A simulation method for combined support of anchor bolts, trays, and metal mesh

Abstract

This invention relates to a simulation method for combined support using anchor bolts, pallets, and metal mesh, belonging to the field of numerical simulation of roadway support. The method includes creating a geometric model of the roadway and surrounding rock in FLAC3D and meshing it; setting necessary calculation entries; automatically calculating to equilibrium; excavating the roadway; installing cable structural elements inside the left and right sides and roof of the roadway to simulate anchor bolts; installing pile structural elements on the surfaces of the left and right sides and roof of the roadway to simulate metal mesh; installing shell structural elements at the outer end nodes of each cable structural element to simulate pallets; establishing connections between structural elements; applying axial tension to the outer end nodes of the cable structural elements to simulate preload; assigning material parameters to the structural elements; and automatically calculating to equilibrium again. This invention overcomes the limitation of using only cable structural elements to simulate combined support using anchor bolts, pallets, and metal mesh, and can be used to study the influence of the coordination relationship between anchor bolts, pallets, and metal mesh on the control of the surrounding rock in roadways.

Description

Technical Field

[0001] This invention belongs to the field of numerical simulation of tunnel support, specifically involving a simulation method for combined support of anchor bolts, trays, and metal mesh. Background Technology

[0002] Tunnel support is a crucial production step in underground coal mining. During underground coal mining, tunnels are supported to prevent significant deformation of the surrounding rock, thus meeting the needs of main and auxiliary transportation, ventilation, and other underground processes. Among various tunnel support methods, bolt support plays a vital role. Compared to lining and scaffolding, bolt support can penetrate deep into the rock mass, forming a unified whole with the surrounding rock to coordinate deformation and control the deformation of the tunnel's surrounding rock. Furthermore, bolt support requires less construction work and can be installed quickly, significantly reducing the labor intensity of underground workers. Therefore, bolt support is widely used in underground coal mining.

[0003] In early bolt support systems, workers simply pushed the bolt into the borehole in the surrounding rock of the roadway and used mechanical anchor heads and chemical anchoring agents to connect the bolt to the surrounding rock. Subsequently, bolt support technology developed rapidly, and workers began to install trays on the outer ends of the bolts to restrain the deformation of the surrounding rock. In addition, based on the trays, workers could easily apply preload to the bolts, thereby actively restraining the deformation of the surrounding rock.

[0004] Engineering practice has shown that using only anchor bolts and support plates for roadway surrounding rock support is still insufficient to meet the requirements for roadway surrounding rock control under certain special geological conditions, especially in situations where the surrounding rock is loose and fractured and prone to roof collapse. To address this issue, construction workers first laid a metal mesh on the surface of the roadway surrounding rock; then, anchor bolts were inserted into the surrounding rock through the metal mesh; finally, support plates were installed at the outer ends of the anchor bolts, preload was applied, and nuts were tightened, thus forming a combined support system consisting of anchor bolts, support plates, and metal mesh.

[0005] Practical application results show that the combined support system consisting of anchor bolts, support plates, and metal mesh can effectively control the deformation of the surrounding rock in the roadway. This is due to the following three reasons: First, the anchor bolts can penetrate into the interior of the roadway's surrounding rock and form a unified whole with it, coordinating deformation together; second, installing support plates helps to constrain the deformation of the surrounding rock near the outer end of the anchor bolts and applies preload based on the support plates, thereby assisting the installed anchor bolts in actively constraining the deformation of the internal roadway's surrounding rock; finally, the metal mesh is tightly bound to the surface of the roadway's surrounding rock by the support plates, preventing loose and broken rocks from tumbling down and creating a net-like effect on the roadway's surrounding rock.

[0006] Numerical simulation has been widely used by researchers and engineers to study the principles of tunnel support. Users can easily set various working conditions and, through parameter adjustment, study the mechanical relationship between support elements and the surrounding rock under different working conditions, thereby helping users quickly grasp the mechanical mechanism of support elements.

[0007] Among various numerical simulation methods, FLAC3D, developed by Itasca, is characterized by its ease of use, concise commands, and powerful functionality. FLAC3D incorporates cable structural elements. Users can utilize these cable structural elements to simulate anchor bolts and reinforce the surrounding rock of tunnels.

[0008] To date, few studies have used FLAC3D to simulate combined support systems consisting of anchor bolts, pallets, and metal mesh. When dealing with combined support systems using these components, users often overlook the pallets and metal mesh. This is because FLAC3D does not have dedicated pallet and metal mesh support elements. Therefore, users cannot directly simulate these support elements.

