Rock mass three-dimensional visualization and disaster early warning method based on velocity structure tomography

Abstract

The invention relates to the technical field of geotechnical engineering, and discloses a rock mass three-dimensional visualization and disaster early warning method based on velocity structure tomography. The method comprises the following steps: acquiring mechanical signals and fracture data of a rock mass under different load effects by utilizing devices such as acoustic emission monitoring and a split Hopkinson pressure bar, inverting the internal speed structure change of the rock mass by adopting a delay double-difference tomography technology, constructing a three-dimensional visual model of a rock mass fracture partition, and finally determining the fracture partition of the rock mass in combination with a rock mass fracture mechanism and a spatio-temporal evolution law. And establishing a disaster early warning mechanism. According to the invention, the problem that the traditional monitoring technology cannot accurately capture the crack extension and dynamic fracture partition in the rock mass in real time is solved, reliable technical support can be provided for rock mass stability evaluation and disaster prevention and control in the scenes of mining, tunnel engineering and the like, and the engineering safety and production efficiency are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rock mass engineering, in particular to a rock mass three-dimensional visualization and disaster warning method based on velocity structure tomography. BACKGROUND

[0002] The rupture evolution and stability of rock mass under loads such as explosion and impact are directly related to engineering safety. Traditional rock mass monitoring technology has many limitations: direct measurement method can only observe the surface rupture of rock mass and cannot grasp the internal part; acoustic wave method and resistance method are easily affected by equipment current and on-site interference, and have low precision; industrial CT scanning has high cost and poor on-site adaptability, and cannot capture transient crack propagation; numerical simulation is difficult to adapt to the dynamic changes of rock mass structure with the advancement of engineering, and cannot provide real-time warning.

[0003] In existing tomography technology, traditional double difference tomography needs to rely on event pairs in the same time period, and cannot accurately invert the velocity structure changes of rock mass in different load stages; delay imaging mostly uses direct wave speed subtraction, which has large errors due to data quality differences, and cannot meet the needs of engineering site for accurate monitoring and warning; therefore, the present application proposes a rock mass three-dimensional visualization and disaster warning method based on velocity structure tomography to solve the above problems. SUMMARY

[0004] In order to solve the above problems, the present application provides a rock mass three-dimensional visualization and disaster warning method based on velocity structure tomography.

[0005] The rock mass three-dimensional visualization and disaster warning method based on velocity structure tomography provided by the present application adopts the following technical scheme:

[0006] The rock mass three-dimensional visualization and disaster warning method based on velocity structure tomography comprises the following steps:

[0007] Step 1, rock mass indoor test: obtain load-rupture correlation data

[0008] 11. Static load test: standard cylindrical rock mass specimens with a diameter of Φ50mm and a height of 100mm are prepared by using in-situ sampling method, and the MTS rock mechanics test system is used to apply graded static load to the specimens. The acoustic emission monitoring device is started synchronously (sampling frequency 1000Hz), and the acoustic emission signals under different stress levels are collected. According to the signal characteristics (such as frequency and amplitude), the elastic stage, yield stage and failure stage of rock mass are divided, the rock mass rupture mechanism in each stage is analyzed, and the velocity structure change precursors before rock mass failure are recorded.

[0009] 12、Impact loading test: Prepare cylindrical specimens with a diameter of Φ50 mm and a height of 25 mm, and apply impact loading with a strain rate of 10^-1~10^2 s^-1 through a split Hopkinson pressure bar (SHPB). At the same time, start the high-speed camera technology (DIC) to capture the surface crack trend of the rock mass at a rate of 1000 frames / s, and combine the acoustic emission monitoring device to collect acoustic emission signals during the impact process. Compare the correlation between surface cracks and internal acoustic emission signals to determine the crack propagation law of rock mass under impact loading.

[0010] 13、Explosion loading test: Prepare a 400x400x200mm cuboid rock mass specimen, and carry out single-hole, double-hole, and three-hole explosion loading in a special explosion test device (such as a 5kg TNT equivalent spherical vacuum explosion bunker). Real-time record the acoustic emission signals during the explosion process through the acoustic emission monitoring device, analyze the influence of different blast hole numbers and initiation methods on rock mass crack propagation, and obtain the dynamic data of rock mass failure under explosion loading.

