Device and method for testing stability of waterproof coal (rock) column in high water pressure environment

Abstract

The invention belongs to the technical field of coupling tests, and particularly relates to a device and a method for testing the stability of a waterproof coal pillar in a high-water-pressure environment, and the device comprises a double-cavity opposed pressure-bearing model bin, wherein a top plate-coal pillar-bottom plate combined sample is embedded in the middle of the double-cavity opposed pressure-bearing model bin; the true triaxial loading frame is used for providing axial pressure sigma1 and two-way confining pressure sigma2 and sigma3 for independent loading; the single-side high-water-pressure loading system comprises a servo plunger pump, a pressure stabilizing energy accumulator and a throttling / back pressure valve; the composite self-tightening sealing assembly comprises a metal conical surface clamping sleeve, a double-O-shaped ring, a trapezoidal lip-shaped ring and a replaceable epoxy sealing gasket; the seepage and pore pressure measuring chain comprises an inlet volume flowmeter and an outlet volume flowmeter; the multi-field monitoring system comprises a strain gauge / optical fiber FBG array, a displacement meter LVDT, a three-dimensional stress cake, an acoustic emission sensor and a thermometer; according to the data acquisition and linkage control platform, synchronous acquisition is conducted on all channels larger than or equal to 1 kHz, and linkage control is conducted on water pressure, confining pressure, axial pressure and seepage flow; a safety pressure relief and blowout prevention shield is composed of two-stage overflow, a rupture disk and a transparent shield.

Description

Technical Field

[0001] This invention belongs to, but is not limited to, the field of coal mine safety technology, and particularly relates to a test device and test method for the stability of water-resistant coal (rock) pillars in high water pressure environments. Background Technology

[0002] With the advancement of deep resource extraction to a second depth of 1000-2000m and the large-scale construction of underground projects such as tunnels and gas storage facilities, the study of the mechanical behavior and disaster mechanisms of rock masses under the "three highs" environment of high stress, high seepage pressure, and high geothermal temperature has become a core requirement for ensuring engineering safety. Rock mass failure is often the result of the coupling effect of multiple fields such as stress field, seepage field, and temperature field. Especially under complex conditions such as pressure relief in goaf areas, high-pressure seepage from the water side, and periodic water inrush, it is necessary to accurately simulate real boundary conditions and capture multi-dimensional response characteristics through indoor experimental devices.

[0003] However, existing triaxial / true triaxial rock sample testing devices face significant technical bottlenecks when dealing with complex engineering scenarios: First, their stress-seepage coordination control capability is insufficient. Traditional devices often employ an equal confining pressure water injection design, making it difficult to achieve independent linkage between the application of high water pressure on one side and the confining pressure and axial pressure. This makes it impossible to reproduce the asymmetric stress field distribution of "high water pressure on the water body side and pressure relief on the goaf side," and this asymmetric boundary is a key factor leading to irregular roadway damage and water inrush disasters. Second, there are defects in sealing and seepage control precision. Conventional end-face water injection or membrane water injection methods are prone to side-seepage at the sample-pressure chamber interface, causing a deviation between the nominal water pressure and the actual applied water pressure. This directly affects the reliability of rock mass stability criteria and the accuracy of permeability coefficient inversion, while accurate permeability coefficient parameters are crucial for soil stability. The sealing safety assessment of projects such as rock dams and gas storage facilities is crucial. Thirdly, the ability to simultaneously monitor multiple physical fields is lacking. Existing devices generally lack a comprehensive high-frequency acquisition system encompassing pore pressure, seepage flow, multi-directional strain / displacement, acoustic emission (AE), and fracture visualization. This makes it difficult to capture subtle signal changes during the rock mass failure incubation stage, hindering a deeper understanding of fracture evolution paths and disaster mechanisms. The fusion of multiple field signals, such as acoustic emission and infrared radiation, is an effective means of identifying rock mass shear failure. Fourthly, the ability to simulate dynamic boundaries is lacking, making it impossible to reproduce time-history effects such as rapid unloading on the goaf side, water pressure pulsations caused by cyclic injection and production, and high water level fluctuations. The evolution of rock mass fatigue damage and sealing performance under multi-cycle loading is a core concern for the long-term safe operation of deep engineering projects. These technical deficiencies lead to significant discrepancies between laboratory test results and actual engineering conditions, making it difficult to support the innovative development of rock mass disaster prediction and engineering control technologies under complex conditions.

