Anchor rod support model test method normal-shear closed loop loading control method and system

Abstract

The application provides a normal-shear closed loop loading control method and system for a model test of an anchor support, the loading control method relies on normal load, shear load, vertical displacement and horizontal displacement parameters collected by equipment, establishes a normal-shear bidirectional coupling closed loop control logic, and executes a control strategy of maintaining, reducing or suspending shear loading according to the size of normal load deviation; meanwhile, the vertical displacement and the change trend of real-time normal load are used to determine whether the sample in the model test box is in a compression state or a shear dilation state, the output pressure of the normal loading device is corrected, the normal pressure is assisted, and the shear loading is restarted after the normal load is restored to stability. The application solves the defects of independent control of normal loading and shear loading, large normal boundary fluctuation, lack of standardized linkage control process and poor test repeatability, realizes automatic coupling pressure stabilization in the whole test process, and improves the accuracy and comparability of the prestressed anchor support model test data.

Description

Technical Field

[0001] This invention belongs to the technical field of indoor model testing of prestressed anchor bolts in geotechnical engineering, specifically involving a method and system for normal-shear closed-loop loading control of anchor bolt support model testing. Background Technology

[0002] Prestressed anchor bolt active support technology is widely used in geotechnical engineering such as tunnels, underground caverns, mine roadways and slopes. Indoor similar model shear tests are the core research method to reveal the stress, deformation and failure mechanism of rock masses supported by anchor bolts.

[0003] like Figure 1 As shown, a typical prestressed anchor active support model test device generally consists of a main frame, a model test chamber, a normal loading device, a shear loading device, a load detection device, a displacement detection device, and a control system. The model test chamber is installed inside the main frame, and geotechnical similar materials are filled inside. Anchors are installed in the specimens according to a set number, spacing, and arrangement. A bearing plate is installed on the top of the model test chamber. The normal loading device (hydraulic cylinder, servo actuator, or electric loading mechanism) is connected to the bearing plate, pushing it downwards to apply a normal load to the specimen. The shear loading device is located on the side of the model test chamber. By pushing the shear box, upper chamber, or corresponding shear components to cause horizontal displacement, it causes relative displacement of the specimen along a preset shear plane. The normal loading device typically includes a normal load sensor to detect the normal load transmitted from the bearing plate to the specimen in real time. A vertical displacement sensor is installed near the bearing plate or normal actuator to detect the vertical movement of the bearing plate and the vertical deformation caused by specimen compression, rebound, or shear dilatation. The shear loading device is equipped with a shear load sensor to detect the real-time shear load, and a horizontal displacement sensor is placed near the shear moving parts to detect the horizontal displacement of the shear box or the specimen. Each sensor transmits the collected signals to the control system, which synchronously records the load, displacement, and time data and generates corresponding test curves.

[0004] The aforementioned existing testing setup typically starts by activating the normal loading device to gradually increase the normal load to a set value. Once the normal load reaches the target value and is maintained for a certain period, the shear loading device is then activated to perform shearing at a constant horizontal displacement rate or a constant loading rate. During the shearing process, the normal loading device generally maintains its original control state, while the shear loading device continues to operate at a pre-set rate until the horizontal displacement reaches the termination value, the shear load decreases to a specified proportion, or the loading device reaches its safe travel distance, at which point the test stops.

[0005] While existing technologies can perform normal loading, horizontal shear loading, and load and displacement data acquisition on model specimens, normal loading and shear loading are usually independent, making it difficult to ensure the stability of normal boundary conditions throughout the shearing process. During shearing, the specimen sequentially undergoes stages such as compaction, shear dilatation, slip, and post-peak failure. Pore closure and particle rearrangement may reduce the normal load, while particle interlocking, structural surface climbing, and crack propagation may increase it. Local slip or breakthrough of the failure surface can also cause abrupt changes in the normal load. Existing control systems typically cannot adjust the normal load output in a timely manner according to these changes, nor can they automatically reduce or pause shear loading based on the degree of normal load deviation. They often only execute emergency stop or protection operations after the load, displacement, or stroke exceeds the safety limit. In addition, although existing equipment can collect vertical displacement data, this data is mostly used for test result analysis and has not been fully used for compaction, shear dilatation state identification and loading control. This can easily cause lag or over-adjustment of normal adjustment response. When shear loading is paused due to abnormal conditions, the normal load recovery range, stabilization time and restart rate usually depend on manual experience to determine, lacking a unified recovery criterion, which is not conducive to the automation of the test process. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the first objective of this invention is to provide a normal-shear closed-loop loading control method for anchor bolt support model tests. This method calculates the normal load deviation in real time during the shearing process and identifies the compaction or shear dilatation state of the specimen by combining it with changes in vertical displacement. Based on the degree of normal load deviation, it automatically maintains, decelerates, or pauses shear loading, and automatically resumes shearing after the normal load stabilizes. This improves the consistency of the loading path and the reliability of the test results in the model test. Based on the same inventive concept, the second objective of this invention is to provide a test system utilizing the aforementioned normal-shear closed-loop loading control method for anchor bolt support model tests.

