Coal fire area crack active enhancement detection test system and method

Abstract

The invention discloses a coal fire area fracture active enhancement detection test system and method, and belongs to the technical field of mine safety and geophysical exploration, and the system comprises a fracture generation module which is used for simulating a heat-force-gas coupling condition of an underground coal fire area, and inducing a coal rock mass test piece to generate a fracture; the fracture detection module is used for synchronously acquiring multi-physics field data of the coal and rock mass test piece in real time; the fracture intervention module is used for injecting a natural medium simulant and an enhanced medium foam gel material into the fracture so as to simulate a real environment and enhance a detection signal; and the intelligent feedback and data fusion module is used for controlling operation parameters of each module, synchronously acquiring detection data, and performing fusion processing, intelligent inversion and four-dimensional visualization on the detection data to realize whole-process monitoring detection of fracture evolution. The invention provides a scientific method for precise delineation and targeted plugging treatment of hidden fractures in a coal fire area, and solves the problems of multiplicity of solution in traditional fracture detection and easy reburning in coal fire treatment.

Description

Technical Field

[0001] This invention belongs to the field of mine safety and geophysical exploration technology, and particularly relates to an active enhanced detection test system and method for fractures in coal-fired areas. Background Technology

[0002] Underground coal fires are a major global geological hazard. Due to their complex geological conditions, large combustion area, long development time, highly concealed combustion state, and complex ventilation channels, underground coal fires result in numerous new fire zones, rapid fire development, insufficient fire suppression speed to keep pace with fire spread, and a high risk of reignition in controlled areas. In the early stages of coal fire control, the heat released from the underground fire's combustion center bakes the surrounding coal and rock. The smoldering coal continuously generates high-temperature gases that circulate and leach into the overlying coal and rock mass, causing changes in the mechanical properties and porosity of the coal and rock. Furthermore, the combustion creates numerous voids, disrupting the original stress balance of the coal and rock, thus creating new oxygen supply channels. Although conventional control technologies can extinguish the fire, these concealed oxygen supply channels are the root cause of the reignition and spread of extinguished fires.

[0003] Currently, geophysical exploration methods are widely used to detect coal fire sources, providing important support for delineating target areas for coal fire control. However, the precise control of extinguished coal fires to prevent reignition still faces severe challenges. The core bottleneck lies in the lack of effective detection methods for the spatial distribution, geometry, and connectivity of underground hidden fissure systems. This severely restricts the precise implementation of sealing processes, causing hidden fissures to continue supplying oxygen to extinguished coal bodies, leading to uncontrolled reignition of extinguished coal bodies and seriously endangering the ecological environment and coal resource reserves.

[0004] To address the aforementioned problems in existing technologies, there is an urgent need to propose an active enhancement detection test system and method for cracks in coal fire zones. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as low accuracy in detecting hidden fractures in coal fire zones, lack of controllable verification platforms, and difficulty in evaluating sealing effectiveness, this invention proposes an active enhancement detection test system and method for fractures in coal fire zones. The aim is to accurately locate and quantitatively characterize the spatial distribution, geometry, and connectivity of hidden fractures; assess the weakening effect of fracture filling materials on geophysical signals; improve fracture detection sensitivity through active enhancement media; and provide a verifiable theoretical basis and technical support for on-site fracture sealing design and reignition prevention decisions.

[0006] To achieve the above objectives, the present invention provides an active enhanced detection test system for fractures in coal fire zones, comprising: The fracture evolution module is used to simulate the thermo-mechanical-gas coupling conditions in underground coal-fired zones and induce fractures in coal and rock mass specimens. The fracture detection module is used to acquire multi-physics field data of coal and rock mass specimens in real time and synchronously. The fracture intervention module is used to inject natural medium simulants and reinforcing medium foam gel materials into fractures to simulate the real environment and enhance the detection signal; The intelligent feedback and data fusion module is used to control the operating parameters of each module, synchronously acquire detection data, and perform fusion processing, intelligent inversion and four-dimensional visualization of the detection data to realize the geometric feature monitoring of the entire process of fracture evolution.

[0007] Optionally, the fracture evolution module includes: A sealed, rigid chamber for accommodating rectangular coal and rock specimens; The servo pressurization unit, installed on the load-bearing frame of the sealed rigid chamber, is used to apply independently controlled four-sided stress to the specimen, forming the force application part; A heating device is located at the bottom of a sealed rigid chamber and is used to provide a heat source from the bottom of the specimen, forming a thermal action section. The gas injection and control system, connected to the sealed rigid chamber, is used to inject gas into the chamber and control the gas circulation, adsorption, and release process, constituting the gas action part.

[0008] Optionally, the fracture detection module includes a sensor array deployed on a sealed rigid chamber and a coal and rock mass specimen, the sensor array comprising: Resistivity probe array for high-density resistivity measurement and resistivity tomography; Acoustic emission sensors are used to monitor acoustic emission signals during the initiation and propagation of cracks. Acoustic wave transmitting and receiving transducers are used to transmit and receive acoustic wave signals. Resistance strain gauges are used to measure strain. Distributed fiber optic sensing networks are used to measure temperature and strain. A magnetic sensor is used to monitor magnetic signals.

[0009] Optionally, the fracture evolution module includes a gas injection and control system, the gas injection and control system comprising: Vacuum pumps, displacement pumps, and mass flow controllers are used for vacuuming the chamber environment, circulating gas in and out of coal and rock, and monitoring pressure and flow throughout the process, enabling gas-induced damage to coal and rock specimens under expansion and contraction.

