A prefabricated rock anchor foundation for power transmission lines and its simulation method

Abstract

This invention belongs to the field of power technology and discloses a prefabricated rock anchor foundation for transmission lines, comprising a prefabricated base plate, prefabricated side plates, connecting steel plates, connectors, and anchor bolts; its key feature is that it also includes longitudinal reinforcement, grouting holes, anchor bolts, prefabricated upper main columns, adjusting nuts, prefabricated lower main columns, concrete dripping, steel mesh, and mortar. This invention has the following main beneficial technical effects: it defines damage variables and plastic shear displacement relationships to simulate the shear stress and shear displacement relationships of the contact surface under different shear slip models; through single-anchor simulation tests, it verifies that the tabular damage evolution form of bonded contact can effectively reflect the residual shear strength characteristics still existing after contact interface damage, and the tabular damage evolution form is closer to the actual situation than the simulation results; overall simulation was conducted, and by analyzing the bearing capacity of each stage of the foundation and the stress conditions of each component, the reliability and rationality of the modeling method were verified.

Description

Technical Field

[0001] This invention belongs to the field of power technology, and in particular discloses a prefabricated rock anchor foundation for transmission lines and a simulation method thereof. Background Technology

[0002] The rock anchor foundation for power transmission lines mainly adopts on-site cast-in-place foundation, but this type of foundation requires a lot of manpower and material resources, has a long construction period, fluctuates greatly in project quality, and has serious environmental problems such as noise and dust at the construction site, and has high requirements for traffic conditions near the construction site.

[0003] CN115821972A discloses a prefabricated rock anchor foundation for power transmission lines and its construction method. This method optimizes the combination of prefabricated tower foundations and rock anchor foundations to form a prefabricated rock anchor foundation. The foundation and main column are divided into multiple prefabricated components of a certain size. The foundation base plate, side plates, and main columns are prefabricated in a factory. These prefabricated components are then transported to the construction site for assembly. This improves the quality of foundation construction, reduces on-site concrete curing time and material usage for the tower foundation, shortens the construction period, reduces construction costs, minimizes environmental problems during construction, expands the application scope of anchor foundations and prefabricated foundations, and facilitates the promotion of mechanized construction in power transmission and transformation projects. It has good socio-economic benefits and engineering application value. However, it lacks pre-construction prediction and cannot foresee related design effects. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to improve upon the shortcomings of existing anchor foundations and to create prefabricated anchor foundations. This invention discloses a prefabricated rock anchor foundation for power transmission lines and a simulation method, which are implemented using the following technical solutions.

[0005] A prefabricated rock anchor foundation for power transmission lines comprises a prefabricated base plate, prefabricated side plates, connecting steel plates, connectors, and anchor rods. Its features include: longitudinal reinforcement, grouting holes, anchor bolts, a prefabricated upper main column, adjusting nuts, a prefabricated lower main column, concrete dripping, a steel mesh, and mortar. The longitudinal reinforcement is parallel to each other and forms a cylindrical structure. The prefabricated upper main column is located outside the longitudinal reinforcement. The grouting holes are located in the center of the longitudinal reinforcement and run vertically. The longitudinal reinforcement is fixed to each other by stirrups, forming a mesh structure. Anchor bolts are pre-embedded in the prefabricated upper main column. Connectors connect the prefabricated upper main column and the prefabricated lower main column. Adjusting nuts are installed above the prefabricated lower main column. The prefabricated side plates are located outside the connecting steel plates and the steel mesh. The prefabricated base plate is located below the prefabricated side plates. The upper end of the anchor rod extends into the prefabricated base plate and is fixed to the connecting steel plate by anchor bolts. Concrete dripping covers the steel mesh and the upper end of the anchor rod and integrates with the prefabricated base plate. Mortar covers the anchor rod.

[0006] The prefabricated rock anchor foundation for power transmission lines described above is characterized by the following assembly method: During construction, a prefabricated base plate is hoisted, allowing the anchor rod to pass through pre-drilled holes in the prefabricated base plate. Then, a prefabricated lower main column is hoisted, and the anchor rod and the reinforcing bars of the prefabricated lower main column are passed through corresponding holes in the connecting steel plate. Adjusting nuts are used for fixing, ensuring that the load is effectively transferred to the anchor rod. Similarly, when assembling the main column, anchor bolts are used to connect the prefabricated upper and lower main columns to the connecting parts, making the prefabricated upper and lower main columns a whole. This avoids the need to weld the reinforcing bars to the flange plate, which is required for traditional prefabricated main columns using flange connections, resulting in extensive quality inspection work and the risk of welding defects. Finally, the prefabricated side plate is hoisted into the groove of the prefabricated base plate, and the remaining gaps are filled with micro-expansion fine stone concrete grouting, making the prefabricated lower main column, prefabricated base plate, prefabricated side plate, connecting steel plate, and anchor rod a whole.