[0007] In this embodiment of the invention, the normal-shear closed-loop loading control method for anchor bolt support model tests is based on a prestressed anchor bolt active support model test system. The test system includes a main frame, a model test chamber, a bearing plate, a normal loading device, a normal load sensor, a vertical displacement sensor, a shear loading device, a shear load sensor, a horizontal displacement sensor, and a control system. The model test chamber is installed inside the main frame, and geotechnical similar material is filled inside the model test chamber. The anchor bolt is installed in the sample. The control method includes the following steps:

[0008] S1. Install prestressed anchor bolts in the model test chamber according to the test plan, fill with soil-rock similar materials, apply prestress, and complete the sample preparation;

[0009] S2. Set the test control parameters through the control system. The test control parameters include the normal target load. Allowable deviation of normal load Normal load suspension threshold Initial shear loading rate Horizontal displacement termination value and safety thresholds;

[0010] S3. Start the normal loading device to apply a normal load to the sample. Collect the normal load and vertical displacement data in real time. After the normal load stabilizes within the preset normal load allowable deviation range and continues to stabilize for a preset time, it is determined that the shear start condition is met.

[0011] S4. Start the shear loading device at the initial shear loading rate. A horizontal shear load was applied to the specimen, and the normal load was collected synchronously throughout the test using a unified time reference. Shear load Vertical displacement Horizontal displacement Real-time data;

[0012] S5. Based on real-time normal load With normal target load Calculate the deviation of normal load According to the normal load deviation The system employs a tiered approach to maintain, reduce, or pause shear loading; it determines whether the specimen in the model test chamber is in a compaction or shear dilatation state based on the changing trends of vertical displacement and real-time normal load, and corrects the output pressure of the normal loading device accordingly.

[0013] When the normal load deviation After excessive shear loading is triggered and paused, the normal load is continuously monitored. State, awaiting normal load After the system returns to a stable state, resume shear loading.

[0014] S6, when horizontal displacement Reaching the horizontal displacement termination value or shear load When the peak shear load is reached Then it decreases to a preset proportion of the peak shear load, or the normal load. Shear load Vertical displacement Horizontal displacement If any parameter in the stroke of the normal loading device and the shear loading device exceeds the safety threshold, stop the normal loading and shear loading, and save the data of the entire test process.

[0015] S7. The test ends, and the control system outputs loading stability evaluation parameters used to evaluate the loading stability of this test.

[0016] In this embodiment of the invention, the anchor bolt support model test normal-shear closed-loop loading test system includes a main frame, a model test chamber, a bearing plate, a normal loading device, a normal load sensor, a vertical displacement sensor, a shear loading device, a shear load sensor, a horizontal displacement sensor, and a control system. The model test chamber is installed inside the main frame, and the soil-rock similar material is filled inside the model test chamber. The anchor bolt is installed in the sample. The control system performs normal loading and shear loading on the sample in the model test chamber according to the loading control method provided in this application.

[0017] Compared with the prior art, the advantages of the preferred technical solution of the present invention include:

[0018] 1. This invention constructs a graded closed-loop control logic based on normal load deviation, breaking through the technical bottleneck of traditional anchor support model tests where normal loading and shear loading are independent and lack standardized linkage control processes. In traditional tests, the shear rate remains constant during shear loading, failing to respond to real-time fluctuations in the normal load, easily leading to significant deviations of the normal boundary load from the set value. This invention calculates the deviation between the real-time normal load and the target load, dividing it into three threshold levels: allowable fluctuation, slight deviation, and severe deviation. Correspondingly, it achieves graded adaptive control of shear loading rate maintenance, deceleration adjustment, and suspension of shear loading. This ensures continuous testing during small fluctuations in the normal load and timely braking and stabilization during significant deviations, effectively avoiding the data distortion problem caused by normal load instability in traditional tests. It improves the boundary stability of the test process from the perspective of loading control logic.

