Goaf gangue compression consolidation-regenerated rock mass mining unloading test device and method

Abstract

The invention discloses a goaf gangue compression consolidation-regenerated rock mass mining unloading test device and method. According to the system, an external bearing frame comprises a supporting bottom plate, supporting columns and a supporting top plate; the vertical loading oil cylinder is mounted on the supporting top plate, and an upper loading plate is fixedly mounted at the telescopic end of the vertical loading oil cylinder; the internal confining pressure loading frame is installed on the supporting bottom plate, and four lateral baffles of the internal confining pressure loading frame are provided with four transverse loading oil cylinders. The oil pressure pumping mechanism is connected with a plurality of loading oil cylinders; a transmitting probe of the acoustic emission monitoring system is mounted in a probe mounting groove of the side loading plate; the pressure sensor I and the displacement sensor I are connected with the vertical loading oil cylinder; the pressure sensor II is connected with the transverse loading oil cylinder; the method comprises the following steps: manually filling the filler; lateral confinement compression; initial stress loading; performing dynamic unloading simulation; carrying out damage simulation; and analyzing an evolution law. According to the device and the method, the compression consolidation-mining unloading test under the real loading process of the gangue can be carried out, and key data support can be provided for the influence of particle size grading on the compression characteristic of the gangue and the stability of the regenerated roof.

Description

Technical Field

[0001] This invention belongs to the field of mechanical testing equipment technology, specifically a test device and method for unloading mining-induced rock mass compression consolidation-regenerated rock mass in goaf areas. Background Technology

[0002] Steeply inclined coal seams are characterized by large variations in thickness, soft coal quality, high gas content, and high pressure, water-rich, loose strata. They are often mined using strike-longwall layered mining. Unlike full-height mining, steeply inclined thick coal seams experience more frequent disasters such as roof collapse, coal wall spalling, support slippage, and debris injuring workers during strike-longwall layered mining. This is because the roof is subjected to tangential loads along the direction parallel to the strata under the influence of the coal seam's dip angle (generating tensile stress perpendicular to the strata). This leads to a sharp increase in the degree of fracture development in the rock mass outside the goaf, and the roof structure within the goaf, cemented by the load, exhibits significant regional characteristics and fracture development. Therefore, achieving stability control of the regenerated roof in strike-longwall layered mining of steeply inclined thick coal seams is crucial for ensuring the safe and efficient mining of these seams.

[0003] During the longwall layered mining of thick coal seams at steep dips, the gangue falling from the upper roof, under the influence of its own weight, continuously collides with the surrounding coal and rock mass and supports during its collapse-rolling / sliding-accumulation process. The degree of gangue crushing and filling density gradually increases from top to bottom along the goaf, forming a non-uniform filling zone with gangue particle size "larger at the top and smaller at the bottom" along the goaf. Under the load of the overlying strata, the gangue is compressed and cemented to form a recycled roof. Affected by the gangue particle size distribution in different areas of the goaf, the strength and deformation characteristics of the recycled roof are significantly asymmetrical. The unloading of the recycled roof in the lower-layer mining process is affected by the dip angle of the coal seam. Compared with the unloading strength characteristics, deformation parameters, failure modes and strength criteria of intact rock mass under different stress paths and loading confining pressure conditions, the unloading mechanical parameters of the recycled roof are closely related to the gangue particle size distribution. That is, the recycled roof in the lower-layer mining process changes from a true triaxial six-sided stress state to a five-sided stress state with single-sided unloading. This process is a continuous process of gangue compression and consolidation under the influence of particle size distribution - unloading of the recycled roof during mining. Therefore, to clarify the mining dynamics of the regenerated roof, it is necessary to conduct targeted true triaxial mechanical tests on gangue compression and mining unloading of the regenerated roof under different particle size distributions. This is based on understanding the collapse structure of the rock mass outside the upper-layer goaf and the gangue particle size distribution in different regions of the goaf space, as well as the stress environment and loading history of the gangue in the goaf. By analyzing the dynamic evolution of stress and strain during the test, an equivalent mechanical constitutive model of mechanical parameters and gangue particle size distribution can be established to effectively reveal the damage and failure mechanism of the regenerated roof.