[0004] Based on the above analysis, the urgent technical problems that need to be solved in the existing technology are:

[0005] 1. Poor independent controllability of stress-seepage: Traditional triaxial / true triaxial rock sampling devices are mostly filled with water under equal confining pressure, which makes it difficult to apply high water pressure to one side of the sample and independently link it with confining pressure and axial pressure. It cannot truly reproduce the asymmetric boundary of "high water pressure on the water body side and pressure relief on the goaf side".

[0006] 2. Leakage and sealing failure: Conventional end-face water injection or membrane water injection is prone to leakage at the connection between the sample and the pressure chamber, resulting in a discrepancy between the nominal water pressure and the actual water pressure on the pressure surface of the sample, affecting the stability criterion and permeability coefficient inversion.

[0007] 3. Insufficient monitoring dimensions: It lacks the ability to simultaneously acquire multiple physical fields at high frequency, such as pore pressure, seepage flow, multi-directional strain / displacement, acoustic emission (AE), fracture visualization, and temperature, making it difficult to identify the incubation stage of failure and the evolution path of the failure surface.

[0008] 4. Difficulty in simulating mining and circulating water pressure: It is difficult to simulate time-history boundaries such as goaf unloading, periodic water inflow / sudden water pulsation, and high water level fluctuations. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a test device and method for testing the stability of water-resistant coal pillars in high water pressure environments.

[0010] This invention is implemented as follows: a stability testing device for water-resistant coal pillars in a high water pressure environment, comprising:

[0011] Double-cavity opposed pressure model chamber (water cavity and goaf cavity): The middle is filled with a combination sample of "roof-coal pillar-floor plate";

[0012] True triaxial loading frame: provides axial pressure σ1, which is independently loaded with biaxial confining pressures σ2 and σ3;

[0013] Single-sided high water pressure loading system: servo plunger pump + pressure accumulator + throttling / back pressure valve, to achieve 0–10 MPa single-sided water pressure P_w closed-loop control and waveform programming;

[0014] Composite self-tightening sealing assembly: metal conical ferrule + double O-ring + trapezoidal lip ring + replaceable epoxy gasket, ensuring "pressure only on the water side, no side leakage";

[0015] Seepage and pore pressure measurement chain: inlet and outlet volumetric flow meters; multi-point pore water pressure gauges (embedded on the water side, core, and near the surface of the goaf side of the coal pillar);

[0016] Multi-field monitoring system: strain gauge / fiber FBG array, displacement meter LVDT, triaxial stress disc, acoustic emission sensor (wideband + positioning array), thermometer; optional viewing window / industrial endoscope interface for crack visualization;

[0017] Data acquisition and linkage control platform: synchronous acquisition of data at ≥1 kHz on each channel; linkage control of water pressure, confining pressure, axial pressure, and seepage flow.

[0018] Safety pressure relief and blowout preventer: dual-stage overflow + rupture disc + transparent protective cover.

[0019] Furthermore, the dual-chamber opposing model chamber has two high-pressure chambers on the left and right. The left chamber is a water chamber (applying P_w), and the right chamber is a goaf chamber (which can maintain low pressure or be evacuated / vented with dry gas). A "sample channel" is opened in the middle to assemble an integral sandwich sample of "bottom rock - coal pillar - roof rock". The sample is radially pre-tightened by trapezoidal sealing rings and metal wedges around it, and the two sides of the coal pillar are directly exposed to the fluid / gas in the two chambers.

[0020] Furthermore, the sealing strategy for the dual-chamber opposed model chamber is as follows:

[0021] 1. Surface sealing: A conical metal sleeve + epoxy transition pad is set at the edge of the water body side in contact with the sample. The higher the pressure, the more self-tightening it becomes.

