A method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test

Abstract

The present invention provides a method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test, which relates to the technical field of mechanical test experiments. The method includes: measuring the axial stiffness and strength of the anchoring interface by using a short bolt pull-out test, and determining the interface stiffness and strength parameters in the elastic stage of bolt pull-out; performing bolt pull-out loading by using a testing machine, monitoring the tensile deformation of the bolt and the total relative displacement of extraction during the pull-out process, and obtaining the relationship curve between the bolt pull-out load and the relative displacement; calculating the relative displacement amount between the bolt and the anchoring matrix; determining the relationship curve between the shear stress and displacement of the anchoring interface; calculating the axial shear strength of the anchoring interface and calculating the axial shear stiffness of the anchoring interface. This method can determine the interface stiffness, shear strength and their damage evolution laws under different bolts, different lithologies, different anchoring agents, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical testing, and in particular to a method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test. Background Art

[0002] The bearing effect of the bolt anchoring system is to drill a hole in the surrounding rock and place a bolt, and use mechanical means or bonding materials to form an effective contact between the bolt and the surrounding rock. The bolt transfers external loads or balances internal loads through the contact interface to fully mobilize the self-bearing capacity of the surrounding rock, thereby forming a strengthened anchoring system of bolt-surrounding rock collaborative work. Therefore, the contact mechanical properties of the anchoring interface are the key to determining the bearing performance of the bolt anchoring system.

[0003] The true interface physical structure and mechanical action of the ribbed steel bar bolt anchoring are relatively complex, including the bonding and mechanical biting interfaces between the bolt and the anchoring agent, and the bonding interface between the anchoring agent and the surrounding rock, which is mainly bonding. If the surrounding rock drill hole is rough, its mechanical biting effect is also obvious. The simulation analysis of the true interface physical structure is relatively difficult, and the simulation parameters are not easy to be calibrated by experiments. The establishment of the interface model lies in simplifying the original model and correctly characterizing the mechanical behavior of the original model. The simplest and most effective method is to simplify the true anchoring interface into a smooth interface, that is, to simplify various ribbed bolts into plain round bolts, simplify the uneven surrounding rock drill hole into a smooth drill hole, and simplify the anchoring agent layer with thickness into a contact surface without thickness. Then, based on experimental calibration and theoretical analysis, the interface mechanical parameters are obtained, especially the interface stiffness and shear strength in the bolt pulling direction, etc., to effectively simulate the indoor test and engineering test results.

[0004] The failure of the bolt anchoring interface is mainly the interface shear failure between the bolt and the anchoring agent or between the anchoring agent and the surrounding rock. The maximum shear stress that the interface can provide is the shear strength. The interface stiffness refers to the ability of the contact interface to resist interface displacement under the action of interface stress, that is, the ability to resist deformation or slip. In finite element calculation, if the interface stiffness value is too large, it will cause difficulties in interface convergence and too high overall stiffness of the structure. If the stiffness value is too small, it will cause too low overall stiffness of the structure. The interface stiffness performance has an important influence on the load transfer and damage of the interface, and is the key factor controlling the overall stiffness and performance of the structure. The size of the interface stiffness is also an important parameter for theoretical analysis and numerical calculation. Summary of the Invention

[0005] In order to clarify the axial shear stiffness and strength parameters of the anchoring interface and effectively analyze and simulate the indoor test and engineering test results, the present invention provides a method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test, and its specific technical solution is as follows.

[0006] A method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test, the method includes:

[0007] S1. Calculate the axial stiffness and strength of the anchoring interface by numerical simulation method for the short bolt pull-out test, and determine the interface stiffness and strength parameters in the elastic stage of bolt pull-out.

[0008] S2. Use a testing machine to conduct a bolt pull-out loading test, monitor the tensile deformation of the bolt and the relative displacement during pull-out, and obtain the relationship curve between the bolt pull-out load and the relative displacement.

[0009] S3. Calculate the relative displacement between the bolt and the anchoring matrix.

[0010] S4. Calculate and determine the relationship curve between the average shear stress and displacement of the anchoring interface.

