A method for designing anchoring length of anchor rod based on in-situ measured interface mechanical parameters

Abstract

A kind of anchor rod anchoring length design method based on field measured interface mechanics parameter, it is related to testing and anchor support technical field.The method includes: engineering field measurement anchoring interface mechanics parameter, by construction drilling and bushing drilling construction, anchor rod is anchored in drill hole, measuring nut is installed on anchor rod, magnetic attraction base is installed on nut, displacement meter is installed on magnetic attraction base, the top rod contact of displacement meter and the surface of anchoring agent contact;Anchor rod pulling and measuring device are installed, pulling test and obtain anchor rod pulling load and anchor rod end displacement relationship curve;The relative displacement amount between anchoring surrounding rock is calculated, the shear stress and displacement relationship curve of anchoring interface is determined, the shear strength of anchoring interface is obtained according to maximum pulling load, interface axial shear stiffness is calculated;Long anchor rod pulling is regarded as the discretization model of n short anchor rod pulling anchoring unit combination, to anchor rod yield or break when anchoring interface just reaches shear strength as condition, anchoring length is determined, to ensure support safety.

Description

Technical Field

[0001] This invention relates to the field of testing and anchor bolt support technology, and in particular to a method for designing the anchorage length of anchor bolts based on field-measured interface mechanical parameters. Background Technology

[0002] Rock bolts have long been used for rock reinforcement, with billions consumed annually in mining projects. However, due to the influence of numerous factors such as anchor length, surrounding rock strength, and the bolt's own strength, the interaction mechanism between the anchor and the surrounding rock is not fully understood, and construction design still lacks theoretical guidance in some aspects. Anchor bolt support design includes parameter design such as anchor selection, anchoring agent selection, anchor spacing, and anchor length. Once the support material and spacing are determined, determining the anchor length is a crucial step.

[0003] For end anchor bolts in coal mines, due to engineering geology and mining influences, if the anchorage length is designed to be too short, the anchorage interface is prone to failure, leading to low bearing capacity or even slippage of the anchor bolt, making it difficult to achieve the anchor bolt's support performance. Conversely, if the anchorage length is too long, the free section of the anchor bolt is too short, reducing its energy absorption capacity. Once the shear strength and stiffness parameters of the anchorage interface are determined, the anchorage length has a significant impact on the ultimate anchorage force. Its rational design should fully consider the influence of factors such as stress environment, anchor bolt type, anchoring agent performance, surrounding rock properties, water content, and construction quality, as the geomechanical conditions of each roadway may be different. The shear strength and stiffness parameters of the anchorage interface can be calibrated through both indoor and engineering tests. However, indoor tests are difficult to accurately reproduce the engineering site conditions, mainly due to the following three issues: First, the engineering environment. Considering conditions such as mining stress in the surrounding rock of deep tunnels, indoor tests often cannot fully reproduce the actual stress state of the anchor bolt in the surrounding rock. Second, the physical and mechanical properties of the rock mass. Indoor tests generally use similar material ratios to prepare surrounding rock materials, but significant differences still exist. Third, anchor bolt anchorage construction usually requires dynamic design, but the current support parameter design based on indoor tests is relatively simple and not convenient for timely adjustments based on on-site measurement results.

[0004] In existing technologies, the design of anchor bolt anchorage length already takes into account the distribution of shear stress at the anchorage interface, making it closer to reality. However, on the one hand, due to the diversity of anchor bolt load transfer mechanical models, the distribution of shear stress at the anchorage interface is uncertain, and this distribution is affected by various factors, making it difficult to measure in actual engineering sites. On the other hand, after the anchor bolt is anchored, as the surrounding rock of the roadway deforms, the shear stress at the anchorage interface first reaches its shear strength at the end of the anchorage interface, and then gradually deteriorates, with the peak shear stress continuously shifting towards the anchorage depth, leading to progressive failure of the anchorage interface. To prevent this situation, when designing the anchor bolt anchorage length, the interface shear stress should be kept away from reaching the stress damage peak. This can be achieved by adjusting the anchorage length to keep the anchorage interface in an elastic stage within the anchor bolt's bearing capacity range.