[0007] This application has the following main beneficial technical effects: (1) In ABAQUS, the tabular damage evolution form of bonded contact is used, and the damage variables and plastic shear displacement relationship are defined by the user. This can simulate the shear stress and shear displacement relationship of the contact surface under different shear slip models. (2) The single anchor simulation test verifies that the tabular damage evolution form of bonded contact in ABAQUS can effectively reflect the residual shear strength characteristics that still exist after the contact interface is damaged. The simulation results show that the tabular damage evolution form is closer to the actual situation. (3) The overall simulation of the prefabricated anchor foundation was carried out. By analyzing the bearing capacity of each stage of the foundation and the stress of each component, the reliability and rationality of the modeling method in this study are verified.

[0008] This invention addresses the shortcomings of existing anchor foundations by optimizing and combining traditional prefabricated tower foundations with anchor foundations, thus creating a novel prefabricated anchor foundation. The mechanical properties of the prefabricated anchor foundation were investigated, further verifying its feasibility. Finite element simulation calculations were performed using ABAQUS, and a finite element modeling method was proposed that effectively reflects the bearing capacity and stress conditions of each component of the prefabricated anchor foundation, considering the influence of residual strength, based on material constitutive modeling, load application methods, and contact behavior. Based on actual experimental data, single-anchor simulation comparisons and overall foundation stress analyses were conducted, obtaining the stress changes on the contact surface under uplift force, the entire process of load influence on the prefabricated anchor foundation, and the stress conditions of each component. This demonstrates the rationality and correctness of the modeling method, providing a reliable and effective basis for the design and construction of prefabricated anchor foundations and similar structures. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the anchor foundation of the present invention.

[0010] Figure 2 A schematic diagram illustrating the application of preload.

[0011] Figure 3 This is a load-displacement curve of a rock anchor bolt in a mountainous area.

[0012] Figure 4 This is the shear stress-displacement curve at the interface between the anchor bar and the mortar under the generalized double exponential curve model.

[0013] Figure 5 This is a schematic diagram of the cross-section of the simulation model.

[0014] Figure 6 The shear stress-displacement curves of the anchor bar and mortar contact surface under different damage evolutions are shown.

[0015] Figure 7 The load-displacement curves of the anchor bar and mortar contact surface under different damage evolutions are shown.

[0016] Figure 8 This is the load-displacement curve of an anchor bolt in a strongly weathered shale formation.

[0017] Figure 9 This is the shear stress-displacement curve at the mortar-rock interface under the generalized double exponential curve model.

[0018] Figure 10 The shear stress-displacement curves at the interface between mortar and rock strata under different damage evolutions are shown.

[0019] Figure 11 The load-displacement curves at the mortar-rock interface under different damage evolutions are shown.

[0020] Figure 12 This is a schematic diagram of a prefabricated anchor foundation.

[0021] Figure 13 This is a schematic diagram of the grid division for prefabricated anchor bolt foundations.

[0022] Figure 14 The curve showing the relationship between the load and displacement at the top of the foundation.

[0023] Figure 15 This is a stress contour diagram of the top surface of the connector.

[0024] Figure 16 This is a stress cloud diagram of the bottom surface of the connector.

[0025] Figure 17 This is a stress contour diagram of the connecting plate.

[0026] Figure 18 This is a stress cloud diagram of the upper main column.

[0027] Figure 19 This is a stress cloud diagram of the lower main column.

[0028] Figure 20 This is a stress cloud diagram of the lower main column and the foundation.

[0029] Figure 21 This is a stress cloud diagram of the foundation anchor bar. Detailed Implementation

[0030] To enable those skilled in the art to better understand and implement this patent, the markings in the accompanying drawings are explained in detail below.

[0031] In the diagram: 1—longitudinal reinforcement, 2—grouting hole, 3—anchor bolt, 4—precast upper main column, 5—connector, 6—adjusting nut, 7—precast lower main column, 8—connecting steel plate, 9—concrete dripping, 10—steel mesh, 11—precast base plate, 12—mortar, 13—anchor bolt, 14—precast side plate.