[0010] Optionally, in the crack evolution module, each servo pressurization unit corresponding to the long side of the specimen includes two independently controlled electro-hydraulic servo actuators and a force transmission pressure plate; each servo pressurization unit corresponding to the short side of the specimen includes an independently controlled electro-hydraulic servo actuator and a force transmission pressure plate. The force transmission plates are all connected to the output end of the actuator; The side of the force-transmitting pressure plate that contacts the coal and rock mass specimen is integrated with a thin-film pressure sensor array, which is used to monitor the contact stress distribution in real time and form a closed-loop feedback control for the servo pressurization unit.

[0011] Optionally, the fracture evolution module further includes an auxiliary heating system, the auxiliary heating system comprising: A closed fluid channel network is integrated inside the force transmission pressure plate; A constant-temperature liquid circulation device is installed on the supporting frame of a sealed rigid chamber and is connected to the sealed fluid channel network through heat-insulated pipelines. It is used to provide high-temperature heat transfer oil as a heating medium for coal and rock mass specimens and to control the temperature and flow rate of the heating medium to achieve heating of the coal and rock mass specimens.

[0012] Optionally, the fracture detection module also includes one or more sets of vertical integrated logging probes pre-embedded inside the coal and rock mass specimen. The probes work in conjunction with the resistivity probe array deployed on the force transmission plate to form a resistivity-acoustic joint three-dimensional detection network.

[0013] Optionally, the vertical integrated logging probe includes a central tube made of insulating material; An acoustic transducer is installed inside the central tube, and an annular electrode is fixedly arranged outside the central tube. The annular electrode is electrically connected to the coal and rock mass through a conductive coupling medium.

[0014] Optionally, the intelligent feedback and data fusion module is used to receive the physical field data fed back in real time by the fracture detection module, and dynamically adjust the stress field, temperature field, atmospheric environment parameters of the fracture evolution module and the injection parameters of the fracture intervention module through machine learning algorithms to achieve adaptive intelligent feedback control of the test process.

[0015] This invention also provides an active enhancement detection method for fractures in coal fire zones. Based on the aforementioned system, the method includes the following steps: Based on specimen preparation and system initialization, the conditions for the evolution of thermo-mechanical-gas coupled fractures were obtained. Simulate the aforementioned thermo-mechanical-gas coupled fracture evolution conditions to induce a fracture network in the coal and rock mass, and simultaneously collect the first physical field data; A natural medium simulant was injected into the fissure, and second physical field data was obtained after the injection. The first physical field data and the second physical field data were compared to obtain the evaluation result of the physical signal weakening effect. Reinforcing medium foam gel material is injected into the crack, and the third physical field data obtained after injection is obtained. The first physical field data, the second physical field data and the third physical field data are compared to obtain the detection enhancement inversion results of the crack and the reinforcing medium. Based on the assessment results of the physical signal weakening effect and the detection enhancement inversion results of the fracture and the reinforcing medium, four-dimensional dynamic visualization is performed to display or reproduce the entire process of fracture evolution and detection in real time.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: 1) The fracture evolution module, through a sealed rigid chamber, servo pressurization unit, heating device, and gas injection and control system, simulates the thermo-mechanical-gas coupling conditions of underground coal fire zones, inducing the formation of fracture networks in the coal and rock mass. This module can precisely control the stress on all four sides, bottom heating, and gas adsorption-desorption cycle, utilizing the gas-induced damage effect to simulate the complex environment of real coal fire zones, providing controllable experimental conditions for fracture evolution.

[0017] 2) The fracture detection module uses a sensor array deployed on the chamber and coal / rock specimens, including a resistivity probe array, acoustic emission sensors, acoustic wave transmitting and receiving transducers, resistance strain gauges, a distributed fiber optic sensor network, and magnetic sensors, to acquire multi-physics field data in real time and synchronously. This module enables high-precision monitoring of the fracture evolution process, capturing the initiation, propagation, and penetration of fractures, providing detailed physical field data support for the detection of the entire fracture evolution process.

[0018] 3) The fracture intervention module injects a natural medium simulant and a reinforcing medium foam gel material into the fracture through a fluid injection system. The natural medium simulant is used to simulate the complex fracture-filling environment of a real coal fire zone and assess the weakening effect of geophysical signals; the reinforcing medium foam gel material is used to enhance the detection signal and improve the sensitivity and accuracy of fracture detection. This module can effectively simulate the real environment and optimize detection conditions, providing a more reliable basis for active signal enhancement in fracture detection.

[0019] 4) The intelligent feedback and data fusion module controls the operating parameters of each module, synchronously collects detection data, and performs data fusion processing, intelligent inversion, and four-dimensional visualization. This module can provide real-time feedback of the physical field data of fracture evolution, dynamically adjust the operating parameters of each module, and achieve adaptive intelligent feedback control of the experimental process. Through four-dimensional visualization technology, the fracture development process and channel morphology are presented intuitively, providing a basis for decision-making in coal fire zone management.

[0020] This invention provides theoretical insights and technical support for the precise delineation and targeted sealing of hidden fissures in coal fire zones, and solves the problems of the ambiguity of traditional fissure detection and the easy re-ignition of coal fires. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the structure of the active enhanced detection test system for fractures in coal fire zones according to an embodiment of the present invention; Figure 2 This is a flowchart of the active enhanced detection method for fractures in coal fire zones according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a vertical probe pre-embedded in a coal and rock mass specimen according to an embodiment of the present invention.