[0011] S5. Calculate the axial shear strength of the anchoring interface and calculate the axial shear stiffness of the anchoring interface.

[0012] S6. Determine the stiffness damage evolution parameters of the anchoring interface.

[0013] Preferably, the steps of the bolt pull-out loading test include:

[0014] Install an anchoring pull-out device on a material tensile testing machine, place the anchoring matrix of the bolt pull-out specimen in the anchoring pull-out device, the testing machine clamps the test bolt, a U-shaped fixing part is installed at the free end of the test bolt, an L-shaped fixing part is installed at the port position of the anchoring matrix, both ends of the extensometer are connected to the U-shaped fixing part and the L-shaped fixing part respectively, and the distance between the U-shaped fixing part and the L-shaped fixing part is equal to the gauge length of the extensometer; the material tensile testing machine applies a pull-out force to the bolt to obtain the relationship curve between the bolt pull-out load and the relative displacement between the fixed point of the extensometer on the bolt.

[0015] Preferably, the relative displacement δ s1 of the bolt pull-out section is calculated as follows:

[0016]

[0017] where δ s0 is the displacement of the bolt pull-out end; l e is the gauge length of the extensometer; d b is the bolt diameter; E b is the elastic modulus of the bolt material.

[0018] Preferably, the average shear stress τ s1 of the anchoring interface is calculated as follows:

[0019]

[0020] where P1 is the short bolt pull-out load; d b is the diameter of the anchoring interface; la is the anchoring length for the short bolt pull-out test.

[0021] Preferably, the axial shear strength [τ s is calculated as follows:

[0022]

[0023] where P 1max is the ultimate pull-out load of the short bolt; d b is the diameter of the anchoring interface; l a is the anchoring length for the short bolt pull-out test.

[0024] Preferably, according to the relationship curve between the average shear stress and displacement of the anchoring interface, the slope k ss1 at the elastic stage point is calculated as follows:

[0025]

[0026] where Δτ s1 is the change in axial shear stress of the anchoring interface; Δδ s1 is the change in relative displacement of the anchoring interface, [τ s is the shear strength corresponding to the ultimate pull-out load; is the shear displacement corresponding to the ultimate pull-out load.

[0027] Preferably, the stiffness damage evolution parameters of the anchoring interface include the post-peak shear strength, post-peak shear stiffness, and post-peak shear stiffness damage parameter.

[0028] Preferably, the post-peak shear strength [τ′ s is calculated as follows:

[0029] [τ s = [τ s (1 - D τ )

[0030] where D τ is the shear strength damage variable, [τ s is the shear strength of the anchoring interface;

[0031] The post-peak shear stiffness k′ ss1 is calculated as follows:

[0032] k′ ss1 = k ss1 (1 - D k )

[0033] where D k is the axial shear stiffness damage variable, k ss1 is the slope at the elastic stage point.

[0034] Preferably, the axial shear stiffness damage variable D k is calculated as follows:

[0035]

[0036] wherein, δ s is the relative displacement of the post-peak anchoring interface; the shear displacement corresponding to the ultimate pulling load; D τ is the shear strength damage variable.

[0037] The beneficial effects of a method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test provided by the present invention include:

[0038] (1) Measuring and calibrating the mechanical parameters of the anchoring interface by using a short bolt pull-out test. Since the anchoring length of the short bolt pull-out is small and the difference in the bolt axial force within the anchoring length is small, the deformation of the bolt along the anchoring length can be ignored, and it is assumed that the interfacial shear stress is uniformly distributed.

[0039] (2) Considering that it is difficult to simulate the physical structure of the real interface and the simulation parameters are not easy to be calibrated by tests, this method simplifies the real anchoring interface into a smooth interface and simplifies the anchoring agent layer with thickness into a contact surface without thickness, so as to obtain the bolt axial interface stiffness, shear strength and interface axial stiffness damage variable, so as to realize effective simulation and determine the test results by simulation.

