Rock friction sliding instability simulation test system and test device

Abstract

The invention relates to the technical field of rock friction experiments, in particular to a rock friction sliding instability simulation test system and device which comprises a loading module, a sample preparation module, a rigidity adjusting module, a multi-parameter sensing module and an instability judgment module. The loading module applies normal stress in a pneumatic pressurization mode and applies vertical shear load through servo control equipment; the sample preparation module is used for clamping and centering a rock sample; the rigidity adjusting module adjusts the equivalent rigidity by replacing a disc spring group; the multi-parameter sensing module synchronously collects multi-physical field signals; the instability judgment module determines a relative stability parameter of the rock according to the acoustic emission event so as to judge an instability type, and determines an instability judgment mode of the rock sample; according to the method, dominant and implicit types of rock instability are accurately distinguished, the instability occurrence time is predicted in advance, and the accuracy and reliability of early warning are effectively improved through the refined instability judgment method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rock friction experiment, in particular to a rock friction sliding instability simulation test system and test device. BACKGROUND

[0002] Rock friction sliding instability is the core physical mechanism of earthquake nucleation, occurrence and rupture propagation. Simulating and studying this process in the laboratory is crucial for understanding fault mechanics and earthquake physics. Although traditional rock friction test devices have played a role in establishing classical friction constitutive relations, they have significant limitations in simulating real fault sliding behavior. First, the equivalent stiffness of the test system is a key parameter that controls the transition of friction stability, but the system stiffness of traditional rigid test machines is usually fixed and too high, making it difficult to effectively simulate the low stiffness surrounding rock environment of underground faults, thus failing to accurately reproduce the triggering conditions of instability (stick-slip). Second, the friction instability process is accompanied by rich precursor physical signals such as acoustic emission and electric charge, but conventional devices mostly only monitor basic mechanical parameters such as force and displacement, lacking the ability to synchronously and integrally monitor multiple physical field information, making it difficult to capture comprehensive instability precursors. In addition, the shortcomings of existing devices in sample clamping, load centering and boundary condition control easily introduce additional stress unevenness and errors, affecting the authenticity and repeatability of the test. Therefore, there is an urgent need in the field for an advanced test system that can flexibly adjust the system stiffness, achieve high-precision coordinated loading and integrate synchronous monitoring of multiple physical fields to overcome the above technical bottlenecks. SUMMARY

[0003] To this end, the present application provides a rock friction sliding instability simulation test system and test device to solve the problem of lack of ability to synchronously and integrally monitor multiple physical field information, making it difficult to capture comprehensive instability precursors, thus making instability judgment not timely.

[0004] To achieve the above purpose, on the one hand, the present application provides a rock friction sliding instability simulation test system, comprising: a loading module for applying controllable normal stress to the rock sample by means of pneumatic pressurization to simulate the crustal confining pressure environment, and applying vertical shear load to the rock sample by means of servo control equipment to simulate the loading process of tectonic stress; a sample preparation module for clamping and accurately centering the rock sample so that the rock sample is coincident with the center of the loading module; a stiffness adjustment module arranged between the output end of the loading module and the rock sample for adjusting the equivalent stiffness by replacing the disc spring set; A multi-parameter sensing module is used to synchronously collect multi-physical field signals in a frictional sliding process, wherein the multi-physical field signals include sliding displacement, shear force, sliding acceleration, acoustic emission event and charge signal; An instability determining module is used to determine a rock relative stability parameter according to the number of acoustic emission events, to determine a rock frictional sliding instability type, to determine a rock sample instability state judging mode according to the rock frictional sliding instability type, including, obtaining the sliding displacement and the shear force, calculating a critical stiffness condition based on a dynamic instability criterion to determine whether to enter an instability state; or, obtaining the charge signal and the sliding acceleration, fitting a power index based on a power-law acceleration precursor characteristic to predict an instability occurrence time; A pre-warning module is used to output a pre-warning signal according to the instability state or the instability occurrence time.

[0005] As a preferred technical solution of the rock frictional sliding instability simulation test system, the loading module includes a normal loading submodule and a shear loading submodule; The normal loading submodule includes: A pneumatic pressurizing unit includes an air compressor, a cylinder in communication with the air compressor through a gas guide pipe, and the cylinder is provided with an air inlet and an air outlet. A force transmission unit includes a first upper steel plate, a second upper steel plate and a bottom steel plate arranged from top to bottom, and the first upper steel plate is connected with the piston rod of the cylinder; A guide unit includes two vertical linear guides and a plurality of sliding blocks in sliding cooperation with the linear guides, and the sliding blocks are fixedly connected between the first upper steel plate and the second upper steel plate; The shear loading submodule includes: A servo loading unit adopts an electro-hydraulic servo testing machine, which includes an actuator head and a fixed crossbeam; A load transmission unit includes a pressure head installed below the actuator head, and the pressure head is in contact with an intermediate sliding test block in the rock sample; A stiffness adjusting interface leaves an installation space between the pressure head and the intermediate sliding test block for accommodating a disc spring set, and the system equivalent stiffness is adjusted by replacing disc springs in different quantities and combination modes.

