A method for determining mechanical properties of embossed anchor cable after peak load

Abstract

The application discloses a kind of methods for determining the mechanical properties of embossed anchor cable after peak load, belong to roadway surrounding rock control field.It includes: creating grid in FLAC3D;Setting grid constitutive model, material parameters, boundary conditions;Creating anchor unit in grid and simulating anchor cable;Define four parameters of anchor unit;Define and execute FISH function curve;The range obtained in experiment is divided into n stages after peak load of anchoring performance curve;Define and execute FISH function vibration;Set the damping oscillation mode of structure unit to combined-local;Set the large deformation calculation mode to true;Record FISH variables force, disp;Pulling speed is applied to the outermost node of anchor unit;Load in time step mode.The method can effectively simulate the mechanical properties of embossed anchor cable after peak load, which helps to reveal the anchoring mechanism of embossed anchor cable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of roadway surrounding rock control, and particularly relates to a method for determining mechanical properties of a knurl anchor after peak load. BACKGROUND

[0002] The knurl anchor is a geotechnical reinforcement component in roadway surrounding rock control. Compared with a common anchor, the knurl anchor has a protruding knurl structure along the extension direction of the anchor body. Therefore, when the knurl anchor is used for geotechnical reinforcement, the knurl structure can be coupled with the anchoring agent to form a wedge-shaped engagement structure, and the anchoring force can be multiplied.

[0003] In order to reveal the anchoring performance of the knurl anchor, researchers often carry out indoor or field anchoring experiments on the knurl anchor, that is, the anchor is pulled out of the rock-soil body. During the pulling process, the anchoring force and the pulling displacement are recorded, so as to obtain the relationship curve between the anchoring force and the pulling displacement, that is, the anchoring performance curve. Subsequently, researchers can quantitatively judge the anchoring performance of the anchor.

[0004] Although the indoor experiment and the field experiment can objectively reflect the anchoring performance of the anchor, they often depend on a large number of experimental equipment and financial investment. Compared with the indoor experiment and the field experiment, numerical calculation has the advantages of convenient operation, low capital investment cost, and dynamic display of stress and strain distribution characteristics in the anchoring system. Therefore, numerical calculation plays an important role in modern geotechnical anchoring performance analysis.

[0005] In the field of numerical calculation, the anchor element developed by Itasca Company is widely used in anchor support simulation. However, direct application of the original anchor element cannot accurately reflect the mechanical properties of the knurl anchor after the peak load. After the knurl anchor is loaded and reaches the peak load (i.e. the maximum anchoring force), the knurl structure periodically detaches and engages with the anchoring agent, resulting in the oscillation behavior of the anchoring force after the peak load. After the peak load, multiple wave peaks and wave troughs are exhibited. However, the original anchor element does not consider the mechanical properties of the knurl anchor after the peak load. Therefore, it is of great significance to propose a method for determining the mechanical properties of the knurl anchor after the peak load to reveal the anchoring mechanism of the knurl anchor. SUMMARY

[0006] The present application aims to provide a method for determining the mechanical properties of a knurl anchor after peak load.

[0007] The application adopts the following technical scheme to provide a method for determining mechanical properties of embossed anchor cable after peak load, comprising the following steps: creating a grid in FLAC3D; setting a grid constitutive model, material parameters and boundary conditions; creating an anchor unit in the grid by using a structure cable create command and simulating the anchor cable; defining four parameters of the anchor unit; defining a FISH function curve and requiring the FISH function curve to be automatically executed at each time step; dividing the peak load range of the obtained anchoring performance curve in the experiment into n stages, wherein the connecting points of the n stages are the wave peaks and wave troughs in the peak load range of the obtained anchoring performance curve in the experiment; defining a FISH function vibration and requiring the FISH function vibration to be automatically executed at each time step; setting the damping oscillation mode of the structure unit to combined-local; setting the large deformation calculation mode to true; recording FISH variables force and disp; applying a constant pulling speed in the pulling direction to the outermost node of the anchor unit, and the size is 1*10 -6 m / s; loading in a time step manner.

[0008] Further description of the above technical scheme:

[0009] The boundary condition is that the boundary surface closest to the pulling end of the anchor unit is supported by a roller, and the other boundary surfaces are free boundaries.