[0011] Step 2, Delayed double difference tomography: Construct a three-dimensional visualization model

[0012] 21、Signal preprocessing: Denoise (using wavelet transform algorithm) and waveform cross-correlation analysis of acoustic emission signals collected in laboratory tests to extract absolute travel time data and event pair relative arrival time difference data. Break through the limitations of traditional technology, construct event pairs from signals at different load stages (such as elastic stage under static load and impact loading stage), and improve data utilization and inversion accuracy.

[0013] 22、Joint inversion calculation: Use high-performance computers and GPU operation servers, combined with self-developed four-dimensional imaging technology, to perform joint inversion of event pairs for source location and rock mass velocity structure changes. During the inversion process, take the change of rock mass wave velocity as the core index (wave velocity reduction corresponds to crack development), and obtain the velocity structure evolution map of the rock mass under different load actions.

[0014] 23、Three-dimensional visualization modeling: According to the velocity structure evolution map, combined with the rock mass failure mechanism, divide the crushed zone (wave velocity reduction by more than 30%), crack zone (wave velocity reduction by 10%-30%), and elastic zone (wave velocity change less than 10%). Use three-dimensional modeling software (such as AutoCAD, Fluent) to construct a three-dimensional visualization model of rock mass failure zoning that dynamically updates with load action. The model can intuitively display the crack propagation path, failure zoning range, and spatio-temporal evolution trend.

[0015] Step 3, Field monitoring and disaster warning: Engineering application

[0016] 31. On-site sensor deployment: Based on the results of indoor tests, microseismic sensors (sampling frequency ≥1000Hz) are deployed at engineering sites such as mines and tunnel working faces at a density of ≤10m between adjacent sensors to ensure coverage of the entire monitoring area and to collect microseismic signals of the rock mass under explosive loads in real time.

[0017] 32. On-site data inversion and model update: The microseismic signals collected on-site are preprocessed and jointly inverted according to the method in step 2. The inversion results are transmitted to the three-dimensional visualization model in real time to update the fracture zoning and fracture propagation state of the rock mass on-site. The model update frequency is no less than once per minute, so as to realize real-time monitoring of dynamic rock mass structure.

[0018] 33. Early Warning Mechanism Establishment and Triggering: Setting Criteria for Rock Mass Instability:

[0019] Level III warning: The propagation rate of rock fracture zone > 0.5 m / h, the abrupt change in rock mass velocity structure > 10%, and the frequency of acoustic emission signal increases by more than 3 times (meeting any one of these conditions);

[0020] Level 1 warning: Two or more of the above criteria are met.

[0021] When the monitoring data reaches the warning threshold, the warning information is pushed in real time through the warning platform (including audible and visual alarms and SMS notifications) to guide on-site personnel to take prevention and control measures (such as suspending operations and reinforcing the rock mass).

[0022] Verification and optimization: The 3D visualization model constructed by the indoor test was compared with the industrial CT scan results to ensure that the model error was ≤8%; the on-site early warning signal was correlated with the actual rock mass stability, and the early warning criteria were continuously optimized to make the early warning accuracy ≥90%.

[0023] In summary, the present invention has at least one of the following beneficial technical effects:

[0024] High monitoring accuracy: It adopts time-delayed double-difference tomography imaging technology, which breaks through the limitations of traditional technology. It can accurately invert the changes in velocity structure inside the rock mass, and the error of the three-dimensional visualization model is ≤8%. It can capture the expansion of cracks and the evolution of fracture zones inside the rock mass in real time.

[0025] Timely and efficient early warning: The on-site model is updated at a frequency of ≥1 time / minute. The early warning criteria combine multiple indicators (wave velocity, fracture velocity, acoustic emission signal), and the early warning accuracy rate is ≥90%. It can trigger disaster warnings in advance and avoid safety accidents.

[0026] Highly adaptable: It can be used for both indoor testing and engineering site testing. It is suitable for various load scenarios such as static load, impact, and explosion. The sensor layout and early warning threshold can be adjusted according to different engineering geological conditions. It is compatible with various rock mass engineering projects such as mines and tunnels.