[0022] 2. Circumferential seal: Double O-rings in series + back pressure groove on the outer side of the lip ring;

[0023] 3. Anti-seepage channel: A circumferential capillary channel and a negative pressure extraction port are installed between the sample and the metal pressure frame. In case of leakage, the leakage will be immediately extracted and a metering alarm will be triggered.

[0024] Furthermore, loading and boundary simulation specifically include:

[0025] True triaxial loading: The upper pressure plate and lower seat provide σ1 (axial); the flexible diaphragm cavities on both sides provide σ2 and σ3 (hydraulic oil / water as confining pressure medium), which can provide equal or unequal confining pressure to simulate burial depth and lateral pressure coefficient.

[0026] Single-sided water pressure: water chamber P_w is an independent closed loop; the goaf can be 0–0.1 MPa (ventilated), or a programmable suction system can be set to form an unloading side.

[0027] Time history boundary: Supports water pressure waveforms such as step, sine, square wave, and pulse, as well as the evolution of goaf depressurization / backfilling; can superimpose time-varying loads of axial pressure / containing pressure to simulate mining disturbances.

[0028] Furthermore, the monitoring and judgment criteria include:

[0029] Mechanical response: stress, strain, displacement—obtaining stress-strain curves, volumetric strain, and lateral deformation.

[0030] Seepage response: inlet / outlet flow rate Q(t), pressure difference Δp(t), and inverted permeability coefficient k(t).

[0031] Pore ​​pressure diffusion: Multi-point pore pressure u(x,t) is used to identify the seepage front.

[0032] Damage and fracture: AE event counting, energy, and location (imaging fracture surface); visual interface for verification.

[0033] Furthermore, the stability criteria include:

[0034] Effective stress: σ′=σ-α·p (α is the Biot coefficient, p is the pore pressure / water pressure). When the effective normal stress on the water side drops to the tensile / shear strength threshold, seepage rupture or shear failure occurs.

[0035] Permissible water pressure difference: When Δp = P_w - P_empty ≥ Δp_cr (derived from Mohr–Coulomb / Hoek–Brown strength and geometric constraints), instability is determined;

[0036] Accompanying indicators: k(t) surge, AE high-energy cluster, displacement jump, u(x,t) anomalous gradient.

[0037] Another objective of this invention is to provide a method for testing the stability of water-resistant coal (rock) pillars in high water pressure environments, comprising:

[0038] S1. Sample preparation: Process the "roof-coal pillar-floor" assembly; the coal pillar can be made from real coal blocks or similar materials; pre-embed borehole pressure gauges and fiber optic sensors on the water side, core, and goaf side.

[0039] S2. Assembly and sealing: Place in the mold chamber and pre-tighten according to the torque-pressure sequence; vacuum check; negative pressure channel test for leak detection.

[0040] S3. Confining pressure and axial pressure loading: Apply target σ1, σ2, σ3 (representing burial depth and lateral pressure); maintain load stability.

[0041] S4. Unilateral pressurization: Increase P_w in a stepped / waveform manner; synchronously collect full data.

[0042] S5. Mining / Unloading Coupling: Adjust the goaf side pressure or reduce the confining pressure in a certain direction according to the design procedure, and superimpose the disturbance cycle.

[0043] S6. Termination and Judgment: Once the preset instability criterion or safety limit is reached, the system will unload / depressurize, and save the data and damage surface record.

[0044] Another object of the present invention is to provide a computer device, the computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the method for testing the stability of a water-impregnated coal pillar in a high water pressure environment.

[0045] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method for testing the stability of a water-impermeable coal pillar in a high water pressure environment.

[0046] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0047] First, this invention constructs a dual-cavity, opposing pressure-bearing model chamber, forming water-side and goaf-side boundaries on both sides of the coal pillar. This achieves an asymmetric stress condition with high water pressure loading on one side and depressurization or ventilation on the other, structurally reproducing the spatial boundary relationship of "water body—water-isolated coal pillar—goaf" in engineering. Compared with the commonly used double-sided isobaric or overall immersion methods in existing experiments, this scheme avoids boundary distortion caused by simultaneous water pressure acting on both sides of the coal pillar. This makes the experimental loading conditions closer to actual working conditions in terms of mechanics and seepage, thereby improving the applicability and reliability of the experimental results for engineering problems.