[0040] (3) When conducting the bolt pull-out loading test in this method, the displacement of the bolt end is measured by fixing an extensometer on the surface of the anchoring matrix and the bolt. The method is simple and practical with high measurement accuracy, and a calculation method for the relative displacement of the anchoring interface is proposed according to the measurement results, and the relationship curve between the interfacial shear stress and the shear displacement of the anchoring interface can be effectively obtained.

[0041] (4) By analyzing the results of the short bolt pull-out test, a calculation method for obtaining the interfacial axial shear strength, stiffness and their damage evolution parameters is given, and a method flow for accurately measuring the relative displacement of the anchoring interface and calibrating its axial mechanical parameters in an indoor test is proposed. Description of the Drawings

[0042] Figure 1 is a schematic diagram for analyzing the pull-out anchoring interface of a deformed steel bar bolt;

[0043] Figure 2 is a schematic diagram for analyzing the pull-out anchoring interface of a round steel bar bolt;

[0044] Figure 3 is a schematic diagram of the structure of an anchoring pull-out device;

[0045] Figure 4It is a schematic diagram for measuring the relative displacement of the anchoring interface of a short bolt pull-out specimen;

[0046] Figure 5 It is a schematic diagram for analyzing the axial shear strength and stiffness of the short bolt pull-out anchoring interface;

[0047] Figure 6 It is a schematic diagram for analyzing the axial shear strength and stiffness of the long bolt pull-out anchoring interface;

[0048] Figure 7 It is a flow chart for analyzing the axial shear strength and stiffness of the short bolt pull-out anchoring interface;

[0049] Figure 8 It is the data curve of the short bolt pull-out test;

[0050] Figure 9 It is the smoothed data curve of the short bolt pull-out test;

[0051] Figure 10 It is the relationship between the axial shear stiffness damage variable and displacement of the anchoring interface;

[0052] Figure 11 It is the test result of the pull-out load-displacement curve of bolts with different anchoring lengths;

[0053] Figure 12 It is the numerical simulation result of the pull-out load-displacement curve of bolts with different anchoring lengths.

[0054] In the figure: 1 - rock; 2 - anchoring agent; 3 - bolt; 4 - unit node; 5 - U-shaped fixture; 6 - L-shaped fixture; 7 - connector; 8 - pin; 9 - anchoring pull-out device; 10 - testing machine; 100 - extensometer. Specific implementation manner

[0055] Combined with Figures 1 to 12 shown, the specific implementation manner of a method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test provided by the present invention is described.

[0056] A method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test starts from the analysis of the relative displacement angle between a node position on one side of the bolt and a certain node on one side of the anchoring matrix, first determines the interface stiffness and strength parameters in the elastic stage of bolt pull-out, and then further calibrates the variation law and corresponding relationship of the strength damage variable and stiffness damage variable of the anchoring interface with displacement.

[0057] The specific steps of this method include:

[0058] S1. Calculate the axial stiffness and strength of the anchoring interface measured in the short bolt pull-out test by numerical simulation, and determine the interface stiffness and strength parameters in the elastic stage of bolt pull-out.

[0059] Specifically, when the bolt is pulled, it mainly bears the shearing force in the pulling direction. There are two important parameters to describe this shearing force, namely the shear strength and the shear stiffness. After these two parameters are determined, numerical calculation methods can be used to simulate the results of indoor tests and engineering tests. For example Figure 1 As shown, the current engineering bolts are usually deformed steel bars. Due to the existence of ribs on the bolt surface, the physical structure of the real interface of bolt anchorage is relatively complex and it is not easy to carry out numerical simulation. Therefore, a suitable interface mechanical model can be adopted to simplify the complex anchorage interface into a Figure 2 smooth anchorage interface as shown. The mechanical model parameters of the complex anchorage interface can be obtained by measuring the axial stiffness and strength of the anchorage interface through the short bolt pull-out test. The specific implementation method process is as Figure 7 shown

[0060] S2. Use a testing machine to conduct a bolt pull-out loading test, monitor the tensile deformation of the bolt and the relative displacement of the pulled-out bolt during the pulling process, and obtain the relationship curve between the bolt pull-out load and the relative displacement