[0006] As a preferred technical solution of the rock frictional sliding instability simulation test system, the sample preparation module includes: A fixing unit includes a bottom steel plate and two grooves arranged thereon, and the grooves accommodate and fix two side fixed test blocks, respectively; The center adjustment unit includes a screw rod and an adjustment valve matched with the screw rod, and the fixed unit is driven to move laterally as a whole by rotating the screw rod to center the intermediate sliding test block with the center of the indenter of the loading module; The constraint unit includes adjustable clamps arranged on the side walls of the groove, which are locked or loosened by operating the adjustment valve to fix the two fixed test blocks in the groove.

[0007] As the preferred technical solution of the rock friction sliding instability simulation test system, the stiffness adjustment module includes: The stiffness providing unit is composed of a group of disc springs; The installation interface unit includes an installation space arranged between the indenter of the loading module and the intermediate sliding test block of the rock sample, and the installation space is used to accommodate the group of disc springs; The connection and fixing unit stably contacts the upper and lower surfaces of the group of disc springs with the indenter and the intermediate sliding test block respectively, and ensures the continuity of force flow transmission through pre-tightening force.

[0008] As the preferred technical solution of the rock friction sliding instability simulation test system, the multi-parameter sensing module includes: The movement sensor group is used to monitor the macro kinematics and dynamics parameters of the rock sample, and obtain the sliding displacement, shear force and sliding acceleration in the friction sliding process; The acoustic emission sensing array is composed of three acoustic emission sensors, which are fixed on different surfaces of the rock sample and are acoustically coupled through a coupling agent to obtain acoustic emission events in the test process; The charge sensing unit is arranged on the friction contact surface of the rock sample to sense the electric signals generated in the process of friction electrification and charge release; The movement sensor group, the acoustic emission sensing array and the charge sensing unit are all connected to a multi-channel synchronous data card to synchronize all physical field signals in time.

[0009] As the preferred technical solution of the rock friction sliding instability simulation test system, the instability judgment module determines the current acoustic emission event frequency highest surface and frequency lowest surface from the acoustic emission events obtained by the acoustic emission sensing array on each surface, and makes a comparison to obtain the rock sample instability coefficient; The instability judgment module determines the highest frequency of acoustic emission events in several experimental processes of the current rock sample, calculates the average value and average deviation, and calculates the ratio of the average deviation to the average value as the rock instability initial parameter; Wherein, the rock sample instability coefficient is greater than or equal to 1, and the rock relative stability parameter is the product of the rock instability initial parameter and the rock sample instability coefficient.

[0010] As the preferred technical scheme of the rock friction sliding instability simulation test system, the instability determination module determines the rock friction sliding instability type according to the rock relative stability parameter, and comprises: According to the determination result that the rock relative stability parameter is greater than or equal to the preset rock instability parameter, the instability determination module determines that the rock is of the explicit instability type; According to the determination result that the rock relative stability parameter is less than the preset rock instability parameter, the instability determination module determines that the rock is of the implicit instability type.

[0011] As the preferred technical scheme of the rock friction sliding instability simulation test system, the instability determination module acquires the sliding displacement and the shear force in response to the judgment result of the explicit instability type, calculates the critical stiffness condition based on the dynamic instability criterion, and determines whether to enter the instability state; If the change of the sliding displacement and the shear force does not meet the critical stiffness condition, it is determined that the rock sample enters the instability state.

[0012] As the preferred technical scheme of the rock friction sliding instability simulation test system, the instability determination module acquires the electric charge signal and the sliding acceleration in response to the judgment result of the implicit instability type, fits the power index based on the power-law acceleration precursor characteristic, and predicts the instability occurrence time.

[0013] On the other hand, the present application also provides a test device of a rock friction sliding instability simulation test system, which comprises: a rigid frame base; A normal loading device group is installed on the rigid frame base and is used to apply a normal stress to the rock sample, which comprises a pneumatic cylinder driven by an air compressor, an upper steel plate connected with the piston rod of the cylinder, and a linear guide rail and a sliding block for guiding; A shear loading device group is located above the normal loading device group and is used to apply a vertical shear load to the rock sample, which comprises a servo actuator and a pressure head connected with the actuator; A sample clamping and centering device group is arranged between the normal loading device group and the shear loading device group, and is used to fix and accurately center the rock sample, which comprises a bottom plate with a groove and a lead screw and an adjusting valve for lateral adjustment; A stiffness adjusting device group is arranged between the pressure head of the shear loading device group and the rock sample, and is used to change the equivalent stiffness of the system, and the core component is a disc spring group; A multi-parameter sensing device group is used to synchronously monitor the physical quantities in the test process, which comprises a displacement sensor for measuring the sliding displacement, a force sensor for measuring the shear force, and an acoustic emission sensor array and a charge sensor.

