Test Method for Evolution of Cumulative Displacement and Bearing Capacity of Anchor Bolts under Cyclic Loading

Abstract

This invention belongs to the field of geotechnical anchoring engineering technology, specifically relating to an experimental method for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading. Based on similarity theory, a model experiment is designed to determine the similarity ratio of geometric, physical, and mechanical parameters, and the experimental scheme is optimized by combining uniform design or hybrid uniform design. By simulating soft rock strata, cyclic loading, and anchor bolt assemblies, the cumulative displacement, stiffness, and ultimate bearing capacity are tested under different cycles and baseline load ratios. Evolutionary equations are established to quantify the performance degradation law of the anchor bolts. This invention solves the problem of the lack of a systematic cyclic loading experimental method in existing technologies, achieving efficient and accurate performance evolution analysis and providing a basis for engineering durability design.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical anchoring engineering technology, specifically relating to a test method for the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading. Background Technology

[0002] Anchoring technology, as a key means of ensuring the stability of soil and rock masses, is widely used in engineering fields such as deep foundation pit support, high slope reinforcement, underground structure anti-buoyancy, and mine roadway support. In recent years, recyclable pressure anchors have gradually emerged due to their environmental and sustainability advantages. However, whether tension or pressure type, anchors in actual engineering projects are subjected to cyclic loads caused by traffic loads, mechanical vibrations, and groundwater level fluctuations for extended periods, leading to performance degradation at the interface between the anchor body and the soil and rock mass. Specifically, this manifests as follows:

[0003] The load-bearing capacity of the anchor bolts decreased;

[0004] The stiffness of the anchor bolts is weakened;

[0005] The cumulative displacement continues to increase;

[0006] The long-term stability of the project is reduced.

[0007] Accurately obtaining the evolution laws of cumulative displacement, stiffness, and ultimate bearing capacity of anchor bolts under cyclic loading is the core basis for ensuring the safety of anchorage engineering design. Although indoor model experiments have the advantages of higher efficiency and controllable conditions compared with field testing, existing technologies still have the following shortcomings:

[0008] Limitations of experimental methods: Existing performance tests of anchor bolts in soft rock formations are mostly designed for static loads, lacking a complete indoor model test method for dynamic loads; the experimental model is not designed based on similarity theory and combined with the characteristics of soft rock formations in actual engineering (such as rock mechanics parameters) and cyclic load parameters (frequency, amplitude, waveform, etc.), resulting in a disconnect between simulation results and actual working conditions.

[0009] The evolutionary laws are not quantified: there is a lack of systematic derivation of the cumulative displacement, stiffness, and ultimate bearing capacity of anchor bolts with the number of cycles from model experimental results. and reference load ratio The evolution equations make it difficult to predict long-term service performance.

[0010] Therefore, there is an urgent need to develop an indoor model test method based on similarity theory that can quantify the evolution of anchor bolt performance under cyclic loading, in order to improve the reliability and sustainability of anchoring projects. Summary of the Invention

[0011] The purpose of this invention is to provide an experimental method for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading. This method solves the problem of the lack of a systematic cyclic loading experimental method in the prior art, and enables efficient and accurate performance evolution analysis, providing a basis for engineering durability design.

[0012] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0013] This invention provides an experimental method for studying the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading, including:

[0014] Step S11: Take undisturbed rock samples from the engineering site and determine the physical and mechanical parameters of the original rock material in the laboratory;

[0015] Step S12: Determine the dimensions and materials of the prototype anchor rod, and the cyclic load parameters based on the actual working conditions.

[0016] Step S13, based on the number of load cycles and reference load ratio As influencing factors, design an indoor model experimental scheme based on uniform design or hybrid uniform design methods. The level number is 5-10. The number of levels is 4 to 9;

[0017] Step S14: Design the similarity ratio of the indoor model experiment and determine the values ​​of each physical quantity in the model experiment;

[0018] Step S15: Design and fabricate the model experimental device and the model anchor assembly;

[0019] Step S16: Conduct indoor model experiments on the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading; Step S17: Analyze the evolution law of cumulative displacement of prototype anchor bolts under cyclic loading in soft rock strata and establish its evolution equation.

[0020] Step S18: Analyze the evolution law of prototype anchor stiffness under cyclic loading in soft rock strata and establish its evolution equation;

[0021] Step S19: Analyze the evolution law of the ultimate bearing capacity of the prototype anchor bolt under cyclic loading in soft rock strata and establish its evolution equation.

[0022] Compared with the prior art, the advantages of this invention are as follows:

[0023] 1. The experimental apparatus of this invention has a simple structure, low manufacturing cost, and a clear operation procedure, exhibiting good repeatability and operability. The design of the model box, loading, and measurement system can flexibly adapt to different geological conditions and engineering needs. By adjusting the similarity ratio, loading parameters, and material proportions, it is widely applicable to various geotechnical environments and dynamic load scenarios. The versatility of the experimental method makes it easy to extend to the study of recyclable anchor bolts under working conditions, providing technical support for different engineering projects and significantly improving experimental efficiency and application value.

[0024] 2. This invention optimizes experimental design and reduces redundant workload. It adopts uniform design and hybrid uniform design methods to design indoor model experimental schemes, which greatly reduces the number of model experiments.

[0025] 3. Based on the experimental results of an indoor model of anchor bolts in soft rock formations designed according to similarity theory, this invention obtains the cumulative displacement of anchor bolts as a function of the number of cyclic loads. and reference load ratio The evolutionary pattern was determined, and for the first time, the correlation of cyclic load numbers was established. and reference load ratio Evolution equation of cumulative displacement of anchor bolt with two parameters.