[0048] Secondly, this invention employs a control method where true triaxial loading and unilateral water pressure loading are independent of each other, allowing axial pressure, biaxial confining pressure, and water pressure on the water body side to be set and loaded according to a time-programmed schedule. Through this fully coupled yet independent loading mechanism, the stress state of the water-resistant coal pillar under different burial depths, different lateral pressure coefficients, and different water pressure evolution paths can be flexibly constructed, realizing arbitrary combinations and superpositions of the stress field and seepage field on a time scale. This feature overcomes the problems of difficulty in decoupling stress loading and seepage loading and the single loading path in existing technologies, providing a foundation for systematically studying the impact of complex factors such as mining disturbances and water pressure fluctuations on the stability of the coal pillar.

[0049] Furthermore, this invention introduces a composite self-tightening sealing structure at the key interface on the water side, combined with a negative pressure seepage drainage mechanism, effectively solving the technical problems of easy seal failure and difficulty in identifying lateral leakage under high water pressure test conditions. As the water pressure increases, the self-reinforcing effect of the sealing structure increases synchronously, ensuring that the nominal applied water pressure during the test can truly act on the coal pillar body, rather than being consumed or transferred through the seepage path. Simultaneously, through the seepage drainage and monitoring mechanism, non-design leakage can be identified and dealt with in real time, avoiding interference with seepage parameter inversion and stability determination, significantly improving the reliability of the test data.

[0050] Furthermore, by arranging multiple types of sensing units, this invention achieves multi-field synchronous high-frequency acquisition of stress, strain, displacement, pore water pressure, seepage flow, and rupture acoustic signals. This makes the entire process of the water-resistant coal pillar, from seepage initiation and crack propagation to overall instability or through-hole failure, identifiable and replayable. Compared to traditional experimental methods that rely solely on macroscopic failure results, this invention can capture key turning points in the stability evolution process, providing direct evidence for instability mechanism analysis and criterion construction.

[0051] In addition, the present invention incorporates multi-stage safety pressure relief and protection devices in the system structure, ensuring that the high water pressure loading process remains under control, meeting the safety requirements for conducting high water pressure tests under laboratory conditions, and avoiding the risk of sudden rupture or ejection.

[0052] This invention effectively solves key technical problems in existing water-tight coal pillar tests, such as the difficulty in accurately loading high water pressure on one side, insufficient sealing reliability, difficulty in independently controlling stress and seepage loading, and difficulty in synchronously monitoring multi-field responses. It can obtain key parameters such as critical water pressure difference, seepage evolution characteristics, stability criteria, and safety envelope for engineering verification, and has important engineering application value for the safety design and risk assessment of water-tight coal pillars in high-water-pressure mining areas. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the stability test device for water-impermeable coal pillars in a high water pressure environment provided in an embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of a dual-cavity opposed pressure-bearing model chamber provided in an embodiment of the present invention;

[0055] Figure 3 This is a flowchart of the stability test method for water-impermeable coal pillars in a high water pressure environment provided in the embodiments of the present invention;

[0056] In the figure: 1. Dual-cavity opposed pressure model chamber; 2. True triaxial loading frame; 3. Single-sided high water pressure loading system; 4. Composite self-tightening sealing assembly; 5. Seepage and pore pressure measurement chain; 6. Multi-field monitoring system; 7. Data acquisition and linkage control platform. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0058] like Figure 1 As shown in the embodiment of the present invention, the stability testing device for water-impermeable coal pillars in a high water pressure environment includes:

[0059] Double-cavity opposed pressure model chamber 1 (water cavity and goaf cavity): The middle is filled with a combination sample of "roof plate - coal pillar - floor plate";

[0060] True triaxial loading frame 2: provides axial pressure σ1, which is independently loaded with biaxial confining pressures σ2 and σ3;

[0061] Single-sided high water pressure loading system 3: servo plunger pump + pressure accumulator + throttling / back pressure valve, to achieve 0–10 MPa single-sided water pressure P_w closed-loop control and waveform programming;