[0014] Compared with the prior art, the rock frictional sliding instability simulation test system has the beneficial effects that: the system adopts a multi-parameter sensing module to synchronously collect multiple physical field information such as sliding displacement, shear force, acoustic emission event and charge signal, and realizes time synchronization through a multi-channel synchronous data card, the multi-physical field coupling monitoring mode can comprehensively capture the complex dynamic changes of the rock in the frictional sliding process, and provides rich data support for instability determination; the instability determination module can accurately distinguish the explicit and implicit instability types and predict the instability occurrence time in advance based on the calculation of the acoustic emission event frequency ratio and the relative stability parameter of the rock, in combination with the dynamic instability criterion and the power-law acceleration precursor characteristics, the fine instability determination method effectively improves the accuracy and reliability of the early warning, and avoids the limitations of the traditional single parameter monitoring method; in addition, the stiffness adjusting module realizes flexible adjustment of the equivalent stiffness of the system by replacing the disc spring group, can simulate the rock mechanical behavior under different geological conditions, and enhances the applicability and universality of the system; finally, the system realizes real-time processing and analysis of the monitoring data through filtering processing and numerical differentiation method, further improves the accuracy and stability of the data, and ensures the scientificity and effectiveness of the instability determination. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Figure 1 is a connection schematic diagram of the rock frictional sliding instability simulation test system according to an embodiment of the present application; Figure 2 Figure 2 is a logic diagram for determining the rock frictional sliding instability type according to an embodiment of the present application; Figure 3 Figure 3 is a structure schematic diagram of the test device according to an embodiment of the present application; Figure 1 is a connection schematic diagram of the rock frictional sliding instability simulation test system according to an embodiment of the present application; 2, normal loading equipment group, 21, sliding block, 22, linear guide rail, 23, upper steel plate; 3, shear loading equipment group, 31, servo actuator, 32, pressure head; 4, adjusting valve; 51, fixed test block, 52, middle sliding test block. DETAILED DESCRIPTION

[0016] In order to make the purpose and advantages of the present application clearer and more apparent, the present application will be further described below in combination with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application.

[0017] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrally connected, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, and can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0018] The embodiments of the present application are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0019] Please refer to Figure 1 As shown in the connection diagram of the rock frictional sliding instability simulation test system, the present embodiment provides a rock frictional sliding instability simulation test system, which comprises: The loading module is used to apply controllable normal stress to the rock sample by a pneumatic pressurization method to simulate the crustal confining pressure environment, and to apply vertical shear load to the rock sample by a servo control device to simulate the loading process of tectonic stress; The sample preparation module is used to clamp and accurately center the rock sample, so that the rock sample is coincident with the center of the loading module; The stiffness adjusting module is arranged between the output end of the loading module and the rock sample, and is used to adjust the equivalent stiffness by replacing the disc spring group; The multi-parameter sensing module is used to synchronously collect multi-physical field signals in the frictional sliding process, wherein the multi-physical field signals include sliding displacement, shear force, sliding acceleration, acoustic emission event, and charge signal; The instability determination module is used to determine the rock relative stability parameter according to the number of acoustic emission events, to determine the rock frictional sliding instability type, to determine the instability judgment mode of the rock sample according to the rock frictional sliding instability type, including, The sliding displacement and shear force are obtained, and the critical stiffness condition is calculated based on the dynamic instability criterion to determine whether to enter the instability state; or, the charge signal and sliding acceleration are obtained, and the power index is fitted based on the power-law acceleration precursor characteristic to predict the instability occurrence time; The early warning module is used to output a warning signal according to the instability state or the instability occurrence time.

[0020] In the present embodiment, the equivalent stiffness is the overall comprehensive stiffness exhibited in the shear direction, which is used to quantify the ability to resist elastic deformation in the shear direction.

[0021] It can be understood that in the context of rock frictional sliding involving complex nonlinear processes, the stability of the power-law acceleration precursor feature is indeed affected by various factors. However, the application of this method in the present technical solution is based on its universal statistical law exhibited in the critical stage of instability nucleation. Despite the complexity of the microscopic mechanism, at the macroscopic level, when the system is driven to the critical point near global instability, its response often exhibits a power-law acceleration behavior across different materials and scales, which is a common critical phenomenon. Therefore, this method is not intended to accurately describe the entire frictional sliding process, but rather focuses on capturing the systematic acceleration trend within the critical time window before instability.

[0022] Specifically, the loading module comprises a normal loading submodule and a shear loading submodule; The normal loading submodule comprises: A pneumatic pressurizing unit comprising an air compressor, a cylinder in communication with the air compressor through a gas guide pipe, the cylinder being provided with an air inlet and an air outlet; A force transmission unit comprising a first upper steel plate, a second upper steel plate and a bottom steel plate arranged in sequence from top to bottom, the first upper steel plate being connected with the piston rod of the cylinder; A guiding unit comprising two vertical linear guides and a plurality of sliding blocks in sliding cooperation with the linear guides, the sliding blocks being fixedly connected between the first upper steel plate and the second upper steel plate; The shear loading submodule comprises: A servo loading unit using an electro-hydraulic servo testing machine, which comprises an actuator head and a fixed crossbeam; A load transmission unit comprising a pressure head mounted below the actuator head, the pressure head being in contact with an intermediate sliding test block in the rock sample; A stiffness adjusting interface, an installation space being left between the pressure head and the intermediate sliding test block for accommodating a disc spring set, the equivalent stiffness of the system being adjusted by replacing disc springs of different quantities and combinations.

