A method and system for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency.

Abstract

This invention relates to the field of marine geotechnical engineering technology, and provides a method and system for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency. The method includes conducting a ring shear test on the calcareous sand to obtain the shear stress-shear displacement curve during the shearing process; attaching an acoustic emission sensor to the loading plate of the ring shear tester and using an acoustic emission monitoring system to collect acoustic emission signals during the shearing process; performing impact detection on the acoustic emission signals and extracting the waveforms of the impact signals; calculating the average centroid frequency of all impact waveforms within each preset time period; and based on the change in the average centroid frequency, analyzing the micromechanical mechanism of shearing in the calcareous sand and providing early warning of shear zone development and failure. This method can monitor the shear state of calcareous sand throughout the entire process and can be used for early warning of shear failure in calcareous sand foundations and other sandy soil materials in marine engineering.

Description

Technical Field

[0001] This invention relates to the field of marine geotechnical engineering technology, specifically to a method and system for monitoring the shear state of calcareous sand based on the acoustic emission centroid frequency. Background Technology

[0002] Calcareous sands are widely distributed on continental shelves and near coastlines in tropical and subtropical regions. With the development of marine engineering, projects such as offshore renewable energy anchoring structures, offshore oil and gas platform foundations, and land reclamation are all built on calcareous sand foundations. Under the complex loads of the superstructure, calcareous sand particles are highly susceptible to shear failure. Shear failure is often a progressive process. Shear stress first causes localized shear failure at stress concentration points. Then, the shear band gradually penetrates and develops, leading to overall shear failure. Therefore, monitoring the shear state of calcareous sand throughout its entire lifecycle is crucial for ensuring the safety of marine engineering projects.

[0003] The overall shear failure of calcareous sand depends on the complex micromechanical behavior between particles, including particle slip and particle breakage. Particle slip refers to the inter-particle displacement and is the main cause of shear displacement development. Particle breakage alters the soil particle size distribution, thus affecting the soil's strength and deformation characteristics. The formation of shear bands within the soil is often accompanied by intense particle slip and breakage. However, existing monitoring methods, such as digital image correlation (DIC) and X-ray computed tomography (XCT), cannot achieve continuous, real-time monitoring of the micromechanical behavior during the shearing process of calcareous sand. Summary of the Invention

[0004] In view of this, the present invention proposes a method and system for monitoring the shear state of calcareous sand based on the acoustic emission centroid frequency, which can monitor the shear state of calcareous sand throughout the entire process and can be used for early warning of shear failure of calcareous sand foundations and other sandy materials in marine engineering.

[0005] To achieve the above objectives, the present invention adopts the following solution:

[0006] A method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency includes the following steps: Step 1: Conduct a ring shear test on the calcareous sand to obtain the shear stress-shear displacement curve during the shearing process of the calcareous sand; Step 2: Acquire acoustic emission signals during the circumferential shearing experiment; Step 3: Perform impact detection on the acoustic emission signal and extract the waveform of the impact signal; Step 4: Calculate the average centroid frequency of all impact waveforms within each preset time period; Step 5: Based on the change in the average centroid frequency, perform shear micromechanical mechanism analysis on calcareous sand and early warning of shear zone development and damage.

[0007] Optionally, step 1 includes: preparing the sample using a layered compaction method, placing the calcareous sand sample into a shear box in layers and compacting it to a predetermined height to achieve a predetermined relative density; applying a constant axial pressure before shearing begins until the sample is consolidated; after consolidation, performing a circumferential shear test under dry conditions using a constant shearing speed until a set shear displacement is reached; collecting shear stress-shear displacement data during the shearing process; and calculating the shear displacement using the average radius of the inner and outer diameters of the circumferential shear sample.