[0004] The mining dynamics of the recycled roof in stratified mining is the result of a combination of internal and external factors. Internal factors include the multi-faceted influence on the formation process of the recycled roof under load and cementation (structural characteristics of the recycled roof). External factors include the secondary activation of the recycled roof structure through repeated mining (mining-induced unloading characteristics of the recycled roof). Characterizing the relationship between mechanical parameters and particle size distribution during the gangue compression-mining-induced unloading process, and quantitatively characterizing the damage evolution during gangue compression-unloading, are crucial for understanding the failure and instability of the recycled roof. However, existing true triaxial testing machines have limited functionality and cannot realistically simulate the continuous damage evolution process of gangue compression and consolidation followed by mining-induced unloading of the recycled roof. Consequently, they cannot accurately reveal how gangue particle size distribution affects its compression characteristics and further correlate with the stability of the recycled roof. To ensure the safe and stable operation of coal mining, there is an urgent need for a test device and method for the mining unloading of gangue compression consolidation-regenerated rock mass in goaf, so as to effectively simulate the continuous evolution process of gangue compression consolidation-regenerated roof mining unloading. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a test device and method for compression consolidation-regenerated rock mass unloading in goaf areas. The device is simple in structure, low in manufacturing cost, and convenient to operate. It can conduct compression consolidation-regenerated unloading tests under the actual loading process of gangue, providing crucial data support for the impact of particle size distribution on the compression characteristics of gangue and the stability of the regenerated roof. The method is simple to implement and low in cost, enabling accurate reproduction of the entire process of gangue compression consolidation-regenerated roof unloading during mining. This provides reliable technical support for stability analysis and support design in deep rock mass engineering.

[0006] To achieve the above objectives, the present invention provides a test device for unloading mining-regenerated rock mass compression consolidation in goaf areas, comprising an external bearing frame, a vertical loading cylinder, an internal confining pressure loading frame, a horizontal loading cylinder, a hydraulic pumping mechanism, an acoustic emission monitoring system, a loading monitoring system, and a control unit. The external load-bearing frame includes a support base plate, support columns, and a support top plate. The support top plate is fixedly connected above the support base plate by multiple support columns, forming a load-bearing space between the support base plate, support columns, and support top plate. The vertical loading cylinder is fixedly installed in the upper mounting hole at the center of the supporting top plate, and an upper loading plate is fixedly installed at its telescopic end; The internal confining pressure loading frame is located at the bottom of the load-bearing space and is fixedly installed on the upper end of the support base plate. The internal confining pressure loading frame is formed by four detachable side baffles, and has a pressure relief chamber in the center for accommodating the sample. Four side mounting holes are opened in the center of the four side baffles. Four transverse loading cylinders are respectively installed in four side mounting holes, and side loading plates are fixedly installed on their telescopic ends; a probe mounting groove is opened on the inner side of the side loading plate; The hydraulic pumping mechanism includes an oil pump and a multi-way directional valve. The oil pump is connected to the vertical loading cylinder and four horizontal loading cylinders respectively through the multi-way directional valve. The acoustic emission probe of the acoustic emission monitoring system is installed in the probe mounting slot and is used to collect acoustic emission data during the test. The loading monitoring system includes a pressure sensor 1, a displacement sensor 1, a pressure sensor 2, and a data logger; all three sensors are high-precision sensors; pressure sensor 1 and displacement sensor 1 are mounted on the vertical loading cylinder; four pressure sensors 2 are mounted on four horizontal loading cylinders respectively; the data logger is connected to pressure sensor 1, displacement sensor 1, and pressure sensor 2 respectively. The control unit is connected to the data logger, the load monitoring system, the acoustic emission monitoring system, and the hydraulic pumping mechanism, respectively.

[0007] Furthermore, in order to obtain a variety of image data and ensure more accurate acquisition of the dynamic evolution law of stress-strain of the specimen, a SEM monitoring system and a high-speed camera connected to the controller are also included. The SEM monitoring system is used to acquire static image data with nanometer-level resolution, and the high-speed camera is set on one side outside the external support frame to acquire dynamic image data during the side failure process of the specimen.

[0008] Furthermore, to ensure connection strength and to facilitate the disassembly of the lateral baffles in any direction, so as to effectively simulate the working condition of changing from a six-sided force state to a five-sided force state, the adjacent two lateral baffles in the internal confining pressure loading frame are fixedly connected by connecting bolts.