[0023] In implementation, the rock sample adopts a double-shear friction structure form, which is composed of three independent rock test blocks to form a complete test assembly for simulating rock mass containing faults, and specifically comprises an intermediate sliding test block and two face-fixed test blocks. The intermediate sliding test block is a regular cuboid and is the only component in the system that undergoes macroscopic sliding, used to simulate one plate of the fault. The two face-fixed test blocks are also regular cuboids and are rigidly fixed during the test, used to simulate the other plate of the fault and the restraining action of the surrounding rock.

[0024] The rock sample is preferably homogeneous and isotropic granite to simulate the fault wall rock commonly found in the earth's crust. Its physical properties include density, wave speed, mineral composition, which need to be measured in advance and kept consistent.

[0025] The normal loading submodule applies controllable normal stress to the rock sample by pneumatic pressurization to simulate the crustal confining pressure environment. The lower surface of the second upper steel plate is in contact with the rock sample. By controlling the output pressure of the air compressor, the cylinder piston rod is extended, and then the normal load is uniformly applied to the rock sample through the force transmission unit and the guide unit. The shear loading submodule applies vertical shear load to the rock sample through a servo control system to simulate the loading process of tectonic stress. The servo loading unit drives the intermediate sliding test block to slide relative to the two fixed test blocks by controlling the actuator head to move downward at a constant speed or constant stress.

[0026] Specifically, the sample preparation module comprises: The fixed unit includes a bottom steel plate and two grooves arranged thereon, which accommodate and fix the two fixed test blocks, respectively. The centering and adjusting unit includes a lead screw and an adjusting valve cooperating with the lead screw. By rotating the lead screw, the fixed unit is driven to move laterally as a whole to center the intermediate sliding test block with the center of the loading module's indenter. The restraint unit includes adjustable clamps arranged on the side walls of the grooves, which are locked or loosened by operating the adjusting valve to fix the two fixed test blocks in the grooves.

[0027] In implementation, the intermediate sliding test block is placed between the two fixed test blocks, with its lower surface extending beyond the lower surfaces of the two fixed test blocks by a certain distance to ensure that the friction contact area remains unchanged during the test, and the center of its lower surface is in contact with the displacement sensor probe in the multi-parameter sensing module.

[0028] Specifically, the stiffness adjustment module comprises: The stiffness providing unit is composed of a set of disc springs. The mounting interface unit includes a mounting space arranged between the indenter of the loading module and the intermediate sliding test block of the rock sample, which is used to accommodate the set of disc springs. The connection and fixation unit stably contacts the upper and lower surfaces of the set of disc springs with the indenter and the intermediate sliding test block, respectively, and ensures the continuity of force flow transmission through pre-tightening force.

[0029] In the implementation, the stiffness adjustment module adjusts the equivalent stiffness of the system by replacing the disc spring group to simulate different elastic responses of the fault surrounding rock; by selecting disc spring groups with different numbers, different stiffness coefficients or different series / parallel combination modes, the equivalent shear loading stiffness of the system is adjusted in the range of 1.6 kN / mm to 127.1 kN / mm.

[0030] Specifically, the multi-parameter sensing module comprises: a moving sensor group for monitoring the macro kinematics and dynamics parameters of the rock sample, and acquiring the sliding displacement, the shear force and the sliding acceleration during the frictional sliding; an acoustic emission sensing array composed of three acoustic emission sensors, which are respectively fixed to the centers of different surfaces of the rock sample, and two of which are located at the two surfaces farthest apart, and the other is located on the surface not in contact with the fixed block, and acoustic coupling is achieved through a coupling agent to acquire acoustic emission events during the test; a charge sensing unit arranged on the frictional contact surface of the rock sample to sense the electrical signals generated during the friction electrification and charge release process; The moving sensor group, the acoustic emission sensing array and the charge sensing unit are all connected to a multi-channel synchronous data card to synchronize all physical field signals in time.

[0031] In the implementation, the moving sensor group uses a needle displacement sensor to measure the sliding displacement of the intermediate sliding block, the probe of which is in contact with the center of the lower surface of the intermediate sliding block; a high-precision force sensor integrated in a servo control device is used to monitor the shear force applied to the rock sample in real time; and a micro accelerometer fixedly installed on the intermediate sliding block is used to measure the acceleration signal during sliding.

[0032] The acoustic emission sensor captures the transient elastic waves generated by the micro-fracture inside the rock, and through a signal conditioning device, the acoustic emission signal is amplified, filtered, and waveform data is recorded at a sampling rate of not less than 100 kHz, so as to realize the positioning and feature extraction of acoustic emission events through analysis of the arrival time difference; The charge sensing unit uses an electrostatic sensor or a metal sensing electrode.

[0033] The selection and fixing method of the above detection device are not specifically limited, which is a prior art and will not be described in detail.