[0026] 4. Based on the experimental results of an indoor model of anchor bolts in soft rock formations designed according to similarity theory, this invention obtains the anchor bolt stiffness as a function of the number of cyclic loading cycles. and reference load ratio The evolutionary pattern was determined, and for the first time, the correlation of cyclic load numbers was established. and reference load ratio Evolution equation of anchor stiffness with two parameters.

[0027] 5. Based on the experimental results of an indoor model of anchor bolts in soft rock formations designed according to similarity theory, this invention obtains the ultimate bearing capacity of anchor bolts as a function of the number of cyclic loading cycles. and reference load ratio The evolutionary pattern was determined, and for the first time, the correlation of cyclic load numbers was established. and reference load ratio Evolution equation of ultimate bearing capacity of anchor bolt with two parameters.

[0028] 6. This invention, through a systematic model experiment method, based on similarity theory and cyclic loading, accurately quantifies the cumulative displacement and bearing capacity evolution of anchor bolts under traffic cyclic loads, reveals the performance degradation mechanism under dynamic loads, and provides a scientific and reliable quantitative basis for engineering durability design and theoretical research, effectively filling the gap in existing technology in the study of anchor bolt dynamic performance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0030] Figure 1 A schematic flowchart of the test method for the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading provided by the present invention;

[0031] Figure 2 Diagram of the experimental setup for a pressure-type anchor bolt model under cyclic loading;

[0032] Figure 3 Diagram of the experimental setup for a tension-type anchor bolt model under cyclic loading;

[0033] Figure 4 This is one of the cumulative displacement evolution diagrams of a pressure-type anchor bolt under cyclic loading provided in Embodiment 1 of the present invention;

[0034] Figure 5 This is one of the stiffness evolution factor diagrams of a pressure-type anchor bolt under cyclic loading provided in Embodiment 1 of the present invention;

[0035] Figure 6 This is one of the evolution factor diagrams of the bearing capacity of a pressure-type anchor bolt under cyclic loading provided in Embodiment 1 of the present invention;

[0036] Figure 7 This is the second diagram showing the cumulative displacement evolution of a tension-type anchor bolt under cyclic loading, provided in Embodiment 2 of the present invention.

[0037] Figure 8 This is the second diagram of the stiffness evolution factor of a tension-type anchor bolt under cyclic loading provided in Embodiment 2 of the present invention;

[0038] Figure 9 This is the second diagram of the evolution factor of the bearing capacity of the tension-type anchor bolt under cyclic load provided in Embodiment 2 of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0041] Please see Figure 1 As shown, this embodiment of the invention provides a test method for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading, including:

[0042] Step S11: Take undisturbed rock samples from the engineering site and determine the physical and mechanical parameters of the original rock material, including density, in the laboratory. Elastic modulus Unconfined compressive strength and tensile strength ;

[0043] Step S12: Determine the dimensions and material of the prototype anchor rod, and the cyclic load parameters based on the actual working conditions, wherein:

[0044] Dimensional parameters include the length of the anchorage section. Length of free segment Anchor body diameter ;

[0045] Material parameters include the density of the anchoring material. Elastic modulus Unconfined compressive strength ,tensile strength ;

[0046] Cyclic load parameters include the cyclic load amplitude acting on the prototype anchor bolt. ,frequency and the reference load ratio ;

[0047] Step S13, based on the number of load cycles and reference load ratio As influencing factors, design an indoor model experimental scheme based on uniform design or hybrid uniform design methods. The level number is 5-10. The number of levels is 4 to 9;

[0048] Step S14: Design the similarity ratio for the indoor model experiment and determine the values ​​of each physical quantity in the model experiment; where:

[0049] The similarity ratio for the indoor model experiment was designed, specifically including:

[0050] Define length similarity ratio Density similarity ratio Elastic modulus similarity ratio Stress similarity ratio Concentration similarity ratio Stiffness similarity ratio Frequency similarity ratio ;

[0051] Sure and Afterwards, according to and calculate and ;

[0052] Determine the values ​​of each physical quantity in the model experiment, specifically including:

[0053] Parameters for calculating soft rock similar materials in the model:

[0054] ;

[0055] In the formula, For prototype physical quantities; For model physical quantities; The density of the soft rock-like material in the model experiment; This refers to the elastic modulus of the soft rock-like material in the model experiment; The unconfined compressive strength of soft rock-like materials in the model experiment; The tensile strength of the soft rock-like material in the model experiment;

[0056] Calculate the anchor bolt size parameters of the model:

[0057] ;

[0058] In the formula, This refers to the length of the anchorage section of the model anchor rod; The length of the free segment; The diameter of the anchor body;

[0059] Calculation model anchor body material parameters:

[0060] ;

[0061] In the formula, The density of the anchor solid-like material in the model experiment; The elastic modulus of the anchor solid similar material in the model experiment; The unconfined compressive strength of the anchor solid similar material in the model experiment; The tensile strength of the anchor solid similar material in the model experiment;

[0062] Calculate the cyclic load parameters of the model:

[0063] ;

[0064] In the formula, The magnitude of the cyclic load acting on the model anchor bolt; The frequency of the cyclic load acting on the model anchor;

[0065] Step S15: Design and fabricate the model experimental device and the model anchor assembly;