[0005] Based on the above analysis, further calibration of the mechanical parameters of the anchorage interface on the engineering site requires comprehensive consideration of various engineering influencing factors. The calibration parameters are used to determine the shear stress distribution law of the anchorage interface under specific engineering conditions, and then the elastic anchorage length is determined, so as to achieve effective guidance for the practice of anchor support engineering. Summary of the Invention

[0006] In order to accurately measure the axial shear strength and shear stiffness of the anchorage interface of the anchor bolt in the roadway, and thus rationally design the required anchorage length of the anchor bolt support project, this invention provides a method for designing the anchorage length of the anchor bolt based on the measured mechanical parameters of the interface in the field. The specific technical solution is as follows.

[0007] A method for designing the anchorage length of an anchor bolt based on field-measured interface mechanical parameters, comprising the following steps:

[0008] S1. Measure the mechanical parameters of the anchorage interface on-site and obtain the relationship curve between the pull-out load of the short anchor and the displacement of the anchor end through pull-out tests;

[0009] S2. Calculate the relative displacement between the anchoring surrounding rock and determine the relationship curve between the shear stress and displacement at the anchoring interface;

[0010] S3. Calculate the shear strength of the anchorage interface based on the maximum pull-out load, and then calculate the axial shear stiffness of the interface.

[0011] S4. Treat the pull-out of long anchor bolts as a discretized model of n short anchor bolt pull-out anchoring units, and calculate and determine the anchoring length based on the condition that the anchoring interface just reaches the shear strength when the anchor bolt yields or breaks.

[0012] Preferably, the pull-out test includes: anchoring the short anchor rod in the drilled hole through construction drilling and casing drilling; installing a measuring nut on the short anchor rod, installing a magnetic base on the nut, installing a displacement gauge on the magnetic base, with the top rod contact of the displacement gauge in contact with the surface of the anchoring agent; installing an anchor rod pull-out and measuring device, monitoring the pull-out load and anchor rod end displacement during the pull-out test, and determining the relationship curve between the anchor rod pull-out load and the anchor rod end displacement.

[0013] Preferably, the short anchor bolts sequentially fix the pull-out reaction plate, the pull-out cylinder, the first pad, the load sensor, the second pad, and the nut; the pull-out cylinder is loaded, and the displacement gauge and the load sensor measure synchronously.

[0014] Furthermore, it is preferable that the relative displacement δ between the anchored surrounding rocks is... s1 The quantity calculation method is as follows:

[0015]

[0016] Where, δ s0 For the displacement of the anchor bolt pull-out end; l e d is the distance from the anchor point of the displacement gauge on the anchor bolt to the surface of the surrounding rock; b E is the diameter of the anchor bolt. b This represents the elastic modulus of the anchor bolt material.

[0017] Furthermore, it is preferable that the shear stress τ at the anchorage interface is... s1 The calculation method is as follows:

[0018]

[0019] Where P1 is the pull-out load of the short anchor bolt in the field; d b The diameter of the anchoring interface; l a This refers to the anchorage length for pulling out short anchor bolts on site.

[0020] Preferably, the shear strength [τ] at the anchorage interface is […]. s The calculation method for ] is as follows:

[0021]

[0022] Among them, P 1max The pull-out elastic limit load of the short anchor bolts on site; d b The diameter of the anchoring interface; l a This refers to the anchorage length for pull-out of short anchor bolts on site.

[0023] Furthermore, the axial shear stiffness k at the interface is also preferred. ss1 The calculation method is as follows:

[0024]

[0025] Where, Δτs1 Δδ represents the change in axial shear stress at the anchorage interface. s1 This represents the relative displacement change at the anchorage interface.

[0026] A further preferred approach is to analyze the interfacial shear stress distribution during the pull-out of long anchor bolts using the anchorage interface mechanical parameters determined by the pull-out of short anchor bolts, wherein the anchorage length l of a single anchorage matrix unit is... a The calculation method is as follows:

[0027]

[0028] Where n is the number of short anchor bolt pull-out anchoring units, L a This represents the total anchorage length of the anchor bolt;

[0029] The axial stiffness of the pull-out interface of the long anchor bolt is adopted using the stiffness calibrated through the pull-out test of the short anchor bolt, that is, the axial shear stiffness of the anchor bolt pull-out interface satisfies:

[0030] k ss =k ss1

[0031] Where, k ss For the axial shear stiffness of the anchorage interface; k ss1 Calibration stiffness of anchorage base unit

[0032] A further preferred approach is to conduct a pull-out test on a long anchor bolt. When the pull-out load is P, the shear stress transmitted at the first node is τ. s1 The displacement of the first node is:

[0033]

[0034] The difference in axial force P between the anchor bolts at node 1 and node 2 (1～2) The calculation method is as follows:

[0035] P (1～2) =τ s1 πd b l a

[0036] Where, τ s1 The shear stress of the first anchoring element; d b The diameter of the anchor rod;

[0037] The relative displacement difference δ between the interfaces of the first anchoring base unit and the second anchoring base unit s(1～2) The calculation method is as follows:

[0038]

[0039] Among them, E b The elastic modulus of the anchor bolt;

[0040] The deformation of the anchor bolt between node 1 and node 2 is calculated as follows:

[0041]

[0042] The deformation of the anchor bolt between the (n-1)th node and the nth node is obtained as follows:

[0043]

[0044] More preferably, the sum of the loads on the anchoring base unit equals the total pull-out force P, satisfying the following relationship:

[0045]

[0046] When τ s1 =[τ s ]season Where χ is the shear stress attenuation coefficient, the shear stress distribution at the anchorage interface when the anchor pull-out reaches the elastic limit state is as follows:

[0047] τ s(n) =[τ s ]χ n-1

[0048] The pull-out elastic limit load of the short anchor is:

[0049]

[0050] The anchorage length of the anchor bolt is calculated and determined as follows:

[0051]

[0052] Among them, P s and P b These are the yield load and breaking load of the anchor rod, respectively.

[0053] The beneficial effects of the anchorage length design method for anchor bolts based on field-measured interface mechanical parameters provided by this invention are:

[0054] This method utilizes a field short anchor pull-out and anchorage interface relative displacement measuring device to measure the mechanical parameters of the anchorage interface. It is simple, practical, and highly operable. It provides an in-situ test calibration method for the mechanical parameters of the anchorage interface, transforming a complex anchorage interface model into a smooth circular interface analysis model. During calibration, engineering geological factors and human factors related to the anchorage support can be taken into account, resulting in comprehensive anchorage interface mechanical parameters. Furthermore, through field parameter calibration and theoretical analysis models, this method proposes methods for determining the shear stress distribution, elastic limit load, and anchorage length at the anchorage interface. These methods can effectively guide anchorage support engineering practice and ensure support safety. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of an in-situ anchor pull-out test.

[0056] Figure 2 This is a schematic diagram illustrating the axial shear strength and stiffness analysis of the pull-out anchorage interface of a short anchor bolt.

[0057] Figure 3 This is a schematic diagram of the axial shear strength and stiffness analysis of the pull-out anchorage interface of a long anchor bolt.

[0058] Figure 4 This is a flowchart of the anchorage length design method based on on-site in-situ anchor pull-out measurement;

[0059] Figure 5 It is the distribution curve of interfacial shear stress along the anchorage length under different interfacial axial stiffness;

[0060] Figure 6 It is the distribution curve of elastic limit anchoring force with anchoring length under different interface axial stiffness;

[0061] In the diagram: 1-surrounding rock of the tunnel; 2-anchor bolt; 3-displacement gauge; 4-nut; 5-pull-out reaction plate; 6-magnetic base; 7-load sensor; 8-pad; 9-anchor bolt nut; 10-pull-out cylinder; 11-hydraulic pump; 12-test data instrument. Detailed Implementation

[0062] Combination Figures 1 to 6 As shown, a specific implementation method for designing anchor bolt anchorage length based on field-measured interface mechanical parameters provided by the present invention will be described.

[0063] An anchorage length design method based on field-measured interface mechanical parameters is proposed. The method calibrates the mechanical parameters of the anchorage interface on the engineering site, and takes into account various engineering influencing factors. The calibration parameters are used to determine the shear stress distribution law of the anchorage interface under specific engineering conditions, and then the elastic anchorage length is determined, which effectively guides the practice of anchorage support engineering.

[0064] The specific steps of this method include:

[0065] S1. Measure the mechanical parameters of the anchorage interface on-site and obtain the relationship curve between the pull-out load of the short anchor and the displacement of the anchor end through pull-out tests.

[0066] The pull-out test includes the following steps: A small hole is drilled first as the anchoring hole, and then a larger hole is drilled as the measurement hole. The diameter of the small hole matches the anchor rod, and the diameter of the larger hole should meet the measurement requirements. The short anchor rod is anchored in the drilled hole, and the anchoring length meets the requirements of the short anchor rod pull-out test. A measuring nut is installed on the short anchor rod, and a magnetic base is installed on the nut. A displacement gauge is installed on the magnetic base, with the displacement gauge's top rod contacting the surface of the anchoring agent. The displacement gauge's top rod is pressed in a certain distance. This displacement gauge is used to measure the pull-out displacement of the anchor rod relative to the surrounding rock. An anchor rod pull-out and measurement devices are installed. During the pull-out test, the pull-out load and the anchor rod end displacement are monitored to determine the relationship curve between the anchor rod pull-out load and the anchor rod end displacement.