[0022] The components include: 1. Sealed rigid chamber; 2. Sensor array; 201. Resistivity probe array; 202. Acoustic wave transmitting and receiving transducer; 3. Displacement pump; 4. Vacuum pump; 5. Electro-hydraulic servo actuator; 6. Force transmission plate; 7. Constant temperature liquid circulation device; 8. Central tube; 9. Coal tar; 10. Flue gas condensate; 11. Injection pump; 12. Acoustic emission sensor. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0025] Example 1 like Figure 1 As shown, this embodiment provides an active enhanced detection test system for fractures in coal fire zones, comprising: The fracture evolution module is used to simulate the thermal-mechanical-gas coupling conditions in underground coal-fired zones, inducing fractures in the coal and rock mass. The fracture detection module is used to acquire multi-physics field data in real time and synchronously to monitor the evolution of fractures. The fracture intervention module is used to inject natural medium simulants and reinforcing medium foam gel materials into fractures to simulate the real environment and enhance the detection signal; The intelligent feedback and data fusion module is used to control the operating parameters of each module, synchronously acquire detection data, and perform fusion processing, intelligent inversion and four-dimensional visualization of the detection data to realize the whole process monitoring of fracture evolution.

[0026] The feasible fracture evolution module is used to reconstruct and precisely control a real underground coal fire environment in a laboratory, actively inducing fractures in the coal and rock mass. It includes a sealed rigid chamber 1 for accommodating a rectangular coal and rock mass specimen with dimensions of 2.0 × 1.0 × 1.0 m. The chamber is mounted on a rigid load-bearing frame, and independent servo pressurization units are installed in five orthogonal directions (excluding the bottom surface) to apply independently controllable four-sided stress to the specimen, forming a force action section. A heating device is installed at the bottom of the chamber to provide a heat source from the bottom of the specimen, forming a heat action section. The chamber is connected to a gas injection and control system for injecting gases, including CH4 and CO2, into the chamber and controlling the adsorption and release processes through programmed control, forming a gas action section.

[0027] Furthermore, the rigid bearing frame and the sealed rigid chamber 1 can preferably be installed as a whole in the underground bedrock trench, and coupled to the bedrock through the vibration isolation foundation, so as to further improve the stability and anti-interference ability of the system.

[0028] Furthermore, in the fracture evolution module, each servo pressurization unit corresponding to the long side of the coal and rock mass specimen includes two independently controlled electro-hydraulic servo actuators 5 and a force transmission pressure plate 6, and each servo pressurization unit corresponding to the short side includes one independently controlled electro-hydraulic servo actuator 5 and a force transmission pressure plate 6; the output ends of the actuators are connected to the force transmission pressure plate 6.

[0029] Furthermore, the force transmission plate 6 is a flexible plate made of flexible composite material, or a pressure head matrix composed of multiple pressure heads that can independently fine-tune the pressure.

[0030] Furthermore, a thin-film pressure sensor array 2 is integrated on the side of the force-transmitting pressure plate 6 that contacts the coal and rock mass specimen, which is used to monitor the contact stress distribution in real time and form a closed-loop feedback control for the servo pressurization unit.

[0031] Furthermore, the gas injection and control system in the fracture evolution module is specifically configured to: achieve gas-induced damage to the coal and rock mass by programmatically controlling the pressure of the injected gas and the number of adsorption-emission cycles, and utilizing the matrix expansion and contraction effect generated by the repeated adsorption and emission processes of gases such as CH4 and CO2 in the pores and fractures of the coal and rock mass.

[0032] As an optional implementation, the gas injection and control system includes a mass flow controller, a displacement pump 3 and a vacuum pump 4, which can realize pressure and flow monitoring of the entire process of vacuuming the cabin environment, gas injection and adsorption / emission.

[0033] Furthermore, the fracture evolution module also includes an auxiliary heating system, which includes: a closed fluid channel network integrated inside the force transmission plate 6; and a constant temperature liquid circulation device 7 installed on the rigid bearing frame, the device being connected to the fluid channel network via a heat-insulated pipeline; the constant temperature liquid circulation device 7 can provide high-temperature heat transfer oil as a heating medium and precisely control its temperature and flow rate, thereby achieving uniform and stable heating of the coal and rock mass specimen.

[0034] The fracture detection module, which is feasible, includes a sensor array 2 distributed on the chamber and the coal and rock mass specimen. The sensor array 2 includes: a resistivity probe array 201 arranged in the pressurization unit and embedded in the specimen for high-density resistivity measurement and resistivity tomography; an acoustic emission sensor 12 arranged on the surface of the specimen; and an acoustic wave emitting and receiving transducer 202 installed in the pressurization unit and embedded in the specimen; a resistance strain gauge arranged in key areas on the surface of the specimen; a distributed optical fiber sensing network arranged inside and on the surface of the specimen; and a magnetic sensor arranged on the inner wall of the chamber.

[0035] Furthermore, such as Figure 3 As shown, the fracture detection module also includes one or more sets of vertical integrated logging probes pre-embedded inside the coal and rock mass specimen; the integrated logging probe integrates one or more sets of annular electrodes for resistivity measurement and acoustic transducers for acoustic measurement arranged along its axial direction; the probe works in conjunction with the sensor array 2 arranged on the force transmission plate 6 to form a resistivity-acoustic joint three-dimensional detection network.

[0036] Furthermore, the vertical integrated logging probe includes a central tube 8 made of insulating material, and the acoustic transducer is sealed and installed inside the central tube 8; the annular electrode is fixedly arranged on the outside of the central tube 8; the probe is integrated with the coal and rock mass specimen through a layer of conductive coupling medium solidified with the coal and rock mass, and the annular electrode establishes an electrical connection with the coal and rock mass through the conductive coupling medium.

[0037] Furthermore, the resistivity probe array 201 of the fracture detection module is arranged in a two-dimensional grid on the force transmission plate 6 on each face, and together with the vertical probes pre-embedded in the coal and rock mass specimen, it forms a three-dimensional detection network; the intelligent feedback and data fusion module is configured to control the three-dimensional network to collect data, and to obtain a three-dimensional distribution image of the resistivity inside the coal and rock mass based on the resistivity tomography algorithm.