[0066] Specifically, in combination Figure 2 and Figure 3 As shown, the model experimental device includes a model box 1, a simulated soft rock stratum 2 located inside the model box 1, a simulated anchor bolt assembly inserted into the simulated soft rock stratum 2, and a loading and measurement system connected to the simulated anchor bolt assembly;

[0067] The simulated anchor bolt assembly is either a pressure-type anchor bolt assembly or a tension-type anchor bolt assembly; for details, see [link to relevant documentation]. Figure 2 As shown, the pressure-type anchor bolt assembly includes an anchor bar 31, an anchor body 32 covering the anchor bar 31, an anchor end bearing plate 33 disposed at the bottom end of the anchor bar 31, and an isolation sleeve 34 sleeved on the anchor bar 31 and located between the anchor bar 31 and the anchor body 32; see also Figure 3 As shown, the tension-type anchor bolt assembly includes an anchor bar 31 and an anchor body 32 covering the anchor bar 31. The anchorage length of the anchor bolt is... The length of the free segment is The diameter of the anchor body is The diameter of the model box is .

[0068] The loading and measurement system includes a servo actuator 41, a servo controller 42, a data acquisition processor 43, a connecting fixture 44, an upper pressure plate 45, a lower pressure plate 46, a pressure rod 47, an adjusting nut 48, a water bladder 49, a column 51, and a crossbeam 52.

[0069] The servo actuator 41 includes an electric cylinder, a displacement sensor, and a load sensor, used to apply cyclic and tensile loads to the simulated anchor bolt assembly, and to measure the magnitude of the load and displacement during the loading process. Specifically, the servo actuator 41 is connected to the anchor bar 31 via the connecting clamp 44.

[0070] The servo controller 42 is connected to the servo actuator 41 and the data acquisition processor 43, and is used to control the loading mode and size of the cyclic load.

[0071] The upright column 51 is erected, and the crossbeam 52 is fixed to the upright column 51. The servo actuator 41 is fixed to the lower side of the crossbeam 52 via the upper pressure plate 45. The lower pressure plate 46 is fixed to the top surface of the model box 1. The pressure rod 47 is disposed between the upper pressure plate 45 and the lower pressure plate 46. The water bladder 49 is disposed between the lower pressure plate 46 and the model box 1.

[0072] The adjusting nut 48 is disposed between the pressure rod 47 and the upper pressure plate 45 to adjust the distance between the upper pressure plate 45 and the lower pressure plate 45.

[0073] Step S16: Conduct indoor model experiments on the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading; specifically including:

[0074] After fabricating and maintaining the model anchor bolt assembly, position it in the center of the model box;

[0075] Fill the soft rock-like material in layers and compact it with vibration;

[0076] Pull-out tests were conducted on the unloaded model anchor rods to measure the initial stiffness. and ultimate bearing capacity ;

[0077] The number of cycles was set according to the experimental design. and benchmark working load ratio Calculate the baseline working load Apply cyclic load to Record the cumulative displacement. ; for the The anchor bolts in the second cycle were subjected to pull-out tests to measure their ultimate bearing capacity. and stiffness :

[0078] ;

[0079] in , The load and displacement corresponding to the 90% peak point of the rising segment of the model anchor load-displacement curve; , The load and displacement corresponding to the 20% peak point of the rising segment of the model anchor load-displacement curve;

[0080] Step S17 involves analyzing the evolution law of cumulative displacement of the prototype anchor bolt under cyclic loading in soft rock strata and establishing its evolution equation, specifically including:

[0081] Based on geometric similarity ratio Calculate the first The cumulative displacement of each prototype anchor rod ( ), and establish the cumulative displacement of the prototype anchor. With the number of load cycles and reference load ratio The evolution equation:

[0082] ;

[0083] In the formula, The cumulative displacement of the prototype anchor rod is derived from the model experiment results; , , , These are parameters obtained through regression analysis of experimental data;

[0084] Step S18 involves analyzing the evolution law of prototype anchor stiffness under cyclic loading in soft rock strata and establishing its evolution equation, specifically including:

[0085] Based on the similarity ratio of elastic modulus Similarity ratio of length Calculate the first Stiffness of a prototype anchor ( ), and establish the stiffness of the prototype anchor rod. With the number of load cycles and reference load ratio The evolution equation:

[0086] ;

[0087] In the formula, The results of the anchor stiffness test on the model without cyclic loading are as follows. The stiffness of the prototype anchor rod was derived. Stiffness evolution factor;

[0088] Step S19 involves analyzing the evolution law of the ultimate bearing capacity of the prototype anchor bolt under cyclic loading in soft rock strata and establishing its evolution equation, specifically including:

[0089] Based on the similarity ratio of elastic modulus Similarity ratio of length Calculate the first Ultimate bearing capacity of a prototype anchor bolt ( ), and establish the ultimate bearing capacity of the prototype anchor. With the number of load cycles and reference load ratio The evolution equation:

[0090] ;

[0091] In the formula, The ultimate bearing capacity test results of the model anchor bolt without cyclic loading. The ultimate bearing capacity of the prototype anchor rod was derived. This is the factor for the evolution of carrying capacity.

[0092] In step S12, the reference load ratio Defined as ,in As the benchmark working load, This represents the ultimate bearing capacity of the prototype anchor bolt.

[0093] In step S13, the uniform design adopts an equal-level number uniform design table, and the mixed uniform design adopts a mixed-level uniform design table.

