theory is of great significance to improve the ability of evaluating the rockfall impact resistance of the shed tunnel and designing the buffer layer structure. Patent application No. CN114996826A provides a rockfall impact open tunnel structure response force calculation method, which comprises the following steps: determining a plurality of rockfall impact force response value influencing factors of the open tunnel structure, and adopting an orthogonal simulation test method to perform a multi-factor level orthogonal simulation experiment; according to the results of the simulation experiment, the average value of the index of a single influencing factor at each level is obtained through curve estimation theory, and each influencing factor is curve fitted; according to the average value of the index of each influencing factor at each level and the curve fitting result of each influencing factor, a calculation model of the rockfall impact response force of the open tunnel is constructed. Although this patent application considers multiple rockfall impact force influencing factors and adopts a multi-element nonlinear regression method to establish an impact response force calculation model, the method uses a soil layer to act on the buffer layer, and the model is constructed based on the multi-factor level orthogonal simulation experiment and the curve fitting method, which has the disadvantages of poor buffer layer rebound effect and complex model construction.

[0004] Therefore, how to provide a tunnel rockfall impact protection near-field dynamics simulation method with convenient simulation process and high simulation accuracy is an urgent problem for people in the technical field. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a tunnel rockfall impact protection near-field dynamics simulation method to solve the problems of inconvenient near-field dynamics simulation process and low simulation accuracy in the prior art.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] In the first aspect, the present application provides a tunnel rockfall impact protection near-field dynamics simulation method, comprising the following steps:

[0008] S10, determining the constitutive model and micro-elastic modulus of the buffer layer material;

[0009] S20, establishing a buffer layer protection tunnel rockfall impact near-field dynamics model;

[0010] S30, setting rockfall impact conditions;

[0011] S40, near-field force theory calculation, and calculating impact force according to bond-based near-field dynamics theory;

[0012] S50, correcting the position of the tunnel material point;

[0013] S60, evaluating the buffer effect of the buffer layer material to guide construction design.

[0014] Further, in the step S10, the MTS universal testing machine is used to carry out uniaxial compression test of the buffer layer material, and the stress-strain relationship of the buffer layer material is obtained, so as to calculate the density expression of the buffer layer material in the elastic stage, the platform stage and the dense stage, and according to the basic theory of two-dimensional bond-based near-field dynamics, the expression of the micro-elastic modulus c is determined:

[0015]

[0016] Wherein, ξ is the relative position between two material points, δ is the near-field range radius of the material point, and E is the elastic modulus of the material;

[0017] According to the definition of near-field dynamics relative elongation, the macroscopic strain concept in classical mechanics theory is replaced, so as to determine the constitutive model of bond force-bond elongation suitable for the buffer layer material.

[0018] Further, in the step S40, a model material point motion equation is established, x represents a currently calculated material point, x' is any point in the near field domain of the material point x, the interaction force between the two material points is transmitted through the bond, and the motion equation of the material point is obtained according to Newton's second law:

[0019]

[0020] wherein f is the bond force between the points x and x', the bond force size is related to the constitutive property of the material itself, t is time, p is material density, and u is displacement, is the acceleration of the point x at time t, b(x, t) is the external force density suffered by the material point, Hx is the near field domain with a selected space radius of d, H = H(x, d), d represents the near field domain radius, and d > 0, V x′ represents the volume formed by all points in the near field domain, and the bond lengths between x and x' before and after deformation are d and d + h respectively.

[0021] According to the basic theory of bond-based near field dynamics, the motion equation of the material point at time t is:

[0022]

[0023] wherein s( d) is the elongation of the bond, which is the ratio of the difference between the bond lengths before and after deformation to the bond length before deformation, and m is a scalar function for judging whether the bond body is broken or not and whether the bond force exists or not.

[0024] Further, the expression of s( d) is as follows:

[0025]

[0026] The expression of m is as follows:

[0027]

[0028] wherein s0 is the critical elongation of the bond body, for the quasi-static failure of concrete or steel, both tensile damage and compressive damage modes are considered, and the expression is as follows:

[0029]

[0030] Herein s0 is related to the calculation of the same material bond and the different material bond, and the method is as follows: when the materials at both ends of the bond body are the same, the bond is judged as the same material bond and is determined by the critical elongation of the material; when the materials at both ends of the bond body are different, the bond is judged as the different material bond and is determined by the critical elongations of the materials at both ends.