[0009] Previous researchers proposed setting the cohesive force of the anchoring agent at the outer end of the cable structural unit to be infinite to simulate a pallet. However, this method has a drawback: the pallet has a certain surface area and can constrain the surrounding rock within that area. When simulating the pallet using this method, only the constraint effect of the pallet on the surrounding rock at the outer end of the anchor bolt can be simulated, which cannot accurately reflect the role of the pallet in real-world working conditions. Furthermore, in actual production, the surface area of ​​the pallet is adjusted according to the working conditions. However, existing methods cannot distinguish between pallets with different surface areas.

[0010] However, simulations of metal mesh in combined support systems are scarce. Therefore, this patent proposes a simulation method for combined support systems composed of anchor bolts, trays, and metal mesh, which is of great significance for revealing the mechanical principles of combined support systems, optimizing roadway support methods, and improving the stability of roadway surrounding rock. Summary of the Invention

[0011] The purpose of this invention is to propose a simulation method for combined support of anchor bolts, pallets, and metal mesh. This method overcomes the limitation of using only cable structural units to effectively simulate pallets and metal mesh, and can effectively simulate combined support composed of anchor bolts, pallets, and metal mesh.

[0012] This invention employs the following technical solution to provide a simulation method for combined support of anchor bolts, pallets, and metal mesh, comprising: creating a geometric model of the roadway and surrounding rock in FLAC3D and meshing it; setting necessary calculation items, including constitutive model, material parameters, boundary conditions, initial conditions, gravitational acceleration, and large deformation calculation mode switch; using automatic calculation to equilibrium; excavating the roadway; installing cable structural elements inside the left and right sides and roof of the roadway to simulate anchor bolts; installing pile structural elements on the surfaces of the left and right sides and roof of the roadway to simulate metal mesh; installing shell structural elements at the outer end nodes of each cable structural element to simulate pallets; deleting the outer nodes of each cable structural element. Connect the end nodes; establish connections between the outer end nodes of each cable structural unit and the shell structural unit nodes at the same location; find the pile structural unit nodes that share the same outer end nodes as the cable structural units and delete the connections of those pile structural unit nodes; find the pile structural unit nodes that share the same outer end nodes as the cable structural units and establish connections between those pile structural unit nodes and the shell structural unit nodes at the same location; apply axial tension to the outer end nodes of each cable structural unit to simulate preload; assign material parameters to the cable structural units, pile structural units, and shell structural units; automatically calculate again until equilibrium is reached.

[0013] As a further description of the above technical solution:

[0014] The large deformation calculation mode switch is set to false.

[0015] As a further description of the above technical solution:

[0016] The standard for balance is that the average unbalanced force ratio calculated by FLAC3D is less than or equal to the threshold set by the user.

[0017] As a further description of the above technical solution:

[0018] The method for excavating the roadway is as follows: use the grid deletion method to delete the unit cells within the roadway outline range.

[0019] As a further description of the above technical solution:

[0020] The cable structure unit ID is 1; the pile structure unit ID is 2; and the shell structure unit ID is 3.

[0021] As a further description of the above technical solution:

[0022] Each cable structural unit is generated in two stages: an inner anchoring section and an outer bearing section. The inner anchoring section is closer to the inside of the rock mass, while the outer bearing section is closer to the outside of the rock mass. The inner anchoring section and the outer bearing section are connected by nodes.

[0023] As a further description of the above technical solution:

[0024] Within the range of the inner anchoring section and the outer bearing section, the number of components in the cable structural unit is greater than or equal to 5.

[0025] As a further description of the above technical solution:

[0026] The pile structural unit has two installation directions: one is to install it on the surface of the surrounding rock of the tunnel and parallel to the direction of the tunnel; the other is to install it on the surface of the surrounding rock of the tunnel and perpendicular to the direction of the tunnel. The pile structural units with the two different installation directions are installed on the surface of the surrounding rock of the tunnel in a perpendicular and intersecting manner to simulate a metal mesh.

[0027] As a further description of the above technical solution:

[0028] The shell structure unit is a quadrilateral structure, and its length and width are set by the user when it is generated.

[0029] As a further description of the above technical solution:

[0030] When installing pile and shell structural units, it is required that there be a pile structural unit node and a shell structural unit node at the outer end node position of the cable structural unit.

[0031] As a further description of the above technical solution:

[0032] When deleting the connection of the outer end node of each cable structure unit, the component-id of the outer end node of each cable structure unit is used for location.

[0033] As a further description of the above technical solution:

[0034] When establishing a connection between the outer end node of each cable structural unit and the shell structural unit node at the same position, the location is determined by the component-id of the outer end node of the cable structural unit; the location is determined by the component-id of the shell structural unit node.