[0062] Composite self-tightening sealing assembly 4: metal conical ferrule + double O-ring + trapezoidal lip ring + replaceable epoxy gasket, ensuring "pressure only on the water side, no side leakage";

[0063] Seepage and pore pressure measurement chain 5: inlet and outlet volumetric flow meters; multi-point pore water pressure gauges (embedded on the water side, core, and near the surface of the goaf side of the coal pillar);

[0064] Multi-field monitoring system 6: strain gauge / fiber optic FBG array, displacement meter LVDT, triaxial stress disc, acoustic emission sensor (wideband + positioning array), thermometer; optional viewing window / industrial endoscope interface for crack visualization;

[0065] Data Acquisition and Linkage Control Platform 7: Synchronous acquisition of data at ≥1 kHz on each channel; linkage control of water pressure, confining pressure, axial pressure, and seepage flow.

[0066] Safety pressure relief and blowout preventer: dual-stage overflow + rupture disc + transparent protective cover.

[0067] like Figure 2 As shown, the dual-cavity opposed model chamber has two high-pressure cavities on the left and right. The left cavity is a water cavity (applied with P_w), and the right cavity is a goaf cavity (which can maintain low pressure or be evacuated / vented with dry gas). A "sample channel" is opened in the middle to assemble an integral sandwich sample of "bottom rock - coal pillar - roof rock". The sample is radially pre-tightened by trapezoidal sealing rings and metal wedges around it. The two sides of the coal pillar are directly exposed to the fluid / gas in the two cavities.

[0068] The sealing strategy for the dual-chamber opposed model chamber is as follows:

[0069] 1. Surface sealing: A conical metal sleeve + epoxy transition pad is set at the edge of the water body side in contact with the sample. The higher the pressure, the more self-tightening it becomes.

[0070] 2. Circumferential seal: Double O-rings in series + back pressure groove on the outer side of the lip ring;

[0071] 3. Anti-seepage channel: A circumferential capillary channel and a negative pressure extraction port are installed between the sample and the metal pressure frame. In case of leakage, the leakage will be immediately extracted and a metering alarm will be triggered.

[0072] Loading and boundary simulation specifically include:

[0073] True triaxial loading: The upper pressure plate and lower seat provide σ1 (axial); the flexible diaphragm cavities on both sides provide σ2 and σ3 (hydraulic oil / water as confining pressure medium), which can provide equal or unequal confining pressure to simulate burial depth and lateral pressure coefficient.

[0074] Single-sided water pressure: water chamber P_w is an independent closed loop; the goaf can be 0–0.1 MPa (ventilated), or a programmable suction system can be set to form an unloading side.

[0075] Time history boundary: Supports water pressure waveforms such as step, sine, square wave, and pulse, as well as the evolution of goaf depressurization / backfilling; can superimpose time-varying loads of axial pressure / containing pressure to simulate mining disturbances.

[0076] Monitoring and criteria include:

[0077] Mechanical response: stress, strain, displacement—obtaining stress-strain curves, volumetric strain, and lateral deformation.

[0078] Seepage response: inlet / outlet flow rate Q(t), pressure difference Δp(t), and inverted permeability coefficient k(t).

[0079] Pore ​​pressure diffusion: Multi-point pore pressure u(x,t) is used to identify the seepage front.

[0080] Damage and fracture: AE event counting, energy, and location (imaging fracture surface); visual interface for verification.

[0081] Stability criteria include:

[0082] Effective stress: σ′=σ-α·p (α is the Biot coefficient, p is the pore pressure / water pressure). When the effective normal stress on the water side drops to the tensile / shear strength threshold, seepage rupture or shear failure occurs.

[0083] Permissible water pressure difference: When Δp = P_w - P_empty ≥ Δp_cr (derived from Mohr–Coulomb / Hoek–Brown strength and geometric constraints), instability is determined;

[0084] Accompanying indicators: k(t) surge, AE high-energy cluster, displacement jump, u(x,t) anomalous gradient.

[0085] like Figure 3 As shown in the embodiment of the present invention, the method for testing the stability of a water-impregnated coal pillar in a high water pressure environment includes:

[0086] S1. Sample preparation: Process the "roof-coal pillar-floor" assembly; the coal pillar can be made from real coal blocks or similar materials; pre-embed borehole pressure gauges and fiber optic sensors on the water side, core, and goaf side.