[0032] Implementation Example 1

[0033] Please see Figure 1 A prefabricated rock anchor foundation for power transmission lines comprises a prefabricated base plate 11, prefabricated side plates 14, connecting steel plates 8, connectors 5, and anchor bolts 13; characterized in that it further comprises longitudinal reinforcement 1, grouting holes 2, anchor bolts 3, prefabricated upper main columns 4, adjusting nuts 6, prefabricated lower main columns 7, concrete dripping grout 9, steel mesh 10, and mortar 12; the longitudinal reinforcement 1 are parallel to each other and form a cylindrical structure, the prefabricated upper main columns 4 are located outside the longitudinal reinforcement 1, the grouting holes 2 are located in the center of the longitudinal reinforcement 1 and run from top to bottom, and the longitudinal reinforcement 1 are fixed together by stirrups to form a mesh structure. Anchor bolts 3 are pre-embedded in the precast upper main column 4. Connector 5 connects the precast upper main column 4 to the precast lower main column 7. Adjusting nut 6 is installed above the precast lower main column 7. Precast side plate 14 is located outside the connecting steel plate 8 and steel mesh 10. Precast bottom plate 11 is located below the precast side plate 14. The upper end of anchor rod 13 extends into the precast bottom plate 11 and is fixed to the connecting steel plate 8 by anchor bolts. Concrete drip 9 covers the steel mesh 10 and the upper end of anchor rod 1 and combines with the precast bottom plate 11 as one unit. Mortar 12 covers anchor rod 13.

[0034] The prefabricated rock anchor foundation for power transmission lines described above is characterized by the following assembly method: During construction, a prefabricated base plate is hoisted, allowing the anchor rod to pass through pre-drilled holes in the prefabricated base plate. Then, a prefabricated lower main column is hoisted, and the anchor rod and the reinforcing bars of the prefabricated lower main column are passed through corresponding holes in the connecting steel plate. Adjusting nuts are used for fixing, ensuring that the load is effectively transferred to the anchor rod. Similarly, when assembling the main column, anchor bolts are used to connect the prefabricated upper and lower main columns to the connecting parts, making the prefabricated upper and lower main columns a whole. This avoids the need to weld the reinforcing bars to the flange plate, which is required for traditional prefabricated main columns using flange connections, resulting in extensive quality inspection work and the risk of welding defects. Finally, the prefabricated side plate is hoisted into the groove of the prefabricated base plate, and the remaining gaps are filled with micro-expansion fine stone concrete grouting, making the prefabricated lower main column, prefabricated base plate, prefabricated side plate, connecting steel plate, and anchor rod a whole.

[0035] Implementation Example 2

[0036] Please see Figures 2 to 21 and refer to Figure 1 A simulation method for prefabricated rock anchor foundations for power transmission lines includes the following steps:

[0037] The first step, model construction and contact relationships, includes: material constitutive model, load application method, and contact relationship definition;

[0038] 1.1 Material Constitutive Model: The basic model mainly includes four materials: steel, concrete, mortar, and rock. The corresponding constitutive relation needs to be selected according to the actual stress conditions. Steel is an isotropic material, and bilinear or trilinear constitutive models are generally used in its elastoplastic analysis. The concrete dispersion cracking model and the concrete damage plasticity model are used. The concrete damage plasticity model uses isotropic elastic damage combined with isotropic tensile or compressive plasticity to simulate the inelastic behavior of concrete and other quasi-brittle materials. It can be used for uniaxial loading. At the same time, considering the plastic strain generated during the test and the change in elastic stiffness caused by the load, it can effectively simulate the tensile cracking and crushing of materials such as concrete. The concrete and mortar constitutive models use the concrete damage plasticity model.

[0039] 1.2 Load Application Method: The loads required in the model include the uplift force borne by the foundation and the bolt preload. The uplift force is applied by applying a certain displacement to the surface of the anchor bolts in the main column. The bolt preload can be directly added in ABAQUS using conventional bolt loads, but this method is limited to the first analysis step and is only suitable for static general analysis. Furthermore, it is prone to errors and iteration convergence is difficult in complex models. Here, a connector is used to equivalently create the bolt preload, and its creation method is as follows: Figure 2As shown, reference points RP-1 and RP-2 are created at the center of the upper and lower hole surfaces of the same bolt hole on the connector, respectively. The surfaces on the upper main column that contact the connector and the bolt that contact the connector are used as coupling surfaces. Motion coupling constraints are created with the two reference points respectively, so that the degrees of freedom of the nodes on the coupling surfaces are constrained with the reference points. Then, the connector function is used to create the line features of RP-1 and RP-2 and the connection section feature is defined as a converter. A connection force is applied to the lines. At this time, the arrow direction is outward and the input value should be negative, thereby realizing the equivalent creation of bolt preload.

[0040] 1.3 Definition of Contact Relationship: The contact between the components of the foundation is simulated using the interaction module in ABAQUS. The normal behavior of the contact surfaces is set to hard contact, and the tangential behavior is set to penalty contact and adhesive contact depending on the contact surface. Penalty contact is used for the contact surfaces between the upper and lower main columns and the connectors, the contact surfaces between bolts and bolt holes, and the contact surfaces between nuts and connectors to simulate the friction characteristics between the contact surfaces. Adhesive contact is used for the contact surfaces between anchor rods and mortar, and between mortar and soil to simulate the adhesive effect between the contact surfaces in actual engineering.