[0010] Further description of the above technical scheme:

[0011] The four parameters are grout-stiffness, grout-cohesion, young and cross-sectional-area; the grout-cohesion parameter is obtained by using a first formula for calculation.

[0012] Further description of the above technical scheme:

[0013] The FISH function curve adopts the following logic structure: calculating according to a second formula, and assigning the result to a variable disp; obtaining a grid node head pointer and assigning it to a variable pnt_gp; defining a variable sum and setting it to zero; traversing all grid nodes, judging whether the traversed grid node is located on the boundary surface closest to the pulling end of the anchor unit, if yes, taking out the unbalanced force of the variable pnt_gp in the pulling direction, and assigning the sum of the unbalanced force and the variable sum to the variable sum.

[0014] Further description of the above technical scheme:

[0015] The FISH function vibration adopts the following logic structure: obtaining an anchor unit head pointer and assigning it to variable pnt_cable; traversing all anchor units; when each anchor unit is traversed, judging that variable disp is located in the i-th stage (1≤i≤n) in the n stages, where n and i are variables; assigning the experimental anchoring force corresponding to the starting point of the i-th stage to variable y1 and the corresponding experimental pullout displacement to variable x1; assigning the experimental anchoring force corresponding to the ending point of the i-th stage to variable y2 and the corresponding experimental pullout displacement to variable x2; substituting variables y1, y2, x1 and x2 into the third formula and the fourth formula to obtain variables k and b, respectively; substituting variables k and b into the fifth formula and assigning the result to the struct.cable.grout.cohesion parameter corresponding to variable pnt_cable.

[0016] As a further description of the above technical solution:

[0017] The first formula is: In the formula, c b1 is the initial cohesion of the anchoring interface; F p is the peak load in the anchoring performance curve obtained based on experiments; and L is the length of the anchor cable.

[0018] As a further description of the above technical solution:

[0019] The second formula is: d=v·s; in the formula, d is the pullout displacement; v is the pullout speed; and s is the time step.

[0020] As a further description of the above technical solution:

[0021] The third formula is:

[0022] As a further description of the above technical solution:

[0023] The fourth formula is:

[0024] As a further description of the above technical solution:

[0025] The fifth formula is: c b2 =ks+b; c b2 is the dynamic cohesion of the anchoring interface.

[0026] The present application has the following beneficial effects:

[0027] (1) define the FISH function vibration and use the FISH function vibration to realize the simulation of the mechanical properties of the embossed anchor cable after the peak load. In the execution process of the FISH function vibration, the user can divide the anchoring performance curve of the anchor cable after the peak load into n stages according to the characteristics of the anchoring performance curve of the anchor cable obtained in the experiment. For each stage after the peak load, the third formula and the fourth formula are designed, which can simulate the mechanical properties of the anchor cable after the peak load.

[0028] (2) the fifth formula is designed. By using the fifth formula, the user can dynamically correct the anchoring performance of the anchor cable after the peak load. Thus, the interfacial cohesion of the anchor cable can be dynamically corrected according to the anchoring performance characteristics of the anchor cable after the peak load, and finally the oscillation behavior of the anchoring force of the anchor cable after the peak load can be simulated.

[0029] (3) define the FISH function curve and use the FISH function curve to automatically record the anchoring force of the anchor cable. In the recording process, the anchoring force of the anchor cable is calculated by extracting the unbalanced force closest to the boundary surface of the anchor unit along the pulling direction at the pulling end. This overcomes the defect that the unbalanced force at the pulling end of the anchor cable along the pulling direction is easily affected by system failure and suddenly changes, and a relatively stable anchoring performance curve can be obtained.

[0030] (4) in the stage after the peak load of the anchor cable, the user can output the anchor cable axial force distribution data, so as to reveal the axial force distribution law of the anchor cable after the peak load and in the oscillation process of the anchoring force, which helps researchers better master the anchoring characteristics of the embossed anchor cable. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. In the drawings:

[0032] Figure 1 is a determination method for reflecting the mechanical properties of the embossed anchor cable after the peak load.

[0033] Figure 2 is a logic structure diagram of the FISH function curve.

[0034] Figure 3 is a logic structure diagram of the FISH function vibration.