[0087] S2. Assembly and sealing: Place in the mold chamber and pre-tighten according to the torque-pressure sequence; vacuum check; negative pressure channel test for leak detection.

[0088] S3. Confining pressure and axial pressure loading: Apply target σ1, σ2, σ3 (representing burial depth and lateral pressure); maintain load stability.

[0089] S4. Unilateral pressurization: Increase P_w in a stepped / waveform manner; synchronously collect full data.

[0090] S5. Mining / Unloading Coupling: Adjust the goaf side pressure or reduce the confining pressure in a certain direction according to the design procedure, and superimpose the disturbance cycle.

[0091] S6. Termination and Judgment: Once the preset instability criterion or safety limit is reached, the system will unload / depressurize, and save the data and damage surface record.

[0092] The stability test method for water-retaining coal pillars in high water pressure environments described in this invention is based on the coupled working conditions of "high water pressure - asymmetric boundary - triaxial stress - mining disturbance" of water-retaining coal pillars in real engineering projects. By combining controlled loading with multi-field monitoring, the stability evolution mechanism of water-retaining coal pillars under high water pressure is systematically revealed.

[0093] In the initial stage of the experiment, an integral composite sample consisting of a roof, coal pillar, and floor was fabricated. This rigidly confined the coal pillar vertically, with the sides corresponding to the water-bearing and goaf boundary conditions, thus structurally reproducing the spatial stress pattern of an impermeable coal pillar in an actual mine. Pore water pressure and fiber optic sensing units were pre-embedded inside the sample and at key interfaces, enabling real-time sensing of pore pressure diffusion, strain evolution, and damage accumulation within the coal pillar during subsequent experiments.

[0094] After the sample assembly was completed, graded pre-tightening and sealing tests were conducted to ensure that the model chamber formed ideal boundary conditions of "pressure only on the water side and no lateral leakage" during subsequent loading, thereby avoiding interference from non-target leakage on seepage and stability determination. Subsequently, a true triaxial loading method was used to apply axial pressure and biaxial confining pressure respectively to simulate the in-situ stress state of the coal pillar under actual burial depth conditions, and to redistribute the internal stress of the sample and achieve relative stability during the load holding stage.

[0095] After the triaxial stress field is stabilized, unilateral water pressure is gradually applied to the water body side. This water pressure propagates inward through the coal pillar structure, inducing pore water pressure diffusion and effective stress redistribution, causing the coal pillar to gradually bear asymmetric hydraulic action while maintaining overall confinement. By controlling the stepped or time-varying loading method of the water pressure, the effects of different working conditions such as water inrush, water storage, or water pressure fluctuations on the stability of the water-resistant coal pillar can be simulated.

[0096] During the hydraulic loading process, mining or unloading disturbances are further introduced. By adjusting the goaf-side pressure or reducing a certain confining pressure component, the stress release and redistribution effects caused by mining activities are simulated. When this process is superimposed on the hydraulic pressure, a more complex force-water-damage coupled response is generated inside the coal pillar, thereby inducing changes in permeability, fracture propagation, and local instability.

[0097] By simultaneously monitoring stress, strain, displacement, pore water pressure, seepage flow, and rupture acoustic signals, the key characteristics of the gradual to abrupt transformation of coal pillar stability are comprehensively identified. When monitoring indicators indicate that the coal pillar has entered an unstable state or reached the upper limit of safety control, unloading and depressurization operations are promptly performed, and the failure mode of the sample is recorded, thereby achieving controllable testing and mechanism analysis of the entire process of water-impregnated coal pillar stability in a high water pressure environment.

[0098] Example 1 (Steady step water pressure test at the scale of engineering rock block)

[0099] Samples and dimensions: The roof and floor plates are fine-grained sandstone blocks, each measuring 150 mm × 150 mm × 50 mm; the coal pillar is 150 mm × 150 mm × 300 mm (width × thickness × height), and the three are bonded together as a whole by epoxy leveling. One 0–10 MPa pore pressure gauge is embedded 5 cm on the water side, in the center, and 5 cm on the goaf side of the coal pillar; a triaxial strain gauge and two LVDT diameter gauges are attached along the height direction in the middle of the coal pillar.