[0038] Implementable, the fracture intervention module includes a fluid injection system in communication with the cabin, the system being configured to: inject into the fractures formed by the fracture evolution module natural media simulants for simulating real environments, including residual coal tar 9, flue gas condensate 10, broken coal and rock fragments, gas or liquid water; and / or inject into the fractures reinforcing media foam gel materials for altering geophysical response characteristics.

[0039] Furthermore, the reinforcing medium foam gel material, by the total mass percentage of the base liquid, comprises the following components: 0.5%~10% conductive material; 5%~30% magnetic particles; 0.1%~5% foaming agent; 0.05%~2% foam stabilizer; the balance being water and water-soluble polymer dispersant; the electrical conductivity of the material after foaming and curing is not less than 1 S / m, and / or the saturation magnetization is not less than 10 emu / g.

[0040] Furthermore, the fluid injection system of the fracture intervention module includes at least one high-precision servo-driven injection pump 11, which can perform constant pressure injection, constant flow injection and pulse injection modes.

[0041] In practice, the intelligent feedback and data fusion module is communicatively connected to the fracture evolution module, fracture detection module, and fracture intervention module, and is used to control the operating parameters of each module, synchronously collect detection data, and perform data fusion processing, intelligent inversion, and four-dimensional visualization.

[0042] Furthermore, the intelligent feedback and data fusion module is configured to: dynamically adjust the stress field, temperature field, atmospheric environment parameters of the fracture evolution module and the injection parameters of the fracture intervention module based on the physical field data fed back in real time by the fracture detection module, through machine learning algorithms, so as to realize adaptive intelligent feedback control of the experimental process.

[0043] Furthermore, the intelligent feedback and data fusion module includes a four-dimensional visualization unit, which is used to map the fused multi-physics field data onto the three-dimensional geometric model of the coal and rock mass specimen, dynamically displaying the spatiotemporal evolution process of fracture initiation, expansion, connection and fluid migration, forming a digital twin.

[0044] like Figure 2 As shown, based on the same general inventive concept, the present invention also provides a method for simulating and actively enhancing the detection of fracture evolution in coal-fired zones, comprising the following steps: (1) Specimen preparation and system initialization: The 2.0×1.0×1.0m cuboid coal and rock mass specimen is placed in the sealed rigid chamber 1, and various sensors of the fracture detection module are installed; (2) Thermal-mechanical-gas coupled fracture evolution: Through the fracture evolution module, four-sided stress and bottom heating are applied sequentially or coupledly, and the adsorption-desorption cycle of CH4 and CO2 gases is controlled by programmed control. By utilizing the gas-induced damage effect, the thermal-mechanical-gas coupled conditions of the underground coal fire zone are simulated to induce the formation of fracture network in the coal and rock mass. (3) Multi-physics field in-situ synchronous detection: During the entire process of fracture evolution, resistivity, acoustic emission, ultrasonic waves, temperature, strain, magnetic signals and other first physical field data are collected in real time and synchronously through the step fracture detection module; (4) Simulation of natural fracture environment and assessment of weakening effect: Through the fracture intervention module, natural medium simulation material is injected into the fracture network formed in step (2) to simulate the complex fracture filling environment of the real coal fire zone, and the weakening effect of geophysical signal is assessed based on the comparison between the first physical field data described in step (3) and the second physical field data detected after injection. (5) Active enhancement detection: Reinforcing medium foam gel material is injected into the fracture network through the fracture intervention module; (6) Enhanced signal acquisition and comparative inversion: The third physical field data is obtained by detection again. By comparing the first, second and third physical field data, the geometric characteristics and spatial distribution of the fracture and the detection enhancement effect of the enhancement medium are quantitatively evaluated. (7) Four-dimensional dynamic visualization: Through the intelligent feedback and data fusion module, the four-dimensional dynamic model of the entire process of fracture evolution and detection is displayed or reproduced in real time.

[0045] Example 2 This embodiment provides an active enhancement detection test system for fractures in coal fire zones, comprising the following four core modules: fracture evolution module, fracture detection module, fracture intervention module, and intelligent feedback and data fusion module; The fracture evolution module is used to reconstruct and precisely control a real underground coal-fire environment in the laboratory, actively inducing fractures in the coal and rock mass. Its core is a sealed, rigid chamber 1 for accommodating a rectangular coal and rock mass specimen measuring 2.0 × 1.0 × 1.0 m, which is bolted to a rigid load-bearing frame. This module integrates three independent physicochemical mechanisms: The force application unit consists of independent servo pressurization units in five orthogonal directions excluding the bottom surface of the chamber. The pressurization unit corresponding to the long side of the specimen includes two independently controlled electro-hydraulic servo actuators 5 and a force-transmitting pressure plate 6. The pressurization unit corresponding to the short side also includes one independently controlled electro-hydraulic servo actuator 5 and a force-transmitting pressure plate 6. The actuators have a rated output force ≥ 500 kN, a stroke ≥ 200 mm, and a control accuracy of ±0.5%FS. The pressure plate dimensions match the corresponding surface of the chamber, and the thickness is randomly changed. The output ends of the actuators are connected to the force-transmitting pressure plate 6 via ball joints to ensure uniform pressure transmission. The force-transmitting pressure plate 6 can be of two types: one is a flexible pressure plate made of flexible composite material to adapt to the non-uniformity of the coal and rock mass specimen surface; the other is a pressure head matrix composed of multiple pressure heads that can independently fine-tune the pressure, enabling precise application of non-uniform stress fields. The side of the force-transmitting pressure plate 6 that contacts the coal and rock mass specimen is integrated with a thin-film pressure sensor array 2 for real-time monitoring of the contact stress distribution, and forms a closed-loop feedback control for the servo pressurization unit to ensure that the deviation between the applied stress and the set value is <3%.