[0009] Furthermore, to ensure the test results, the dimensions of the upper loading plate are adapted to the dimensions of the pressure relief chamber. A connecting plate is fixedly connected to the outer side of the lower end of the internal confining pressure loading frame, and this connecting plate is fixedly connected to the supporting base plate via connecting bolt two, and to the side baffles via connecting bolt three. The connecting plate provides radial restraint to the four side baffles, effectively ensuring the load-bearing capacity of the internal confining pressure loading frame. Simultaneously, when one side baffle is removed, the connecting plate can continue to maintain the load-bearing capacity of the internal confining pressure loading frame by radially restraining and fixing the remaining three side baffles, thus ensuring the reliability of the test.

[0010] Furthermore, to ensure the accuracy of the monitoring data, the acoustic emission monitoring system uses a DS5-16B multi-channel full-information acoustic emission analyzer; the SEM monitoring system uses a FlexSEM1000 high and low vacuum scanning electron microscope; and the displacement sensor is a rope displacement sensor.

[0011] Furthermore, to facilitate the power supply of various electrical devices during the test, a power supply mechanism is also included. The power supply mechanism includes a trolley and a distribution box. The distribution box is installed on the trolley and connected to the power supply for supplying power.

[0012] In this invention, an external load-bearing frame is formed by a supporting base plate, supporting columns, and a supporting top plate, which facilitates providing a stable load-bearing space for the experiment. A vertical loading cylinder is installed at the center of the supporting top plate, which, through its telescopic movement, works in conjunction with the loading plate to apply axial pressure to the sample. The internal confining pressure loading frame is enclosed by four detachable lateral baffles, solving the problem of non-removable side plates in traditional true triaxial testing machines. Without detachable side plates, it is impossible to effectively simulate how the free surface of the recycled roof fails under the influence of mining during stratified mining. Furthermore, it is difficult to visualize the free surface during the experiment, making it impossible to obtain dynamic images of the failure process that cannot be directly observed or captured by a high-speed camera. Installing four transverse loading cylinders on the four sides of the internal confining pressure loading frame allows for independent application of lateral pressure to the sample in the pressure relief chamber via the side loading plates, thus enabling flexible adjustment of the pressure state in various directions during the experiment. Based on this, by selectively removing a side baffle, the sample can be transformed from a six-sided stress state to a five-sided stress state under single-sided unloading, effectively simulating the unloading condition of the recycled roof during mining, thus perfectly simulating the complete process of gangue compression and consolidation—recycled roof unloading. A probe mounting slot is provided on the inner side of the side baffle to facilitate the installation of the acoustic emission probe. This allows for reliable acquisition of acoustic emission monitoring data without affecting the experiment or even contacting the cemented sample. For the hydraulic pump mechanism, the pump is connected to multiple loading cylinders via multiple independent supply and return oil channels on a multi-way directional valve. This not only provides a stable power source but also allows for independent control of the extension and retraction of the loading cylinders through the control of the multi-way directional valve. The acoustic emission monitoring system allows for accurate identification of each stage of sample fracture compaction, unloading, and imbalance failure through parameters such as energy, amplitude, and frequency, facilitating accurate revelation of the brittle fracture mechanism of the sample. The loading monitoring system integrates pressure and displacement sensors, and, in conjunction with a data logger, can acquire axial pressure, axial displacement, and lateral pressure data in real time. Furthermore, all three sensors—pressure sensor one, displacement sensor one, and pressure sensor two—are high-precision sensors, effectively adapting to force monitoring test conditions with low megapascals, thus effectively accommodating the characteristic that the bearing capacity of cemented bodies is lower than that of normal rock samples. Therefore, this invention supports comprehensive and accurate analysis of strength characteristics, deformation characteristics, and failure modes.

[0013] The device has a simple structure, low manufacturing cost, and convenient operation. It can carry out compression consolidation-mining unloading tests under the real loading process of gangue, breaking through the limitations of traditional true triaxial testing machines. It can provide key data support for the influence of particle size distribution on the compression characteristics of gangue and the stability of the recycled roof.