[0061] Among them, the steps of the bolt pull-out loading test include: installing an anchorage pull-out device on a material tensile testing machine, placing the anchorage matrix of the bolt pull-out specimen in the anchorage pull-out device. The anchorage pull-out device is a rectangular frame with an open bottom, and its upper part is connected to the testing machine through a pin; the lower part of the testing machine clamps the test bolt. A U-shaped fixing piece is installed at the free end of the test bolt, and an L-shaped fixing piece is installed at the port position of the anchorage matrix. The two ends of the extensometer are respectively connected to the U-shaped fixing piece and the L-shaped fixing piece. The distance between the U-shaped fixing piece and the L-shaped fixing piece is equal to the gauge length of the extensometer, and the extensometer monitors the relative displacement between the two fixing pieces. The material tensile testing machine applies a pull-out force to the bolt to obtain the relationship curve between the bolt pull-out load and the relative displacement between the fixed point of the extensometer on the bolt, that is, the P1-δ s0 curve

[0062] The most important thing in the short bolt pull-out test is to accurately measure the relative displacement between the bolt and the anchorage matrix. When measuring, the deformation of the anchoring agent is included in the mechanical analysis model of the anchorage interface, that is, it is considered that the anchoring construction factors are taken into account when calibrating the interface mechanical model

[0063] S3. Calculate the relative displacement between the bolt and the anchorage matrix

[0064] The relative displacement δ s0 includes the relative displacement between the bolt and the anchorage matrix and the deformation of the free section of the bolt within the gauge length of the extensometer. It is necessary to separate the two to obtain only the relative displacement between the bolt and the anchorage matrix. The calculation method of the relative displacement δ s1 of the bolt pull-out section is as follows

[0065]

[0066] Among them, δ s0 is the displacement of the end of the anchor bolt pull-out; l e is the gauge length of the extensometer (i.e., the distance from the fixed point of the extensometer on the anchor bolt to the anchoring matrix); d b is the diameter of the anchor bolt; E b is the elastic modulus of the anchor bolt material.

[0067] S4. Calculate and determine the relationship curve between the average shear stress and displacement of the anchoring interface.

[0068] The average shear stress τ s1 of the anchoring interface is calculated as follows:

[0069]

[0070] Among them, P1 is the pull-out load of the short anchor bolt; d b is the diameter of the anchoring interface (equivalent diameter of the anchor bolt); l a is the anchoring length of the short anchor bolt pull-out.

[0071] S5. Calculate the axial shear strength of the anchoring interface and calculate the axial shear stiffness of the anchoring interface.

[0072] According to the relationship curve between the shear stress and displacement of the anchoring interface, the end point of its elastic stage is the maximum shear strength. According to the assumption of the average distribution of the short anchor bolt pull-out shear stress, the axial shear strength [τ s of the anchoring interface can be obtained from the maximum pull-out load, and its calculation method is as follows:

[0073]

[0074] Among them, P 1max is the ultimate pull-out load of the short anchor bolt; d b is the diameter of the anchoring interface (equivalent diameter of the anchor bolt); l a is the anchoring length of the short anchor bolt pull-out.

[0075] According to the relationship curve between the average shear stress and displacement of the anchoring interface, the slope is calculated by taking points in the elastic stage, which is the axial shear stiffness of the interface. Calculate the slope k ss1 at the points in the elastic stage, and its calculation method is as follows:

[0076]

[0077] Among them, Δzτ s1 is the change in the axial shear stress of the anchoring interface; Δδ s1 is the change in the relative displacement of the anchoring interface, [τ s is the shear strength corresponding to the ultimate pull-out load; δ s is the shear displacement corresponding to the ultimate pull-out load.

[0078] S6. Determine the stiffness damage evolution parameters of the anchoring interface.

[0079] Among them, the stiffness damage evolution parameters of the anchoring interface include the post-peak shear strength, the post-peak shear stiffness, and the post-peak shear stiffness damage parameter.