[0031] Further, in the step S40, the expression of the impact force is:

[0032]

[0033] Where d is the minimum distance between material points, calculated using the following formula:

[0034] d = min{0.9|x j -x i |,1.35△x}.

[0035] Furthermore, in step S50, based on the vector from the center of mass of the falling rock to the material point in the tunnel, and the vector product of the material point in the tunnel and the normal direction vector of the tunnel surface, it is determined whether the falling rock has impacted the material point in the tunnel. If an impact has occurred, and to ensure that the two material points do not penetrate each other, the position of the material point in the tunnel at this time is corrected.

[0036] Furthermore, in step S60, the resultant force f of the impact force on the upper surface of the buffer layer is extracted. u That is, the resultant force f of the incident impact force without the buffer layer and the impact force on the lower surface of the buffer layer. d The ratio of the projected impact force after passing through the buffer layer to the applied impact force is used as an evaluation index for the buffering effect of the buffer layer material, thereby guiding construction design. The formula is as follows:

[0037]

[0038] Furthermore, in step S20, the buffer layer is laid above the arched tunnel with a certain thickness, and the material points are discrete at a certain interval Δx, and different material properties are assigned to the material points, including the buffer layer material, concrete and steel reinforcement.

[0039] Furthermore, in step S30, the rockfall impact conditions include the shape, geometric dimensions, mass, initial velocity, and initial center of gravity position of the rockfall.

[0040] On the other hand, the present invention also provides a near-field dynamics simulation system for tunnel rockfall impact protection, comprising:

[0041] The material parameter input module is used to determine the constitutive model and microelastic modulus of the buffer layer material. It inputs the stress-strain expression of the buffer layer material to determine its microelastic modulus and peri-field dynamic bond force-bond length constitutive model. The model construction module is used to establish a peri-field dynamic model of rockfall impact in the buffer layer protected tunnel. It inputs geometric parameters (discrete spacing, tunnel dimensions, etc.) and physical parameters (density, elastic modulus, etc.), discretizes the model, assigns corresponding properties, and generates a peri-field dynamic model containing multiple material properties. The impact parameter input module is used to configure the impact conditions of the rockfall. It allows input or selection of parameters such as the shape, geometric dimensions, mass, initial velocity, and initial center of gravity position of the rockfall, forming a standardized impact condition dataset to provide input for simulation calculations. The peri-field force calculation module is used for peri-field dynamics theory calculations of the impact. The system establishes the motion equations of the material points and solves for the acceleration of the material points in the near-field region based on Newton's second law and the characteristics of bond force transmission. It introduces the bond elongation s and critical elongation judgment function to calculate the magnitude of the bond force and the fracture state. Combining the calculation formula for the minimum distance d between material points, the impact force expression is modified to prevent material points from penetrating each other. A collision detection and position correction module is used to detect the impact state of falling rocks and tunnels and correct the positions of the material points. The system detects whether an impact has occurred by calculating the vector from the center of mass of the falling rock to the material point in the tunnel, and the vector product of the material point in the tunnel and the normal direction vector of the surface. If an impact occurs, the position of the material point in the tunnel is corrected in real time based on the principle of non-penetration. A buffer effect evaluation module is used to evaluate the buffer performance of the buffer layer material and generate construction design suggestions. The system extracts the resultant force f of the incident impact force on the upper surface of the buffer layer. u and the resultant force f of the impact force projected onto the lower surface d The system calculates the ratio of the two parameters as an evaluation index for the buffering effect; based on the evaluation results, it generates optimization suggestions for parameters such as buffer layer thickness and material properties to guide construction design; the data storage and output module is used to store simulation process data and visualize the output results. The system stores intermediate data during the simulation process (such as material point coordinates, stress-strain values, impact force curves, etc.) and outputs the results in the form of visual charts (such as model schematic diagrams, impact force time history curves, buffering effect comparison charts) and numerical reports. The material parameter input module, model construction module, impact parameter input module, near-field force calculation module, collision detection and position correction module, buffering effect evaluation module, and data storage and output module are sequentially connected in communication.