[0019] 2. This invention integrates vertical displacement deformation characteristics with normal load variation trends to identify the two core deformation states—compaction and dilatation—during the shearing process of the specimen, and conducts targeted pre-correction adjustment of the normal loading pressure. Traditional tests can only passively compensate and adjust after a significant deviation in the normal load, resulting in defects such as response lag, over-adjustment, and repeated load fluctuations. This invention actively increases the normal output pressure when the load decreases due to specimen compaction and actively decreases the normal output pressure when the load surges due to specimen dilatation, achieving predictive pressure stabilization control of the normal load. This effectively offsets the load disturbance caused by inherent pore compaction, particle interlocking, and volume expansion during the shear deformation of the soil and rock specimen, narrows the normal load fluctuation range, and ensures that the normal boundary conditions always conform to the preset working conditions throughout the test.

[0020] 3. The present invention establishes a standardized and quantifiable normal load stability judgment criterion and a staged shear restart mechanism, and abandons the extensive operation mode of traditional tests that rely on manual experience to judge load stability and manually resume loading. The present invention defines the numerical interval threshold for normal load stability. After shear loading is suspended due to load instability, once the load automatically recovers to the standard interval and meets the stability standard, shear loading is restarted at a low speed first to avoid impact load, and the initial test rate is restored after stabilization, with no manual intervention required throughout the whole process. The present invention realizes the full-process automated closed-loop operation of loading disturbance, pressure stabilization repair and test restart, and improves the standardization degree of test operations.

[0021] 4. The loading stability evaluation parameters of the present invention include core indicators such as the average deviation of normal load, the maximum deviation of normal load, the fluctuation degree of normal load, the number of shear loading decelerations, the number of shear loading pauses, and the cumulative time proportion of the normal load within the allowable range, forming a complete test effect evaluation system. Traditional tests can only qualitatively judge the loading effect based on test curves, without quantitative evaluation basis. There is no unified evaluation standard for test data of different batches and different working conditions, resulting in extremely poor test repeatability and data comparability. Through the quantitative parameters, the present invention can accurately determine the validity of a single set of test data, intuitively compare the loading stability differences between different test groups, effectively screen qualified test data, and solve the problems of low credibility of traditional model test data, which is difficult to be used for accurate analysis of bolt support mechanism and parameter optimization.

[0022] 5. The supporting normal-shear closed-loop loading test system of the present invention is upgraded based on the traditional prestressed bolt model test equipment, no hardware equipment replacement is required, and two-way coupling closed-loop regulation can be realized only by optimizing the control system logic, with strong equipment adaptability and compatibility. This test system can be adapted to support model tests with different geotechnical similar materials, different bolt layout parameters, and different normal pre-compression loads, unifying the loading control standards and test procedures under various working conditions. Compared with the problems of low test success rate and many invalid test times of traditional equipment, this test system reduces test consumables loss and test cycle, effectively reduces the scientific research cost of indoor model tests while greatly improving the test accuracy, and provides an efficient and reliable test platform for the optimization research of bolt support parameters in geotechnical engineering such as tunnels, slopes and roadways. Brief Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of a prestressed bolt active support model test device, and also a schematic structural diagram of the normal-shear closed-loop loading test system for the bolt support model test of the present application.

[0024] Figure 2 is a flow block diagram of the normal-shear closed-loop loading control method for the bolt support model test according to the embodiment. Detailed Description of the Embodiments

[0025] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] This embodiment provides a normal-shear closed-loop loading control method for anchor bolt support model tests, such as... Figure 2 As shown, in a preferred embodiment, it includes the following steps:

[0027] S1. Prestressed anchor bolts (hereinafter referred to as anchor bolts) are laid out in the model test chamber according to the test plan. The chamber is then filled with soil-like material, prestress is applied, and the specimen is prepared; this specimen is also called the model specimen. The test plan mainly involves the anchor bolt length, diameter, number, spacing, arrangement angle, and prestress value. These parameters can be adjusted accordingly based on the test conditions. The model specimen preparation process includes: installing anchor bolts at preset positions, filling the model test chamber with soil-like material in layers, and applying prestress to the anchor bolts after specimen formation.