[0035] Figure 4 is a comparison diagram of the indoor embossed anchor cable anchoring performance experiment results and the calculation results of the present application.

[0036] Figure 5is a force distribution diagram in the cable body of the embossed anchor cable at different stages after the peak load in the calculation process of the present application. DETAILED DESCRIPTION

[0037] As Figure 1 shown, the present application provides a determination method reflecting the mechanical properties of the embossed anchor cable after the peak load, comprising the following steps: creating a grid in FLAC3D; setting the grid constitutive model, material parameters, boundary conditions; creating anchor units in the grid and simulating anchor cables by using the structure cable create command; defining four parameters of the anchor units; defining the FISH function curve and requiring the FISH function curve to automatically execute at each time step; dividing the range after the peak load of the anchoring performance curve obtained in the experiment into n stages, the connection points of the n stages being the wave peaks and wave troughs in the range after the peak load of the anchoring performance curve obtained in the experiment; defining the FISH function vibration and requiring the FISH function vibration to automatically execute at each time step; setting the damping oscillation mode of the structure unit to combined-local; setting the large deformation calculation mode to true; recording the FISH variables force and disp; applying a constant pulling speed of 1x10 -6 m / s to the outermost node of the anchor unit in the pulling direction; loading in a time step manner.

[0038] In a specific embodiment:

[0039] The boundary condition is that the boundary surface closest to the pulling end of the anchor unit is supported by a roller, and the other boundary surfaces are free boundaries.

[0040] In a specific embodiment:

[0041] The four parameters are grout-stiffness, grout-cohesion, young, and cross-sectional-area; the grout-cohesion parameter is obtained by calculating using a first formula.

[0042] In a specific embodiment:

[0043] The FISH function curve uses the following logical structure: calculating according to a second formula and assigning the result to the variable disp; obtaining the grid node head pointer and assigning it to the variable pnt_gp; defining the variable sum and setting it to zero; traversing all grid nodes, judging whether the traversed grid node is located on the boundary surface closest to the pulling end of the anchor unit, if so, taking out the unbalanced force of the variable pnt_gp in the pulling direction, and assigning the sum of the unbalanced force and the variable sum to the variable sum.

[0044] In a specific embodiment,

[0045] The FISH function vibration adopts the following logic structure: the anchor unit head pointer is obtained and assigned to variable pnt_cable; all anchor units are traversed; when each anchor unit is traversed, it is judged that variable disp is located in the i-th stage (1≤i≤n) of the n stages, where n and i are variables; the experimental anchoring force corresponding to the starting point of the i-th stage is assigned to variable y1, and the corresponding experimental pullout displacement is assigned to variable x1; the experimental anchoring force corresponding to the end point of the i-th stage is assigned to variable y2, and the corresponding experimental pullout displacement is assigned to variable x2; variables y1, y2, x1 and x2 are substituted into the third formula and the fourth formula to obtain variables k and b respectively; variables k and b are substituted into the fifth formula, and the result is assigned to the struct.cable.grout.cohesion parameter corresponding to variable pnt_cable.

[0046] In a specific embodiment,

[0047] The n and i are variables.

[0048] In a specific embodiment,

[0049] The first formula is: In the formula, c b1 is the initial cohesion of the anchoring interface; F p is the peak load in the anchoring performance curve obtained based on experiments; and L is the length of the anchor cable.

[0050] In a specific embodiment,

[0051] The second formula is: d=v·s; in the formula, d is the pullout displacement, v is the pullout speed, and s is the time step.

[0052] In a specific embodiment,

[0053] The third formula is:

[0054] In a specific embodiment,

[0055] The fourth formula is:

[0056] In a specific embodiment,

[0057] The fifth formula is: c b2 =ks+b; c b2 is the dynamic cohesion of the anchoring interface.

[0058] To verify the effectiveness of the present application, the embossed anchor cable pull-out test results shown in the paper "Numerical simulation of the pull-out behaviour of fully grouted cable bolts" are simulated as an example.

[0059] A cylindrical grid is created in FLAC3D, with a diameter of 300 mm and a height equal to the anchor cable anchoring length, i.e. 320 mm. A strain-softening model is set for the entire grid. The grid material parameters are defined, including bulk of 5.4 GPa, shear of 3.7 GPa, tension of 2 MPa, density of 2300 kg / m 3 , cohesion of 24.5 MPa, and friction of 15°. The boundary conditions are set, with the boundary surface closest to the anchor unit pull-out end being a drum support, and the other boundary surfaces being free boundaries.