[0067] The short anchor bolt is sequentially fixed with a pull-out reaction plate, a pull-out cylinder, a first pad, a load sensor, a second pad, and an anchor bolt nut. A hydraulic pump drives the pull-out cylinder to apply load, while a displacement gauge and load sensor simultaneously measure the load. The measurement results are transmitted to a data analyzer to obtain the curve showing the relationship between the pull-out load and the displacement at the anchor bolt end, i.e., P1-δ. s0 curve.

[0068] S2. Calculate the relative displacement between the anchored surrounding rock and determine the relationship curve between the shear stress and displacement at the anchoring interface.

[0069] The relative displacement δ between the anchored surrounding rocks s1 The quantity calculation method is as follows:

[0070]

[0071] Where, δ s0 For the displacement of the anchor bolt pull-out end; l e d is the distance from the anchor point of the displacement gauge on the anchor bolt to the surface of the surrounding rock; b E is the diameter of the anchor bolt. b This represents the elastic modulus of the anchor bolt material.

[0072] Anchorage interface shear stress τ s1 The calculation method is as follows:

[0073]

[0074] Where P1 is the pull-out load of the short anchor bolt in the field; d b The diameter of the anchoring interface; l a This refers to the anchorage length for pulling out short anchor bolts on site.

[0075] Based on the relationship curve between the pull-out load and the displacement at the end of the short anchor rod, the relationship curve between the shear stress and displacement at the anchorage interface, i.e., τ, can be obtained. s1 -δ s0 curve.

[0076] S3. Calculate the shear strength of the anchorage interface based on the maximum pull-out load, and then calculate the axial shear stiffness of the interface.

[0077] According to the shear stress-displacement relationship curve at the anchorage interface, the endpoint of the elastic stage is the maximum shear strength. Based on the assumption of uniform distribution of pull-out shear stress in short anchor bolts, the shear strength at the anchorage interface [τ] s The calculation method for ] is as follows:

[0078]

[0079] Among them, P 1max The pull-out elastic limit load of the short anchor bolts on site; d b The diameter of the anchoring interface; l a This refers to the anchorage length for pull-out of short anchor bolts on site.

[0080] Based on the relationship curve between shear stress and displacement at the anchorage interface, the slope is calculated by taking points in the elastic stage, which is the axial shear stiffness k of the interface. ss1 The calculation method is as follows:

[0081]

[0082] Where, Δτ s1 Δδ represents the change in axial shear stress at the anchorage interface. s1 This represents the relative displacement change at the anchorage interface.

[0083] S4. Treat the pull-out of long anchor bolts as a discretized model of n short anchor bolt pull-out anchoring units, and calculate and determine the anchoring length based on the condition that the anchoring interface just reaches the shear strength when the anchor bolt yields or breaks.

[0084] Under the same anchoring conditions, stiffness, as a structural interface property, is independent of the anchoring length and depends only on factors such as interface structure, material properties, and construction quality. Therefore, the interface shear stress distribution of long anchor pull-out can be analyzed using the mechanical parameters of the anchoring interface determined by the pull-out of short anchors. The pull-out of long anchors can be considered as a discretized model composed of n short anchor pull-out anchoring units, with the unit node displacements numbered 1, 2, 3…n.

[0085] The distribution of interfacial shear stress during the pull-out of long anchor bolts is analyzed using the mechanical parameters of the anchorage interface determined by the pull-out of short anchor bolts. The anchorage length *l* of a single anchorage matrix unit is considered. a The calculation method is as follows:

[0086]

[0087] Where n is the number of short anchor bolt pull-out anchoring units, L a This represents the total anchorage length of the anchor bolt;

[0088] The axial stiffness of the pull-out interface of the long anchor bolt is adopted using the stiffness calibrated through the pull-out test of the short anchor bolt, that is, the axial shear stiffness of the anchor bolt pull-out interface satisfies:

[0089] k ss =k ss1

[0090] Where, k ss For the axial shear stiffness of the anchorage interface; k ss1 Calibration stiffness of anchorage base unit

[0091] A pull-out test was conducted on a long anchor bolt. When the pull-out load was P, the shear stress transmitted at the first node was τ. s1 The displacement of the first node is:

[0092]

[0093] The displacement of the next node equals the displacement of the previous node minus the relative deformation of the anchor bolts between the two nodes. The relative deformation is equal to the ratio of the difference in axial load (axial force difference) between the anchor bolts between the two nodes to the tensile stiffness of the anchor bolts. The difference in axial force P between the first and second nodes is... (1～ 2) is calculated as follows:

[0094] P (1～2) =τ s1 πd b l a

[0095] Where, τ s1 The shear stress of the first anchoring element; d b The diameter of the anchor rod;

[0096] The relative displacement difference δ between the interfaces of the first anchoring base unit and the second anchoring base unit s(1～2) The calculation method is as follows:

[0097]

[0098] Among them, E b The elastic modulus of the anchor bolt;

[0099] Combining the above formulas, the anchor bolt deformation between node 1 and node 2 can be calculated as follows:

[0100]

[0101] Similarly, the deformation of the anchor bolt between the (n-1)th node and the nth node can be obtained as follows:

[0102]

[0103] Therefore, the relationship between the displacement of node n and node 1 can be obtained as follows:

[0104]

[0105] It can be obtained that the shear stress at node n decreases relative to the shear stress at node 1 as follows:

[0106]

[0107] The sum of the loads on the anchorage base element equals the total pull-out force P, satisfying the following relationship:

[0108]

[0109] When τ s1 =[τ s ]season Where χ is the shear stress attenuation coefficient, the formula for the shear stress distribution at the anchorage interface when the anchor pull-out reaches the elastic limit state is:

[0110] τ s(n) =[τ s ]χ n-1

[0111] The formula for calculating the pull-out elastic limit load of an anchor bolt is:

[0112]

[0113] The anchorage length of the anchor bolt is calculated and determined as follows:

[0114]

[0115] Among them, P s and P b These are the yield load and breaking load of the anchor rod, respectively.

[0116] Combination Figure 4 The specific implementation of the present invention will be further explained through specific field test examples.

[0117] According to the flowchart, a short anchor pull-out test is first conducted on-site, and the anchorage length l of the short anchor pull-out is determined. a =50mm, length of exposed end of anchor bolt l e =200mm; the pull-out load-displacement curve was obtained from the field test, and then the shear stress-displacement curve was obtained. The diameter d of the anchor rod used. b =20mm, elastic modulus E b =200GPa. The axial shear strength [τ] at the in-situ anchorage interface is calculated. s = 9.55MPa, axial shear stiffness k ss =5.0MPa / mm, take k as another value ssA comparative analysis was conducted at 25.0 MPa and 50 MPa.

[0118] Based on the formula for shear stress distribution at the anchorage interface, the distribution curve of shear stress along the anchor rod axis under the elastic limit state at the anchorage interface is obtained, as follows: Figure 5 As shown, the magnitude of the axial shear stiffness of the interface has a significant impact on the distribution of shear stress at the interface. The smaller the stiffness, the more uniform the distribution; the larger the stiffness, the more drastic the attenuation of shear stress along the anchorage length.

[0119] The variation of anchor pull-out load with anchor length under the elastic limit load of anchor bolts in the elastic limit state is obtained according to the formula for calculating the elastic limit load of anchor bolts. Figure 6 As shown. When the axial shear strength of the anchorage interface is the same, the smaller the axial shear stiffness of the interface, the greater the pull-out limit load that the anchorage interface can withstand. Assuming that the anchorage length is designed based on the anchor bolt yield load, and the anchor bolt yield load is 100kN, when k ss = 5.0 MPa / mm, anchorage length is about 400 mm; when k ss =25.0MPa, anchorage length approximately 550mm; when k ss =50.0MPa, anchorage length is about 1000mm.

[0120] According to this method, as long as the axial shear strength and shear stiffness of the anchorage interface are measured at the engineering site, the anchorage length of the anchor bolt under the same engineering conditions can be calculated and estimated, and a safety assessment can be performed.

[0121] Furthermore, this method utilizes on-site short anchor pull-out and anchorage interface relative displacement measurement devices to measure the mechanical parameters of the anchorage interface in a simple, practical, and highly operable manner. It transforms complex anchorage interface models into smooth circular interface analysis models, allowing for the consideration of engineering geological factors and human factors during calibration, resulting in comprehensive anchorage interface mechanical parameters. The method also proposes methods for determining the shear stress distribution, elastic limit load, and anchorage length at the anchorage interface, effectively guiding anchorage support engineering practices and ensuring support safety.