[0035] As a further description of the above technical solution:

[0036] When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, the component-id of that pile structural unit node is used for location when deleting its connection.

[0037] As a further description of the above technical solution:

[0038] When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, and establishing a connection between this pile structural unit node and a shell structural unit node at the same location, the component-id of the pile structural unit node is used for positioning; the component-id of the shell structural unit node is used for positioning.

[0039] As a further description of the above technical solution:

[0040] The material parameters of the cable structural unit include: young, grout-perimeter, cross-sectional-area, grout-stiffness, grout-cohesion, and grout-friction.

[0041] As a further description of the above technical solution:

[0042] For each cable structural unit, the following parameters are the same within the inner anchorage section and the outer load-bearing section: young, grout-perimeter, and cross-sectional-area; for each cable structural unit, the following parameters may differ within the inner anchorage section and the outer load-bearing section: grout-stiffness, grout-cohesion, and grout-friction; for the inner anchorage section, grout-stiffness, grout-cohesion, and grout-friction are all greater than zero.

[0043] As a further description of the above technical solution:

[0044] The material parameters of the pile structural unit include: coupling-stiffness-normal, coupling-stiffness-shear, young, poisson, cross-sectional-area, moi-polar, moi-y, and moi-z; coupling-stiffness-normal and coupling-stiffness-shear are both zero; moi-y and moi-z are equal and half of moi-polar; moi-polar is calculated according to the following formula: In the formula: P is the polar moment of inertia, i.e., moi-polar; D is the diameter of the pile structural unit.

[0045] As a further description of the above technical solution:

[0046] The material parameters of the shell structural unit include: isotropic and thickness.

[0047] Beneficial effects

[0048] The main beneficial effects of this invention include:

[0049] (1) This invention provides a simulation method for combined support of anchor bolts, pallets, and metal mesh. Based on this method, users can simulate the effect of combining anchor bolts, pallets, and metal mesh on the control of surrounding rock in roadways. It overcomes the limitation that cable structural units can only simulate anchor bolt support, and provides users with a method and approach for simulating combined support of anchor bolts with other elements.

[0050] (2) Each cable structural unit is divided into an inner anchorage section and an outer load-bearing section. For the outer load-bearing section, the user can set grout-stiffness, grout-cohesion, and grout-friction to be greater than zero to simulate full-length anchorage; the user can also set grout-stiffness, grout-cohesion, and grout-friction to be equal to zero to simulate end anchorage. Therefore, various working conditions such as full-length anchorage and end anchorage can be simulated conveniently and flexibly.

[0051] (3) The inner anchorage section and the outer bearing section are connected by nodes, so the user can accurately control the length of the inner anchorage section to match the actual working conditions by controlling the node coordinates. This avoids the problem of the inner anchorage section length not matching the actual working conditions caused by inappropriate component division when generating cable structural units at one time.

[0052] (4) Using shell structural units to simulate trays. Since shell structural units have surface area that can be adjusted by the user, users can simulate trays with different surface areas when using shell structural units to simulate trays. In addition, the connection between shell structural units and cable structural units is established, which can better simulate the combined effect of anchors and trays.

[0053] (5) When installing pile structural units on the surface of the surrounding rock of the roadway, the pile structural units are installed in different directions and form vertical intersections, which can simulate the metal mesh used in the support of underground roadways. When installing the pile structural units, the connection between the pile structural units and the shell structural units is established, which can simulate the effect of the metal mesh being compressed on the surface of the surrounding rock of the roadway by the tray in the actual working condition, and the metal mesh being connected to the tray.

[0054] (6) This invention patent proposes a simulation method for combined support of anchor bolts, trays, and metal mesh. Based on this method, users can study the influence of the coordination relationship of the three elements—anchor bolts, trays, and metal mesh—under different sizes and parameter conditions on the control of the surrounding rock of the roadway. Based on this invention patent, users can optimize the size, parameters, and coordination relationship of the three elements—anchor bolts, trays, and metal mesh—in roadway support, thereby providing a theoretical basis for combined support. Attached Figure Description

[0055] The accompanying drawings, which constitute a part of this application, are used to provide a further understanding of the invention and do not constitute an undue limitation of the invention. In the drawings:

[0056] Figure 1 This is a flowchart illustrating the operation of a simulation method for combined support using anchor bolts, trays, and metal mesh as described in this invention.

[0057] Figure 2 This is a planar geometric model diagram of the tunnel and surrounding rock described in this invention.