[0028] The soil-rock similarity material is prepared based on the physical and mechanical parameters and similarity relationships of the surrounding rock to be simulated. It is prepared according to the required physical and mechanical parameters of the surrounding rock (density, elastic modulus, cohesion, internal friction angle, etc.) and a similarity ratio is selected (the similarity ratio is the ratio of the prototype quantity to the model quantity, specifically including the size similarity ratio, stress similarity ratio, and gravity similarity ratio). For example, the size similarity ratio... =7, stress similarity ratio =5, similarity ratio of gravitational acceleration =1, then the similarity ratios of density, Poisson's ratio, strain, and friction angle are: Similarity ratios of strength, cohesion, and elastic modulus: After calculating the target physical and mechanical parameters of the model material based on the above similarity relationship, the material density was measured by changing the proportions of aggregate, cementitious material, filler material and water content, and uniaxial compression test, tensile test and direct shear test were carried out. The material proportion in which the deviation of each parameter from the target value is within the preset allowable range was selected.

[0029] S2. Set the test control parameters through the human-machine interface of the control system. The test control parameters include the normal target load. Allowable deviation of normal load Normal load suspension threshold Initial shear loading rate Shear loading rate adjustment coefficient Horizontal displacement termination value The test parameters were initialized by setting the shear load attenuation termination ratio and safety threshold.

[0030] Among them, the normal target load To determine the target normal stress of the model specimen based on the test plan, the normal load setpoint needs to be maintained during the test. and according to the target normal stress The normal target load is calculated by multiplying the load by the actual stress area A of the specimen.

[0031] Allowable deviation of normal load The allowable range of normal load fluctuation under normal shear loading conditions is related to the test requirements and equipment conditions, and is determined based on the allowable range of normal load fluctuation for this set of tests. Before the actual test, a pre-test of normal loading can be conducted, with the target load in the normal direction. Maintain loading nearby and observe the actual load fluctuation range of the equipment under steady-state conditions, then determine the appropriate load based on the test requirements for normal boundary stability. This ensures that normal equipment fluctuations do not frequently trigger adjustments, while also reflecting the actual deviation of the normal load in a timely manner.

[0032] When the normal load is in a steady state, the real-time normal load is... In [ - , + ] interval, where, For the normal target load, This represents the allowable deviation of the normal load, used to define the stability range of the normal load. When the real-time normal load... Higher than + At that time, reduce the output pressure of the normal loading device until the real-time normal load is reached. In [ - , + [Interval; when real-time normal load] Below - At the same time, increase the output pressure of the normal loading device to apply the normal load in real time. In [ - , + ] interval.

[0033] Normal load suspension threshold The normal load deviation limit that triggers the suspension of shear loading. Used to determine whether the normal load has deviated to the point where shear loading needs to be paused; the setting should be higher than... Large. The degree of influence of the deviation of the normal load on the shear test results is determined, for example, based on the setting of a certain test group. For 2kN, it can Set to 5kN; when the normal load deviation is less than 2kN, normal shearing is performed; when the deviation exceeds 2kN but is less than 5kN, the shearing rate is reduced; when the deviation reaches 5kN, shear loading is paused.

[0034] Initial shear loading rate The initial shear loading rate was determined based on the test plan and the deformation characteristics of the specimen, serving as the initial operating rate of the shear loading device after the normal load stabilized. Select the required shear rate for the test within the range of loading rates allowed by the equipment, and use this rate as... Input control system, for example, if the test requires shearing at 2 mm / min, then set... =2mm / min.

[0035] Horizontal displacement termination value The maximum horizontal shear displacement allowed in the experiment is determined based on the model specimen size, the preset shear plane location, and the required degree of shear deformation. If the experiment requires obtaining the complete peak and post-peak shear responses, the maximum horizontal shear displacement to be achieved should be determined according to the experimental design, and this value should be used as the baseline. Input control system; and should also ensure The maximum horizontal displacement stroke allowed by the equipment shall not exceed the limit.

[0036] For the safety threshold, the safety threshold is determined based on the rated load and maximum displacement stroke of the normal loading device and the shear loading device, as well as the safe operating range of the prestressed anchor active support model test system. During the test, the limit value lower than the rated bearing capacity and maximum stroke of the equipment can be input into the control system. When any real-time parameter reaches the corresponding safety threshold, the normal loading and shear loading are stopped.