[0034] Please refer to Figure 2As shown, it is a logic diagram for determining the rock friction sliding instability type according to an embodiment of the application, the instability determination module determines the current acoustic emission event frequency highest surface and the frequency lowest surface according to the acoustic emission events obtained by each surface in the acoustic emission sensing array, and makes a ratio to obtain the rock sample instability coefficient; The instability determination module determines the highest frequency of acoustic emission events in the current rock sample during several experiments, calculates the average value and the average deviation, and then calculates the ratio of the average deviation to the average value as the rock instability initial parameter; Wherein, the rock sample instability coefficient is greater than or equal to 1, and the rock relative stability parameter is the product of the rock instability initial parameter and the rock sample instability coefficient.

[0035] For example, in a selected time window, the number of acoustic emission events recorded by the three sensors is respectively: The upper surface S1: 150 times, the left side surface S2: 45 times, the lower surface S3: 105 times, the highest frequency surface is S1, and the lowest frequency surface is S2; The rock sample instability coefficient is calculated as 150 / 45 ≈3.33.

[0036] Select 10 rock samples of the same batch and the same rock type, and the highest frequency of acoustic emission events of each rock sample in the stable sliding stage is [280, 310, 265, 290, 330, 270, 300, 285, 295, 320], the average value μ=294.5, and the average deviation MAD≈17.5; The rock instability initial parameter is calculated as the average deviation / average value=17.5 / 294.5 ≈0.0594; The rock relative stability parameter is calculated as the rock instability initial parameter×rock sample instability coefficient=0.0594×3.33≈0.198.

[0037] It can be understood that when an acoustic emission event occurs at point P, the elastic wave acoustic emission signal generated by it will spread in all directions at a specific wave speed, for example, the longitudinal wave speed in granite is about 6.67 km / s. Due to different propagation paths, there will be a slight difference in the time when the signal reaches different sensors, that is, the time difference. By accurately measuring the absolute time of the signal reaching each sensor or the time difference between them, and combining the known sensor coordinates and wave speed, the system can use geometric positioning algorithms, such as hyperbolic positioning method, to calculate the three-dimensional spatial coordinates (X, Y, Z) of the event occurrence point; If the event coordinates show obvious clustering on the space-time diagram, that is, a large number of events continuously occur in a certain specific area of the future main rupture surface before instability, it indicates that the rupture is nucleated here, which is a clear precursor to instability, and if the event coordinates are evenly and randomly distributed in the entire sample on the space-time diagram without forming an obvious clustering area, it indicates that the rock is in a uniform damage or stable rupture stage, rather than a pre-instability state.

[0038] In addition, the closer a sensor is to the acoustic emission source, the higher the signal strength it receives, and the easier it is to trigger the recording threshold, so it is counted by the system. When an acoustic emission event occurs inside the sample, the elastic wave signal generated by it will undergo geometric attenuation and material attenuation when propagating in the rock medium. Therefore, the sensor closest to the event occurrence point will receive the strongest and earliest arriving signal, which is most likely to be effectively captured and recorded by the system as an effective event. The sensors farther away may not be able to trigger the recording because the signal has decayed below the threshold, or their signal signal-to-noise ratio is too low to be filtered out.

[0039] In implementation, before the rock friction instability, the micro-fracture activity will change from random distribution to high concentration near the potential sliding surface, forming a nucleation area. At this time, the number of events recorded by the sensor closest to the nucleation area, that is, the highest frequency surface, will be significantly more than that of the sensor far away from the area, that is, the lowest frequency surface. This ratio directly reflects the spatial inhomogeneity of stress release inside the sample. The larger the ratio, the more concentrated the stress release in a particular area, which is a typical feature of the instability precursor. Normalization based on the lowest frequency surface eliminates the dimensional influence of the absolute number of events, allowing the coefficient to be compared across different test conditions. As the localization of damage intensifies, the number of events on the highest frequency surface increases, and the number of events on the lowest frequency surface decreases relatively, resulting in a monotonically increasing coefficient, which is consistent with the irreversibility of the instability process.

[0040] In this embodiment, when the sample is in a stable sliding or uniform damage stage, the number of events on each surface is comparable, and the coefficient tends to 1. When the coefficient consistently exceeds a certain critical value and shows an upward trend, it indicates that the system has entered the instability nucleation stage.

[0041] In implementation, when determining the initial parameters of rock instability, a number of rock samples in the same area with the same shape parameters are determined, and the number is not less than 10.

[0042] The rock instability initial parameter is based on the coefficient of variation calculated from several times of rock data in the same area, which quantifies the inherent dispersion level of acoustic emission activity of a specific sample in a stable state. The final rock relative stability parameter is obtained by multiplying the real-time instability coefficient with the historical dispersion parameter. When the rock sample is stable, the value of the composite parameter will be approximately equal to the historical dispersion level of the sample, which acknowledges and accommodates the rationality of the high dispersion sample in a stable state, effectively avoiding misjudgment. When instability begins, the significant increase of the real-time instability coefficient will be amplified by the historical dispersion level, so that whether it is a high dispersion or a low dispersion sample, its composite parameter will produce a clear and identifiable jump signal relative to its own benchmark, thereby ensuring the sensitivity and reliability of the instability warning under the premise of considering individual differences.

[0043] It can be understood that for a rock that has already entered an unstable state, the total number of acoustic emissions may be in a relatively stable high-frequency situation. If only the dispersion judgment is used, the actual instability situation may be ignored. The combination coefficient can avoid misjudgment of instability.