[0027] Cost-controllable: Relying on existing MTS test system, SHPB device and other equipment, combined with self-developed signal processing and imaging algorithms, there is no need to rely on expensive special equipment, thus reducing the cost of engineering applications. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the technical route of an embodiment of the invention. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0030] Example 1:

[0031] I. Experimental Preparation and Acquisition of Basic Indoor Data

[0032] Specimen preparation: Following the "Experimental Methods" requirements in the open fund application, samples were taken in situ from the target mine's stope (lithology being the actual sandstone found in the mine), and standard specimens were prepared according to the following specifications:

[0033] Static load test specimens: Cylindrical specimens with a diameter of Φ50mm and a height of 100mm were prepared using the in-situ sampling method, with 3 parallel specimens per group to ensure the integrity of the specimens (no obvious initial cracks) and to meet the loading requirements of the MTS rock mechanics testing system;

[0034] Impact load test specimen: Prepare cylindrical specimens with a diameter of Φ50mm and a height of 25mm. The surface is polished (flatness error ≤0.02mm) to meet the impact loading requirements of the split Hopkinson bar (SHPB) device;

[0035] Explosive load test specimen: A rectangular specimen of 400×400×200mm is machined, with a 10mm diameter blast hole (150mm depth) pre-drilled inside the specimen to simulate the actual blast hole layout parameters in the mine, for single-hole, double-hole and triple-hole explosive loading tests.

[0036] Indoor test execution

[0037] Static load test: Using the MTS816 electro-hydraulic servo rock testing system of the "National Key Laboratory for Deep Coal Mine Mining Response and Disaster Prevention (Jointly Constructed by the Ministry of Industry and Information Technology)", graded static loads were applied (loading rate 0.5 MPa / s, load range 0~60 MPa). Simultaneously, an acoustic emission tester (sampling frequency 1000 Hz, amplitude threshold 40 dB) was used to collect acoustic emission signals. Based on signal characteristics, the bearing stages were divided as follows: elastic stage (0~25 MPa, acoustic emission signal frequency <5 times / minute), yielding stage (25~45 MPa, acoustic emission signal frequency 10~20 times / minute), and failure stage (45~60 MPa, acoustic emission signal frequency increases sharply to over 50 times / minute). Changes in the rock mass velocity structure before failure were recorded—the wave velocity decreased by 18% compared to the initial value, providing basic data for on-site instability judgment.

[0038] Impact loading test: Using a laboratory-mounted SHPB experimental setup, impact loads with strain rates ranging from 10^-1 to 10^2 s^-1 (a total of 5 strain rate gradients) were applied to the specimens. Simultaneously, a CamRecord1000 high-speed camera (1000 frames / second) was used to capture the surface crack propagation. The signal correlation was analyzed using an acoustic emission monitoring device. Results showed that when the strain rate was 50 s^-1, the surface crack propagation length reached 12 mm, corresponding to a peak acoustic emission signal amplitude of 80 dB, and an internal wave velocity reduction of 22%, clearly demonstrating the correlation between crack propagation and signal intensity under impact loading.

[0039] Explosion load test: The test was conducted in a spherical vacuum explosive bunker with a diameter of 5 meters and a TNT equivalent of 5 kg, which was developed in the laboratory. Low-sensitivity explosives (charges of 20g, 30g, and 50g) were used for single-hole detonation, and the explosion process signals were recorded using an acoustic emission device (sampling frequency 2000Hz). Data showed that with a charge of 50g, the fracture zone expanded to 55 times the borehole radius (approximately 2.75m) within 35ms after the explosion, and the wave velocity decreased by 28%, providing a basis for matching blasting parameters on site.

[0040] II. On-site monitoring system construction and data inversion

[0041] Sensor Deployment: Based on the results of indoor tests, microseismic sensors were deployed in the mine (15m bench height, 65° slope angle) according to the principle of "grid + densification in key areas".

[0042] Basic grid: One sensor is deployed every 10m along the step direction, for a total of 15 sensors;

[0043] Key areas (such as above adjacent goaf areas and jointed sections): Five additional sensors will be installed, with the spacing between adjacent sensors reduced to 5m to ensure coverage of the entire monitoring area. All sensors will use the GJY-1 engineering detector with a sampling frequency of 1500Hz. Signal transmission will employ both wireless and wired backups to prevent data loss due to on-site interference.

[0044] Data preprocessing and inversion: The microseismic signals acquired on-site are first denoised using a self-developed "microseismic data clustering analysis technology" (to remove interference signals such as equipment current and mechanical vibration, and improve the signal-to-noise ratio to over 30dB). Then, absolute travel time data and event pairs are extracted and compared to time difference data. This eliminates the limitation of traditional double-difference tomography that "event pairs must come from the same time period". Event pairs are constructed from three time periods: before blasting (stable stage), during blasting (load action stage), and after blasting (stable stage), thereby improving inversion accuracy.