[0037] S3. Activate the normal loading device to push the bearing plate downwards and apply a normal load to the specimen inside the model test chamber. During the test, the normal load sensor synchronously collects the normal load in real time. Vertical displacement sensor collects vertical displacement in real time The data control system adjusts the output of the normal loading device based on real-time data fed back from the normal load sensor, so that the normal load... Gradually approaching and stabilizing at the normal target load ; wait until the normal load stabilizes within the preset allowable deviation range of the normal load ( ± After continuously stabilizing the voltage for a preset time, the control system determines that the normal loading state meets the shear start condition.

[0038] S4. After the normal load stabilizes to the target, start the shear loading device at the initial shear loading rate. A horizontal shear load was applied to the specimen inside the model test chamber. A unified time reference was used throughout the test, and the shear load was synchronously collected by a shear load sensor and a horizontal displacement sensor. Horizontal displacement In conjunction with normal loads Vertical displacement It enables real-time synchronous acquisition, storage and recording of four parameters, ensuring that different physical quantities correspond to each other and remain continuous and complete at the same time.

[0039] S5, the control system is based on real-time normal load. With normal target load Calculate the deviation of normal load According to the normal load deviation The system employs a tiered approach to maintain, reduce, or suspend shear loading; based on the changing trends of vertical displacement and real-time normal load, it determines whether the specimen in the model test chamber is in a compaction or shear dilatation state, and corrects the output pressure of the normal loading device accordingly.

[0040] Specifically, the formula for calculating the normal load deviation is as follows:

[0041]

[0042] in, This refers to the deviation of the normal load. The preset target load in the normal direction is obtained by manually inputting the preset value through the human-machine interface of the control system. The real-time normal load is obtained through real-time sampling by a normal load sensor.

[0043] Different shear control strategies are implemented based on the magnitude of the normal load deviation, including:

[0044] 1) When the absolute value of the normal load deviation Less than or equal to the allowable deviation of normal load At that time, that is This indicates that the real-time normal load is within the allowable fluctuation range, the control system maintains the current normal loading state, and controls the shear loading device to maintain the initial shear loading rate. Constant operation;

[0045] 2) When the absolute value of the normal load deviation Greater than the allowable deviation of normal load And less than the normal load suspension threshold At that time, that is This indicates that the normal load has exceeded the allowable fluctuation range, but has not yet reached the point where shear loading needs to be suspended. At this time, the control system adjusts the output pressure of the normal loading device according to the normal load deviation, allowing the real-time normal load to... Under normal target load The corresponding allowable deviation range [ - , + Simultaneously, reducing the shear loading rate slows down the development of shear deformation in the specimen, providing time for the normal load to recover. The formula for adjusting the shear loading rate is as follows:

[0046]

[0047] in, The adjusted shear loading rate; The initial shear loading rate is obtained by manually inputting a preset value through the human-machine interface of the control system; This is the shear loading rate adjustment coefficient, with a value range of 0 < <1, Before the formal test, in step S2, the shear loading rate adjustment coefficient is preset and entered through the control system. .

[0048] 3) When the absolute value of the normal load deviation Greater than or equal to the normal load suspension threshold At that time, that is This indicates a significant deviation in the normal load. The control system immediately halts the shear loading device and locks the current horizontal displacement. The load remains unchanged, while the normal loading device is adjusted to achieve voltage stabilization. During the pause, the control system continues to collect the normal load. and vertical displacement Only when the normal load Restore to Within the specified range, and after the preset time is reached continuously and stably within that range, the control system resumes shear loading.

[0049] In this embodiment, the support plate is connected to the actuator of the normal loading device, and the vertical displacement sensor is used to collect the vertical displacement of the actuator of the normal loading device and the support plate connected to it relative to the fixed reference position in real time. The vertical movement of the support plate can be achieved through vertical displacement. Quantization is performed, and the control system uses the vertical displacement obtained from continuous sampling. Calculate the displacement change between adjacent sampling times:

[0050]

[0051] in, This represents the change in vertical displacement between adjacent sampling times. and These are the vertical displacement values ​​at the current sampling time and the previous sampling time, respectively. Based on the vertical displacement obtained from continuous sampling, the change in vertical displacement between adjacent sampling times is calculated. The direction of vertical displacement is defined as the movement of the bearing plate into the sample. This is achieved when a preset number of consecutive sampling times are reached. When the value is positive, it is determined that the bearing plate has a tendency to move into the sample; the number of consecutive preset sampling times is... When the value is negative, it indicates that the bearing plate has an upward rebound tendency. Displacement changes within the normal signal fluctuation range are not included in the state judgment.