[0041] In ABAQUS, bonded contacts are often used to simulate bonded materials with approximately zero thickness. Their shear stress and shear displacement curves can be divided into elastic and damage stages. In the elastic stage, it is assumed that the stress and relative displacement at the contact surface are linearly elastic before reaching the ultimate bond strength. The damage stage uses a damage variable D to simulate the failure and stiffness reduction of the bonded material. The damage evolution calculation of the viscous surface is similar to that of ductile metals. ABAQUS provides three forms of damage stage evolution: linear, exponential, and tabular. During simulations, it was found that if the damage stage uses a linear or exponential form, it cannot reflect the residual shear strength stage that still exists after damage at the anchor contact interface in actual conditions. Furthermore, the shear slip model that can be simulated has limitations. The shear slip model is the foundation and key to analyzing load transfer at the anchor contact interface. To make the simulation results closer to the actual shear stress and shear displacement relationship at the anchor interface, a tabular evolution form is used to define the damage variable D and the plastic shear displacement S. P The relationship between these parameters is established, and the values ​​of the stiffness coefficient K and shear stress τ are determined. This method can effectively simulate the shear stress and shear displacement curves under different shear slip models in the tabular evolution form. The relationship can be expressed as follows:

[0042]

[0043]

[0044] In the formula: τ0 represents the shear stress without damage; τ0 represents the peak shear stress in the elastic stage; S0 represents the shear displacement at the peak of the elastic stage. In the shear slip model, the three-stage linear function model uses linear functions to describe the rising segment, falling segment, and residual segment of the shear stress-shear displacement curve at the anchor contact interface. It can concisely express the load transfer process of the contact surface under anchor force and is widely used. However, it cannot reflect the nonlinear characteristics of the shear slip process. Here, the generalized double exponential curve shear slip model is adopted. This model can effectively reflect the nonlinear characteristics of shear slip at the anchor contact interface and can effectively analyze the stress characteristics of the anchor considering the residual shear strength. At the same time, the model function is relatively simple and has fewer parameters, which is convenient for fitting the actual anchor tensile test data. The relationship between shear stress and shear displacement at the anchor interface in the generalized double exponential curve shear slip model is as follows:

[0045] τ=aexp(-bs)-(a+τ r )exp(-2bs)+τ r (5)

[0046] In the formula, τ r The residual shear strength is given by τ, where a≥0 and b>0 are model parameters. r a and b can be directly calculated from geotechnical parameters or obtained by inversion from actual test data; to determine the parameter τ r Using the load-displacement curve inversion method, based on the relationship between the anchor load-displacement and the shear slip model, the load-displacement relationship of the anchor in the generalized double exponential curve shear slip model is obtained as follows:

[0047]

[0048] In the formula, E is the elastic modulus of the anchor body; A is the cross-sectional area of ​​the anchor body; and U is the perimeter of the anchor body.

[0049] When the anchor rod and mortar are considered as a whole, the cross-sectional area A is the sum of the cross-sectional areas of the anchor rod and the mortar, and the elastic modulus E is the equivalent elastic modulus of the anchor rod and mortar as a whole.

[0050]

[0051] In the formula, A a and A b E represents the cross-sectional area of ​​the anchor bar and the mortar, respectively. a and E b The elastic moduli of the anchor bolt and mortar are respectively given; then, τ is obtained by fitting the load-displacement curve of the actual anchor bolt pull-out test using the least squares method. r The values ​​of a and b;

[0052] The second step, single anchor simulation and comparison, includes: the contact surface between the anchor bar and the mortar, and the contact surface between the mortar and the rock strata.

[0053] To ensure the accuracy of the foundation stress results and the correctness of the modeling method, before simulating the entire foundation, it is necessary to obtain the shear stress and shear displacement relationships at the anchor bar and mortar interface, as well as the shear stress and shear displacement relationships at the mortar and rock layer interface, based on existing experimental results. Then, when simulating the entire foundation, these data are used as input parameters to perform simulation analysis and obtain the foundation's stress conditions. Therefore, it is necessary to perform single-anchor simulations for these two interfaces to verify the accuracy of the obtained shear stress and shear displacement relationships during the simulation process, ensuring that the simulation results closely resemble the actual stress conditions.