[0060] An anchor unit is created in the grid using the structure cable create command to simulate the anchor cable, with a length of 320 mm and a component number of 10 in the anchor unit. Four parameters of the anchor unit are defined: grout-stiffness, grout-cohesion, young, and cross-sectional-area. Among them, grout-stiffness is 280 MPa, young is 201 GPa, and cross-sectional-area is 637.94 mm 2 . The grout-cohesion parameter is obtained by calculation using the first formula, which is 1192 kN / m.

[0061] The first formula is as follows: In the formula, c b1 is the initial cohesion of the anchoring interface; F p is the peak load in the anchoring performance curve obtained based on the experiment; and L is the length of the anchor cable.

[0062] A FISH function curve is defined and required to be automatically executed at each time step. The FISH function curve is calculated according to the second formula and the result is assigned to the variable disp, as shown in the following logical structure: Figure 2 The grid node head pointer is obtained and assigned to the variable pnt_gp. The variable sum is defined and set to zero. All grid nodes are traversed, and it is judged whether the traversed grid node is located on the boundary surface closest to the anchor unit pull-out end. If so, the unbalanced force of the variable pnt_gp in the pull-out direction is taken out, and the unbalanced force is summed with the variable sum and then assigned to the variable sum.

[0063] The second formula is: d = v * s; in the formula, d is a drawing displacement; v is a drawing speed; and s is a time step.

[0064] The post-peak load range of the anchoring performance curve obtained in the experiment is divided into 10 stages, and the connection points of the 10 stages are the peaks and troughs in the post-peak load range of the anchoring performance curve obtained in the experiment.

[0065] A FISH function vibration is defined and required to be automatically executed at each time step. The FISH function vibration adopts the following logic structure, as shown in the following formula: Figure 3 As shown in the formula, the anchor unit head pointer is obtained and assigned to the variable pnt_cable; all anchor units are traversed; when each anchor unit is traversed, it is judged that the variable disp is located in the i-th stage (1≤i≤10) of the 10 stages, wherein i is a variable; the experimental anchoring force corresponding to the starting point of the i-th stage is assigned to the variable y1, and the experimental drawing displacement is assigned to the variable x1; the experimental anchoring force corresponding to the end point of the i-th stage is assigned to the variable y2, and the experimental drawing displacement is assigned to the variable x2; the variables y1, y2, x1 and x2 are substituted into the third formula and the fourth formula to obtain the variables k and b respectively; the variables k and b are substituted into the fifth formula, and the result is assigned to the struct.cable.grout.cohesion parameter corresponding to the variable pnt_cable.

[0066] The third formula is: The fourth formula is: The fifth formula is: b2 = ks + b; c b2 is a dynamic cohesion of an anchoring interface.

[0067] The structure unit damping oscillation mode is set to combined-local. The large deformation calculation mode is set to true. The FISH variables force and disp are recorded. A constant drawing speed of 1×10 -6 m / s is applied to the outermost node of the anchor unit in the drawing direction. The loading is performed in a time step manner, and the time step is 51000.

[0068] The experimental results and the calculation results of the present application are compared, as shown in the following formula: Figure 4 The scattered dot circles are experimental results, and the continuous solid line is the calculation result of the present application. The calculation result of the present application is highly consistent with the experimental result, which verifies the effectiveness of the present application. Figure 4In the diagram, the dashed line represents the original calculation results. In these results, after the anchor cable reaches its peak load, the anchoring force drops to approximately 290 kN. Subsequently, the anchoring force decreases monotonically to 260 kN. However, this is clearly inconsistent with the mechanical characteristics of the anchor cable after peak load as observed in the experiment. In the experiment, after the anchor cable reaches its peak load, the anchoring force oscillates periodically between 247 kN and 297 kN. This is due to the periodic debonding and re-bonding of the embossed structure and the anchoring agent. The original calculation results cannot reflect this mechanical characteristic of the anchor cable after peak load.