[0042] Compared with existing technologies, the near-field dynamics simulation method and system for tunnel rockfall impact protection provided by this invention have at least the following advantages:

[0043] Currently, most simulations of rockfall impacts are based on the finite element method (FEM), such as Anasys and Aabaqus software. However, the FEM method, based on classical continuum theory, suffers from singularity issues when solving for discontinuities. While the extended finite element method (EPF) addresses this problem further, simulating cracks requires continuous meshing, thus reducing simulation efficiency. This invention features a simple structure and convenient operation. It employs a buffer layer as a rockfall protection structure in tunnels and solves the entire process, from obtaining the mechanical properties of the buffer layer to the conceptual conversion related to near-field dynamics calculations, facilitating direct calculation of near-field forces and improving process convenience. Furthermore, it proposes a near-field dynamics simulation method for rockfall impacts, allowing for the customization of the rockfall's shape, geometry, mass, initial velocity, and initial center of gravity position. This method enables the simulation of structural damage evolution, crack propagation, and buffering effect evaluation, improving the accuracy of near-field dynamics simulations and providing valuable guidance for structural design. Attached Figure Description

[0044] To more clearly illustrate the solution of the present invention, a brief introduction will be given to the drawings used in the description of the embodiments below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 A flowchart of a near-field dynamics simulation method for rockfall impact protection in tunnels, provided by an embodiment of the present invention;

[0046] Figure 2 The stress-strain curve of the buffer layer material in a near-field dynamic simulation method for rockfall impact protection in tunnels provided in this embodiment of the invention;

[0047] Figure 3 This is a schematic diagram of the near-field dynamics model of a buffer layer protecting against rockfall impact in a near-field dynamics simulation method for tunnel rockfall impact provided in an embodiment of the present invention.

[0048] Figure 4 A schematic diagram of the near-field dynamics model of a buffer layer protected against rockfall impact in a tunnel according to a near-field dynamics simulation method for rockfall impact protection provided in an embodiment of the present invention, when the rockfall impact is centered on the buffer layer.

[0049] Figure 5 A schematic diagram of the near-field dynamics model of rockfall impact protection in a tunnel with buffer layer protection when the rockfall falls at 2 / 3 of its length, as provided in the near-field dynamics simulation method for rockfall impact protection in a tunnel according to an embodiment of the present invention.

[0050] Figure 6 This is a framework diagram of a near-field dynamics simulation system for tunnel rockfall impact protection provided in an embodiment of the present invention. Detailed Implementation

[0051] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0053] This invention provides a near-field dynamics simulation method for tunnel rockfall impact protection, applied to the design of reinforced concrete tunnel structures with a buffer layer at the tunnel entrance. The near-field dynamics simulation method for tunnel rockfall impact protection includes the following steps:

[0054] S10. Determine the constitutive model and microelastic modulus of the buffer layer material; S20. Establish a near-field dynamic model of rockfall impact in the tunnel protected by the buffer layer; S30. Set the rockfall impact conditions; S40. Calculate the near-field force theoretically and calculate the impact force based on the bond-based near-field dynamic theory; S50. Correct the position of the material points in the tunnel; S60. Evaluate the buffering effect of the buffer layer material to guide the construction design.

[0055] This invention features a simple process and convenient operation, improving the convenience and accuracy of near-field dynamics simulation of rockfall impacts in tunnels protected by buffer layers.

[0056] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0057] This invention provides a near-field dynamics simulation method for rockfall impact protection in tunnels, applied to the design of reinforced concrete tunnel structures with a buffer layer at the tunnel entrance, combined with... Figures 1 to 5 In this embodiment, the near-field dynamics simulation method for tunnel rockfall impact protection includes the following steps:

[0058] S10. Determine the constitutive model and microelastic modulus of the buffer layer material.

[0059] Specifically, in this embodiment, an MTS universal testing machine is used to conduct uniaxial compression tests on the buffer layer material to obtain the stress-strain relationship of the buffer layer material. This allows for the derivation of the density expressions for the buffer layer material in the elastic, plateau, and compaction stages. Furthermore, based on the fundamental theory of two-dimensional bond-based near-field dynamics, the expression for the micro-elastic modulus c is determined.

[0060]

[0061] Where ξ is the relative position between the two material points, δ is the near-field radius of the material point, and E is the elastic modulus of the material.

[0062] Furthermore, in this embodiment, based on the definition of near-field dynamic relative elongation s, it is equivalently replaced by the macroscopic strain concept in classical mechanics, thereby determining the constitutive model of near-field dynamic bond force-bond elongation applicable to the buffer layer material, which facilitates near-field force calculation. The formula is as follows:

[0063]

[0064] Where ξ is the relative position between the two material points, and η is the relative displacement between the two material points.