[0046] The thermal action section includes a main heating device and an auxiliary heating system. The main heating device is located at the bottom of the chamber and uses armored electric heating tubes to achieve stepped heating, simulating the combustion path of coal fire from bottom to top. The auxiliary heating system includes a closed fluid channel network integrated inside the force transmission plate 6 and a constant temperature liquid circulation device 7 set on a rigid load-bearing frame. The constant temperature liquid circulation device 7 is connected to the fluid channel network through high-temperature resistant heat-insulated pipes and can provide high-temperature heat transfer oil as the heating medium. Its flow rate is precisely controlled by a variable frequency pump, thereby achieving uniform and stable heating of the coal and rock mass specimen.

[0047] The gas injection and control system, connected via a flange interface, is used to programmatically inject gases such as CH4 and CO2 into the chamber and control their pressure and adsorption-emission cycles. The gas injection and control system includes a mass flow controller, a displacement pump 3, and a vacuum pump 4, enabling vacuuming of the chamber environment, gas injection, and pressure and flow monitoring throughout the entire adsorption / emission process. By programmatically controlling the injected gas pressure (adjustable from 0-10 MPa) and the number of adsorption-emission cycles (adjustable from 0-10 times, single cycle time controllable from 1-72 hours), the system utilizes the matrix expansion and contraction effects generated by the repeated adsorption and emission of gases such as CH4 and CO2 in the pores and fractures of the coal and rock mass to achieve gas-induced damage to the coal and rock mass, simulating the long-term effects of gases on coal and rock in a real coal fire zone.

[0048] In addition, the rigid load-bearing frame and the sealed rigid chamber 1 can preferably be installed as a whole in the underground bedrock trench (bedrock trench depth ≥ 2m, the perimeter is reinforced with C30 concrete, and coupled with the bedrock through the vibration isolation foundation (the vibration isolation foundation adopts a spring-damped vibration isolation system, natural frequency ≤ 5Hz, damping ratio 0.05-0.1), effectively isolating external vibration interference (vibration attenuation rate ≥ 90%), and further improving the stability and anti-interference ability of the system.

[0049] The fracture detection module is used for in-situ, real-time, and three-dimensional transparent observation of the entire fracture evolution process. The sampling frequency can be set from 0.1 to 1000 Hz depending on the detection type. Its core is a distributed, multi-physics sensor array 2, specifically including: A resistivity probe array, arranged in a two-dimensional grid (grid spacing 20-50mm) on the force-transmitting plates 6 on each face, together with vertical probes (made of brass, diameter 2-5mm, length 100-200mm, pre-embedded spacing 50-100mm) embedded in the coal and rock mass specimen, forms a three-dimensional detection network. The resistivity probe array 201 is connected to a high-precision resistivity meter or a resistivity tomography acquisition module for high-density resistivity measurement and three-dimensional resistivity tomography. It can capture changes in resistivity inside the coal and rock mass in real time, thereby inverting the generation and propagation of fractures.

[0050] The acoustic detection array includes acoustic emission sensors 12 and acoustic transducers. Acoustic emission sensors 12 (resonant frequency 100-300kHz, sensitivity ≥80dB, preamplification 40dB) are bonded to the surface of the specimen using a high-temperature coupling agent to monitor micro-fracture events generated during the initiation and propagation of fractures in coal and rock masses. The acoustic transducers are divided into two parts: one part is installed on the force transmission plates 6 of the pressurization unit, with 4-8 transducers on each plate; the other part is pre-embedded in a fixing device within the specimen. The fixing device is made of high-temperature resistant ceramic with a temperature resistance ≥500℃, thus forming a multi-channel acoustic emission and reception network for actively transmitting and receiving acoustic signals. By analyzing changes in acoustic wave velocity, amplitude, and attenuation coefficient, the degree of fracture development is assessed through the constructed acoustic-acoustic emission joint detection technology.

[0051] Resistance strain gauges are placed in key areas on the surface of the specimen; a distributed optical fiber sensing network, using high-temperature resistant quartz optical fiber, is deployed by pre-embedding or surface bonding and connected to a distributed optical fiber strain gauge and a distributed optical fiber thermometer, for continuous and high-precision measurement of the fine spatiotemporal distribution of temperature and strain field inside the specimen, and to capture local strain concentration and temperature anomalies caused by crack propagation.

[0052] The magnetic sensor, employing a high-sensitivity Hall effect magnetic sensor, is fixedly arranged on the inner wall of the chamber via a bracket, with 4-8 sensors on each side of the chamber (50-100mm away from the surface of the specimen). It is used to monitor magnetic anomalies caused by high temperature and the injection of magnetic enhancement medium, and combined with resistivity signals to achieve dual verification of the distribution of the enhancement medium in the crack.

[0053] Vertical integrated logging probe: The fracture detection module also includes one or more sets of vertical integrated logging probes pre-embedded inside the coal and rock mass specimen; the integrated logging probe integrates one or more sets of annular electrodes for resistivity measurement and acoustic transducers for acoustic wave measurement arranged along its axial direction; the probe works in conjunction with the sensor array 2 arranged on the force transmission plate 6 to form a resistivity-acoustic wave joint three-dimensional detection network. The vertical integrated logging probe includes a central tube 8 made of insulating material, and the acoustic transducer is sealed and installed inside the central tube 8; the annular electrodes are fixedly arranged on the outside of the central tube 8; the probe is integrated with the coal and rock mass specimen through a conductive coupling medium solidified with the coal and rock mass, and the annular electrodes are electrically connected to the coal and rock mass through the conductive coupling medium.