[0014] This invention also provides a method for unloading mining-induced compression consolidation-regenerated rock mass in goaf areas, employing a testing device for unloading mining-induced compression consolidation-regenerated rock mass in goaf areas, comprising the following steps: Step 1: Installation of the acoustic emission probe and manual filling of the filler; Four acoustic emission probes were installed in four probe mounting slots respectively; gangue particles were loaded into the pressure relief chamber to form the initial sample; Step 2: Lateral compression; Control the vertical loading cylinder to drive the upper loading plate to press down, compress the initial sample to a cubic cement body of a set size, stop the pressing process, record the current axial pressure σ1, and then place it in a set temperature and humidity environment to stabilize the pressure for a set time. Step 3: Initial stress loading; S31: Keep the axial pressure σ1 constant, and start synchronously loading the lateral pressure in the front and rear directions and the lateral pressure in the left and right directions according to the hydrostatic pressure conditions until the lateral pressure in the front and rear directions reaches σ2 and the lateral pressure in the left and right directions reaches σ3, then keep the load to simulate the initial triaxial stress state of the regenerated top plate. S32: Based on the lateral pressure σ2, increase the lateral pressure in the front and rear directions to reach σ2', and establish a triaxial stress field that matches the actual mining area; Step 4: Dynamic unloading simulation; S41: Keep the lateral pressure σ2' in the front-to-back direction unchanged, directly remove the lateral baffle on the right side to make the pressure in the right direction zero, and form a free unloading surface on the right side of the sample. At the same time, reduce the pressure σ3 in the left direction to the residual stress σ3' to simulate the condition of radial stress reduction after unloading in the lower layer mining, and realize the stress path and boundary condition transformation process of the rock mass near the excavation boundary under tangential stress. S42: Create artificial speckle patterns on the unloading surface to form multiple independently distributed spots; Step 5: Failure simulation; Maintaining the lateral pressure σ2' and residual stress σ3' in the front-to-back direction unchanged, continuously increase the axial pressure until the specimen fails; Simultaneously, the load and displacement data of the specimen during the failure process are collected by the loading monitoring system; the acoustic emission data of the specimen during the failure process is collected by the acoustic emission monitoring system; and the dynamic image data of the spots on the unloading surface during the failure process are collected by the high-speed camera. Step Six: Evolutionary Pattern Analysis; Based on the obtained experimental data, the stress-strain response, crack propagation and dynamic deformation were analyzed to obtain the dynamic evolution law of stress-strain, and the relationship equation between mechanical parameters and gangue particle size distribution was established.

[0015] Furthermore, to ensure that the high-definition camera can accurately identify the speckles, the artificial speckle pattern is created in step four, S42, as follows: S42-1: First, spray a layer of white paint evenly on the unloading surface to form a uniform background color; S42-2: After the background color has dried, spray black paint evenly onto the unloading surface to form multiple black spots that are randomly and independently distributed.

[0016] As a preferred option, static image data with nanometer-resolution is acquired using a SEM monitoring system after the sample is damaged.

[0017] As a preferred option, in step five, a high-definition camera is used to acquire dynamic image data of the spots in real time during the destruction simulation process.

[0018] This invention provides a method for testing the compression consolidation of gangue in goaf-regenerated rock mass during mining-induced unloading. First, gangue particles are manually filled before the sample is prepared, which helps preserve its natural gradation and pore structure, avoiding the heterogeneity errors of traditional pre-prepared samples. Next, vertical loading compresses the loose gangue into a cubic cemented mass, simulating the natural compaction process and ensuring the stability of the sample's mechanical properties. After compaction, pressure is stabilized in a set temperature and humidity environment, which helps eliminate stress concentration within the sample and improves the reliability of the test results. Subsequently, while maintaining constant axial pressure, lateral pressure is simultaneously applied under hydrostatic pressure conditions, accurately reproducing the initial triaxial stress state of the regenerated roof. The stress is increased from σ2 to σ2', matching the actual stress distribution conditions in the stope and enhancing the engineering applicability of the test. Furthermore, by combining a load monitoring system, an acoustic emission monitoring system, and a high-speed camera, synchronous recording of load-displacement, acoustic emission signals, and dynamic images can be achieved. Multi-source data can be cross-verified through multi-parameter synchronous acquisition, which is beneficial for accurately analyzing brittle / ductile failure modes and crack propagation patterns. Finally, stress-strain response, crack propagation, and dynamic deformation analysis can reveal the spatiotemporal evolution characteristics of gangue failure. Combining particle size distribution data to establish a quantitative relationship between mechanical parameters (such as strength and modulus) and gangue properties can provide a reliable theoretical basis for engineering optimization.