[0094] In step S14, the length similarity ratio Density similarity ratio Elastic modulus similarity ratio Stress similarity ratio Concentration similarity ratio Stiffness similarity ratio Frequency similarity ratio They are respectively expressed by the following formulas:

[0095] .

[0096] In step S16, soft rock-like materials are filled into the model box in 3 to 5 layers.

[0097] In step S16, the amplitude of the cyclic load and frequency Configured via servo controller 42.

[0098] The following detailed description of the experimental method for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading provided by the present invention is based on specific embodiments.

[0099] Example 1

[0100] Example 1 provides a highly adaptable, practical, and efficient experimental method for studying the evolution of cumulative displacement and bearing capacity of pressure-type anchor bolts under cyclic loading, specifically including:

[0101] The first step is to select the target strata and test the original rock samples;

[0102] A roadbed slope anchoring project was selected as the prototype for the indoor model experiment. Original rock samples were drilled from the weathered soft rock strata at the project site. The physical and mechanical parameters of the samples were measured in the laboratory according to the "Code for Geotechnical Investigation (GB 50021-2009)" and the "Standard for Test Methods of Engineering Rock Mass (GB / T50266-2014)". These parameters included density. It is 2100 kg / m³, and its elastic modulus is 2100 kg / m³. 720 MPa, unconfined compressive strength The tensile strength is 10.8 MPa. It is 1.08 MPa.

[0103] The second step is to determine the dimensions, material, and load parameters of the prototype anchor bolt;

[0104] Based on the design data of the actual project, the anchorage length of the prototype anchor rod was analyzed and determined. =3m, length of free segment =3m, anchor body diameter =0.15m, and the density of the anchor material. =2400kg / m 3 Elastic modulus =25.5GPa, unconfined compressive strength =20MPa, tensile strength =1.54MPa; Based on actual working conditions and combined with investigation and research, the amplitude of the cyclic load acting on the prototype anchor was determined. =42kN, frequency =0.288Hz, and the reference load ratio The value range is 0.2 to 0.8.

[0105] The third step is to determine the indoor model experiment scheme based on the uniform design method.

[0106] Based on the number of load cycles and reference load ratio To account for influencing factors, a uniform design table with 7 levels was used to design an indoor model experiment scheme for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading in soft rock strata, as shown in Table 1. The number of load cycles is listed in Table 1. The number of levels is 7, and the reference load ratio is... The level number is 7.

[0107] Table 1. Indoor model experimental scheme for the evolution of cumulative displacement and bearing capacity of pressure-type anchor bolts under cyclic loading.

[0108]

[0109] The fourth step is to determine the similarity ratio between the model and the experiment;

[0110] Based on the experimental objectives and laboratory conditions, the geometric similarity ratio of the model experiment should be determined first. 3. Density similarity ratio The similarity ratio is 1.2; then, based on similarity theory, the elastic modulus similarity ratio of the model experiment is derived. =3.6 stress similarity ratio =3.6, similarity ratio of concentrated force =32.4, Stiffness similarity ratio =10.8, frequency similarity ratio =0.577. The simulated values ​​of each physical quantity in the model experiment are determined according to the definition of the similarity ratio, and the specific steps are as follows:

[0111] ① Density of soft rock-like materials in model experiments =1750kg / m 3 elastic modulus =200MPa, unconfined compressive strength =3.0MPa and tensile strength =0.3MPa, and based on this, a soft rock-like material was prepared;

[0112] ② Length of the anchorage section of the model anchor bolt =1.0m, free segment length =1.0m and anchor body diameter =0.05m;

[0113] ③ Density of similar materials to the anchor body in the model experiment =2000kg / m 3 Elastic modulus =7.08GPa, unconfined compressive strength =5.56MPa and tensile strength =0.43MPa, and based on this, a similar material for anchor solids was prepared;

[0114] ④ Amplitude of cyclic load on the model anchor bolt =1.30kN, frequency =0.5Hz.

[0115] Step S15, combined Figure 2 and Figure 3 As shown, construct the model experimental setup;

[0116] The model experimental device includes a model box 1, a simulated soft rock strata 2, a simulated anchor bolt assembly, and a loading and measurement system.

[0117] The simulated anchor bolt assembly is either a pressure-type anchor bolt assembly or a tension-type anchor bolt assembly; for details, see [link to relevant documentation]. Figure 2As shown, the pressure-type anchor bolt assembly includes an anchor bar 31, an anchor body 32 covering the anchor bar 31, an anchor end bearing plate 33 disposed at the bottom end of the anchor bar 31, and an isolation sleeve 34 sleeved on the anchor bar 31 and located between the anchor bar 31 and the anchor body 32; see also Figure 3 As shown, the tension-type anchor bolt assembly includes an anchor bar 31 and an anchor body 32 covering the anchor bar 31.

[0118] The loading and measurement system includes a servo actuator 41, a servo controller 42, a data acquisition processor 43, a connecting fixture 44, an upper pressure plate 45, a lower pressure plate 46, a pressure rod 47, an adjusting nut 48, a water bladder 49, a column 51, and a crossbeam 52.

[0119] The servo actuator 41 includes an electric cylinder, a displacement sensor, and a load sensor, used to apply cyclic and tensile loads to the simulated anchor bolt assembly, and to measure the magnitude of the load and displacement during the loading process. Specifically, the servo actuator 41 is connected to the anchor bar 31 via the connecting clamp 44.

[0120] The servo controller 42 is connected to the servo actuator 41 and the data acquisition processor 43, and is used to control the loading mode and size of the cyclic load.