[0058] Figure 3 It is a cable structure unit installed inside the left and right sides and the roof of the tunnel as described in this invention.

[0059] Figure 4 It is a metal mesh simulated by the pile structural unit of the present invention in a vertically intersecting manner.

[0060] Figure 5 It is a tray simulated by the shell structure unit described in this invention. Detailed Implementation

[0061] like Figure 1As shown, this invention provides a simulation method for combined support of anchor bolts, pallets, and metal mesh, comprising: creating a roadway and surrounding rock geometric model and meshing it in FLAC3D; setting necessary calculation items, including constitutive model, material parameters, boundary conditions, initial conditions, gravitational acceleration, and large deformation calculation mode switch; using automatic calculation to equilibrium; excavating the roadway; installing cable structural elements inside the left and right sides and roof of the roadway to simulate anchor bolts; installing pile structural elements on the surfaces of the left and right sides and roof of the roadway to simulate metal mesh; installing shell structural elements at the outer end nodes of each cable structural element to simulate pallets; and deleting the outer end nodes of each cable structural element. Connect the points; establish connections between the outer end nodes of each cable structural unit and the shell structural unit nodes at the same location; find the pile structural unit nodes that share the same outer end nodes as the cable structural units and delete the connections of those pile structural unit nodes; find the pile structural unit nodes that share the same outer end nodes as the cable structural units and establish connections between those pile structural unit nodes and the shell structural unit nodes at the same location; apply axial tension to the outer end nodes of each cable structural unit to simulate preload; assign material parameters to the cable structural units, pile structural units, and shell structural units; automatically calculate again until equilibrium is reached.

[0062] In one specific embodiment:

[0063] The large deformation calculation mode switch is set to false.

[0064] In one specific embodiment:

[0065] The standard for balance is that the average unbalanced force ratio calculated by FLAC3D is less than or equal to the threshold set by the user.

[0066] In one specific embodiment:

[0067] The method for excavating the roadway is as follows: use the grid deletion method to delete the unit cells within the roadway outline range.

[0068] In one specific embodiment:

[0069] The cable structure unit ID is 1; the pile structure unit ID is 2; and the shell structure unit ID is 3.

[0070] In one specific embodiment:

[0071] Each cable structural unit is generated in two stages: an inner anchoring section and an outer bearing section. The inner anchoring section is closer to the inside of the rock mass, while the outer bearing section is closer to the outside of the rock mass. The inner anchoring section and the outer bearing section are connected by nodes.

[0072] In one specific embodiment:

[0073] Within the range of the inner anchoring section and the outer bearing section, the number of components in the cable structural unit is greater than or equal to 5.

[0074] In one specific embodiment:

[0075] The pile structural unit has two installation directions: one is to install it on the surface of the surrounding rock of the tunnel and parallel to the direction of the tunnel; the other is to install it on the surface of the surrounding rock of the tunnel and perpendicular to the direction of the tunnel. The pile structural units with the two different installation directions are installed on the surface of the surrounding rock of the tunnel in a perpendicular and intersecting manner to simulate a metal mesh.

[0076] In one specific embodiment:

[0077] The shell structure unit is a quadrilateral structure, and its length and width are set by the user when it is generated.

[0078] In one specific embodiment:

[0079] When installing pile and shell structural units, it is required that there be a pile structural unit node and a shell structural unit node at the outer end node position of the cable structural unit.

[0080] In one specific embodiment:

[0081] When deleting the connection of the outer end node of each cable structure unit, the component-id of the outer end node of each cable structure unit is used for location.

[0082] In one specific embodiment:

[0083] When establishing a connection between the outer end node of each cable structural unit and the shell structural unit node at the same position, the location is determined by the component-id of the outer end node of the cable structural unit; the location is determined by the component-id of the shell structural unit node.

[0084] In one specific embodiment:

[0085] When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, the component-id of that pile structural unit node is used for location when deleting its connection.

[0086] In one specific embodiment:

[0087] When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, and establishing a connection between this pile structural unit node and a shell structural unit node at the same location, the component-id of the pile structural unit node is used for positioning; the component-id of the shell structural unit node is used for positioning.

[0088] In one specific embodiment:

[0089] The material parameters of the cable structural unit include: young, grout-perimeter, cross-sectional-area, grout-stiffness, grout-cohesion, and grout-friction.

[0090] In one specific embodiment:

[0091] For each cable structural unit, the following parameters are the same within the inner anchorage section and the outer load-bearing section: young, grout-perimeter, and cross-sectional-area; for each cable structural unit, the following parameters may differ within the inner anchorage section and the outer load-bearing section: grout-stiffness, grout-cohesion, and grout-friction; for the inner anchorage section, grout-stiffness, grout-cohesion, and grout-friction are all greater than zero.