[0019] Compared with the prior art, the advantages of the present invention are as follows: 1. Full-process digital closed-loop control: Digital closed-loop control is realized from loading to unloading, which greatly improves the accuracy of the test and ensures repeatability.

[0020] 2. Multi-parameter synchronous monitoring: Integrating mechanical, acoustic emission, and image acquisition technologies, it achieves multi-dimensional data fusion analysis, effectively improving monitoring accuracy. Simultaneously, through multi-parameter synchronous monitoring, it can obtain extremely rich and mutually corroborating data on the failure process of rock samples, comprehensively and accurately revealing the mechanical behavior, damage evolution, and fracture mechanism of the samples.

[0021] 3. Highly realistic engineering scenario: During the test, by removing the lateral baffle on one side, the sample can be continuously transformed from a six-sided stress state to a single-sided unloading and five-sided stress state. Combined with dynamic unloading and stress field adjustment, the complete process of gangue compression and consolidation and regenerated roof mining unloading can be perfectly simulated. This ensures that the process of obtaining multi-source information such as stress and strain is continuous and can truly reflect the continuous change process of gangue compression and consolidation in the upper layer goaf and roof fracture in the lower layer remining.

[0022] 4. Quantification of the influence of particle size distribution: By establishing the relationship equation between mechanical parameters and gangue characteristics, a scientific basis can be provided for engineering material selection and design.

[0023] 5. Balance between cost and efficiency: The adoption of a detachable confining pressure loading frame and a digital closed-loop system reduces equipment costs while improving test efficiency.

[0024] This method is simple to implement and has low implementation costs. It enables continuous and accurate reproduction of the entire process of gangue compression and consolidation-regenerated roof mining and unloading, providing reliable technical support for stability analysis and support design in deep rock mass engineering. The research results using this method can be directly used for stability assessment and support design of the regenerated roof. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a graph showing the stress and time in the method section of this invention; Figure 3 This is the stress-strain curve of the gangue lateral compression-mining unloading test in this invention.

[0026] In the diagram: 1. External load-bearing frame, 2. Internal confining loading frame, 3. Support base plate, 4. Support column, 5. Support top plate, 6. Vertical loading cylinder, 7. Horizontal loading cylinder, 8. Upper loading plate, 9. Side loading plate, 10. Connecting enclosure plate, 11. Probe mounting slot, 12. Pressure relief chamber, 13. Side baffle. Detailed Implementation

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] like Figure 1As shown, the present invention provides a test device for unloading mining of gangue compression consolidation-regenerated rock mass in goaf areas, including an external bearing frame 1, a vertical loading cylinder 6, an internal confining pressure loading frame 2, a horizontal loading cylinder 7, a hydraulic pumping mechanism, an acoustic emission monitoring system, a loading monitoring system, and a control unit. The external load-bearing frame 1 includes a support base plate 3, support columns 4 and a support top plate 5. The support top plate 5 is fixedly connected above the support base plate 3 by multiple support columns 4, forming a load-bearing space between the support base plate 3, support columns 4 and support top plate 5. The vertical loading cylinder 6 is fixedly installed in the upper mounting hole at the center of the support top plate 5, and is used to apply axial pressure to the sample. Its telescopic end is located below the support top plate 5, and an upper loading plate 8 is fixedly installed thereon. The internal confining pressure loading frame 2 is located at the bottom of the load-bearing space and is fixedly installed on the upper end of the support base plate 3. The internal confining pressure loading frame 2 is formed by four detachable side baffles 13, and has a pressure relief chamber 12 for accommodating the sample in the center. Four side mounting holes are opened in the center of the four side baffles 13. Four transverse loading cylinders 7 are respectively installed in four side mounting holes, with their telescopic ends located in the pressure relief chamber 12, and a side loading plate 9 is fixedly installed thereon. The transverse loading cylinders 7 are used to apply lateral pressure to the sample; a probe mounting groove 11 is provided on the inner side of the side loading plate 9. The hydraulic pumping mechanism includes an oil pump and a multi-way directional valve. The oil pump is connected to the vertical loading cylinder 6 and four horizontal loading cylinders 7 respectively through the multi-way directional valve. The acoustic emission probe of the acoustic emission monitoring system is installed in the probe mounting slot 11 and is used to collect acoustic emission data during the test. The loading monitoring system includes a pressure sensor 1, a displacement sensor 1, a pressure sensor 2, and a data logger; all three sensors are high-precision sensors; the pressure sensor 1 and displacement sensor 1 are mounted on the vertical loading cylinder 6 and are used to collect axial pressure signals and axial displacement signals in real time, respectively; the four pressure sensors 2 are mounted on the four horizontal loading cylinders 7 and are used to collect lateral pressure signals in real time; the data logger is connected to the pressure sensor 1, displacement sensor 1, and pressure sensor 2 respectively. The control unit includes a controller, which is connected to the data logger, the load monitoring system, the acoustic emission monitoring system, and the hydraulic pumping mechanism. Preferably, the controller is a PLC controller, but an industrial computer can also be used.