[0045] 3D visualization model construction and updating: Using a high-performance laboratory computer (including a GPU computing server) and a self-developed "four-dimensional imaging technology," the source location and velocity-structure changes of the event pairs were jointly inverted. The inversion results were imported into 3D modeling software (AutoCAD Civil 3D) in real time, and the rupture zones were divided according to the following criteria:

[0046] The pulverization zone: the wave velocity is reduced by more than 30% compared to the initial value (corresponding to the area within 0.5m around the borehole with a charge of 50g in the indoor test).

[0047] Fractured zone: Wave velocity decreases by 10%~30% (corresponding to the fracture propagation range in indoor tests);

[0048] Elastic zone: Wave velocity change is less than 10%. The model update frequency is set to 1 time / minute, which can intuitively show the crack propagation path after blasting (such as preferential propagation along the joint direction) and the dynamic changes of the fracture zone (such as the crack zone expanding to a range of 3m 5 minutes after blasting).

[0049] III. Disaster Early Warning Triggering and On-site Prevention and Control

[0050] Early warning criteria: Combining indoor test data and historical mine accident cases, a three-level early warning mechanism is established:

[0051] Level 3 Warning (Attention Level): Meets any of the following conditions: ① Rock mass fracture zone propagation rate > 0.5 m / h; ② Rock mass velocity structure abrupt change > 10%; ③ Acoustic emission signal frequency increases more than 3 times compared to the stable stage;

[0052] Level II Warning (Alert Level): Both of the above conditions must be met;

[0053] Level 1 Warning (Emergency Level): All three conditions are met or the characteristic of "connection between the fracture zone and the goaf" appears;

[0054] Early warning triggering and response: After a bench blast (10kg charge, 3m borehole spacing), monitoring data showed that:

[0055] Two minutes after the blast: the fracture zone expansion rate reached 0.7 m / h, triggering a level three warning. The warning platform (including on-site audible and visual alarms and management personnel's mobile APP) immediately pushed out a notification message, the on-site loading operation was suspended, and personnel were arranged to patrol.

[0056] Five minutes after the blast: the fissure expansion rate increased to 1.2 m / h, and the frequency of acoustic emission signals increased by 4 times, triggering a level one warning. The platform pushed an emergency alarm, and the on-site emergency plan was activated—all personnel and equipment were evacuated, and temporary reinforcement of the fissure development section was carried out using "anchor bolts + shotcrete".

[0057] Effect Verification: After reinforcement, monitoring showed that the crack propagation rate dropped to 0.2 m / h, and the wave velocity change stabilized within 5%, thus the warning was lifted. Subsequent inspection of the reinforced area using a borehole digital camera (deep hole digital drilling camera) showed a 92% match between the borehole imaging results and the 3D visualization model, verifying the accuracy of the method.

[0058] Example 2: Rockburst Early Warning in Tunnel Excavation

[0059] I. Indoor Targeted Tests

[0060] Considering the characteristics of a deep-buried tunnel (800m depth) and granite lithology, a combined static and impact load test was conducted. Φ50×100mm granite specimens were prepared, and a static load of 30MPa (simulating tunnel confining pressure) was applied first, followed by impact loads with different strain rates applied using a SHPB (Stone Shock Barrier). The results showed that under confining pressure, the frequency of acoustic emission signals before granite failure increased sharply by 5 times, while the wave velocity decreased by 25%. Furthermore, crack propagation was more concentrated under impact load (unlike the diffuse cracks without confining pressure), providing a specific criterion for tunnel rockburst early warning.

[0061] II. Field Application

[0062] Eight microseismic sensors (6m spacing, covering the excavation face and a 10m radius behind) were deployed at the tunnel working face (6m excavation diameter) to monitor the tunnel blasting excavation (2kg charge, 40cm spacing between perimeter holes). After one excavation, the 3D model showed a 23% decrease in rock wave velocity above the working face and a fracture zone propagation rate of 0.6m / h, triggering a level-three warning. The excavation plan was immediately adjusted on-site—the charge was reduced to 1.5kg, pre-splitting blasting was adopted, and advanced anchor bolt support was installed at the working face. Subsequent monitoring showed no further warnings, and the tunnel excavation proceeded smoothly.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for rock mass 3D visualization and disaster warning based on velocity structure tomography, characterized in that: The method comprises the following steps: Step 1, Carrying out rock mass laboratory test to obtain the mechanical properties and fracture data of the rock mass under different loads; Step 2, 21. Constructing a three-dimensional visualization model of rock mass fracture zoning based on the delay double-difference tomography technology:

22. Preprocessing the acoustic emission signals collected in step one, extracting absolute travel time data and event pair relative arrival time difference data, and constructing event pairs from signals at different load stages; 23. Based on the constructed event pairs, jointly inverting the source location and the velocity structure change of the rock mass to obtain the velocity structure evolution law of the rock mass under different loads; 24. According to the velocity structure evolution law, combined with the rock mass fracture mechanism, the rock mass crushing zone, the fractured zone and the elastic zone are divided, and the three-dimensional visualization model of rock mass fracture zoning dynamically changing with the load is constructed; Step 3, Carrying out engineering site rock mass monitoring and disaster warning:

31. According to the laboratory test results, microseismic sensors are arranged at the engineering site to collect microseismic signals of the rock mass under explosive load in real time; 32. Using the delay double-difference tomography technology in step 2, the internal fracture propagation law and the spatio-temporal evolution characteristics of the fracture zoning of the rock mass are inverted, and the three-dimensional visualization model of the rock mass fracture zoning is updated; 33. Based on the spatio-temporal evolution law of the rock mass fracture zoning and the fracture mechanism, the rock mass instability criterion is set, when the monitoring of the rock mass velocity structure change and the fracture propagation rate reaches the preset threshold, the disaster warning signal is triggered, and the rock mass disaster warning is completed.

2. The method according to claim 1, wherein the method is characterized in that: The step 1 comprises:

11. Preparing standard rock mass specimens, applying static load by MTS rock mechanics test system, synchronously collecting acoustic emission signals of the rock mass under static load by acoustic emission monitoring device, dividing rock mass bearing stages and analyzing fracture mechanism; 12. Imparting impact load of different strain rates to the rock mass specimen by using split Hopkinson pressure bar (SHPB), capturing the rock mass surface crack trend by high-speed camera technology (DIC), and collecting acoustic emission signals under impact load by acoustic emission monitoring device; 13. Building an indoor explosion loading test system, performing single-hole, double-hole and three-hole explosion loading on the cuboid rock mass specimen, recording acoustic emission signals of the rock mass under explosive load by acoustic emission monitoring device, and obtaining fracture expansion dynamic data.

3. The method according to claim 2, wherein the method is characterized in that: In the step 11, the standard rock mass specimen is a cylinder with a diameter of Φ50mm and a height of 100mm; in the step 12, the rock mass specimen is a cylinder with a diameter of Φ50mm and a height of 25mm; in the step 13, the rock mass specimen is a cuboid with a size of 400×400×200mm, and all the specimens are prepared by in-situ sampling method to ensure that the specimen has the same characteristics as the rock mass at the engineering site.

4. The method according to claim 1, wherein the method is characterized in that: In the step 21, the preprocessing of the acoustic emission signals includes signal noise reduction and waveform cross-correlation analysis to improve the accuracy of the absolute travel time data and the relative arrival time difference data, wherein the waveform cross-correlation analysis uses a self-developed signal processing algorithm with a calculation accuracy error of not more than 5%.

5. The method according to claim 1, wherein the method is characterized in that: In step 22, the joint inversion process uses high-performance computers and GPU operation servers, combined with the self-developed four-dimensional imaging technology, to realize real-time calculation of the speed structure evolution, and the inversion result updating frequency is not less than 1 time / minute.

6. The method according to claim 1, wherein the method is characterized by: In step 31, the layout density of the microseismic sensor is determined according to the scale and geological conditions of the rock mass on the construction site, the distance between adjacent sensors is not more than 10 m, and the sensor sampling frequency is not less than 1000 Hz, ensuring the integrity of the microseismic signal collection.

7. The method according to claim 1, wherein the method is characterized by: In step 33, the rock mass instability criterion includes: the crack zone expansion rate of the rock mass exceeds 0.5 m / h, the speed structure mutation amplitude of the rock mass exceeds 10%, and the acoustic emission signal frequency increases by more than 3 times. When any criterion is met, a three-level warning is triggered, and when two or more criteria are met, a first-level warning is triggered.

8. The method according to claim 1, wherein the method is characterized in that: It also includes a verification step for the three-dimensional visualization model and the early warning mechanism: comparing the three-dimensional visualization model constructed by the indoor test with the industrial CT scanning results, the model error is not more than 8%; correlating the on-site early warning signal with the actual rock mass stability, the early warning accuracy is not less than 90%.

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