[0092] In one specific embodiment:

[0093] The material parameters of the pile structural unit include: coupling-stiffness-normal, coupling-stiffness-shear, young, poisson, cross-sectional-area, moi-polar, moi-y, and moi-z; coupling-stiffness-normal and coupling-stiffness-shear are both zero; moi-y and moi-z are equal and half of moi-polar; moi-polar is calculated according to the following formula: In the formula: P is the polar moment of inertia, i.e., moi-polar; D is the diameter of the pile structural unit.

[0094] In one specific embodiment:

[0095] The material parameters of the shell structural unit include: isotropic and thickness.

[0096] To verify the validity of this invention patent, we first set up Case 1, with the following specific conditions: A three-dimensional tunnel and surrounding rock geometric model is created in FLAC3D. The projection of this geometric model onto the xoz plane is as follows... Figure 2 As shown (y-axis perpendicular to the paper and pointing inwards), the geometric model has a width of 50m along the x-axis and a height of 50m along the z-axis. A rectangular tunnel is defined in the center of the model. This rectangular tunnel has a width of 5m along the x-axis and a height of 4m along the z-axis. The entire geometric model has a thickness of 300mm along the y-axis. The 3D tunnel and surrounding rock geometric model is then meshed. The entire mesh consists of 28,200 elements and 33,537 nodes.

[0097] Set the necessary calculation parameters, including a Mohr-Coulomb constitutive model. Set material parameters, including young = 15 GPa, poisson = 0.25, cohesion = 1 MPa, friction = 31°, and tension = 0.5 MPa. Set boundary conditions, including roller support boundary conditions at the front, back, left, right, and bottom of the entire model; and a compressive stress boundary condition of 25 MPa at the top. Set initial conditions, including a density of 2300 kg / m³. 3 The initial stress matches the stress at the top boundary of the model, and the lateral pressure coefficient is 0.5. The gravitational acceleration is set to 10 m / s². 2 And downwards along the z-axis. Set the large deformation calculation mode switch to false.

[0098] The system uses automatic calculation to achieve equilibrium, where the equilibrium standard is that the average unbalanced force ratio calculated by FLAC3D is less than or equal to 1×10⁻⁶ set by the user. -5 The grid deletion method is used to delete cells within the tunnel outline to simulate the tunnel excavation process.

[0099] Cable structural units with an ID of 1 are installed inside the left and right sides of the tunnel and inside the roof to simulate anchor bolts, such as... Figure 3 As shown. Each cable structural unit is generated in two stages: an inner anchoring section and an outer bearing section. The section closer to the inside of the rock mass is the inner anchoring section; the section closer to the outside of the rock mass is the outer bearing section. The inner anchoring section and the outer bearing section are connected by nodes. The length of the inner anchoring section is 1m; the length of the outer anchoring section is 2m. Within the range of the inner anchoring section and the outer bearing section, the number of components in the cable structural unit is 7 and 13, respectively.

[0100] Material parameters are assigned to the cable structural units. These parameters include: young, grout-perimeter, cross-sectional-area, grout-stiffness, grout-cohesion, and grout-friction. For each cable structural unit, within the inner anchorage section and the outer load-bearing section, the following parameters are identical: young, grout-perimeter, and cross-sectional-area, where young is 200 GPa; grout-perimeter is 87.96 mm; and cross-sectional-area is 615.75 mm. 2 For each cable structural unit, the following parameters differ within the inner anchorage section and the outer load-bearing section: grout-stiffness, grout-cohesion, and grout-friction. Within the inner anchorage section, grout-stiffness is 100 MPa, grout-cohesion is 100 kN / m, and grout-friction is 32°; within the outer load-bearing section, grout-stiffness is 60 MPa, grout-cohesion is 80 kN / m, and grout-friction is 28°, thus simulating a full-length anchor bolt.

[0101] An axial tensile force of 70 kN was applied to the outer end nodes of each cable structural unit to simulate preload. The system was then automatically calculated to equilibrium to simulate the deformation of the surrounding rock in the roadway when only anchor bolts were used for support. After reaching equilibrium, the results showed that the maximum axial force of the anchor bolts was 147.1 kN; the maximum horizontal displacement of the roadway was 6.18 mm; the maximum vertical displacement of the roadway was 13.3 mm; the maximum displacement of the roadway was 13.3 mm; and the volume of the plastic zone in the surrounding rock was 20.32 m³. 3 .