[0044] In determining the rock relative stability parameter, the rock sample instability coefficient selected is the median value of the coefficients corresponding to all rock instability initial parameters, reducing the possibility of misjudgment caused by a single excessively high coefficient.

[0045] Specifically, the instability determination module determines the rock friction sliding instability type according to the rock relative stability parameter, comprising: According to the determination result that the rock relative stability parameter is greater than or equal to the preset rock instability parameter, the instability determination module determines that the rock is of an explicit instability type; According to the determination result that the rock relative stability parameter is less than the preset rock instability parameter, the instability determination module determines that the rock is of an implicit instability type.

[0046] In implementation, the preset rock instability parameter is obtained by selecting no less than ten standard rock samples with the same lithology and the same processing technology, and performing systematic testing under standard test conditions to obtain acoustic emission data sequences of each sample in the stable sliding stage. Through analysis of these data sequences, the information of the rock relative stability parameter of each sample in a stable state is calculated. The numerical distribution of the rock relative stability parameter of all samples in the stable stage is obtained. Using statistical analysis method, the upper quartile of the distribution is taken as the reference value to obtain the final preset rock instability parameter threshold.

[0047] For example, the preset rock instability parameter threshold determined by 10 standard rock samples with the same lithology and the same processing technology is 0.15.

[0048] The relative stability parameter of the rock is calculated to be approximately 0.198, which is greater than 0.15.

[0049] Therefore, the system determines that the rock sample is currently of the explicit instability type.

[0050] In the present application, by collecting acoustic emission data sequences of the same lithology standard sample in the stable sliding stage, a statistically representative reference value is established. Considering the inherent physical property differences of different rock samples, a discriminant reference conforming to the intrinsic characteristics of rock materials is constructed, which avoids misjudgment caused by individual differences, making the instability type identification result have better reliability and consistency. The upper quartile of the distribution of the stable stage parameter value is calculated as the reference value by using statistical analysis method, which captures the upper limit of the normal fluctuation range of the rock in the stable state through statistical law, establishes a discriminant threshold that can reflect the inherent characteristics of the material and contains appropriate safety margin, and can effectively distinguish the normal fluctuation in the stable state from the real instability precursor signal, improving the accuracy of instability warning.

[0051] Specifically, the instability determination module obtains the sliding displacement and shear force in response to the judgment result of the explicit instability type, calculates the critical stiffness condition based on the dynamic instability criterion, to determine whether to enter the instability state; If the change of the sliding displacement and the shear force does not meet the critical stiffness condition, it is determined that the rock sample enters the instability state.

[0052] In implementation, by monitoring the sliding displacement and shear force in real time, the current dynamic state of the system is calculated, and continuous comparison and judgment are carried out. Once the critical condition is met, it is determined to enter the instability state. Based on the energy conservation and dynamic balance relationship of the spring-block system, the stability boundary of the system is directly represented by the monitorable quantity.

[0053] The system monitors the sliding displacement and shear force in real time, and calculates the change rate dF / du of the shear force with the sliding displacement by numerical differentiation method, F is the shear force, and u is the sliding displacement. At the same time, the system obtains the current sliding speed v and the preset loading speed v0. Based on the dynamic instability criterion, the critical stiffness condition is determined by the following relationship: when the system satisfies -dF / du = k(1-v0 / v), the system is in the instability critical state, wherein k is the equivalent stiffness of the system. The physical basis of the relationship is that at the instability transition point of the system, the balance relationship between the work done by external force and the energy release of the system is broken.

[0054] The system first filters the collected sliding displacement and shear force data to eliminate high-frequency noise interference. Then, the central difference method is used to calculate the rate of change of shear force with sliding displacement dF / du, and the real-time sliding speed v is obtained by differentiating the displacement with respect to time. The system compares the preset loading speed v0 with the real-time sliding speed v, and calculates the speed ratio term (1-v0 / v). Finally, the system compares -dF / du with k(1-v0 / v) in real time, and when it is first detected that -dF / du is greater than or equal to k(1-v0 / v), it is determined that the system has entered an unstable state.

[0055] The system equivalent stiffness k in the critical stiffness condition is obtained by experimental calibration. In the initial calibration stage of the system, the known stiffness disc spring group is tested under static load, and the load-deformation curve is established. The slope of the linear segment is the equivalent stiffness k of the system. This calibration process needs to be repeated under different stiffness disc spring combinations to ensure the accuracy of the stiffness value. In practical application, the system automatically calls the corresponding stiffness value according to the currently installed disc spring group to participate in the critical condition calculation.

[0056] In the present application, the stability boundary is directly represented by the real-time dynamics state of the system, realizing the transition from static instability criterion to dynamic instability criterion, which can accurately capture the critical state transition of the system in the process of energy accumulation and release, providing more accurate judgment basis for instability warning. By real-time monitoring of sliding displacement and shear force, and calculating the rate of change of shear force with sliding displacement and the real-time comparison of the system critical stiffness condition, the dynamic coupling relationship between system stiffness, loading speed and real-time sliding speed is fully considered, so that the judgment of instability state not only depends on the change of a single parameter, but also is based on the cooperative evolution relationship of multiple key parameters, improving the accuracy and reliability of the judgment.