[0052] Vertical displacement It is mainly used to reflect the vertical deformation trend of the specimen and the normal load. Used to reflect the normal load relative to the normal target load. The changes in these two factors are combined to determine whether the specimen is currently in a state of compression or shear dilatation, and based on this, to determine the adjustment direction of the normal loading device. When the bearing plate continues to move inwards towards the specimen, and the real-time normal load... Relative to the normal target load When the trend is downward, it is determined that the sample has become compacted; when the bearing plate rebounds upward, and the real-time normal load... Relative to the normal target load When the trend is upward, it is determined that the sample has undergone shear dilatation.

[0053] To avoid load impact caused by sudden activation of the shear loading device, when resuming shear loading, the shear loading device should first operate at the adjusted shear loading rate. Restart cut loading, adjusted cut loading rate Below the initial shear loading rate and continuously monitor the normal load. When the normal load remains stable within the allowable deviation range [ - , + After that, the load rate is restored to the initial shear loading rate. run.

[0054] Specifically, based on the changing trends of vertical displacement and real-time normal load, the method for determining whether the specimen in the model test chamber is in a compaction or shear dilatation state, and correcting the output pressure of the normal loading device, is as follows:

[0055] 1) When the vertical displacement change indicates that the bearing plate continues to move inward into the specimen, and the real-time normal load... When the load shows a decreasing trend, the sample is determined to be in a compacted state. The output pressure of the normal loading device is gradually increased until the real-time normal load is reached. In [ - , + The range is used to compensate for the decrease in normal load caused by sample compaction;

[0056] 2) When the vertical displacement change indicates that the specimen has undergone vertical rebound or volume expansion, and the real-time normal load... When the load shows an increasing trend, the specimen is determined to be in a state of shear dilatation. The output pressure of the normal loading device is gradually reduced until the real-time normal load is reached. In [ - , + The range is used to reduce the increase in normal load caused by sample shear dilation, achieve pre-compensation adjustment, and avoid control lag and overshoot problems.

[0057] The above technical solution uses whether the real-time normal load recovers to the allowable deviation range of the target load as the adjustment termination criterion, so that... In [ - , + Since different samples, test schemes, and loading conditions have different requirements, this method avoids insufficient or excessive adjustment caused by a fixed pressure increase.

[0058] S6, when horizontal displacement Reaching the horizontal displacement termination value or shear load When the peak shear load is reached The load then decreases to a preset percentage of the peak shear load (i.e., the shear load attenuation termination percentage, which is pre-entered and recorded by the control system in step S2), or the normal load. Shear load Vertical displacement Horizontal displacement When any parameter in the stroke of the normal loading device and the shear loading device exceeds the safety threshold, the control system stops the normal loading and shear loading and saves the data of the entire test process.

[0059] S7. The test ends. The control system outputs the time-normal load curve, time-shear load curve, time-vertical displacement curve, time-horizontal displacement curve, shear load-horizontal displacement curve, and normal load deviation curve. Based on the aforementioned test data, the system obtains loading stability evaluation parameters to assess the loading stability of this test. These parameters include the average deviation of the normal load, the maximum deviation of the normal load, the degree of fluctuation of the normal load, the number of times the shear load is decelerated, the number of times the shear load is paused, and the cumulative proportion of time during which the normal load is within the allowable range. These parameters are used to evaluate the loading stability of this test.

[0060] The loading stability evaluation parameters are used to determine whether the loading boundary conditions of this model test meet the test requirements, and serve as the basis for evaluating the validity of the test data and the comparability of results from different test groups. This indirectly provides a basis for determining the support parameters in actual engineering projects, rather than directly serving as on-site construction control parameters. When the loading stability evaluation results meet the preset requirements, it indicates that the normal loading conditions of this test group are relatively stable. The obtained test results, such as shear load, horizontal displacement, and failure characteristics, can be used for subsequent comparative analysis of anchor bolt support parameters. Furthermore, combined with the test results of different support parameters, it can provide experimental basis for selecting anchor bolt support parameters, comparing support schemes, and optimizing construction parameters in actual engineering projects.