[0065] S20. Establish a near-field dynamic model of rockfall impact in the buffer layer protection tunnel.

[0066] Specifically, in this embodiment, a buffer layer of a certain thickness is laid above the arched tunnel, and material points are discrete at a certain interval Δx, and different material properties (such as density, elastic modulus, critical elongation, etc.) are assigned to the material points, including buffer layer material, concrete and steel reinforcement.

[0067] S30, Set the conditions for rockfall impact.

[0068] Specifically, in this embodiment, the rockfall impact conditions include the shape, geometric dimensions (penrad), mass (penmass), initial velocity (penvx, penvy), and initial center of gravity position (penicx, pennicy) of the rockfall.

[0069] S40, near-field force theory calculation, and impact force calculation based on bond group near-field dynamics theory.

[0070] Specifically, in this embodiment, the equation of motion for the model material point is established, where x represents the currently calculated material point, and x′ is any particle within the near-field region of material point x. The interaction force between the two material points is transmitted through bonds. According to Newton's second law, the equation of motion for the material point is:

[0071]

[0072] Where f is the bond force between particles x and x′, the magnitude of which is related to the constitutive properties of the material itself, describing the interaction force state between x and x′, t is time, ρ is the material density, and u is the displacement. Let V be the acceleration of particle x at time t, b(x,t) be the external force density acting on the particle, Hx be the near-field region with a selected spatial radius δ, H = H(x,δ), where δ represents the radius of the near-field region and δ > 0, V x′ Let x represent the volume formed by all particles in the near-field region, and let ξ and ξ+η be the bond lengths between x and x′ before and after deformation, respectively.

[0073] According to the basic theory of near-field dynamics of bond groups, the equation of motion of the matter point at time t is:

[0074]

[0075] Where s(ξ) is the bond elongation, which is the ratio of the bond length difference before and after deformation to the bond length before deformation. The expression for s(ξ) is as follows:

[0076]

[0077] μ is a scalar function that determines whether a bond has broken and whether bond forces exist. The expression for μ is as follows:

[0078]

[0079] Where s0 is the critical elongation of the bond, for quasi-static failure of concrete or steel (i.e., s˙ < 10-3s-1), both tensile and compressive damage modes are considered, and the expression is as follows:

[0080]

[0081] Here, s0 involves the calculation of bonds of the same substance and bonds of different substances. The method is as follows: when the substances at both ends of the bond are the same, the bond is determined to be a bond of the same substance, which is determined by the critical elongation of the substance; when the substances at both ends of the bond are different, the bond is determined to be a bond of different substances, which is determined by the critical elongation of the substances at both ends.

[0082] Furthermore, in this embodiment, the impact force is calculated based on the bond-based near-field dynamics theory. However, since the two material points in the house penetrate each other, the short-range repulsive force should be considered. Therefore, the expression for the impact force is:

[0083]

[0084] Where d is the minimum distance between material points, calculated using the following formula:

[0085] d = min{0.9|x j -xi |,1.35△x}.

[0086] S50, Correct the location of the material point in the tunnel.

[0087] Specifically, in this embodiment, based on the vector from the center of mass of the falling rock to the material point in the tunnel, and the vector product of the material point in the tunnel and the normal direction vector of the tunnel surface, it is determined whether the falling rock has impacted the material point in the tunnel. If an impact has occurred and it is necessary to ensure that the two material points do not penetrate each other, the position of the material point in the tunnel at this time is corrected.

[0088] S60. Evaluate the buffering effect of the buffer layer material to guide the construction design.

[0089] Specifically, in this embodiment, the resultant force f of the impact force on the upper surface of the buffer layer is extracted. u That is, the resultant force f of the incident impact force without the buffer layer and the impact force on the lower surface of the buffer layer. d The ratio of the projected impact force after passing through the buffer layer to the applied impact force is used as an evaluation index for the buffering effect of the buffer layer material, thereby guiding construction design. The formula is as follows:

[0090]