[0054] The fracture intervention module is used to modify the physical properties of fractures to optimize detection or simulate real-world environments. It includes a high-precision fluid injection system comprising at least one high-precision servo-driven injection pump 11, capable of performing three modes: constant pressure injection (pressure range 0-15 MPa, control accuracy ±0.1 MPa), constant flow injection (flow rate range 0.1-100 mL / min, control accuracy ±0.01 mL / min), and pulse injection (pulse frequency 0-10 Hz, pulse pressure difference 0-10 MPa). The system is configured to perform two functional modes: The environmental simulation mode involves injecting natural media simulating the real environment into the generated fractures. These media include: residual coal tar (simulated as a mixture of residual tar and gas condensate tar (mass ratio 1:1-5:1), the viscosity of which can be adjusted by temperature; flue gas condensate (simulated as a mixture of 5%-15% carbon black, 1%-5% sodium sulfide, and water, with a solid content of 10%-30%); crushed coal and rock fragments (coal particles of the same material as the test specimen with a particle size of 0.1-5mm, injected by dry mixing or mixing with water, with a volume fraction of 10%-50%); and gas or liquid water (air or N2 for gas, and deionized water or rainwater for liquid water). By injecting these natural media, the complex fracture filling environment of a real coal fire zone is simulated, and the weakening effects of different filling material types, contents, and distributions on geophysical signals, such as resistivity signal attenuation rate and acoustic signal attenuation coefficient, are quantitatively studied.

[0055] The active enhancement mode involves injecting a reinforcing medium foam gel material into the fracture to alter its geophysical response characteristics. This material, by weight percentage of the base liquid, comprises the following components: conductive material (0.5%-10%), selected from one or more of graphene, carbon black, or carbon fiber, ensuring excellent conductivity after curing; magnetic particles (5%-30%), selected from one of iron(II,III) oxide, neodymium iron boron, or carbonyl iron, imparting strong magnetic response characteristics; foaming agent (0.1%-5%), using sodium dodecyl sulfate or sodium fatty alcohol polyoxyethylene ether sulfate, foamed by mechanical stirring; foam stabilizer, using guar gum or xanthan gum, to extend the foam's half-life and prevent bubble bursting that could reduce material density; the balance being water and a water-soluble polymer dispersant, which prevents the conductive material and magnetic particles from agglomerating, ensuring uniform material performance. After foaming and curing for 2-8 hours, the reinforced medium foam gel material has an electrical conductivity of not less than 1 S / m and / or a saturation magnetization of not less than 10 emu / g, which can significantly amplify the resistivity and magnetic signal response of the crack target and solve the problem of low signal-to-noise ratio in the detection of small cracks.

[0056] In addition, the fracture intervention module also includes a media recovery and monitoring subsystem: unfilled media is recovered through the discharge port equipped with a shut-off valve and filter at the bottom of the chamber to avoid waste and pollution; at the same time, pressure sensors and flow sensors are installed in the injection pipeline to monitor pressure fluctuations and flow changes in real time during the injection process, and to determine the transport status of the media in the fracture, such as whether blockage has occurred or whether the fracture is filled.

[0057] The intelligent feedback and data fusion module serves as the central nervous system of the system. It connects to other modules via an industrial bus and possesses the following core functions: Multi-module collaborative control, with 10-20 preset parameters for typical coal fire zone conditions, which can be directly called or customized; control commands are sent to each module through the PLC controller to synchronously control the stress loading rate, heating temperature, and gas injection pressure of the fracture evolution module, the sampling frequency of the fracture detection module, and the injection mode and injection volume of the fracture intervention module. The control command response time is <100ms, ensuring the timing synchronization of each module.

[0058] Adaptive intelligent feedback: Based on real-time feedback of multi-physics field data from the fracture detection module, such as resistivity, number of acoustic emission events, acoustic wave velocity, and magnetic signal intensity, the system dynamically adjusts operating parameters through built-in machine learning algorithms (such as random forest and neural networks, with a model training sample size of ≥1000 groups). If the fracture detection module detects a fracture propagation rate lower than 0.1 mm / h, it automatically increases the heating temperature or gas injection pressure of the fracture evolution module to accelerate fracture evolution. If the magnetic signal intensity increases less than 3 times after the fracture intervention module injects the reinforcing medium, it automatically increases the proportion of magnetic particles in the base liquid (increase by 1%-5%) or increases the injection pressure (increase by 0.5-1 MPa) to ensure the enhancement effect. The feedback adjustment cycle can be set to 1-10 minutes to achieve adaptive optimization of the experimental process, reduce manual intervention, and obtain the best experimental operating conditions.

[0059] Data fusion and intelligent inversion: First, the multi-source data collected by the fracture detection module is preprocessed, the resistivity data is denoised, and the acoustic emission data is used for event localization and parameter extraction; the acoustic wave data is corrected for wave velocity; then, the preprocessed resistivity, acoustic emission, acoustic wave, and magnetic signal data are fused using data fusion algorithms (such as DS evidence theory and Kalman filtering) to construct a multi-physics coupled dataset; then, based on resistivity tomography and acoustic tomography algorithms, the three-dimensional spatial distribution, geometric morphology, and connectivity of fractures inside the coal and rock mass are inverted.