[0054] 2.1 Anchor Bar and Mortar Contact Surface: An analysis was conducted using a pull-out load test of a rock anchor in a mountainous area to obtain the relationship between shear stress and shear displacement at the anchor bar and mortar interface. The anchor bar anchorage depth was 3000 mm, the anchor bar diameter was 42 mm, the overall anchor bar diameter was 150 mm, and the mortar material was fine aggregate concrete with a compressive strength of 27.1 MPa and an elastic modulus of 2.6 × 10⁻⁶. 4 MPa. The measured anchor load-displacement curve was fitted using the load-displacement relationship (6) of the anchor in the generalized double exponential curve shear slip model, and the parameters a = 8.309, b = 5.414, and τ were obtained. r =0.92, the measured anchor load-displacement curve and fitting results are as follows: Figure 3 As shown, the obtained model parameters are substituted into equation (5) to obtain the relationship between shear stress and shear displacement under the generalized double exponential curve shear slip model, as follows: Figure 4 As shown; ABAQUS was used to model and simulate the pull-out test load test of the rock anchor bolts in the mountainous area. To make the shear stress and shear displacement relationship between the anchor bolt and the mortar interface close to the test results, the parameters and dimensions of each component of the model were based on the test data. During the simulation, only the interaction between the anchor bolt and the mortar was considered. The contact surface between the anchor bolt and the mortar was set as bonded contact, and the contact surface between the mortar and the rock layer was set as bound to restrict the mutual movement between the two. The boundary conditions constrained the horizontal and vertical displacements of the lower boundary of the rock mass according to the actual stress of the anchor bolt, and also constrained the horizontal displacements of the two side boundaries of the rock mass. The load application method adopted was to apply displacement to the top of the anchor bolt. The model cross-section is shown in the figure. Figure 5 As shown, the damage variable D and plastic shear displacement S are calculated using equation (1) based on the relationship between shear stress and shear displacement obtained from the experimental data. P The relationship between them was analyzed, and the data was substituted into a table of adhesive contact evolution for simulation calculations; as a comparison, Figure 6 and Figure 7The shear stress and shear displacement curves of the contact surface and the load-displacement curve of the anchor bolt are presented under different damage evolution forms in the model. The figures show that the tabular evolution of the damage stages of bonded contact in ABAQUS better reflects the actual shear stress and shear displacement relationship between the anchor bolt and mortar contact surface than the linear evolution form. It effectively reflects the residual shear strength characteristics remaining after damage to the contact interface. Furthermore, the load-displacement curves obtained using the tabular damage evolution form are similar to the actual experimental values, and the curve trends are similar. Therefore, the rationality and correctness of this modeling method are evident.

[0055] 2.2 Mortar-rock interface: To obtain the relationship between shear stress and shear displacement at the mortar-rock interface, a pull-out test of a strongly weathered shale was used as the object of analysis to obtain the relationship between shear stress and shear displacement at the mortar-rock interface. The anchorage depth was 6500mm, the anchor bar diameter was 32mm, the overall diameter of the anchor was 100mm, the rock stratum was strongly weathered shale, and the saturated uniaxial compressive strength was 12.8-18.7MPa. Equation (5) was used to inversely fit the measured anchor load-displacement curve to obtain the parameters a=0.449, b=1.474, τ r =0.04, the measured anchor load-displacement curve and fitting results are as follows: Figure 8 As shown, the relationship between shear stress and shear displacement is as follows: Figure 9 As shown; ABAQUS was used to model and simulate the pull-out test of a strongly weathered shale. To make the shear stress and shear displacement relationship at the mortar-rock interface closely resemble the test results, only the effect of the mortar-rock interface was considered. The mortar-rock interface was set as bonded contact, and the anchor bar-mortar interface was set as bound. Other conditions were the same as in the previous section. Finally, the shear stress and shear displacement curves of the interface and the load-displacement curve of the anchor bar under different damage evolution forms were obtained, as shown in the figure. Figure 10 and Figure 11 As shown in the figure, the table evolution form can also effectively represent the shear stress and shear displacement relationship of the mortar-rock interface. At the same time, compared with the anchor bar-mortar interface, the maximum shear stress of the mortar-rock interface is smaller and the load it can withstand is slightly lower. Therefore, the bearing capacity of the interface should be considered when performing overall foundation simulation.

[0056] The third step is the simulation analysis of the prefabricated anchor bolt foundation, which includes: the establishment of the prefabricated anchor bolt foundation model and data analysis.

[0057] 3.1 Establishment of Prefabricated Anchor Foundation Model: A finite element model of the prefabricated anchor foundation was established for analysis. The foundation uses four anchors arranged in a square, with an anchoring depth of 3000mm, an anchor bar diameter of 32mm, and an anchor hole diameter of 100mm. The rock stratum dimensions are defined as length × width × height = 7.5m × 7.5m × 3.2m. Penalty contact is used for the contact between components in the model. The contact between the anchor bar and the mortar, as well as the contact between the mortar and the rock stratum, are both bond contact models using tabular damage evolution. C3DR8 solid elements are used for the foundation and the rock stratum in the model. The pre-embedded stirrups and steel mesh in the foundation are T3D2 truss elements and embedded in the concrete components using embedded region constraints. The load was applied by displacing the anchor bolts to analyze the foundation's bearing capacity; the bolt preload was set to 50 kN. Boundary conditions constrained the horizontal and vertical displacements of the lower boundary of the rock mass, and also constrained the horizontal displacements of the two side boundaries of the rock mass. To facilitate model convergence, the analysis process employed four steps to complete the application of ground stress equilibrium, gravity, bolt preload, and foundation pull-out load. The specific model established is as follows: Figure 12 and 13 As shown;

[0058] 3.2 Data Analysis: The finite element simulation of the prefabricated anchor foundation conducted using the above modeling method obtained the stress conditions of each component of the foundation and the contact conditions of each contact surface under the action of uplift load. The following analysis focuses on the bearing capacity of the foundation and the stress conditions of components such as connecting plates, connectors, concrete, and anchor bars.