[0121] The upright column 51 is erected, and the crossbeam 52 is fixed to the upright column 51. The servo actuator 41 is fixed to the lower side of the crossbeam 52 via the upper pressure plate 45. The lower pressure plate 46 is fixed to the top surface of the model box 1. The pressure rod 47 is disposed between the upper pressure plate 45 and the lower pressure plate 46. The water bladder 49 is disposed between the lower pressure plate 46 and the model box 1.

[0122] The adjusting nut 48 is disposed between the pressure rod 47 and the upper pressure plate 45 to adjust the distance between the upper pressure plate 45 and the lower pressure plate 45.

[0123] Step 6: Indoor model experiment on the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading;

[0124] Based on the indoor model experiment scheme set in step three, indoor model experiments were conducted to investigate the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading. The steps of the model experiment included:

[0125] ① Based on the similarity ratio design results of the model anchors obtained in step four, the anchor components were fabricated and positioned in the center of the model box after curing for 14 days;

[0126] ② Based on the similarity ratio design results of the soft rock similar material obtained in step 4, prepare the soft rock similar material, and fill the prepared soft rock similar material into the model box in 3 to 5 layers, and vibrate each layer until it is compacted;

[0127] ③ Install the loading and testing device, and use the connecting clamp 44 to connect and fix the anchor bar 31 of the model anchor rod without cyclic load to the servo actuator 41; perform a pull-out test on the model anchor rod to measure its initial stiffness. =14.0kN / mm and ultimate bearing capacity =39.25kN;

[0128] ④ The number of cycles set according to the experimental design in step three. ( =1, 2, … , 7) and the reference working load ratio ( =1, 2, … , 7), determine the reference working load. Set the number of test cycle loads in the data acquisition system. Reference working load , amplitude of cyclic load and frequency The model anchor bolts are cyclically loaded until... Next, record its cumulative displacement. (See Table 1);

[0129] ⑤ To undergo Pull-out tests were conducted on the model anchor under cyclic loading, and its load-displacement curves were recorded. The ultimate bearing capacity of the model anchor was also measured. and stiffness (See Table 1):

[0130] ;

[0131] in , The load and displacement corresponding to the 90% peak point of the rising segment of the model anchor load-displacement curve; , This represents the load and displacement corresponding to the 20% peak point of the rising segment of the model anchor load-displacement curve.

[0132] Step 7: Analyze the evolution law of cumulative displacement of prototype anchor bolts under cyclic loading in soft rock strata and establish its evolution equation;

[0133] Combined Figure 4 As shown, based on the geometric similarity ratio set in step four... The result obtained from the sixth step of the test The cumulative displacement of each model anchor rod The corresponding first number can be calculated. The cumulative displacement of each prototype anchor rod ( ), to establish the cumulative displacement of the prototype anchor rod With the number of load cycles and reference load ratio The evolution equation is as follows:

[0134] ;

[0135] In the formula, The cumulative displacement of the prototype anchor rod is derived from the model experiment results.

[0136] The eighth step is to analyze the evolution law of the stiffness of the prototype anchor bolt under cyclic loading in soft rock strata and establish its evolution equation.

[0137] Combined Figure 5 As shown, based on the similarity ratio set in step four, the result obtained from the test in step six is... Stiffness of the model anchor rod The corresponding first number can be calculated. Stiffness of a prototype anchor ( Establish the stiffness of the prototype anchor rod. With the number of load cycles and reference load ratio The evolution equation is as follows:

[0138] ;

[0139] In the formula, The results of the anchor stiffness test on the model without cyclic loading are as follows. The stiffness of the prototype anchor rod was derived. This is the stiffness evolution factor.

[0140] The ninth step is to analyze the evolution law of the ultimate bearing capacity of the prototype anchor bolt under cyclic loading in soft rock strata and establish its evolution equation.

[0141] Combined Figure 6 As shown, based on the similarity ratio set in step four, the result obtained from the test in step six is... Ultimate bearing capacity of individual model anchors The corresponding first number can be calculated. Ultimate bearing capacity of a prototype anchor bolt ( Establish the ultimate bearing capacity of the prototype anchor. With the number of load cycles and reference load ratio The evolution equation is as follows:

[0142] ;

[0143] In the formula, The ultimate bearing capacity test results of the model anchor bolt without cyclic loading. The ultimate bearing capacity of the prototype anchor rod was derived. This is the factor for the evolution of carrying capacity.

[0144] Example 2

[0145] Example 2 provides a highly adaptable, practical, and efficient experimental method for studying the evolution of cumulative displacement and bearing capacity of tension-type anchor bolts under cyclic loading, specifically including:

[0146] The first step is to select the target strata and test the original rock samples;

[0147] An anti-buoyancy anchoring project for an underground rail transit system in a certain city was selected as the prototype for indoor model experiments. Original rock samples were drilled from the weathered soft rock strata at the project site. According to the "Code for Geotechnical Investigation (GB 50021-2009)" and the "Standard for Testing Methods of Engineering Rock Mass (GB / T 50266-2014)," the physical and mechanical parameters of the samples were measured in the laboratory, including density. It is 2280 kg / m³, and its elastic modulus is 2280 kg / m³. 900MPa, unconfined compressive strength The tensile strength is 14.4 MPa. It is 1.44 MPa.