[0008] Optionally, step 2 includes: attaching the acoustic emission sensor to the surface of the loading plate on the ring shearing apparatus, applying a coupling agent between the sensor and the contact surface to reduce acoustic energy loss; collecting the ambient and equipment noise amplitudes, using the amplitudes as a threshold for threshold-triggered sampling, and collecting only acoustic emission signals whose amplitudes exceed the threshold; the acoustic emission sensor collects acoustic emission signals generated by the slippage and breakage of calcareous sand particles during the ring shearing experiment, and the acoustic emission signals are amplified by a preamplifier and then collected by a data acquisition instrument; the collected acoustic emission signals are stored in voltage form and contain all frequency information.

[0009] Optionally, step 3 includes: performing impact detection on the acquired acoustic emission signal, recording acoustic emission signals exceeding the threshold as an impact; setting corresponding peak definition time, impact definition time, and impact lockout time to divide the impact waveform; when extracting the impact waveform, extracting 0.1 times more impact definition time forward from the starting threshold point and extracting 0.2 times more impact definition time backward from the ending point.

[0010] Optionally, step 4 includes: performing a fast Fourier transform on the impact waveform, calculating the centroid frequency of the impact signal, and then calculating the average centroid frequency of all impact signals within each preset time period.

[0011] Optionally, the preset time period is 10 seconds.

[0012] Optionally, in step 5, the analysis of the shear micromechanical mechanism based on the change of the average center of gravity frequency includes: when the average center of gravity frequency increases, it indicates that the high-frequency acoustic emission signal generated by particle breakage is dominant and the particle slippage is small; when the average center of gravity frequency decreases, it indicates that the low-frequency acoustic emission signal generated by particle slippage is dominant and the soil produces significant shear displacement.

[0013] Optionally, the shear zone development and damage early warning based on the characteristic value of the change in average centroid frequency includes: taking the initial value of the average centroid frequency as early warning value 1 and the peak value of the average centroid frequency as early warning value 2; issuing a first damage warning based on the average centroid frequency increasing from the initial value to the peak value, and issuing a second damage warning based on the average centroid frequency decreasing from the peak value to below the initial value.

[0014] A shear state monitoring system for calcareous sand based on acoustic emission centroid frequency includes a ring shearing instrument, an acoustic emission acquisition module, an impact detection module, a frequency calculation module, and an analysis and early warning module. The ring shear apparatus is used to conduct ring shear experiments on calcareous sand and obtain the shear stress-shear displacement curve during the sand shearing process. The acoustic emission acquisition module is used to acquire acoustic emission signals during the ring shearing experiment; The impact detection module is used to perform impact detection on the acoustic emission signal and extract the waveform of the impact signal; The frequency calculation module is used to calculate the average centroid frequency of all impact waveforms within each preset time period. The analysis and early warning module is used to analyze the shear micromechanical mechanism of sand and soil and provide early warning of shear zone development and failure based on the change of the average centroid frequency.

[0015] Optionally, the acoustic emission acquisition module includes: an acoustic emission sensor, a magnetic clamp, a preamplifier, and a data acquisition instrument; the acoustic emission sensor is mounted on the side wall of the loading plate on the ring shearing machine via the magnetic clamp, and a coupling agent is applied between the sensor and the side wall; the preamplifier provides a 40dB preamplifier gain, and the data acquisition instrument acquires acoustic emission signals exceeding a threshold.

[0016] The beneficial effects of this invention are as follows: First, this solution uses an acoustic emission sensor to collect acoustic emission signals during the shearing process in real time. Combined with impact detection and average center of gravity frequency calculation, it can track the evolution of particle slippage and breakage, overcoming the shortcomings of traditional digital imaging methods and X-ray tomography that cannot continuously and in real time monitor.

[0017] Moreover, based on the rising or falling trend of the average center of gravity frequency, this scheme can clearly distinguish between the particle crushing-dominated stage and the particle slip-dominated stage during shearing, thereby revealing the microscopic mechanism of calcareous sand from local shear failure to overall shear failure.

[0018] In addition, this scheme uses the initial and peak values ​​of the average center of gravity frequency as early warning thresholds. The first warning is issued when the frequency rises to the peak value, and the second warning is issued when the frequency falls below the initial value, providing an effective predictive basis for marine engineering safety.