[0061] Example 2

[0062] This embodiment provides an experimental system for a normal-shear closed-loop loading control method in an anchor bolt support model test, such as... Figure 1 As shown, the test system includes a main frame, a model test chamber, a bearing plate, a normal loading device, a normal load sensor, a vertical displacement sensor, a shear loading device, a shear load sensor, a horizontal displacement sensor, and a control system. The control system is a computer control system. The model test chamber is installed inside the main frame, and the soil-like material is filled inside the model test chamber. Anchor bolts are installed in the specimen according to a set number, spacing, and arrangement. A bearing plate is set on the top of the model test chamber. The normal loading device is connected to the bearing plate and pushes the bearing plate downward through the normal actuator of a hydraulic cylinder, servo actuator, or electric loading mechanism to apply a normal load to the specimen. The shear loading device is set on the side of the model test chamber. By pushing the shear box, the upper box, or the corresponding shear component to cause horizontal displacement, the specimen will undergo relative displacement along a preset shear plane. The control system performs normal and shear loading on the specimen in the model test chamber according to the loading control method of Example 1.

[0063] A normal load sensor is installed in the normal loading device to detect the normal load transmitted from the bearing plate to the specimen in real time. A vertical displacement sensor is installed near the bearing plate or normal actuator to detect the vertical movement of the bearing plate and the vertical deformation caused by specimen compression, springback, or shear dilatation. A shear load sensor is installed in the shear loading device to detect the real-time shear load, and a horizontal displacement sensor is installed near the shear moving parts to detect the horizontal displacement of the shear box or specimen. The normal load sensor, vertical displacement sensor, shear load sensor, and horizontal displacement sensor transmit the collected signals to the control system. The control system synchronously records the load (including normal load and shear load), displacement (including vertical displacement and horizontal displacement), and time data, and generates corresponding test curves.

[0064] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A normal-shear closed-loop loading control method for anchor bolt support model tests, implemented based on a prestressed anchor bolt active support model test system. The test system includes a main frame, a model test chamber, a bearing plate, a normal loading device, a normal load sensor, a vertical displacement sensor, a shear loading device, a shear load sensor, a horizontal displacement sensor, and a control system. The model test chamber is installed inside the main frame, and geotechnical similar material is filled inside the model test chamber. The anchor bolt is installed in the sample. Its characteristic is that... The control method includes the following steps: S1. Install prestressed anchor bolts in the model test chamber according to the test plan, fill with soil-rock similar materials, apply prestress, and complete the sample preparation; S2. Set the test control parameters through the control system. The test control parameters include the normal target load. Allowable deviation of normal load Normal load suspension threshold Initial shear loading rate Horizontal displacement termination value and safety thresholds; S3. Start the normal loading device to apply a normal load to the sample. Collect the normal load and vertical displacement data in real time. After the normal load stabilizes within the preset normal load allowable deviation range and continues to stabilize for a preset time, it is determined that the shear start condition is met. S4. Start the shear loading device at the initial shear loading rate. A horizontal shear load was applied to the specimen, and the normal load was collected synchronously throughout the test using a unified time reference. Shear load Vertical displacement Horizontal displacement Real-time data; S5. Based on real-time normal load With normal target load Calculate the deviation of normal load According to the normal load deviation The system employs a tiered approach to maintain, reduce, or pause shear loading; it determines whether the specimen in the model test chamber is in a compaction or shear dilatation state based on the changing trends of vertical displacement and real-time normal load, and corrects the output pressure of the normal loading device accordingly. When the normal load deviation After excessive shear loading is triggered and paused, the normal load is continuously monitored. State, awaiting normal load After the system returns to a stable state, resume shear loading. S6, when horizontal displacement Reaching the horizontal displacement termination value or shear load When the peak shear load is reached Then it decreases to a preset proportion of the peak shear load, or the normal load. Shear load Vertical displacement Horizontal displacement If any parameter in the stroke of the normal loading device and the shear loading device exceeds the safety threshold, stop the normal loading and shear loading, and save the data of the entire test process. S7. The test ends, and the control system outputs loading stability evaluation parameters used to evaluate the loading stability of this test.