[0059] By organizing the data, relevant curves regarding the displacement at the top of the foundation and the uplift load were plotted, such as... Figure 14As shown. Based on the simulation results and the development trend of the load-displacement curve, it can be found that the relative displacement between the anchor bar and the mortar is very small. Therefore, the failure of the foundation should occur at the interface between the mortar and the rock layer. The ultimate pull-out bearing capacity of the foundation is 510kN, which is mainly determined by the ultimate bond bearing capacity between the anchor bar and the rock layer. In the first stage, when the pull-out load is between 0 and 160kN, the load-displacement curve is basically linear. The bond contact at the top of the anchor bar mortar-rock layer interface is in the linear elastic stage, and the shear stress increases linearly with the shear displacement. In the second stage, when the pull-out load is between 160 and 349kN, as the load increases, the rate of displacement increases, the load-displacement curve bends, and the bond contact at the top of the anchor bar mortar-rock layer interface enters the strain hardening stage. The shear stress increases nonlinearly and monotonically with the shear displacement and reaches the ultimate bond strength between the mortar and the rock layer. In the third stage, when the pull-out load is between 349kN and 510kN, the load borne by the foundation gradually approaches the limit. At the ultimate value, the bond between the anchor mortar and the rock stratum begins to enter the strain softening stage and quickly enters the final residual shear strength stage. The shear stress decreases with the increase of shear displacement and eventually stabilizes at a certain value. During this process, as the load increases, the trend of the bond between the anchor mortar and the rock stratum will be transmitted downward along the anchor until the shear stress at the bottom contact surface reaches the ultimate bond strength between the mortar and the rock stratum. At this time, the foundation is in the ultimate pull-out bearing state. Subsequently, the entire mortar and rock stratum contact surface will enter the residual strength stage, and the load that the foundation can bear will decrease sharply. This change process is consistent with the actual engineering application.

[0060] Under the ultimate pull-out bearing state, the stress distribution of the connectors and connecting plates in the foundation is shown in Figures 15-17. The bearing surface stress near the bolt holes connecting the connectors to the anchor bolts and longitudinal reinforcement of the upper main column ranges from 79.84 to 139.00 MPa, while the bearing surface stress near the bolt holes connecting the connectors to the longitudinal reinforcement of the lower main column ranges from 119.3 to 198.20 MPa, with a local maximum of 237.6 MPa, demonstrating a good simulation effect of bolt preload. The bearing surface stress near the holes connecting the connecting plates to the longitudinal reinforcement of the lower main column ranges from 14.74 to 29.23 MPa, while the bearing surface stress near the holes connecting the connecting plates to the anchor bars ranges from 17.16 to 21.99 MPa, indicating that the pull-out load can be transferred to the anchor rods through the connecting plates.

[0061] Stress distribution of foundation concrete members as follows Figure 18-20 As shown, under the action of load and bolt preload, the bearing surface stress near the anchor bolt holes and longitudinal reinforcement holes on the bottom surface of the upper main column is between 2.54 and 5.04 MPa, and the bearing surface stress near the longitudinal reinforcement holes of the lower main column is between 3.20 and 7.02 MPa. This indicates that the load can be effectively transferred from the upper main column to the lower main column through the connecting parts.

[0062] Stress distribution of foundation anchor bars as follows Figure 21As shown, under the action of uplift load, the stress on the anchor bar decreases from top to bottom. Under the ultimate uplift bearing state, the maximum tensile stress at the top of the anchor bar is 174.1 MPa, which is still within the bearable range.

[0063] As can be seen from the above analysis, this model can effectively simulate the entire process of load influence on prefabricated anchor foundations considering the influence of residual strength, as well as the stress conditions of each component. It can also show the stress changes on the anchor contact surface, demonstrating the feasibility and rationality of the model establishment method in this application.

[0064] In this invention, the following effects are achieved through the above simulation:

[0065] (1) In ABAQUS, the adhesive contact with tabular damage evolution can be simulated by defining the damage variables and plastic shear displacement relationship, and the shear stress and shear displacement relationship of the contact surface under different shear slip models.

[0066] (2) The single anchor simulation test verified that the tabular damage evolution form of the bonded contact in ABAQUS can effectively reflect the residual shear strength characteristics that still exist after the contact interface is damaged. Compared with the simulation results, the tabular damage evolution form is closer to the actual situation.