[0019] Furthermore, this method for analyzing the micromechanical mechanism of shear and for early warning of shear zone development and failure is not only applicable to calcareous sand, but also to other types of sand, possessing good versatility and scalability. It provides a unified and reliable technical approach for the study of shear characteristics and early warning of failure in different types of sand. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart of a method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency, provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the ring shear-acoustic emission structure connection in the monitoring system provided in an embodiment of the present invention; Figure 3 The graph shows the variation of shear stress and average centroid frequency with shear displacement, as provided in an embodiment of the present invention. Figure 4 The shear failure early warning diagram provided in the embodiments of the present invention, namely Figure 3 Enlarged view of the shear displacement 25mm from the front.

[0022] The following are the labels in the diagram: 1. Ring shear apparatus; 2. Ring shear specimen; 3. Acoustic emission sensor; 4. Preamplifier; 5. Data acquisition instrument; 6. Data storage device; 7. Shear box; 8. Upper loading plate. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in the embodiments of this invention are also intended to include the plural forms unless the context clearly indicates otherwise.

[0026] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0027] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0028] Example 1 Combination Figure 1 The flowchart shown illustrates an embodiment of the present invention that provides a method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency, used to identify changes in the micromechanical mechanisms of shear and the development and failure of shear bands. The method includes the following steps: Step 1: Conduct a ring shear test on the calcareous sand to obtain the shear stress-shear displacement curve during the shearing process of the calcareous sand.

[0029] In this embodiment of the invention, step 1 specifically includes: The calcareous sand used has a particle size distribution of 0.5-1 mm, a specific gravity of 2.84, and a maximum dry density of 0.98 g / cm³. 3 The minimum dry density is 0.59 g / cm³. 3 In this embodiment, the outer diameter of the shear box 7 is 100 mm, the inner diameter is 70 mm, and the height is 15 mm. A layered compaction method is used for sample preparation: each group of samples is divided into four equal parts, poured into the shear box 7 of the ring shear apparatus 1 in batches, and compacted to a predetermined height, controlling the relative density of the samples to be 60%. After sample preparation, a constant axial pressure is applied, which in this embodiment is 200 kPa, until the samples are consolidated. After consolidation, a ring shear test is performed under dry conditions at a shear rate of 6.74° / min, until a shear displacement of 100 mm is achieved. Shear stress-shear displacement data are collected every 10 seconds during the shearing process. Since the shear displacement varies at different radii of the ring shear sample 2, the average radius of the inner and outer diameters of the ring shear sample 2 is used to calculate the shear displacement. The calculation formula is as follows: ; ; In the formula, and These are the outer and inner diameters of the ring shear specimen 2, respectively; The average radius; Shear rate; This represents the corresponding shearing time.

[0030] Step 2: Acoustic emission signals are collected during the circumferential shearing experiment.

[0031] In this embodiment of the invention, step 2 specifically includes: like Figure 2 As shown, an acoustic emission sensor 3 is attached to the loading plate of the ring shearing apparatus 1. Specifically, a magnetic clamp is used to fix the acoustic emission sensor 3 to the side wall of the upper loading plate 8, and a coupling agent is applied between the sensor and the contact surface to reduce sound wave energy loss. Before the experiment, the ambient and equipment noise amplitudes under the operating conditions of the equipment are collected. In this embodiment, the ambient noise is approximately 40dB. Based on this noise value, a trigger threshold of 44dB is set for threshold triggering sampling, and only acoustic emission signals exceeding the 44dB threshold are collected. During the ring shearing process, the acoustic emission sensor 3 collects the acoustic emission signals generated by the slippage and breakage of calcareous sand particles. The acoustic emission signals are amplified by the preamplifier 4 and then collected by the high-resolution data acquisition instrument 5. The collected acoustic emission signals are stored in the computer in the form of voltage, containing all frequency information. In this embodiment, the preamplifier 4 can provide a preamplifier gain of 40dB, and the high-resolution data acquisition instrument 5 collects data at a speed of 2MHz / s.