[0100] Assembly: Install according to the sealing scheme in section 3.2; negative pressure channel -0.06 MPa, random sampling for 10 minutes, no leakage.

[0101] load:

[0102] Confining pressure: σ2=σ3=2.0 MPa; Axial pressure: σ1=8.0 MPa (simulated burial depth / lateral pressure coefficient).

[0103] Water pressure: P_w stepped loading 0→1→2→3→4 MPa, each step stabilized for 30 min; the cavity was vented at atmospheric pressure 0.02 MPa with dry air.

[0104] Recording metrics: Q_in / Q_out, k(t) inversion; u(x,t) diffusion curve; stress-strain; AE events and energy.

[0105] Criteria and Output: When a step increase in k(t), a series of high-energy AE bursts, and a sudden jump in lateral displacement occur, and u(x,t) forms a steep gradient in the coal pillar thickness direction, it is judged as "permeability channel formation". The critical water pressure difference Δp_cr and the corresponding stress state (σ1,σ2,σ3) are output.

[0106] Example 2 (Similar material scale-down + "circulating water pressure / mining unloading" coupled test)

[0107] Similarity ratio and model: configured according to a 1:100 similarity ratio; coal body material with cement:quartz sand:gypsum:water = 1:4:0.5:0.6 and mixed with fly ash and graphite lubricating powder to adjust brittleness; the strength of the roof / bottom plate similar material is 1.8 times that of the coal body; prepare model blocks (width 600 mm × thickness 120 mm × height 400 mm), with prefabricated bedding and weak noodle strips inside.

[0108] Boundary settings: True triaxial loading to σ1=4.0 MPa, σ2=2.5 MPa, σ3=1.8 MPa; the goaf is set to be linearly unloaded over time (from 0.1 MPa to 0.01 MPa within 10 min) to simulate mining; a sinusoidal circulating water pressure P_w(t)=2.5±1.0 MPa with a period T=120 s is applied to the water cavity for 60 min.

[0109] Monitoring: A 12-channel AE array was deployed for positioning imaging; a transparent observation window (small-area sapphire window + endoscope port) was pre-embedded in the visible seam of the coal pillar; speckle imaging of the DIC surface was sampled at 10 Hz to obtain the evolution of the main strain band on the surface.

[0110] Evaluation indicators:

[0111] Disrupts the initial loop count N_cr and the corresponding peak value of P_w;

[0112] Contact state between the effective stress path and the Mohr envelope;

[0113] The apparent damage variable D (characterized by the decrease in elastic modulus / irreversible part of volumetric strain).

[0114] The jump at the breakthrough moment k(t) corresponds to the positioning of AE with a certain degree of agreement.

[0115] Output: Obtain the relationship curve between the safe water pressure envelope P_w,allow(σ1,σ2,σ3,cyclic parameters) under the condition of "circulating water pressure + unloading coupling" and the minimum safe coal pillar thickness - water pressure difference (for design verification).

[0116] Temperature-pressure coupling module: A constant temperature jacket or electric heating is added to the water cavity to investigate the effect of temperature on permeability and strength, forming a P–T–σ fully coupled database.

[0117] Reinforcement measures verification interface: reserved grouting port and controllable crack trigger, used to verify the inhibition effect of grouting material / ribbed anchoring, etc. on Δp_cr and seepage channel formation.

[0118] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of a method for testing the stability of a water-resistant coal pillar in a high water pressure environment.

[0119] An application embodiment of the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of a method for testing the stability of a water-impregnated coal pillar in a high water pressure environment.