[0057] Specifically, the instability judgment module obtains the charge signal and sliding acceleration in response to the judgment result of the implicit instability type, and fits the power index based on the power-law acceleration precursor characteristic to predict the instability occurrence time.

[0058] In implementation, the setting purpose of the fitting process is to establish a quantitative relationship model between sliding speed and acceleration, and the principle is based on the voight empirical relationship, which converts the nonlinear acceleration process into a linearly fitted form through mathematical transformation.

[0059] The collected sliding velocity v and sliding acceleration dv / dt data are screened, and continuous data segments in the precursor stage of instability are selected. The rate of change of sliding velocity with respect to time is calculated by numerical differentiation method, and the corresponding sequence of sliding acceleration and sliding velocity is established. Then the sliding velocity v and sliding acceleration dv / dt are taken as natural logarithm, and the data sequence of ln(v) and ln(dv / dt) is obtained. The system adopts least square method to carry out linear regression analysis on ln(dv / dt) and ln(v), and the slope of the fitted straight line is the power index α. In order to ensure the reliability of the fitting result, the system sets a correlation coefficient threshold, and when the correlation coefficient of the fitted straight line is lower than the threshold, the abnormal data points are automatically removed and re-fitted.

[0060] The correlation coefficient threshold is determined by historical data statistics, and the fitting quality of a plurality of effective instability precursor sequences is analyzed in the system calibration stage, and the lower quartile value of the correlation coefficient distribution is taken as the threshold reference. The preferred value is in the interval of 0.80 to 0.85.

[0061] Please refer to Figure 3 The application also provides a test device of a rock friction sliding instability simulation test system, which comprises a rigid frame base 1, a normal loading device group 2 installed on the rigid frame base 1 and used for applying a normal stress to a rock sample, a shear loading device group 3 located above the normal loading device group 2 and used for applying a vertical shear load to the rock sample, a sample clamping and centering device group arranged between the normal loading device group 2 and the shear loading device group 3 and used for fixing and accurately centering the rock sample, a rigidity adjusting device group arranged between the pressure head 32 of the shear loading device group 3 and the rock sample and used for changing the equivalent rigidity of the system, and a multi-parameter sensing device group used for synchronously monitoring physical quantities in the test process. The normal loading device group 2 comprises a pneumatic cylinder driven by an air compressor, an upper steel plate 23 connected with a piston rod of the pneumatic cylinder, and a linear guide rail 22 and a sliding block 21 used for guiding. The shear loading device group 3 comprises a servo actuator 31 and a pressure head 32 connected with the actuator. The sample clamping and centering device group comprises a bottom plate with a groove and a lead screw and an adjusting valve 4 used for transverse adjustment. The rigidity adjusting device group comprises a disc spring group as a core component. The multi-parameter sensing device group comprises a displacement sensor used for measuring sliding displacement, a force sensor used for measuring shear force, and an acoustic emission sensor array and a charge sensor.

[0062] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will all fall within the protection scope of the present application.

[0063] The above are only preferred embodiments of the present application and are not used to limit the present application; for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A rock frictional sliding instability simulation test system, characterized in that, The device comprises: a loading module, which is used to apply controllable normal stress to a rock sample by means of pneumatic pressurization to simulate the crustal confining pressure environment, and to apply vertical shear load to the rock sample by means of a servo control device to simulate the loading process of tectonic stress; a sample preparation module, which is used to clamp and accurately center the rock sample so that the rock sample is coincident with the center of the loading module; a stiffness adjustment module, which is arranged between the output end of the loading module and the rock sample, and is used to adjust the equivalent stiffness by replacing disc spring groups; a multi-parameter sensing module, which is used to synchronously collect multi-physical field signals in the process of frictional sliding; a instability determination module, which is used to determine the rock relative stability parameter according to the number of acoustic emission events, to determine the rock frictional sliding instability type, and to determine the instability judgment mode of the rock sample according to the rock frictional sliding instability type, including, calculating the critical stiffness condition based on the dynamic instability criterion to determine whether to enter the instability state; or, fitting the power index based on the power law acceleration precursor characteristic to predict the instability occurrence time; a early warning module, which is used to output a early warning signal according to the instability state or the instability occurrence time.

2. The rock frictional sliding instability analog test system of claim 1, wherein, The loading module comprises a normal loading submodule and a shear loading submodule; The normal loading submodule comprises: a pneumatic pressurization unit, which comprises an air compressor and a cylinder in communication with the air compressor through a gas guide pipe, the cylinder being provided with an air inlet and an air outlet; a force transmission unit, which comprises first, second and bottom steel plates arranged in sequence from top to bottom, the first upper steel plate being connected with the piston rod of the cylinder; a guide unit, which comprises two vertically arranged linear guides and a plurality of sliders in sliding cooperation with the linear guides, the sliders being fixedly connected between the first and second upper steel plates; The shear loading submodule comprises: a servo loading unit, which adopts an electro-hydraulic servo testing machine comprising an actuator head and a fixed crossbeam; a load transmission unit, which comprises a pressure head mounted below the actuator head, the pressure head being in contact with an intermediate sliding test block in the rock sample; a stiffness adjustment interface, which leaves an installation space between the pressure head and the intermediate sliding test block for accommodating disc spring groups, and adjusts the system equivalent stiffness by replacing disc springs in different quantities and combinations.