[0091] This invention also provides a near-field dynamics simulation system for tunnel rockfall impact protection, such as... Figure 6As shown, in this embodiment, the near-field dynamics simulation system for tunnel rockfall impact protection includes: a material parameter input module, used to determine the constitutive model and microelastic modulus of the buffer layer material, inputting the stress-strain expression of the buffer layer material to determine its microelastic modulus and near-field dynamic bond force-bond length constitutive model; a model construction module, used to establish a near-field dynamics model of rockfall impact in the buffer layer protected tunnel, inputting geometric parameters (discrete spacing, tunnel size, etc.) and physical parameters (density, elastic modulus, etc.), discretizing the model and assigning corresponding properties to generate a near-field dynamics model containing multiple material properties; an impact parameter input module, used to configure the impact conditions of the rockfall, allowing input or selection of parameters such as the shape, geometric dimensions, mass, initial velocity, and initial center of gravity position of the rockfall, forming a standardized impact condition dataset to provide input basis for simulation calculation; and near-field force calculation. The system employs several modules for near-field dynamics theory to calculate impact forces. The system establishes the motion equations of the material points and, based on Newton's second law and bond force transmission characteristics, solves for the acceleration of the material points in the near-field domain. It introduces the bond elongation s and critical elongation judgment function to calculate the bond force magnitude and fracture state. Combining the calculation formula for the minimum distance d between material points, the impact force expression is modified to prevent material points from penetrating each other. The collision detection and position correction module detects the impact state of falling rocks and tunnels and corrects the positions of the material points. The system detects whether an impact has occurred by calculating the vector from the center of mass of the falling rock to the material point in the tunnel, and the vector product of the material point in the tunnel and the normal direction vector of the surface. If an impact occurs, the position of the material point in the tunnel is corrected in real time based on the non-penetration principle. The buffer effect evaluation module assesses the buffer performance of the buffer layer material and generates construction design suggestions. The system extracts the resultant force f of the incident impact force on the upper surface of the buffer layer. u and the resultant force f of the impact force projected onto the lower surface d The system calculates the ratio of the two parameters as an evaluation index for the buffering effect; based on the evaluation results, it generates optimization suggestions for parameters such as buffer layer thickness and material properties to guide construction design; the data storage and output module is used to store simulation process data and visualize the output results. The system stores intermediate data during the simulation process (such as material point coordinates, stress-strain values, impact force curves, etc.) and outputs the results in the form of visual charts (such as model schematic diagrams, impact force time history curves, buffering effect comparison charts) and numerical reports. The material parameter input module, model construction module, impact parameter input module, near-field force calculation module, collision detection and position correction module, buffering effect evaluation module, and data storage and output module are sequentially connected in communication.

[0092] The near-field dynamics simulation method for tunnel rockfall impact protection described in the above embodiments differs from existing technologies. Current rockfall impact simulations are mostly based on the finite element method (FEM), such as Anasys and Aabaqus software. However, the FEM method, based on classical continuous medium theory, suffers from singularity issues at discontinuities. While the extended finite element method addresses this issue, it still requires continuous meshing for crack simulation, thus reducing simulation efficiency. This invention offers a simple and convenient process. It uses a buffer layer as the tunnel rockfall protection structure and solves the entire process, from obtaining the mechanical properties of the buffer layer to the conceptual conversion related to near-field dynamics calculations, facilitating direct calculation of near-field forces and improving process convenience. The proposed near-field dynamics simulation method for rockfall impact includes customizing the rockfall's shape, geometry, mass, initial velocity, and initial center of gravity position to perform structural damage evolution, crack propagation, and buffer effect evaluation, improving the accuracy of near-field dynamics simulation and providing further guidance for structural design.

[0093] Obviously, the embodiments described above are merely preferred embodiments of the present invention, and not all embodiments. The accompanying drawings illustrate preferred embodiments of the present invention, but do not limit the scope of the patent. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the scope of patent protection of this invention.

Claims

1. A near-field dynamic simulation method for rockfall impact protection in tunnels, characterized in that, Includes the following steps: S10. Determine the constitutive model and microelastic modulus of the buffer layer material; S20. Establish a near-field dynamic model of rockfall impact in a buffer layer protected tunnel; S30. Set the conditions for rockfall impact; S40, near-field force theory calculation, and impact force calculation based on bond group near-field dynamics theory; S50. Correct the location of the material point in the tunnel; S60. Evaluate the buffering effect of the buffer layer material to guide the construction design.

2. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S10, a uniaxial compression test of the buffer layer material is conducted using an MTS universal testing machine to obtain the stress-strain relationship of the buffer layer material. This allows for the derivation of the density expressions for the buffer layer material in the elastic, plateau, and compaction stages. Furthermore, based on the fundamental theory of two-dimensional bond-based near-field dynamics, the expression for the micro-elastic modulus c is determined. Where ξ is the relative position between the two material points, δ is the near-field radius of the material point, and E is the elastic modulus of the material. Based on the definition of relative elongation in near-field dynamics, and by equivalent substitution with the macroscopic strain concept in classical mechanics, a constitutive model for near-field dynamic bond force-bond elongation applicable to buffer layer materials is determined.

3. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S40, the equations of motion for the model material points are established, where x represents the currently calculated material point, and x′ is any particle within the near-field region of material point x. The interaction force between the two material points is transmitted through bonds. According to Newton's second law, the equations of motion for the material points are: Where f is the bond force between particles x and x′, the magnitude of which is related to the constitutive properties of the material itself, t is time, ρ is the material density, and u is displacement. Let H be the acceleration of particle x at time t, b(x,t) be the density of the external force acting on the particle, and H be the acceleration of particle x at time t. x For a near-field region with a selected spatial radius of δ, H = H(x,δ), where δ represents the radius of the near-field region and δ > 0, V x′ The volume represents the volume formed by all particles in the near field, and the bond lengths between x and x′ before and after deformation are ξ and ξ+η, respectively. According to the basic theory of near-field dynamics of bond groups, the equation of motion of the matter point at time t is: Where s(ξ) is the bond elongation, which is the ratio of the bond length difference before and after deformation to the bond length before deformation, and μ is a scalar function for judging whether the bond is broken and whether the bond force exists.

4. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, The expression for s(ξ) is as follows: The expression for μ is as follows: Where s0 is the critical elongation of the bond. For quasi-static failure of concrete or steel, both tensile and compressive damage modes are considered, and the expression is as follows: Here, s0 involves the calculation of bonds of the same substance and bonds of different substances. The method is as follows: when the substances at both ends of the bond are the same, the bond is determined to be a bond of the same substance, which is determined by the critical elongation of the substance; when the substances at both ends of the bond are different, the bond is determined to be a bond of different substances, which is determined by the critical elongation of the substances at both ends.

5. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 4, characterized in that, In step S40, the expression for the impact force is: Where d is the minimum distance between material points, calculated using the following formula: d=min{0.9|x j -x i |,1.35△x}。 6. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S50, based on the vector from the center of mass of the falling rock to the material point in the tunnel, and the vector product of the material point in the tunnel and the normal vector of the tunnel surface, it is determined whether the falling rock has impacted the material point in the tunnel. If an impact has occurred, and to ensure that the two material points do not penetrate each other, the position of the material point in the tunnel at this time is corrected.

7. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S60, the resultant force f of the impact force on the upper surface of the buffer layer is extracted. u That is, the resultant force f of the incident impact force without the buffer layer and the impact force on the lower surface of the buffer layer. d The ratio of the projected impact force after passing through the buffer layer to the applied impact force is used as an evaluation index for the buffering effect of the buffer layer material, thereby guiding construction design. The formula is as follows:

8. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S20, a buffer layer of a certain thickness is laid above the arched tunnel, and material points are discrete at a certain interval Δx, giving the material points different material properties, including buffer layer material, concrete, and steel reinforcement.

9. The near-field dynamics simulation method for tunnel rockfall impact protection according to claim 1, characterized in that, In step S30, the rockfall impact conditions include the shape, geometric dimensions, mass, initial velocity, and initial center of gravity position of the rockfall.

10. A near-field dynamic simulation method for rockfall impact protection in tunnels, characterized in that, include: The material parameter input module is used to determine the constitutive model and microelastic modulus of the buffer layer material; The model building module is used to establish a near-field dynamic model of rockfall impact in a buffer layer protected tunnel. The impact parameter input module is used to configure the impact conditions of falling rocks; The near-field force calculation module is used to calculate impact force based on near-field dynamics theory. The collision detection and position correction module is used to detect the impact of falling rocks and tunnels and correct the position of the material points. The buffering effect evaluation module is used to assess the buffering performance of buffer layer materials and generate construction design suggestions; The data storage and output module is used to store simulation process data and visualize the output results; The material parameter input module, model construction module, impact parameter input module, near-field force calculation module, collision detection and position correction module, buffer effect evaluation module, and data storage and output module are sequentially connected in communication.

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