[0069] In contrast, the calculation results of this invention show that after the anchor cable reaches the peak load, the anchoring force decreases rapidly. However, when it drops to around 247 kN, the anchoring force begins to rise. When it rises to 295 kN, the anchoring force begins to decrease again. This periodic rise and fall of the anchoring force continues to occur after the peak load. The trend of the anchoring force change is consistent with the experimental results, and the magnitude of the rise and fall of the anchoring force is consistent with the experimental results. This not only proves the effectiveness of the calculation results of this invention, but also highlights the superiority of this invention over the original calculation method.

[0070] Furthermore, based on this invention, users can utilize FLAC3D to output anchor cable axial force distribution data at different stages after the peak load. After the peak load, the anchoring force first decreases to 247kN, then increases to 295kN, and then decreases to 271kN. The axial force distribution within the cable is as follows: Figure 5 As shown, the axial force within the cable gradually decreases from the pulled-out end to the non-pulled-out end. This helps researchers better understand the anchoring mechanism of the embossed anchor cable during the oscillation of anchoring force after peak load. Because the original calculation results could not reflect the mechanical characteristics of the oscillation of anchoring force after peak load, they could not demonstrate the axial force distribution characteristics of the anchor cable during this oscillation process. This again demonstrates the superiority of the present invention compared to the original calculation results.

[0071] 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 method for determining the mechanical properties of embossed anchor cables after peak load, characterized in that, include: Creating a mesh in FLAC3D; Set the mesh constitutive model, material parameters, and boundary conditions; Anchor elements are created in the mesh using the `structure cablecreate` command, and anchor cables are simulated. Four parameters for the anchor elements are defined. The `FISH function curve` is defined and required to execute automatically at each time step. The peak load range of the anchoring performance curve obtained in the experiment is divided into... The stages, the The connection points for each stage are the peaks and troughs within the range of the peak load on the anchoring performance curve obtained in the experiment; define the FISH function `vibration` and require that the FISH function `vibration` be executed automatically at each time step; set the structural element damping oscillation mode to `combined-local`; set the large deformation calculation mode to `true`; record the FISH variables `force` and `disp`; A constant pull-out velocity of 1 × 10⁻⁶ is applied along the pull-out direction to the outermost node of the anchor unit. -6 m / s; loading is performed in time step mode; the four parameters are: grout-stiffness, grout-cohesion, young, and cross-sectional-area; the grout-cohesion parameter is calculated using the first formula; the FISH function curve adopts the following logical structure: calculate according to the second formula and assign the result to the variable disp; obtain the grid node head pointer and assign it to the variable pnt_gp; define the variable sum and set it to zero; traverse all grid nodes, determine whether the traversed grid node is located on the boundary surface closest to the pull-out end of the anchor element, if so, extract the unbalanced force of the variable pnt_gp along the pull-out direction, sum the unbalanced force with the variable sum and assign it to the variable sum; the FISH function vibration adopts the following logical structure: obtain the anchor element head pointer and assign it to the variable pnt_cable; traverse all anchor elements; when traversing to each anchor element, determine whether the variable disp is located on the boundary surface closest to the pull-out end of the anchor element. The first stage Each stage (1≤ ≤ ),in , All are variables; the first The experimental anchoring force corresponding to the starting point of each stage is assigned to a variable. The corresponding experimental pull-out displacement is assigned to the variable. ; will the first The experimental anchoring force corresponding to the end point of each stage is assigned to a variable. The corresponding experimental pull-out displacement is assigned to the variable. ; variables , , , Substitute into the third and fourth formulas to obtain the variables respectively. ,variable ; variables ,variable Substitute the values ​​into the fifth formula and assign the result to the struct.cable.grout.cohesion parameter corresponding to the variable pnt_cable; the first formula is: ;In the formula: This represents the initial cohesive force at the anchoring interface; This refers to the peak load in the anchorage performance curve obtained from experiments; Where is the anchor cable length; the second formula is: ;In the formula: For pull-out displacement; For drawing speed; The number of time steps; the third formula is: The fourth formula is: The fifth formula is: ; This refers to the dynamic cohesion at the anchoring interface.

2. The method for determining the mechanical properties of embossed anchor cables under peak load according to claim 1, characterized in that, The boundary condition is that the boundary surface closest to the pull-out end of the anchor unit is supported by a roller, while the other boundary surfaces are free boundaries.

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