[0032] Step 3: Perform impact detection on the acoustic emission signal and extract the waveform of the impact signal.

[0033] In this embodiment of the invention, step 3 specifically includes: Impact detection was performed on the acquired acoustic emission signals: signals exceeding a threshold of 44 dB were recorded as one impact. The peak definition time was set to 50 μs, the impact definition time to 150 μs, and the impact latch-up time to 300 μs to divide the impact waveform and extract the waveform of the impact signal. To prevent waveform truncation, the impact definition time was extracted by 0.1 times forward from the starting threshold point and by 0.2 times backward from the ending threshold point.

[0034] Step 4: Calculate the average centroid frequency of all impact waveforms within each preset time period.

[0035] In this embodiment of the invention, the preset time period is 10 seconds, and the step specifically includes: A Fast Fourier Transform (FFT) is performed on each extracted impact waveform to convert the signal from the time domain to the frequency domain, and the centroid frequency of that impact is calculated. The centroid frequency... The weighted average value of the AE signal frequencies, where the weights are the amplitudes at each frequency point, is calculated using the following formula: ; In the formula, For the first Frequency values ​​at each frequency point; For the first The amplitude at each frequency point; This represents the number of frequency points.

[0036] Then, the average centroid frequency of all impact signals within every 10 seconds is further calculated. The calculation formula is as follows: ; In the formula, This represents the total number of impacts within every 10 seconds.

[0037] Step 5: Based on the change in average centroid frequency, analyze the shear micromechanical mechanism of calcareous sand and provide early warning of shear zone development and damage.

[0038] In this embodiment of the invention, graphs are plotted showing the changes in shear stress and average centroid frequency as a function of shear displacement, such as... Figure 3 As shown in the figure, the shear stress in calcareous sand first increases to the peak strength with shear displacement, and then gradually decreases to the residual strength. Similarly, the average centroid frequency first increases to the peak value, and then decreases with shear displacement, fluctuating around a stable value. Therefore, the micromechanical mechanism of shear is analyzed based on the change in the average centroid frequency, including: When the average center of gravity frequency increases, it indicates that the high-frequency acoustic emission signal generated by particle breakage is dominant and the particle slippage is small; when the average center of gravity frequency decreases, it indicates that the low-frequency acoustic emission signal generated by particle slippage is dominant and the soil produces significant shear displacement.

[0039] On the other hand, early warning of shear zone development and damage is based on the characteristic values ​​of the average centroid frequency change, as shown in the figure. Figure 4 The shear failure warning diagram shown is... Figure 3 A magnified view of the shear displacement in the first 25mm of the middle section; specific early warning methods include: The initial value of the average centroid frequency As warning value 1; the peak value of the average centroid frequency. As warning value 2; initial value This indicates that the soil has just been subjected to shear stress, and the particle slippage and breakage are both small, with slippage and breakage in a relatively balanced state.

[0040] When the average centroid frequency is from Increase to peak At this time, the first damage warning is issued. At this point, the high-frequency acoustic emission signal generated by particle breakage dominates, a large amount of particle breakage occurs in the soil, and shear slip is relatively small. Figure 4The development of intermediate shear stress indicates that the soil is in the hardening stage, and local shear failure begins to occur inside the soil.

[0041] When the average centroid frequency changes from the peak Reduce to The second damage warning is issued when the following occurs. At this point, the low-frequency acoustic emission signal generated by particle slippage becomes dominant, significant soil slippage occurs, and particle breakage and slippage reach a critical point of equilibrium. From Figure 4 The development of shear stress shows that the shear stress is roughly at its peak at this point, the soil is about to soften, and the local shear zone is further developing.