[0148] The second step is to determine the dimensions, material, and load parameters of the prototype anchor bolt;

[0149] Based on the design data of the actual project, the anchorage length of the prototype anchor rod was analyzed and determined. =2.4m, free segment length =3m, anchor body diameter =0.15m, and the density of the anchor material. =2400kg / m 3 Elastic modulus =22GPa, unconfined compressive strength =15MPa, tensile strength =1.27MPa; Based on actual working conditions and combined with investigation and research, the amplitude of the cyclic load acting on the prototype anchor was determined. =38.88kN, frequency =0.346Hz, and the reference load ratio The value range is 0.2 to 0.8.

[0150] The third step is to determine the indoor model experiment scheme based on the hybrid homogeneous design method.

[0151] Based on the number of load cycles and reference load ratio To account for influencing factors, a mixed homogeneous design table was used to design an indoor model experiment scheme for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading in soft rock strata, as shown in Table 2. The number of load cycles is listed in Table 2. N The number of levels is 8, and the reference load ratio is... The number of levels is 4.

[0152] Table 2. Indoor model experimental scheme for the evolution of cumulative displacement and bearing capacity of tension-type anchor bolts under cyclic loading.

[0153]

[0154] The fourth step is to determine the similarity ratio between the model and the experiment;

[0155] Based on the experimental objectives and laboratory conditions, the geometric similarity ratio of the model experiment should be determined first. 3. Density similarity ratio The similarity ratio is 1.2; then, based on similarity theory, the elastic modulus similarity ratio of the model experiment is derived. =3.6 stress similarity ratio =3.6, similarity ratio of concentrated force =32.4, Stiffness similarity ratio =10.8, frequency similarity ratio =0.577. The simulated values ​​of each physical quantity in the model experiment are defined according to the similarity ratio, and the specific steps are as follows:

[0156] ① Density of soft rock-like materials in model experiments =1900kg / m 3 elastic modulus =250MPa, unconfined compressive strength =4.0MPa and tensile strength =0.4MPa, and based on this, a soft rock-like material was prepared;

[0157] ② Length of the anchorage section of the model anchor bolt =0.8m, free segment length =1.0m and anchor body diameter =0.05m;

[0158] ③ Density of similar materials to the anchor body in the model experiment =2000kg / m 3 Elastic modulus =6.11GPa, unconfined compressive strength =4.16MPa and tensile strength =0.35MPa, and then prepare a similar material for the anchor solid based on this;

[0159] ④ Amplitude of cyclic load on the model anchor bolt =1.20kN, frequency =0.6Hz.

[0160] Step S15, combined Figure 2 and Figure 3 As shown, construct the model experimental setup;

[0161] The model experimental device includes a model box 1, a simulated soft rock strata 2, a simulated anchor bolt assembly, and a loading and measurement system;

[0162] The simulated anchor bolt assembly is either a pressure-type anchor bolt assembly or a tension-type anchor bolt assembly; for details, see [link to relevant documentation]. Figure 2 As shown, the pressure-type anchor bolt assembly includes an anchor bar 31, an anchor body 32 covering the anchor bar 31, an anchor end bearing plate 33 disposed at the bottom end of the anchor bar 31, and an isolation sleeve 34 sleeved on the anchor bar 31 and located between the anchor bar 31 and the anchor body 32; see also Figure 3 As shown, the tension-type anchor bolt assembly includes an anchor bar 31 and an anchor body 32 covering the anchor bar 31.

[0163] The loading and measurement system includes a servo actuator 41, a servo controller 42, a data acquisition processor 43, a connecting fixture 44, an upper pressure plate 45, a lower pressure plate 46, a pressure rod 47, an adjusting nut 48, a water bladder 49, a column 51, and a crossbeam 52.

[0164] The servo actuator 41 includes an electric cylinder, a displacement sensor, and a load sensor, used to apply cyclic and tensile loads to the simulated anchor bolt assembly, and to measure the magnitude of the load and displacement during the loading process. Specifically, the servo actuator 41 is connected to the anchor bar 31 via the connecting clamp 44.

[0165] The servo controller 42 is connected to the servo actuator 41 and the data acquisition processor 43, and is used to control the loading mode and size of the cyclic load.

[0166] The upright column 51 is erected, and the crossbeam 52 is fixed to the upright column 51. The servo actuator 41 is fixed to the lower side of the crossbeam 52 via the upper pressure plate 45. The lower pressure plate 46 is fixed to the top surface of the model box 1. The pressure rod 47 is disposed between the upper pressure plate 45 and the lower pressure plate 46. The water bladder 49 is disposed between the lower pressure plate 46 and the model box 1.

[0167] The adjusting nut 48 is disposed between the pressure rod 47 and the upper pressure plate 45 to adjust the distance between the upper pressure plate 45 and the lower pressure plate 45.

[0168] Step 6: Indoor model experiment on the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading;

[0169] Based on the indoor model experiment scheme set in step three, indoor model experiments were conducted to investigate the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading. The steps of the model experiment included:

[0170] ① Based on the similarity ratio design results of the model anchors obtained in step four, the anchor components were fabricated and positioned in the center of the model box after curing for 14 days;

[0171] ② Based on the similarity ratio design results of the soft rock similar material obtained in step 4, prepare the soft rock similar material, and fill the prepared soft rock similar material into model box 1 in 3 to 5 layers to form simulated soft rock strata 2. Each layer is vibrated to compaction.