[0102] To verify the combined support effect of anchor bolts, pallets, and metal mesh, Case 2 was set up. Case 2's working condition is: based on Case 1, a metal mesh simulated by pile structural elements and a pallet simulated by shell structural elements are added.

[0103] The specific operational steps are as follows: Before the second automatic calculation in Case 1, pile structural units with an ID of 2 are installed on the left and right sidewalls and roof surface of the roadway to simulate a metal mesh. The pile structural units are installed in two directions: one is installed on the roadway surrounding rock surface parallel to the roadway direction; the other is installed on the roadway surrounding rock surface perpendicular to the roadway direction. These pile structural units with different installation directions are installed perpendicularly and intersectingly on the roadway surrounding rock surface to simulate a metal mesh. For example, the pile structural units installed on the left sidewall surface of the roadway are as follows: Figure 4 As shown.

[0104] A shell structural unit with an ID of 3 is installed at the outer end node of each cable structural unit to simulate a tray. The shell structural unit is a quadrilateral structure, and one of the installed trays is as follows: Figure 5 As shown. The pallet length is 400mm; the pallet width is 300mm.

[0105] Locate each cable structure unit by its component-id and delete the connection between each cable structure unit's outer end node. Establish a connection between each cable structure unit's outer end node and the shell structure unit node at the same location.

[0106] Find the pile structure unit node that shares a common point with the outer end node of the cable structure unit, locate it using its component-id, and delete the connection of the pile structure unit node; find the pile structure unit node that shares a common point with the outer end node of the cable structure unit, and establish a connection between the pile structure unit node and the shell structure unit node at the same position.

[0107] Material parameters are assigned to the pile structural units. These parameters include: coupling-stiffness-normal, coupling-stiffness-shear, young, poisson, cross-sectional-area, moi-polar, moi-y, and moi-z. Coupling-stiffness-normal and coupling-stiffness-shear are both zero. Young is 210 GPa; poisson is 0.25; and cross-sectional-area is 19.64 mm. 2 The moi-polar diameter is 61.36 mm. 4 The moi-y and moi-z are equal and half the size of the moi-polar, both being 30.68 mm.4 .

[0108] Material parameters are assigned to the shell structural unit. These parameters include isotropic and thickness. The isotropic value is 220 GPa, and the thickness is 10 mm.

[0109] Automatic calculations were performed until equilibrium was reached. After equilibrium was achieved, the results showed that the maximum axial force of the anchor bolt was 247.2 kN; the maximum horizontal displacement of the roadway was 5.45 mm; the maximum vertical displacement of the roadway was 12.4 mm; the maximum displacement of the roadway was 12.4 mm; and the volume of the plastic zone of the surrounding rock in the roadway was 19.76 m³. 3 The maximum displacement of the tray simulated by the shell structural unit is 12.4 mm; the maximum displacement of the metal mesh simulated by the pile structural unit is 12.4 mm.

[0110] It can be seen that the maximum displacement of the tray simulated by the shell structural element is the same as the maximum displacement of the metal mesh simulated by the pile structural element, both equal to the maximum displacement of the roadway. This indicates that the tray simulated by the shell structural element and the metal mesh simulated by the pile structural element are accurately installed on the roadway surrounding rock surface and can deform in tandem with the roadway surrounding rock surface.

[0111] Comparing the results of Case 1, it can be seen that using shell structural elements to simulate the pallet and using pile structural elements to simulate the metal mesh resulted in a 68% increase in the maximum axial force of the anchor bolts; an 11.8% reduction in the maximum horizontal displacement of the roadway; a 6.8% reduction in the maximum vertical displacement of the roadway; a 6.8% reduction in the maximum displacement of the roadway; and a 2.8% reduction in the volume of the plastic zone of the surrounding rock. Therefore, the pallet simulated by shell structural elements and the metal mesh simulated by pile structural elements effectively improved the stability of the surrounding rock of the roadway; while increasing the axial force of the anchor bolts, they effectively controlled the deformation of the surrounding rock. This also demonstrates that, compared with simple anchor bolt support, the combined support consisting of anchor bolts, pallets, and metal mesh has a better effect on controlling the deformation of the surrounding rock of the roadway. This is consistent with actual working conditions and verifies the effectiveness of this invention patent.

[0112] To further illustrate the operability of this invention, Case No. 3 is presented. The difference between Case No. 3 and Case No. 2 is that for the outer load-bearing section of the cable structure unit, grout-stiffness, grout-cohesion, and grout-friction are all set to zero, meaning that the anchoring agent is not considered in the outer load-bearing section to simulate the end-anchored anchor rod. The combined support effect of the end-anchored anchor rod, the tray, and the metal mesh is then analyzed.