[0122] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for designing the anchorage length of an anchor bolt based on field-measured interface mechanical parameters, characterized by the following steps: include: S1. Measure the mechanical parameters of the anchorage interface on-site and obtain the relationship curve between the pull-out load of the short anchor and the displacement of the anchor end through pull-out tests; S2. Calculate the relative displacement between the anchoring surrounding rock and determine the relationship curve between the shear stress and displacement at the anchoring interface; S3. Calculate the shear strength of the anchorage interface based on the maximum pull-out load, and then calculate the axial shear stiffness of the interface. S4. Treat the pull-out of long anchor bolts as a discretized model combining n short anchor bolt pull-out anchoring units. Calculate and determine the anchoring length based on the condition that the anchoring interface just reaches its shear strength when the anchor bolt yields or breaks. The relative displacement between the anchoring surrounding rock The quantity calculation method is as follows: in, This refers to the displacement of the anchor bolt pull-out end; This is the distance from the fixed point of the displacement gauge on the anchor bolt to the surface of the surrounding rock where the anchor is anchored. The diameter of the anchor bolt; The elastic modulus of the anchor bolt material; The shear stress at the anchorage interface The calculation method is as follows: in, For the pull-out load of short anchor bolts on site; The diameter of the anchoring interface; This refers to the anchorage length for pull-out of short anchor bolts on site. The shear strength of the anchorage interface The calculation method is as follows: in, The pull-out elastic limit load of the short anchor bolts on site; The diameter of the anchoring interface; This refers to the anchorage length for pull-out of short anchor bolts on site. The axial shear stiffness of the interface The calculation method is as follows: in, This represents the change in axial shear stress at the anchorage interface. This represents the relative displacement change at the anchorage interface. The distribution of interfacial shear stress during the pull-out of long anchor bolts is analyzed using the mechanical parameters of the anchorage interface determined by the pull-out of short anchor bolts. The anchorage length of a single anchorage matrix unit is considered. The calculation method is as follows: Where n is the number of short anchor bolt pull-out anchoring units. This represents the total anchorage length of the anchor bolt; The axial stiffness of the pull-out interface of the long anchor bolt is adopted using the stiffness calibrated through the pull-out test of the short anchor bolt, that is, the axial shear stiffness of the anchor bolt pull-out interface satisfies: in, The axial shear stiffness of the anchorage interface; The calibration stiffness of the anchoring base unit; A pull-out test was conducted on a long anchor bolt. When the pull-out load was P, the shear stress transmitted through the first node was: The displacement of the first node is: The difference in anchor bolt axial force between node 1 and node 2 The calculation method is as follows: in, This represents the shear stress of the first anchoring unit. The diameter of the anchor rod; The relative displacement difference at the interface between the first anchoring base unit and the second anchoring base unit The calculation method is as follows: in, The elastic modulus of the anchor bolt; The deformation of the anchor bolt between node 1 and node 2 is calculated as follows: The deformation of the anchor bolt between the (n-1)th node and the nth node is obtained as follows: ； The sum of the loads on all anchorage base elements equals the total pull-out force P, satisfying the following relationship: when season ,in Given the shear stress attenuation coefficient, the shear stress distribution at the anchorage interface when the anchor pull-out reaches the elastic limit state is as follows: The pull-out elastic limit load of the anchor bolt is: The anchorage length of the anchor bolt is calculated and determined as follows: in, and These are the yield load and breaking load of the anchor rod, respectively.

2. The anchorage length design method for anchor bolts based on field-measured interface mechanical parameters according to claim 1, characterized in that, The pull-out test includes: anchoring a short anchor rod in a drilled hole through construction drilling and casing drilling; installing a measuring nut on the short anchor rod, a magnetic base on the nut, and a displacement gauge on the magnetic base, with the top rod contact of the displacement gauge in contact with the surface of the anchoring agent; installing an anchor rod pull-out and measuring device, monitoring the pull-out load and anchor rod end displacement during the pull-out test, and determining the relationship curve between the anchor rod pull-out load and the anchor rod end displacement.

3. The anchorage length design method for anchor bolts based on field-measured interface mechanical parameters according to claim 2, characterized in that, The short anchor rod sequentially fixes the pull-out reaction plate, pull-out cylinder, first pad, load sensor, second pad, and nut; the pull-out cylinder is loaded, and the displacement gauge and load sensor measure synchronously.

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