[0172] ③ Install the loading and testing device, and use a connecting clamp to connect and fix the anchor bar in the model anchor rod without cyclic load to the servo actuator; perform a pull-out test on the model anchor rod to measure its initial stiffness. =12.0kN / mm and ultimate bearing capacity =34.54kN;

[0173] ④ The number of cycles set according to the experimental design in step three. ( =1, 2, … , 8) and the reference working load ratio ( =1, 2, … , 8), determine the reference working load. Set the number of test cycle loads in the data acquisition system. Reference working load , amplitude of cyclic load and frequency The model anchor bolts are cyclically loaded until... Next, record its cumulative displacement. (See Table 2);

[0174] ⑤ To undergo Pull-out tests were conducted on the model anchor under cyclic loading, and its load-displacement curves were recorded. The ultimate bearing capacity of the model anchor was also measured. and stiffness (See Table 2):

[0175] ;

[0176] in , The load and displacement corresponding to the 90% peak point of the rising segment of the model anchor load-displacement curve; , This represents the load and displacement corresponding to the 20% peak point of the rising segment of the model anchor load-displacement curve.

[0177] Step 7: Analyze the evolution law of cumulative displacement of prototype anchor bolts under cyclic loading in soft rock strata and establish its evolution equation;

[0178] Combined Figure 7 As shown, based on the geometric similarity ratio set in step four... The result obtained from the sixth step of the test The cumulative displacement of each model anchor rod The corresponding first number can be calculated. The cumulative displacement of each prototype anchor rod ( ), to establish the cumulative displacement of the prototype anchor rod With the number of load cycles and reference load ratio The evolution equation is as follows:

[0179] ;

[0180] In the formula, The cumulative displacement of the prototype anchor rod is derived from the model experiment results.

[0181] The eighth step is to analyze the evolution law of the stiffness of the prototype anchor bolt under cyclic loading in soft rock strata and establish its evolution equation.

[0182] Combined Figure 8 As shown, based on the similarity ratio set in step four, the result obtained from the test in step six is... Stiffness of the model anchor rod The corresponding first number can be calculated. Stiffness of a prototype anchor ( Establish the stiffness of the prototype anchor rod. With the number of load cycles and reference load ratio The evolution equation is as follows:

[0183] ;

[0184] In the formula, The results of the anchor stiffness test on the model without cyclic loading are as follows. The stiffness of the prototype anchor rod was derived. This is the stiffness evolution factor.

[0185] The ninth step is to analyze the evolution law of the ultimate bearing capacity of the prototype anchor bolt under cyclic loading in soft rock strata and establish its evolution equation.

[0186] Combined Figure 9 As shown, based on the similarity ratio set in step four, the result obtained from the test in step six is... Ultimate bearing capacity of individual model anchors The corresponding first number can be calculated. Ultimate bearing capacity of a prototype anchor bolt ( Establish the ultimate bearing capacity of the prototype anchor. With the number of load cycles and reference load ratio The evolution equation is as follows:

[0187] ;

[0188] In the formula, The ultimate bearing capacity test results of the model anchor bolt without cyclic loading. The ultimate bearing capacity of the prototype anchor rod was derived. As a factor for the evolution of carrying capacity; This is the baseline load ratio.

[0189] In summary, based on Example 1 Figures 4 to 6 and Example 2 Figures 7 to 9 It can be seen that the reference load ratio This is key to controlling the displacement accumulation mode. Under low load ratios, displacement accumulates slowly and steadily in a deceleration mode; once the load ratio exceeds a critical value, displacement accumulation will switch to an acceleration mode, growing rapidly and unstablely.

[0190] Reference load ratio It mainly determines the stiffness The ultimate damage limit, and the number of cycles. Then the driving stiffness decreases exponentially until it reaches this limit.

[0191] Reference load ratio and number of loops Jointly driving load-bearing capacity It decays gradually in an exponential manner, eventually stabilizing at a value consisting of... The level of residual bearing capacity is determined.