[0060] Four-dimensional visualization and digital twins integrate four-dimensional visualization units to correlate fused multiphysics data with a three-dimensional geometric model of the coal and rock mass specimen (built at a 1:1 scale). This dynamically displays the spatiotemporal evolution of fracture initiation (development from micropores to microcracks, pore size 1-100μm), expansion (crack length expanding from <10mm to >100mm), connection (formation of a connected network with ≥3 connected paths), and fluid transport (medium transport velocity in fractures 0.1-10mm / min, filling range displayed in real time). The time step can be set from 1 to 60 seconds. Simultaneously, a digital twin of the experimental process is constructed to achieve real-time synchronization between the physical experiment and the digital model. The digital twin allows viewing the physical field distribution (such as temperature field, stress field, and medium concentration field) at any cross-section inside the specimen. It also allows for simulation of different working conditions by modifying digital model parameters (such as increasing the number of fractures or adjusting medium viscosity), predicting physical test results, and guiding the optimization of experimental schemes.

[0061] A method for active enhancement detection of fractures in coal fire zones, based on the aforementioned active enhancement detection test system for coal fire zones, includes the following steps: (1) Specimen preparation and system initialization: Prepare cubic meter-sized coal and rock mass specimens and place them in the chamber, and simultaneously deploy integrated internal and external sensor arrays 2.

[0062] (2) Thermal-mechanical-gas coupled fracture evolution: Through the fracture evolution module, non-uniform stress on four sides, bottom gradient heating and programmed gas adsorption-desorption cycle are coupled to simulate the complex environment of underground coal fire zone and actively induce fracture network.

[0063] (3) Multi-physics field in-situ synchronous detection: Throughout the entire evolution process, the crack detection module collects real-time and synchronous physical field data of the entire site, including electrical, acoustic, thermal, magnetic, and strain data.

[0064] (4) Simulation and weakening assessment of natural fracture environment: Natural medium simulation is injected into the fracture through the fracture intervention module to assess the weakening effect of complex filling environment on geophysical signal and establish background-interference response model.

[0065] (5) Active enhancement detection: Injecting reinforcing medium foam gel material into the crack through the crack intervention module.

[0066] (6) Enhance signal comparison and intelligent inversion: The crack detection module is used again for detection. The intelligent feedback and data fusion module is used to compare and analyze the data before and after enhancement. The geometric features and spatial distribution of the crack are accurately delineated through the intelligent inversion algorithm.

[0067] (7) Four-dimensional dynamic visualization and verification: The dynamic model of the entire process from crack evolution to precise detection is displayed or reproduced in real time through intelligent feedback and data fusion module, forming a digital twin synchronized with the physical experiment for result verification and mechanism analysis.

[0068] Compared with the prior art, this embodiment achieves the following: (1) From blind to transparent observation: Existing technologies for observing fractures in coal and rock masses are mostly surface monitoring or discrete point measurements, such as single-point acoustic emission and local resistivity testing, which cannot cover the entire life cycle of fractures. This embodiment, through the built-in, multi-dimensional in-situ sensing network, especially the synergy of the pre-embedded resistivity-acoustic wave joint probe and distributed optical fiber, has for the first time achieved in-situ, real-time, three-dimensional, and dynamic CT-like observation of the entire life cycle of fracture initiation (micropore expansion) - expansion - connection (formation of connected network) - filling (medium migration) in a large rock mass experiment. This provides continuous and refined data support for the study of the evolution mechanism of fracture channels in coal and fire areas, which cannot be achieved by existing technologies.

[0069] (2) A new paradigm of active enhancement detection has been established: Traditional geophysical detection relies on the differences in the physical properties of coal and rock masses, such as natural resistivity and acoustic impedance. In complex coal-fired areas with fissures filled with coal tar 9 and flue gas condensates 10, the signal is severely weakened, and the signal-to-noise ratio is generally lower than 5:1, making it difficult to identify hidden fissures. This embodiment injects a specially made reinforcing medium foam gel material into the fissures, transforming the passive reception of weak signals into the active creation of strong anomalies. This increases the resistivity signal change amplitude by 5-100 times and the magnetic signal intensity by 5-50 times, fundamentally solving the core bottleneck of low detection accuracy of hidden targets in complex backgrounds.

[0070] (3) An integrated scientific research platform with multi-field coupling and multi-module collaboration has been constructed: Existing coal fire simulation devices can only realize a single physical field, and the detection and intervention modules are independent of each other, requiring multiple devices to be used together, resulting in poor experimental consistency. This embodiment integrates four-sided gradient stress loading, bottom-circumferential coordinated heating, gas programmed damage, multi-physical field synchronous detection, intelligent fluid injection and closed-loop control into one unprecedented system. The entire chain of environmental simulation-crack evolution-detection verification-intervention optimization can be completed in one system, avoiding the accumulation of errors from multiple devices. The experimental efficiency is greatly improved compared with the existing technology, and it can reproduce typical coal fire conditions in different mines. The platform's versatility is significantly better than that of existing single-function devices.

[0071] (4) Intelligent upgrade of adaptive control and four-dimensional visualization has been achieved: Existing test devices require frequent manual adjustment of parameters, and the data is mostly presented in tabular form, making it difficult to intuitively associate with the crack evolution process. This embodiment uses machine learning algorithms of intelligent feedback and data fusion modules to dynamically adjust operating parameters based on real-time detection data; at the same time, it transforms massive amounts of data into dynamic visualization models of crack initiation and propagation and medium transport through four-dimensional digital twins, allowing for intuitive viewing of the temperature field and stress field distribution of any cross section, thus building a data-application transformation bridge from laboratory mechanism research to on-site engineering decisions (such as optimization of sealing material usage).