[0042] Subsequently, the average centroid frequency rapidly decreased to The following values, eventually fluctuating around a stable value, indicate that the low-frequency acoustic emission signal generated by particle slippage is absolutely dominant at this point, and large-scale soil slippage has occurred. From Figure 4 The development of shear stress indicates that the shear stress is at its residual strength at this point, and the soil has already undergone overall shear failure.

[0043] This embodiment uses calcareous sand as an example for description, but those skilled in the art will understand that, since different sand materials have similar particle slip and particle breakage mechanisms during shearing, this method for analyzing the micromechanical mechanism of shearing and the method for early warning of shear zone development and failure are not only applicable to calcareous sand, but also to other types of sand.

[0044] Example 2 Combination Figure 2 The present invention also provides a calcareous sand shearing state monitoring system based on acoustic emission centroid frequency for implementing the above method, including a ring shearing instrument 1, an acoustic emission acquisition module, an impact detection module, a frequency calculation module, and an analysis and early warning module.

[0045] Specifically, the ring shearing apparatus 1 is provided with a shearing box 7 for containing the calcareous sand ring shearing sample 2; the upper loading plate 8 of the ring shearing apparatus 1 is located above the shearing box 7.

[0046] The acoustic emission acquisition module includes an acoustic emission sensor 3, a magnetic clamp, a preamplifier 4, and a data acquisition device 5. The acoustic emission sensor 3 is mounted on the side wall of the upper loading plate 8 of the ring shearing device 1 via the magnetic clamp. The acoustic emission sensor 3, the preamplifier 4, and the data acquisition device 5 are electrically connected in sequence. The trigger terminal of the data acquisition device 5 is linked to the control terminal of the ring shearing device 1, and the acoustic emission signal acquired by the data acquisition device 5 is stored in the data memory 6 in the form of voltage.

[0047] The impact detection module is electrically connected to the data acquisition instrument 5 and is used to detect impacts in the acoustic emission signal and extract the waveform. The frequency calculation module is electrically connected to the impact detection module and is used to calculate the average centroid frequency of the impact waveform. The analysis and early warning module is electrically connected to the frequency calculation module and is used to output micromechanical mechanism analysis results and shear band failure early warning signals based on changes in the average centroid frequency.

[0048] In summary, the technical solution provided by this invention includes a method that involves conducting a ring shear test on calcareous sand to obtain the shear stress-shear displacement curve during the shearing process; attaching an acoustic emission sensor 3 to the loading plate of the ring shear apparatus 1 and using an acoustic emission monitoring system to collect acoustic emission signals during the shearing process; performing impact detection on the acoustic emission signals and extracting the waveforms of the impact signals; calculating the average centroid frequency of all impact waveforms within every 10 seconds; and based on the change in the average centroid frequency, analyzing the micromechanical mechanism of shearing in calcareous sand and providing early warning of shear zone development and failure. This method can monitor the shear state of calcareous sand throughout the entire process and can be used for early warning of shear failure of calcareous sand foundations and other sandy materials in marine engineering, providing an effective predictive basis for marine engineering safety.

[0049] The specific embodiments of the present invention have been described in detail above with reference to the figures, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency, characterized in that, Includes the following steps: Step 1: Conduct a ring shear test on the calcareous sand to obtain the shear stress-shear displacement curve during the shearing process of the calcareous sand; Step 2: Acquire acoustic emission signals during the circumferential shearing experiment; Step 3: Perform impact detection on the acoustic emission signal and extract the waveform of the impact signal; Step 4: Calculate the average centroid frequency of all impact waveforms within each preset time period; Step 5: Based on the change in the average centroid frequency, perform shear micromechanical mechanism analysis on calcareous sand and early warning of shear zone development and damage.

2. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 1, characterized in that, Step 1 includes: preparing the sample using a layered compaction method, loading the calcareous sand sample into the shear box (7) in layers and compacting it to a predetermined height to achieve a predetermined relative density; applying a constant axial pressure before shearing until the sample is consolidated, and then performing a ring shear test under dry conditions at a constant shearing speed until the set shear displacement is reached, collecting shear stress-shear displacement data during the shearing process; and calculating the shear displacement using the average radius of the inner and outer diameters of the ring shear sample (2).

3. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 1, characterized in that, Step 2 includes: attaching the acoustic emission sensor (3) to the surface of the upper loading plate (8) of the ring shearing instrument (1), and applying coupling agent between the sensor and the contact surface; collecting the ambient and equipment noise amplitude, using the amplitude as a threshold for threshold-triggered sampling, and collecting only acoustic emission signals whose amplitude exceeds the threshold; the acoustic emission sensor (3) collects the acoustic emission signals generated by the slippage and breakage of calcareous sand particles during the ring shearing experiment, and the acoustic emission signals are amplified by the preamplifier (4) and then collected by the data acquisition instrument (5); the collected acoustic emission signals are stored in the form of voltage and contain all frequency information.

4. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 1, characterized in that, Step 3 includes: performing impact detection on the collected acoustic emission signal, recording acoustic emission signals exceeding the threshold as an impact; setting corresponding peak definition time, impact definition time, and impact lockout time to divide the impact waveform; when extracting the impact waveform, extracting 0.1 times more impact definition time forward from the starting threshold point and 0.2 times more impact definition time backward from the ending point.

5. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 1, characterized in that, Step 4 includes: performing a fast Fourier transform on the impact waveform, calculating the centroid frequency of the impact signal, and then calculating the average centroid frequency of all impact signals within each preset time period.

6. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 5, characterized in that: The preset time period is 10 seconds.

7. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 1, characterized in that: In step 5, the analysis of the shear micromechanical mechanism based on the change of the average center of gravity frequency includes: when the average center of gravity frequency increases, it indicates that the high-frequency acoustic emission signal generated by particle breakage is dominant and the particle slippage is small; when the average center of gravity frequency decreases, it indicates that the low-frequency acoustic emission signal generated by particle slippage is dominant and the soil produces significant shear displacement.

8. The method for monitoring the shear state of calcareous sand based on acoustic emission centroid frequency according to claim 6, characterized in that: Early warning of shear zone development and damage based on characteristic values ​​of average centroid frequency change includes: using the initial value of average centroid frequency as warning value 1 and the peak value of average centroid frequency as warning value 2; issuing the first damage warning based on the average centroid frequency increasing from the initial value to the peak value, and issuing the second damage warning based on the average centroid frequency decreasing from the peak value to below the initial value.

9. A shear state monitoring system for calcareous sand based on acoustic emission centroid frequency, used to implement the method described in any one of claims 1-8, characterized in that: It includes a ring shearing device (1), an acoustic emission acquisition module, an impact detection module, a frequency calculation module, and an analysis and early warning module; The ring shear apparatus (1) is used to perform ring shear experiments on calcareous sand and obtain the shear stress-shear displacement curve during the sand shearing process. The acoustic emission acquisition module is used to acquire acoustic emission signals during the ring shearing experiment; The impact detection module is used to perform impact detection on the acoustic emission signal and extract the waveform of the impact signal; The frequency calculation module is used to calculate the average centroid frequency of all impact waveforms within each preset time period. The analysis and early warning module is used to analyze the shear micromechanical mechanism of sand and soil and provide early warning of shear zone development and failure based on the change of the average centroid frequency.

10. A calcareous sand shear state monitoring system based on acoustic emission centroid frequency according to claim 9, characterized in that, The acoustic emission acquisition module includes: an acoustic emission sensor (3), a magnetic clamp, a preamplifier (4), and a data acquisition instrument (5); the acoustic emission sensor (3) is installed on the side wall of the upper loading plate (8) of the ring shearing instrument (1) by the magnetic clamp, and a coupling agent is applied between the sensor and the side wall; the preamplifier (4) provides a 40dB preamplifier gain, and the data acquisition instrument (5) acquires acoustic emission signals exceeding the threshold.

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