[0029] To acquire diverse image data and ensure more accurate understanding of the dynamic evolution of stress-strain in the specimen, a SEM monitoring system and a high-speed camera connected to the controller are included. The SEM monitoring system acquires static image data with nanometer-level resolution, while the high-speed camera, positioned on one side outside the external support frame 1, acquires dynamic image data during the specimen's side failure process. The high-speed camera, combined with DIC (Digital Image Correlation) technology, can non-contactly, comprehensively, and with high precision record the displacement and strain field evolution of the specimen surface, providing a direct visual representation of the macroscopic crack propagation process and the overall deformation behavior of the specimen.

[0030] To ensure connection strength and facilitate the disassembly of the lateral baffles in any direction, so as to effectively simulate the working condition of changing from a six-sided force state to a five-sided force state, the two adjacent lateral baffles 13 in the internal confining pressure loading frame 2 are fixedly connected by connecting bolts.

[0031] To ensure the test results, the dimensions of the upper loading plate 8 are matched with the dimensions of the pressure relief chamber 12. A connecting plate 10 is fixedly connected to the outer side of the lower end of the internal confining pressure loading frame 2, and the connecting plate 10 is fixedly connected to the supporting base plate 3 by connecting bolt two, and to the side baffles 13 by connecting bolt three. The connecting plate allows for radial restraint of the four side baffles, effectively ensuring the load-bearing capacity of the internal confining pressure loading frame. Furthermore, even after one side baffle is removed, the connecting plate can continue to maintain the load-bearing capacity of the internal confining pressure loading frame by radially restraining and fixing the remaining three side baffles, thus ensuring the reliability of the test.

[0032] To ensure the accuracy of the monitoring data, the acoustic emission monitoring system uses a DS5-16B multi-channel full-information acoustic emission analyzer; the SEM monitoring system uses a FlexSEM1000 high and low vacuum scanning electron microscope; and the displacement sensor is a rope displacement sensor.

[0033] To facilitate the power supply of various electrical devices during the test, a power supply mechanism is also included. The power supply mechanism includes a trolley and a distribution box. The distribution box is installed on the trolley and connected to the power supply for supplying power.