[0072] (5) It has broad application value for cross-domain expansion and high-efficiency transformation: This system and method not only directly solves the problem of crack detection and precise sealing in coal fire areas, but also has significant ecological benefits; in addition, multi-field coupling simulation, active enhanced detection and digital twin can be directly extended to oil and gas shale gas hydraulic fracturing monitoring, geothermal development reservoir evaluation, CO2 geological storage, radioactive waste disposal and other fields, which have extremely high promotion value and potential cross-industry social benefits.

[0073] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A test system for active enhancement detection of fractures in coal fire zones, characterized in that, include: The fracture evolution module is used to simulate the thermo-mechanical-gas coupling conditions in underground coal-fired zones and induce fractures in coal and rock mass specimens. The fracture detection module is used to acquire multi-physics field data of coal and rock mass specimens in real time and synchronously. The fracture intervention module is used to inject natural medium simulants and reinforcing medium foam gel materials into fractures to simulate the real environment and enhance the detection signal; The intelligent feedback and data fusion module is used to control the operating parameters of each module, synchronously acquire detection data, and perform fusion processing, intelligent inversion and four-dimensional visualization of the detection data to realize the geometric feature monitoring of the entire process of fracture evolution.

2. The system according to claim 1, characterized in that, The fracture evolution module includes: A sealed, rigid chamber for accommodating rectangular coal and rock specimens; The servo pressurization unit, installed on the load-bearing frame of the sealed rigid chamber, is used to apply independently controlled four-sided stress to the specimen, forming the force application part; A heating device is located at the bottom of a sealed rigid chamber and is used to provide a heat source from the bottom of the specimen, forming a thermal action section. The gas injection and control system, connected to the sealed rigid chamber, is used to inject gas into the chamber and control the gas circulation, adsorption, and release process, constituting the gas action part.

3. The system according to claim 1, characterized in that, The fracture detection module includes a sensor array deployed on a sealed rigid chamber and a coal and rock mass specimen. The sensor array includes: Resistivity probe array for high-density resistivity measurement and resistivity tomography; Acoustic emission sensors are used to monitor acoustic emission signals during the initiation and propagation of cracks. Acoustic wave transmitting and receiving transducers are used to transmit and receive acoustic wave signals. Resistance strain gauges are used to measure strain. Distributed fiber optic sensing networks are used to measure temperature and strain. A magnetic sensor is used to monitor magnetic signals.

4. The system according to claim 1, characterized in that, The fracture generation module includes a gas injection and control system, which includes: Vacuum pumps, displacement pumps, and mass flow controllers are used for vacuuming the chamber environment, circulating gas in and out of coal and rock, and monitoring pressure and flow throughout the process, enabling gas-induced damage to coal and rock specimens under expansion and contraction.

5. The active enhancement detection test system for fractures in coal fire zones according to claim 2, characterized in that, In the fracture evolution module, each servo pressurization unit corresponding to the long side of the specimen includes two independently controlled electro-hydraulic servo actuators and a force transmission pressure plate; each servo pressurization unit corresponding to the short side of the specimen includes an independently controlled electro-hydraulic servo actuator and a force transmission pressure plate. The force transmission plates are all connected to the output end of the actuator; The side of the force-transmitting pressure plate that contacts the coal and rock mass specimen is integrated with a thin-film pressure sensor array, which is used to monitor the contact stress distribution in real time and form a closed-loop feedback control for the servo pressurization unit.

6. The system according to claim 5, characterized in that, The fracture evolution module also includes an auxiliary heating system, which comprises: A closed fluid channel network is integrated inside the force transmission pressure plate; A constant-temperature liquid circulation device is installed on the supporting frame of a sealed rigid chamber and is connected to the sealed fluid channel network through heat-insulated pipelines. It is used to provide high-temperature heat transfer oil as a heating medium for coal and rock mass specimens and to control the temperature and flow rate of the heating medium to achieve heating of the coal and rock mass specimens.

7. The system according to claim 3, characterized in that, The fracture detection module also includes one or more sets of vertical integrated logging probes pre-embedded inside the coal and rock mass specimen. The probes work together with the resistivity probe array deployed on the force transmission plate to form a resistivity-acoustic joint three-dimensional detection network.

8. The system according to claim 7, characterized in that, The vertical integrated logging probe includes a central tube made of insulating material; An acoustic transducer is installed inside the central tube, and an annular electrode is fixedly arranged outside the central tube. The annular electrode is electrically connected to the coal and rock mass through a conductive coupling medium.

9. The system according to claim 1, characterized in that, The intelligent feedback and data fusion module is used to receive the physical field data fed back in real time by the fracture detection module, and dynamically adjust the stress field, temperature field, atmospheric environment parameters of the fracture evolution module and the injection parameters of the fracture intervention module through machine learning algorithms to achieve adaptive intelligent feedback control of the experimental process.

10. A method for actively enhancing the detection of fractures in coal fire zones, characterized in that, Based on the system according to any one of claims 1-9, the method comprises the following steps: Based on specimen preparation and system initialization, the conditions for the evolution of thermo-mechanical-gas coupled fractures were obtained. Simulate the aforementioned thermo-mechanical-gas coupled fracture evolution conditions to induce a fracture network in the coal and rock mass, and simultaneously collect the first physical field data; A natural medium simulant was injected into the fissure, and second physical field data was obtained after the injection. The first physical field data and the second physical field data were compared to obtain the evaluation result of the physical signal weakening effect. Reinforcing medium foam gel material is injected into the crack, and the third physical field data obtained after injection is obtained. The first physical field data, the second physical field data and the third physical field data are compared to obtain the detection enhancement inversion results of the crack and the reinforcing medium. Based on the assessment results of the physical signal weakening effect and the detection enhancement inversion results of the fracture and the reinforcing medium, four-dimensional dynamic visualization is performed to display or reproduce the entire process of fracture evolution and detection in real time.

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