[0192] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0193] Furthermore, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0194] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A test method for the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading, characterized in that, include: Step S11: Take undisturbed rock samples from the engineering site and determine the physical and mechanical parameters of the original rock material in the laboratory. The physical and mechanical parameters include density. Elastic modulus Unconfined compressive strength and tensile strength ; Step S12: Determine the dimensions and material of the prototype anchor rod, as well as the cyclic load parameters, based on the actual working conditions; the dimensional parameters include the length of the anchorage section. Length of free segment Anchor body diameter Material parameters include the density of the anchoring material. Elastic modulus Unconfined compressive strength ,tensile strength Cyclic load parameters include the amplitude of the cyclic load acting on the prototype anchor bolt. ,frequency and the reference load ratio Wherein, the reference load ratio Defined as ,in As the benchmark working load, This represents the ultimate bearing capacity of the prototype anchor bolt. Step S13, based on the number of load cycles and reference load ratio As influencing factors, indoor model experimental schemes were designed based on uniform design or hybrid uniform design methods; among them, The level number is 5-10. The number of levels is 4 to 9; Step S14: Design the similarity ratio for the indoor model experiment and determine the values ​​of each physical quantity in the model experiment; designing the similarity ratio for the indoor model experiment specifically includes: Define length similarity ratio Density similarity ratio Elastic modulus similarity ratio Stress similarity ratio Concentration similarity ratio Stiffness similarity ratio Frequency similarity ratio ; Determine the length similarity ratio And density similarity ratio Then, according to the formula and Calculate stress similarity ratio Similarity to concentration ; Determine the values ​​of each physical quantity in the model experiment, specifically including: Parameters for calculating soft rock similar materials in the model: ； In the formula, For prototype physical quantities; For model physical quantities; The density of the soft rock-like material in the model experiment; This refers to the elastic modulus of the soft rock-like material in the model experiment; The unconfined compressive strength of soft rock-like materials in the model experiment; The tensile strength of the soft rock-like material in the model experiment; Calculate the anchor bolt size parameters of the model: ； In the formula, This refers to the length of the anchorage section of the model anchor rod; The length of the free segment; The diameter of the anchor body; Calculation model anchor body material parameters: ； In the formula, The density of the anchor solid-like material in the model experiment; The elastic modulus of the anchor solid similar material in the model experiment; The unconfined compressive strength of the anchor solid similar material in the model experiment; The tensile strength of the anchor solid similar material in the model experiment; Calculate the cyclic load parameters of the model: ； In the formula, The magnitude of the cyclic load acting on the model anchor bolt; The frequency of the cyclic load acting on the model anchor; Step S15: Design and fabricate a model experimental device and a model anchor bolt assembly; the model experimental device includes a model box, a simulated soft rock stratum located inside the model box, a simulated anchor bolt assembly inserted into the simulated soft rock stratum, and a loading and measurement system connected to the simulated anchor bolt assembly; the simulated anchor bolt assembly is a pressure-type anchor bolt assembly or a tension-type anchor bolt assembly; Step S16: Conduct indoor model experiments on the evolution of cumulative displacement and bearing capacity of anchor bolts under cyclic loading; Step S17 involves analyzing the evolution law of cumulative displacement of the prototype anchor bolt under cyclic loading in soft rock strata and establishing its evolution equation, specifically including: Based on geometric similarity ratio Calculate the first The cumulative displacement of each prototype anchor rod And establish the cumulative displacement of the prototype anchor rod. With the number of load cycles and reference load ratio The evolution equation: ； In the formula, The cumulative displacement of the prototype anchor rod is derived from the model experiment results; , , , These are parameters obtained through regression analysis of experimental data; Step S18 involves analyzing the evolution law of prototype anchor stiffness under cyclic loading in soft rock strata and establishing its evolution equation, specifically including: Based on the similarity ratio of elastic modulus Similarity ratio of length Calculate the first Stiffness of a prototype anchor And establish the stiffness of the prototype anchor rod. With the number of load cycles and reference load ratio The evolution equation: ； In the formula, The results of the anchor stiffness test on the model without cyclic loading are as follows. The stiffness of the prototype anchor rod was derived. Stiffness evolution factor; Step S19 involves analyzing the evolution law of the ultimate bearing capacity of the prototype anchor bolt under cyclic loading in soft rock strata and establishing its evolution equation, specifically including: Based on the similarity ratio of elastic modulus Similarity ratio of length Calculate the first Ultimate bearing capacity of a prototype anchor bolt And establish the ultimate bearing capacity of the prototype anchor. With the number of load cycles and reference load ratio The evolution equation: ； In the formula, The ultimate bearing capacity test results of the model anchor bolt without cyclic loading. The ultimate bearing capacity of the prototype anchor rod was derived. This is the factor for the evolution of carrying capacity.

2. The test method for the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading according to claim 1, characterized in that, Length similarity ratio Density similarity ratio Elastic modulus similarity ratio Stress similarity ratio Concentration similarity ratio Stiffness similarity ratio Frequency similarity ratio They are respectively expressed by the following formulas: 。 3. The test method for the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading according to claim 1, characterized in that, In step S15, the pressure-type anchor bolt assembly includes an anchor bar, an anchor body covering the anchor bar, an anchor end bearing plate disposed at the bottom end of the anchor bar, and an isolation sleeve sleeved on the anchor bar and located between the anchor bar and the anchor body; the tension-type anchor bolt assembly includes an anchor bar and an anchor body covering the anchor bar. The loading and measurement system includes a servo actuator, a servo controller, a data acquisition processor, a connecting fixture, an upper pressure plate, a lower pressure plate, a pressure rod, an adjusting nut, a water bladder, a column, and a crossbeam. The servo actuator includes an electric cylinder, a displacement sensor, and a load sensor, used to apply cyclic loads and pull-out loads to the simulated anchor bolt assembly, and to measure the magnitude of the load and displacement during the loading process; the servo actuator is connected to the anchor bar through the connecting clamp; The servo controller connects the servo actuator and the data acquisition processor, and is used to control the loading method and size of the cyclic load. The column is erected vertically, and the crossbeam is fixed to the column; the servo actuator is fixed to the lower side of the crossbeam via the upper pressure plate; the lower pressure plate is fixed to the top surface of the model box; the pressure rod is disposed between the upper pressure plate and the lower pressure plate; the water bladder is disposed between the lower pressure plate and the model box. The adjusting nut is positioned between the pressure rod and the upper pressure plate to adjust the distance between the upper pressure plate and the lower pressure plate.

4. The test method for the evolution law of cumulative displacement and bearing capacity of anchor bolts under cyclic loading according to claim 1, characterized in that, Step S16 specifically includes: After fabricating and maintaining the model anchor bolt assembly, position it in the center of the model box; Fill the soft rock-like material in layers and compact it with vibration; Pull-out tests were conducted on the unloaded model anchor rods to measure the initial stiffness. and ultimate bearing capacity ; The number of cycles was set according to the experimental design. and benchmark working load ratio Calculate the baseline working load Apply cyclic load to Record the cumulative displacement. ; for the The anchor bolts in the second cycle were subjected to pull-out tests to measure their ultimate bearing capacity. and stiffness .

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