[0080] The calculation method of the post-peak shear strength [τ′ s is as follows:

[0081] [τ′ s = [τ s (1 - D τ )

[0082] Among them, D τ is the shear strength damage variable, and [τ s is the shear strength of the anchoring interface;

[0083] The calculation method of the post-peak shear stiffness k′ ss1 is as follows:

[0084] k′ ss1 = k ss1 (1 - D k )

[0085] Among them, D k is the axial shear stiffness damage variable, and k ss1 is the slope at the elastic stage point.

[0086] The calculation method of the axial shear stiffness damage variable D k is as follows:

[0087]

[0088] Among them, δ s is the relative displacement of the post-peak anchoring interface; the shear displacement corresponding to the ultimate pull-out load; D τ is the shear strength damage variable.

[0089] This method is based on the indoor pull-out test of short bolts, and accurately measures the relative displacement of the anchoring interface to obtain the anchoring interface parameters. For the measurement of the deformation of a certain point on the bolt specimen, the most commonly used method is the extensometer measurement method. When the length dimension of the bolt is small, it can be assumed that the shear stress along the length direction of the bolt on the anchoring interface is evenly distributed, and the relative shear displacement (relative displacement between the bolt and the anchoring matrix) at different positions on the interface is also assumed to be the same. On this basis, according to a method for measuring the shear mechanical parameters of the anchoring interface using an indoor pull-out test provided by the present invention, the stiffness and shear strength of the anchoring interface and their damage evolution laws under different bolts, different lithologies, different anchoring agents, etc. can be determined.

[0090] As shown Figure 5 below, the following specific embodiments are provided:

[0091] Among them, the anchoring length l of the short bolt pull-out a = 50 mm, and the measuring length l of the extensometer 100 on the exposed section of the bolt e = 200 mm; As shown Figure 6 below, the length L of the anchoring section of the long bolt pull-out a = 500 mm, and the measuring length L of the extensometer 100 on the exposed section of the bolt e = 200 mm; Then the ratio n of the anchoring lengths of the short and long bolts is 10. The bolt diameter d b = 20 mm, and the elastic modulus E b = 200 GPa.

[0092] As shown Figure 8 below is the pull-out load - interface displacement curve measured in the short bolt pull-out test. Based on this curve, the anchoring interface shear stress - interface displacement curve as shown Figure 9 below is obtained. According to the calculation method of the axial shear strength [τ s of the anchoring interface, the axial shear strength [τ s = 9.55 MPa is obtained; According to the calculation method of the slope k ss1 at the elastic stage point, the axial shear stiffness of the anchoring interface is k ss1 = 5.0 MPa / mm; According to the calculation method of the axial shear stiffness damage variable D k , the variation curve of the axial shear stiffness damage variable of the anchoring interface with the interface displacement is obtained. As shown Figure 10 below, and then the value list of the damage variable D k is obtained, as shown in the following table.

[0093] <![CDATA[Damage variable D k > <![CDATA[Shearing displacement δ s / mm]]> 0 0 0.19 0.55 0.32 1.04 0.4 1.73 0.54 2.49 0.67 4.02 0.77 5.61 0.85 7.69 0.91 11.29 0.97 18.07 0.98 27.29 1 46.68

[0094] This method simplifies the real anchoring interface into a smooth interface and simplifies the anchoring agent layer with thickness into a contact surface without thickness, obtaining the axial interface stiffness, shear strength and interface axial stiffness damage variable of the bolt to achieve effective simulation and determine the test results. When conducting the bolt pull-out loading test, the displacement of the bolt end is measured by fixing extensometers on the surface of the anchoring matrix and the bolt. The method is simple and practical with high measurement accuracy. A calculation method for the relative displacement of the anchoring interface is proposed based on the measurement results, and the relationship curve between the shear stress and shear displacement of the anchoring interface can be effectively obtained. By analyzing the results of the short bolt pull-out test, a calculation method for obtaining the axial shear strength, stiffness and their damage evolution parameters of the interface is given, and a method process for accurately measuring the relative displacement of the anchoring interface and calibrating its axial mechanical parameters in the laboratory test is also proposed. This method can effectively determine the stiffness, shear strength and their damage evolution laws of the anchoring interface under different bolts, different lithologies, different anchoring agents, etc.