2. The anchor bolt support model test normal-shear closed-loop loading control method according to claim 1, characterized in that, In step S5, the formula for calculating the normal load deviation is as follows: in, This refers to the deviation of the normal load. The preset target load in the normal direction is obtained by manually inputting the preset value through the human-machine interface of the control system. The real-time normal load is obtained through real-time sampling by a normal load sensor.

3. The anchor bolt support model test normal-shear closed-loop loading control method according to claim 1, characterized in that, In step S5, the different shear control strategies implemented according to the magnitude of the normal load deviation specifically include: When the absolute value of the normal load deviation Less than or equal to the allowable deviation of the normal load At the same time, maintain a constant initial shear loading rate; When the absolute value of the normal load deviation Greater than the allowable deviation of normal load And less than the normal load suspension threshold At that time, the output pressure of the normal loading device is adjusted according to the normal load deviation to allow the real-time normal load to be adjusted. Under normal target load The corresponding allowable deviation range, while reducing the shear loading rate; When the absolute value of the normal load deviation Greater than or equal to the normal load suspension threshold Immediately pause shear loading and lock the current horizontal displacement. The voltage remains unchanged, and the voltage is stabilized by adjusting the normal loading device.

4. The anchor bolt support model test normal-shear closed-loop loading control method according to claim 3, characterized in that, The formula for adjusting the shear loading rate is as follows: in, The adjusted shear loading rate; The initial shear loading rate is obtained by manually inputting a preset value through the human-machine interface of the control system; This is the shear loading rate adjustment coefficient, with a value range of 0 < <1, calibrated according to test conditions.

5. The anchor bolt support model test normal-shear closed-loop loading control method according to claim 1, characterized in that, In step S5, based on the changing trends of vertical displacement and real-time normal load, it is determined whether the specimen in the model test chamber is in a compaction state or a shear dilatation state. The specific method for correcting the output pressure of the normal loading device is as follows: When the vertical displacement change indicates that the bearing plate continues to move inward into the specimen, and the real-time normal load... When the pressure shows a decreasing trend, it is determined that the sample is in a compacted state, and the output pressure of the normal loading device is increased. When the vertical displacement change indicates that the specimen has undergone vertical rebound or volume expansion, and the real-time normal load... When the pressure shows an upward trend, it is determined that the sample is in a state of shear dilation, and the output pressure of the normal loading device is reduced.

6. The anchor bolt support model test normal-shear closed-loop loading control method according to claim 1, characterized in that, In step S5, the method for restoring shear loading is as follows: after the normal load is restored to the allowable deviation range corresponding to the normal target load, the shear loading device first applies the adjusted shear loading rate. Restart cut loading, adjusted cut loading rate Below the initial shear loading rate The normal load is continuously monitored; once the normal load remains stable within the allowable deviation range, the load is restored to the initial shear loading rate. run.

7. The anchor bolt support model test normal-shear closed-loop loading control method according to any one of claims 1-6, characterized in that, When the normal load is in a steady state, the real-time normal load is... In [ - , + ] interval, where, For the normal target load, This represents the allowable deviation of the normal load, used to define the stability range of the normal load. When real-time normal load Higher than + At that time, reduce the output pressure of the normal loading device until the real-time normal load is reached. In [ - , + [Interval; when real-time normal load] Below - At the same time, increase the output pressure of the normal loading device to apply the normal load in real time. In [ - , + ] interval.

8. The anchor bolt support model test normal-shear closed-loop loading control method according to any one of claims 1-6, characterized in that, In step S7, the loading stability evaluation parameters include the average deviation of the normal load, the maximum deviation of the normal load, the degree of fluctuation of the normal load, the number of times the shear load is decelerated, the number of times the shear load is paused, and the cumulative proportion of time during which the normal load is within the allowable range.

9. A test system for the anchor bolt support model test normal-shear closed-loop loading control method according to any one of claims 1-8, characterized in that, It includes a main frame, a model test chamber, a bearing plate, a normal loading device, a normal load sensor, a vertical displacement sensor, a shear loading device, a shear load sensor, a horizontal displacement sensor, and a control system. The model test chamber is installed inside the main frame, the geotechnical similar material is filled inside the model test chamber, and the anchor rod is installed in the sample. The control system applies normal and shear loading to the specimen in the model test chamber according to the loading control method of any one of claims 1-8.

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