[0113] The results show that the maximum axial force of the anchor bolt is 183.3 kN; the maximum horizontal displacement of the roadway is 5.57 mm; the maximum vertical displacement of the roadway is 12.55 mm; the maximum displacement of the roadway is 12.55 mm; and the volume of the plastic zone of the surrounding rock in the roadway is 19.76 m³. 3 The maximum displacement of the pallet simulated by the shell structural element is 12.55 mm; the maximum displacement of the metal mesh simulated by the pile structural element is 12.54 mm. It can be seen that when the anchor bolt support is end-anchored, the maximum displacements of the pallet, metal mesh, and roadway simulated by the shell structural element, and the maximum roadway displacement are almost identical. This further demonstrates that the pallet simulated by the shell structural element and the metal mesh simulated by the pile structural element are accurately installed on the roadway surrounding rock surface and can deform in tandem with the roadway surrounding rock surface. Furthermore, comparing Case 3 with Case 2 shows that compared to the combined support consisting of full-length anchor bolts, pallets, and metal mesh, using the combined support consisting of end-anchored anchor bolts, pallets, and metal mesh results in a 25.8% decrease in the maximum axial force of the anchor bolts; a 2.2% increase in the maximum horizontal displacement of the roadway; a 1.2% increase in the maximum vertical displacement of the roadway; and a 1.2% increase in the maximum displacement of the roadway. This indicates that the combined support system consisting of end-anchored anchor bolts, trays, and metal mesh is less effective than that consisting of full-length anchored anchor bolts, trays, and metal mesh. This aligns with field practice and theoretically explains why, in engineering practice, full-length anchored anchor bolt support is recommended for roadways with poor geological conditions.

[0114] Furthermore, this invention patent incorporates three elements simultaneously: anchor bolts, support plates, and metal mesh, each with corresponding material parameters. Users can adjust the material parameters of these three elements—anchor bolts, support plates, and metal mesh—to further investigate their effects on roadway surrounding rock control under different combinations. Previous methods, which only used cable structural units to simulate anchor bolt support, could not simulate the impact of the combination of these three elements on roadway surrounding rock control.

[0115] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention include:

[0116] (1) This invention provides a simulation method for combined support of anchor bolts, pallets, and metal mesh. Based on this method, users can simulate the effect of combining anchor bolts, pallets, and metal mesh on the control of surrounding rock in roadways. It overcomes the limitation that cable structural units can only simulate anchor bolt support, and provides users with a method and approach for simulating combined support of anchor bolts with other elements.

[0117] (2) Each cable structural unit is divided into an inner anchorage section and an outer load-bearing section. For the outer load-bearing section, the user can set grout-stiffness, grout-cohesion, and grout-friction to be greater than zero to simulate full-length anchorage; the user can also set grout-stiffness, grout-cohesion, and grout-friction to be equal to zero to simulate end anchorage. Therefore, various working conditions such as full-length anchorage and end anchorage can be simulated conveniently and flexibly.

[0118] (3) The inner anchorage section and the outer bearing section are connected by nodes, so the user can accurately control the length of the inner anchorage section to match the actual working conditions by controlling the node coordinates. This avoids the problem of the inner anchorage section length not matching the actual working conditions caused by inappropriate component division when generating cable structural units at one time.

[0119] (4) Using shell structural units to simulate trays. Since shell structural units have surface area that can be adjusted by the user, users can simulate trays with different surface areas when using shell structural units to simulate trays. In addition, the connection between shell structural units and cable structural units is established, which can better simulate the combined effect of anchors and trays.

[0120] (5) When installing pile structural units on the surface of the surrounding rock of the roadway, the pile structural units are installed in different directions and form vertical intersections, which can simulate the metal mesh used in the support of underground roadways. When installing the pile structural units, the connection between the pile structural units and the shell structural units is established, which can simulate the effect of the metal mesh being compressed on the surface of the surrounding rock of the roadway by the tray in the actual working condition, and the metal mesh being connected to the tray.

[0121] (6) This invention patent proposes a simulation method for combined support of anchor bolts, trays, and metal mesh. Based on this method, users can study the influence of the coordination relationship of the three elements—anchor bolts, trays, and metal mesh—under different sizes and parameter conditions on the control of the surrounding rock of the roadway. Based on this invention patent, users can optimize the size, parameters, and coordination relationship of the three elements—anchor bolts, trays, and metal mesh—in roadway support, thereby providing a theoretical basis for combined support.