[0095] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for determining the shear mechanical parameters of an anchoring interface by using an indoor pull-out test, characterized in that, The method includes: S1. Calculate the axial stiffness and strength of the anchoring interface through numerical simulation in the short bolt pull-out test, and determine the interface stiffness and strength parameters in the elastic stage of bolt pull-out; S2. Use a testing machine to conduct a bolt pull-out loading test, monitor the tensile deformation of the bolt and the relative displacement during pull-out in the process, and obtain the relationship curve between the bolt pull-out load and the relative displacement; S3. Calculate the relative displacement between the bolt and the anchoring matrix; S4. Calculate and determine the relationship curve between the average shear stress and displacement of the anchoring interface; S5. Calculate the axial shear strength of the anchoring interface and calculate the axial shear stiffness of the anchoring interface; S6. Determine the stiffness damage evolution parameters of the anchoring interface; The stiffness damage evolution parameters of the anchoring interface include the post-peak shear strength, post-peak shear stiffness, and post-peak shear stiffness damage parameter; the calculation method of the post-peak shear strength [τ′ s is as follows: [τ′ s = [τ s (1 - D τ ) Among them, D τ is the shear strength damage variable, and [τ s is the shear strength of the anchorage interface; The post-peak shear stiffness k′ ss1 is calculated as follows: k′ ss1 = k ss1 (1 - D k ) Among them, D k is the axial shear stiffness damage variable, and k ss1 is the slope at the elastic stage point.

2. The method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test according to claim 1, characterized in that The steps of the bolt pull-out loading test include: Install an anchoring pull-out device on a material tensile testing machine, place the anchoring matrix of the bolt pull-out specimen in the anchoring pull-out device, the testing machine clamps the test bolt, a U-shaped fixing piece is installed at the free end of the test bolt, an L-shaped fixing piece is installed at the port position of the anchoring matrix, both ends of the extensometer are connected to the U-shaped fixing piece and the L-shaped fixing piece respectively, and the distance between the U-shaped fixing piece and the L-shaped fixing piece is equal to the gauge length of the extensometer; the material tensile testing machine applies a pull-out force to the bolt to obtain the relationship curve between the bolt pull-out load and the relative displacement between the fixed point of the extensometer on the bolt.

3. A method for measuring the shear mechanical parameters of the anchoring interface by using an indoor pull-out test according to claim 1, characterized in that, The relative displacement δ of the bolt pulling section s1 is calculated as follows: Among them, δ s0 is the displacement of the end of the anchor rod pull-out; l e is the gauge length of the extensometer; d b is the diameter of the anchor rod; E b is the elastic modulus of the anchor rod material.

4. A method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test according to claim 1, characterized in that, The average shear stress τ of the anchoring interface s1 is calculated as follows: Among them, P1 is the pull-out load of the short bolt; d b is the diameter of the anchoring interface; l a is the anchoring length of the short bolt for pull-out.

5. A method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test according to claim 1, characterized in that The axial shear strength [τ s of the anchoring interface is calculated as follows: Among them, P 1max is the ultimate pull-out load of the short bolt; d b is the diameter of the anchoring interface; l a is the anchoring length of the short bolt pull-out.

6. A method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test according to claim 1, characterized in that, Calculate the slope k at the elastic stage point according to the relationship curve between the average shear stress and displacement of the anchoring interface ss1 The calculation method is as follows: Among them, Δτ s1 is the change in the axial shear stress of the anchoring interface; Δδ s1 is the change in the relative displacement of the anchoring interface, [τ s is the shear strength corresponding to the ultimate pull-out load; is the shear displacement corresponding to the ultimate pull-out load.

7. A method for measuring the shear mechanical parameters of an anchoring interface by using an indoor pull-out test according to claim 1, characterized in that The calculation method of the axial shear stiffness damage variable D k is as follows: Among them, δ s is the relative displacement of the post-peak anchoring interface; the shear displacement corresponding to the ultimate pull-out load; D τ is the shear strength damage variable.

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