[0067] (3) An overall simulation of the prefabricated anchor foundation was carried out. By analyzing the bearing capacity of each stage of the foundation and the stress of each component, the reliability and rationality of the modeling method in this study were verified.

[0068] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A simulation method of a prefabricated rock anchor foundation for a power transmission line, the prefabricated rock anchor foundation for a power transmission line having a prefabricated bottom plate, a prefabricated side plate, a connecting steel plate, a connecting piece, an anchor rod, longitudinal reinforcement, a grouting hole, a foundation bolt, a prefabricated upper main column, an adjusting nut, a prefabricated lower main column, concrete grout, a steel mesh, and mortar; the longitudinal reinforcement is parallel to each other and forms a cylindrical structure, the prefabricated upper main column is located outside the longitudinal reinforcement, the grouting hole is located in the center of the cylindrical structure formed by the longitudinal reinforcement and penetrates from top to bottom, the longitudinal reinforcement is fixed by stirrups and forms a mesh structure between the longitudinal reinforcement, the foundation bolt is embedded in the prefabricated upper main column, the connecting piece connects the prefabricated upper main column and the prefabricated lower main column, the adjusting nut is installed above the prefabricated lower main column, the prefabricated side plate is located outside the connecting steel plate and the steel mesh, the prefabricated bottom plate is located below the prefabricated side plate, the upper end of the anchor rod extends into the prefabricated bottom plate and is fixed with the connecting steel plate through the foundation bolt, the concrete grout covers the steel mesh and the upper end of the anchor rod and is integrated with the prefabricated bottom plate, and the mortar covers the anchor rod; characterized in that, The simulation method comprises the following steps: First step, model construction and contact relationship: including: material constitutive, load application method, contact relationship definition; Second step, single anchor simulation and comparison: including: anchor and mortar contact surface, mortar and rock contact surface; Third step, simulation analysis of assembled anchor rod foundation: including: establishment of assembled anchor rod foundation model, data analysis; In the first step: the load application method is: the load required in the model includes the uplift force borne by the foundation and the bolt pretightening force, the uplift force is applied by applying force on the surface of the foundation bolt in the prefabricated upper main column to generate displacement, the bolt pretightening force is created by connecting the connector in ABAQUS, the upper hole surface and the lower hole surface center of the same bolt hole on the connecting piece are respectively created reference points RP-1 and RP-2, and the surface in contact with the connecting piece on the prefabricated upper main column and the surface in contact with the connecting piece on the bolt are taken as the coupling surface, the motion coupling constraint is created with the two reference points respectively, so that the degrees of freedom of the nodes on the coupling surface are constrained together with the reference points, then the RP-1 and RP-2 line features are created using the connector function and the connection cross section feature is defined as a converter, the connection force is applied to the line, the arrow direction is outward at this time, the input value should be negative, thus the equivalent creation of the bolt pretightening force is realized; In the first step: the contact relationship is defined as follows: the contact between the various components of the foundation is simulated using the interaction module in ABAQUS. The normal behavior of the contact surfaces is set as hard contact, and the tangential behavior is set as either penalty contact or bonded contact depending on the different contact surfaces. Penalized contact is used for the contact surfaces between the precast upper and lower main columns and the connectors, the contact surfaces between bolts and bolt holes, and the contact surfaces between nuts and connectors among the various assembled components to simulate the frictional characteristics between the contact surfaces. Bonded contact is used for the contact surfaces between the anchor rod and the mortar, and between the mortar and the soil to simulate the bonding effect between the contact surfaces in actual engineering. The shear slip model is the foundation and key to analyzing the load transfer at the anchor rod contact interface. To make the simulation results close to the relationship between shear stress and shear displacement in the actual anchorage interface, damage variables and plastic shear displacement are defined in tabular evolution form. The relationship between them was determined, and the stiffness coefficient K and shear stress were determined. The value of can be used to effectively simulate the shear stress and shear displacement curves under different shear slip models in the tabular evolution form. The relationship is expressed as follows: (1) ; (2) ; (3) ; (4); wherein: is the shear stress at the time of no damage; is the peak shear stress in the elastic phase; is the shear displacement at the time of peak in the elastic phase.

2. The simulation method of the assembled rock anchor foundation for power transmission line according to claim 1, characterized in that, The assembly method of the anchor rod foundation is: during construction, the prefabricated bottom plate is hoisted to make the anchor rod pass through the reserved hole of the prefabricated bottom plate, then the prefabricated lower main column is hoisted, the anchor rod and the steel bar of the prefabricated lower main column pass through the corresponding hole of the connecting steel plate, the adjusting nut is used for fixation, so that the load can be effectively transmitted to the anchor rod, similarly, when assembling the main column, the foundation bolt is used to connect the prefabricated upper and lower main columns with the connecting piece, so that the prefabricated upper and lower main columns become a whole, at the same time, the need to weld and fix the steel bar and the flange plate when the flange connection is used in the traditional assembled main column is avoided; finally, the prefabricated side plate is hoisted in the groove of the prefabricated bottom plate, the remaining gap is filled with micro-expanding fine aggregate concrete grouting, so that the prefabricated lower main column, the prefabricated bottom plate, the prefabricated side plate, the connecting steel plate and the anchor rod form a whole.