[0122] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A simulation method for combined support of anchor bolts, trays, and metal mesh, characterized in that, include: Create the tunnel and surrounding rock geometry model and mesh it in FLAC3D; Set the necessary calculation entries, including constitutive model, material parameters, boundary conditions, initial conditions, gravitational acceleration, and large deformation calculation mode switch; use automatic calculation to equilibrium; excavate the tunnel; install cable structural elements inside the left and right sides and roof of the tunnel to simulate anchor bolts; install pile structural elements on the surfaces of the left and right sides and roof of the tunnel to simulate metal mesh; install shell structural elements at the outer end node of each cable structural element to simulate a pallet; delete the connections at the outer end nodes of each cable structural element. Establish a connection between the outer end node of each cable structural unit and the shell structural unit node at the same position; Find the pile structural unit node that shares a common point with the outer end node of the cable structural unit, and delete the connection of the pile structural unit node. Find the pile structural unit node that shares a common point with the outer end node of the cable structural unit, and establish a connection between the pile structural unit node and the shell structural unit node at the same position. An axial tensile force is applied to the outer end node of each cable structural element to simulate preload; material parameters are assigned to the cable structural element, pile structural element, and shell structural element; and the system is automatically calculated again until equilibrium is reached.

2. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, The large deformation calculation mode switch is set to false; the balancing standard is that the average unbalanced force ratio calculated by FLAC3D is less than or equal to the threshold set by the user; the method for excavating the roadway is as follows: use the mesh deletion method to delete the unit within the roadway outline range; the cable structure unit ID is 1; the pile structure unit ID is 2; the shell structure unit ID is 3; each cable structure unit is generated twice, generating an inner anchoring section and an outer bearing section respectively; the section closer to the inside of the rock mass is the inner anchoring section; the section closer to the outside of the rock mass is the outer bearing section; the inner anchoring section and the outer bearing section are connected by nodes.

3. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 2, characterized in that, Within the range of the inner anchoring section and the outer bearing section, the number of components in the cable structural unit is greater than or equal to 5.

4. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, The pile structural unit has two installation directions: one is to be installed on the surface of the surrounding rock of the tunnel and parallel to the direction of the tunnel; the other is to be installed on the surface of the surrounding rock of the tunnel and perpendicular to the direction of the tunnel. The pile structural units with the two different installation directions are installed on the surface of the surrounding rock of the tunnel in a perpendicular and intersecting manner to simulate a metal mesh. The shell structural unit is a quadrilateral structure, and its length and width are set by the user when generating it. When installing the pile structural unit and the shell structural unit, it is required that there is one pile structural unit node and one shell structural unit node at the outer end node position of the cable structural unit. When deleting the connection of the outer end node of each cable structure unit, the component-id of the outer end node of each cable structure unit is used for location.

5. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, When establishing a connection between the outer end node of each cable structural unit and the shell structural unit node at the same position, the component-id of the outer end node of the cable structural unit is used for positioning; the component-id of the shell structural unit node is used for positioning. When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, the component-id of that pile structural unit node is used for location when deleting its connection.

6. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, When searching for a pile structural unit node that shares a common point with the outer end node of a cable structural unit, and establishing a connection between this pile structural unit node and a shell structural unit node at the same location, the component-id of the pile structural unit node is used for positioning; the component-id of the shell structural unit node is used for positioning.

7. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, The material parameters of the cable structural unit include: young, grout-perimeter, cross-sectional-area, grout-stiffness, grout-cohesion, and grout-friction.

8. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 2, characterized in that, For each cable structural unit, within the inner anchorage section and the outer load-bearing section, the following parameters are the same: young, grout-perimeter, and cross-sectional-area; for each cable structural unit, within the inner anchorage section and the outer load-bearing section, the following parameters are different: grout-stiffness, grout-cohesion, and grout-friction; for the inner anchorage section, grout-stiffness, grout-cohesion, and grout-friction are all greater than zero.

9. The simulation method for combined support of anchor bolts, trays, and metal mesh according to claim 1, characterized in that, The material parameters of the pile structural unit include: coupling-stiffness-normal, coupling-stiffness-shear, young, poisson, cross-sectional-area, moi-polar, moi-y, and moi-z; coupling-stiffness-normal and coupling-stiffness-shear are both zero; moi-y and moi-z are equal and half of moi-polar; moi-polar is calculated according to the following formula: In the formula: P is the polar moment of inertia, i.e., moi-polar; D is the diameter of the pile structural unit; the material parameters of the shell structural unit include: isotropic and thickness.

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