3. The rock frictional sliding instability analog test system of claim 1, wherein, The sample preparation module comprises: a fixing unit, which comprises a bottom steel plate and two grooves arranged thereon, the grooves accommodating and fixing two side fixed test blocks respectively; a centering adjustment unit, which comprises a lead screw and an adjustment valve cooperating with the lead screw, the fixed unit being driven to move laterally as a whole by rotating the lead screw to center the intermediate sliding test block with the center of the pressure head of the loading module; a constraint unit, which comprises adjustable clamps arranged on the side walls of the grooves, the two side fixed test blocks being fixed in the grooves by locking or loosening the adjustment valve.

4. The rock frictional sliding instability analog test system of claim 1, wherein, The stiffness adjustment module comprises: a stiffness providing unit, which is composed of a group of disc springs; an installation interface unit, which comprises an installation space arranged between the pressure head of the loading module and the intermediate sliding test block of the rock sample, the installation space being used to accommodate the disc spring group; A connecting and fixing unit, which stably contacts the upper and lower surfaces of the disc spring group with the pressure head and the intermediate sliding block respectively, and ensures the continuity of force flow transmission through pre-tightening force.

5. The rock frictional sliding instability analog test system of claim 1, wherein, The multi-parameter sensing module comprises: A moving sensor group, which is used to monitor the macro kinematics and dynamics parameters of the rock sample, and obtain the sliding displacement, shear force and sliding acceleration during the frictional sliding process; An acoustic emission sensing array, which is composed of three acoustic emission sensors, is fixed on different surfaces of the rock sample, and is acoustically coupled through a coupling agent to obtain acoustic emission events during the test; A charge sensing unit, which is arranged on the frictional contact surface of the rock sample, is used to sense the electric signals generated during the friction electrification and charge release process; The moving sensor group, the acoustic emission sensing array and the charge sensing unit are connected to a multi-channel synchronous data card, so that all physical field signals are synchronized in time, and the multi-physical field signals include sliding displacement, shear force, sliding acceleration, acoustic emission events and charge signals.

6. The rock frictional sliding instability analog test system of claim 5, wherein, The instability determination module determines the current acoustic emission event frequency highest surface and frequency lowest surface from the acoustic emission events obtained by the acoustic emission sensing array, and compares them to obtain the rock sample instability coefficient; The instability determination module determines the highest frequency of acoustic emission events during several experiments of the current rock sample, calculates the average value and average deviation, and calculates the ratio of the average deviation to the average value as the rock instability initial parameter; The rock sample instability coefficient is greater than or equal to 1, and the rock relative stability parameter is the product of the rock instability initial parameter and the rock sample instability coefficient.

7. The rock frictional sliding instability analog test system of claim 6, wherein, The instability determination module determines the rock frictional sliding instability type according to the rock relative stability parameter, including: According to the determination result that the rock relative stability parameter is greater than or equal to the preset rock instability parameter, the instability determination module determines that the rock is of the explicit instability type; According to the determination result that the rock relative stability parameter is less than the preset rock instability parameter, the instability determination module determines that the rock is of the implicit instability type.

8. The rock frictional sliding instability analog test system of claim 7, wherein, The instability determination module obtains the sliding displacement and shear force in response to the judgment result of the explicit instability type, calculates the critical stiffness condition based on the dynamic instability criterion, and determines whether to enter the instability state; If the change of the sliding displacement and the shear force does not meet the critical stiffness condition, it is determined that the rock sample enters the instability state.

9. The rock frictional sliding instability analog test system of claim 8, wherein, The instability determination module obtains the charge signal and sliding acceleration in response to the judgment result of the implicit instability type, fits the power index based on the power-law acceleration precursor characteristics, and predicts the instability occurrence time.

10. A test device applied to the rock frictional sliding instability simulation test system according to any one of claims 1-9, characterized in that, It comprises: A rigid frame base; A normal loading device group, which is installed on the rigid frame base and is used to apply a normal stress to the rock sample, comprises a gas cylinder driven by an air compressor, an upper steel plate connected with the piston rod of the gas cylinder, and a linear guide rail and a sliding block for guiding; A shear loading device group, which is located above the normal loading device group and is used to apply a vertical shear load to the rock sample, comprises a servo actuator and a pressure head connected with the actuator; A sample clamping and centering device group is arranged between the normal loading device group and the shear loading device group, and is used for fixing and accurately centering the rock sample, which includes a grooved base plate and a screw and adjusting valve for lateral adjustment; A stiffness adjusting device group is arranged between the pressure head of the shear loading device group and the rock sample, and is used for changing the equivalent stiffness of the system, and the core component is a disc spring group; A multi-parameter sensing device group is used for synchronously monitoring the physical quantities in the test process, which includes a displacement sensor for measuring sliding displacement, a force sensor for measuring shear force, and an acoustic emission sensor array and a charge sensor.

Images