[0120] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0121] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A test device for the stability of a water-impermeable coal pillar in a high water pressure environment, characterized in that, include: Dual-chamber opposed pressure model chamber, true triaxial loading system, single-sided hydraulic loading system, and data acquisition and linkage control system; The dual-cavity opposed pressure model chamber forms a water cavity, a sample channel and a goaf cavity sequentially along the sample axis. The sample channel is equipped with an integral roof rock, coal pillar and floor rock combination sample, so that one side of the coal pillar is directly connected to the water cavity and the other side is directly connected to the goaf cavity. The true triaxial loading system applies axial pressure and independent biaxial confining pressure to the combined specimen to construct a true triaxial stress environment. The single-sided water pressure loading system only loads controllable water pressure into the water cavity, so that the coal pillar bears a single-sided high water pressure boundary under triaxial stress, while the goaf maintains a low pressure or controlled unloading state. Through the above structural synergy, the stability evolution simulation of the water-blocking coal pillar under high water pressure and asymmetric boundary conditions is realized.

2. The stability test device for water-impermeable coal pillars in a high water pressure environment as described in claim 1, characterized in that: The water cavity and the goaf cavity respectively form opposing pressure cavities. The combined sample is assembled in the sample channel under radially confined conditions, so that the two ends of the coal pillar are directly exposed to the water medium and the goaf medium respectively, thereby forming an asymmetric seepage and stress interface.

3. A sealed, anti-seepage structure for stability testing of water-proof coal pillars in high water pressure environments, characterized in that, Located at the interface between the water cavity and the sample channel, and including: A surface sealing unit consisting of a metal conical clamping structure and a transition sealing layer is used to form a self-reinforcing seal when the water pressure increases. A multi-stage elastic sealing unit is set along the circumference of the sample to block radial leakage paths; A circumferential anti-seepage channel and a drainage interface connected to it are installed between the sample and the pressure-bearing structure. In the event of undesigned leakage, the anti-seepage channel will immediately guide and pump out the leaking medium, achieving the test boundary condition that only the water body is pressurized and there is no interference from lateral seepage.

4. The sealing and anti-leakage structure as described in claim 3, characterized in that: The surface sealing unit generates a combined axial and radial clamping effect under water pressure, which makes the sealing capacity increase synchronously with the increase of water pressure; The seepage prevention channel is connected to the monitoring device and is used to measure abnormal leakage and trigger a safety alarm.

5. A multi-field linkage control and judgment system for stability testing of water-impregnated coal pillars in a high water pressure environment, characterized in that, include: Mechanical loading control unit, used to coordinate the adjustment of axial pressure and confining pressure; Water pressure loading control unit, used to independently adjust the water pressure in the water chamber; A multi-physical quantity monitoring unit is used to simultaneously collect stress, strain, displacement, pore water pressure, seepage flow, and rupture acoustic information; The stability determination unit is used to identify the instability state of the water-resistant coal pillar based on the cooperative evolution relationship of the above-mentioned multiple physical quantities. The control and judgment system achieves dynamic capture of the instability process of the water-resistant coal pillar by real-time linkage of loading parameters and monitoring results.

6. The multi-field linkage control and judgment system as described in claim 5, characterized in that: The stability determination is based on at least two types of coordinated anomalies among effective stress evolution, abrupt change in permeability, rupture energy release, and displacement abrupt change as instability triggering conditions.

7. The multi-field linkage control and judgment system as described in claim 5, characterized in that: The control unit is used to perform controlled unloading of the goaf side pressure or a certain confining pressure direction during the loading process, so as to simulate the impact of mining disturbance on the stability of the water-resistant coal pillar.

8. A method for testing the stability of a water-impermeable coal pillar in a high-water-pressure environment using the apparatus described in any one of claims 1 to 7, characterized in that, include: Sample preparation, assembly and sealing, triaxial stress loading, unilateral water pressure loading, synchronous monitoring of multiple parameters, and stability determination steps; By applying unilateral water pressure under triaxial stress conditions and introducing a controlled disturbance process, the mechanical, seepage, and fracture evolution characteristics of water-resistant coal pillars in a high water pressure environment were obtained.

9. The test method as described in claim 8, characterized in that: The unilateral water pressure loading is carried out in a graded or time-varying manner and is coordinated with the change process of axial pressure or confining pressure to construct the evolution path under real engineering conditions.

10. The test method as described in claim 8, characterized in that: When the monitoring results meet the preset instability conditions or reach the safety threshold, synchronous unloading and depressurization operations are performed, and the sample failure mode and data results are recorded.

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