3. The simulation method of the assembled rock anchor foundation for power transmission line according to claim 2, characterized in that, In the first step: the material constitutive is: the materials contained in the foundation model include steel, concrete, mortar and rock, the corresponding constitutive relationship needs to be selected according to the actual stress condition, the steel is an isotropic material, the double or triple fold line constitutive is used in the elastic-plastic analysis of the steel; in the concrete dispersion cracking model and the concrete damage plasticity model, the concrete damage plasticity model adopts isotropic elastic damage combined with isotropic tensile or compressive plasticity, which is used to simulate the inelastic behavior of the quasi-brittle material of concrete, can be used in the case of one-way loading, and can effectively simulate the tensile cracking and crushing of the material considering the plastic strain generated in the test process and the elastic stiffness change caused by the load, the concrete and mortar constitutive model adopts the concrete damage plasticity model.

4. The simulation method of the assembled rock anchor foundation for power transmission lines according to claim 3, characterized in that, The bonded contact in ABAQUS is commonly used to simulate the nearly zero-thickness cohesive material, whose shear stress-shear displacement curve is divided into elastic stage and damage stage. In the elastic stage, the stress and relative displacement of the contact surface are assumed to be linearly elastic before reaching the ultimate bond strength. In the damage stage, the damage variable is used to simulate the damage and stiffness degradation of the cohesive material, and the damage evolution of the cohesive surface is similar to that of the ductile metal. ABAQUS provides three forms of damage stage evolution: linear, exponential, and table form. It is found that if the linear or exponential form is used in the damage stage, the residual shear strength stage of the anchor contact interface after damage cannot be reflected, and the shear slip model that can be simulated has limitations.

5. The simulation method of a fabricated rock anchor foundation for a power transmission line according to claim 4, characterized in that, In the shear slip model, the three-stage linear function model uses a linear function to describe the rising segment, descending segment, and residual segment of the anchor contact interface shear stress-shear displacement curve. The generalized double exponential curve shear slip model is used to effectively analyze the force characteristics of the anchor under consideration of the residual shear strength and to fit the actual anchor tensile test data. The relationship between the anchorage interface shear stress and shear displacement in the generalized double exponential curve shear slip model is: (5); wherein is the residual shear strength, and are model parameters, wherein , and can be calculated directly from geotechnical parameters or obtained by inversion from actual test data; to determine the parameters , and , a load displacement curve inversion method is used, according to the relationship between the load displacement of the anchor and the shear slip model, the load displacement relationship of the anchor in the generalized double exponential curve shear slip model is obtained as: (6); where E is the elastic modulus of the anchoring body, A is the cross-sectional area of the anchoring body, and U is the circumference of the anchoring body. When the anchor and mortar are regarded as a whole, the cross-sectional area A is the sum of the cross-sectional areas of the anchor and mortar, and the elastic modulus E is the equivalent elastic modulus of the anchor and mortar as a whole: (7); wherein, and are the cross-sectional areas of the anchor bar and the mortar, respectively, and are the elastic moduli of the anchor bar and the mortar, respectively; and then the values of , and are obtained by fitting the actual load-displacement curve of the anchor bar in the uplift test according to the least square method.

6. The simulation method of a fabricated rock anchor foundation for a power transmission line according to claim 5, characterized in that, In the second step, the anchor and mortar contact surface is analyzed based on the certain mountain rock anchor pullout test and load test to obtain the relationship between the anchor and mortar interface shear stress and shear displacement.

7. The simulation method of a fabricated rock anchor foundation for a power transmission line according to claim 6, characterized in that, In the second step, the mortar and rock stratum contact surface is analyzed based on the certain strong weathered shale pullout test to obtain the relationship between the mortar and rock stratum interface shear stress and shear displacement.

8. The simulation method of a fabricated rock anchor foundation for a power transmission line according to claim 7, characterized in that, In the third step, the assembled anchor foundation model is established by analyzing the finite element model of the entire assembled anchor foundation. The contact between components in the model components is penalized, and the contact between the anchor and mortar and the contact between the mortar and rock stratum are modeled using the bonded contact model with table damage evolution form.

9. The simulation method of a fabricated rock anchor foundation for a power transmission line according to claim 8, characterized in that, In the third step, data analysis is performed by modeling the finite element simulation of the assembled anchor foundation to obtain the stress conditions of each component of the foundation and the contact conditions of each contact surface under uplift load. By organizing the data, the relevant curve of the foundation top displacement and uplift load is drawn.

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