[0034] In this invention, an external load-bearing frame is formed by a supporting base plate, supporting columns, and a supporting top plate, which facilitates providing a stable load-bearing space for the experiment. A vertical loading cylinder is installed at the center of the supporting top plate, which, through its telescopic movement, works in conjunction with the loading plate to apply axial pressure to the sample. The internal confining pressure loading frame is enclosed by four detachable lateral baffles, solving the problem of non-removable side plates in traditional true triaxial testing machines. Without detachable side plates, it is impossible to effectively simulate how the free surface of the recycled roof fails under the influence of mining during stratified mining. Furthermore, it is difficult to visualize the free surface during the experiment, making it impossible to obtain dynamic images of the failure process that cannot be directly observed or captured by a high-speed camera. Installing four transverse loading cylinders on the four sides of the internal confining pressure loading frame allows for independent application of lateral pressure to the sample in the pressure relief chamber via the side loading plates, thus enabling flexible adjustment of the pressure state in various directions during the experiment. Based on this, by selectively removing a side baffle, the sample can be transformed from a six-sided stress state to a five-sided stress state under single-sided unloading, effectively simulating the unloading condition of the recycled roof during mining, thus perfectly simulating the complete process of gangue compression and consolidation—recycled roof unloading. A probe mounting slot is provided on the inner side of the side baffle to facilitate the installation of the acoustic emission probe. This allows for reliable acquisition of acoustic emission monitoring data without affecting the experiment or even contacting the cemented sample. For the hydraulic pump mechanism, the pump is connected to multiple loading cylinders via multiple independent supply and return oil channels on a multi-way directional valve. This not only provides a stable power source but also allows for independent control of the extension and retraction of the loading cylinders through the control of the multi-way directional valve. The acoustic emission monitoring system allows for accurate identification of each stage of sample fracture compaction, unloading, and imbalance failure through parameters such as energy, amplitude, and frequency, facilitating accurate revelation of the brittle fracture mechanism of the sample. The loading monitoring system integrates pressure and displacement sensors, and, in conjunction with a data logger, can acquire axial pressure, axial displacement, and lateral pressure data in real time. Furthermore, all three sensors—pressure sensor one, displacement sensor one, and pressure sensor two—are high-precision sensors, effectively adapting to force monitoring test conditions with low megapascals, thus effectively accommodating the characteristic that the bearing capacity of cemented bodies is lower than that of normal rock samples. Therefore, this invention supports comprehensive and accurate analysis of strength characteristics, deformation characteristics, and failure modes.

[0035] The device has a simple structure, low manufacturing cost, and convenient operation. It can carry out compression consolidation-mining unloading tests under the real loading process of gangue, breaking through the limitations of traditional true triaxial testing machines. It can provide key data support for the influence of particle size distribution on the compression characteristics of gangue and the stability of the recycled roof.

[0036] like Figure 2As shown, the present invention also provides a method for unloading mining-induced rock mass compression consolidation-regenerated rock mass in goaf areas, employing a goaf area gangue compression consolidation-regenerated rock mass unloading testing device, comprising the following steps: Step 1: Installation of the acoustic emission probe and manual filling of the filler; Four acoustic emission probes are pre-coated with Vaseline and placed in the four probe mounting slots 11 of the four side baffles 13 to accurately monitor the acoustic emission data throughout the destruction process of the sample without adversely affecting the sample process. At the same time, a layer of dimethyl silicone oil is coated on the inner surface of the side loading plate 13 to reduce the friction between the material and the inner wall of the chamber and ensure the smoothness of the sample surface. The gangue particles were loaded into the pressure relief chamber 12 to form the initial sample; The gangue filler is prepared through the following process: large mudstone and sandy mudstone gangue are crushed using a PEX jaw crusher. The two types of gangue are then divided into five groups by using a 0-20mm crushing gangue sieve: 0-4mm, 4-8mm, 8-12mm, 12-16mm, and 16-20mm. The gangue and other materials are weighed using an electronic scale. There are a total of 10 groups for the two types of rocks. The same lithology groups are numbered sequentially from 1 to 5. 1-2kg of crushed stone is prepared from each group, and each group of materials is placed into different containers.

[0037] Step 2: Lateral compression; The vertical loading cylinder 6 drives the upper loading plate 8 to press down, compressing the initial sample into a cubic cemented body of a set size. After that, the pressing process is stopped, the current axial pressure σ1 is recorded, and then the sample is placed in a set temperature and humidity environment to stabilize for a set time. Preferably, the stabilization time is 24 hours. Step 3: Initial stress loading; S31: Keep the axial pressure σ1 constant, and start synchronously loading the lateral pressure in the front and rear directions and the lateral pressure in the left and right directions according to the hydrostatic pressure conditions until the lateral pressure in the front and rear directions reaches σ2 and the lateral pressure in the left and right directions reaches σ3, then keep the load to simulate the initial triaxial stress state of the regenerated top plate. S32: Based on the lateral pressure σ2, increase the lateral pressure in the front and rear directions to reach σ2', and establish a triaxial stress field that matches the actual mining area; Step 4: Dynamic unloading simulation; S41: Keep the lateral pressure σ2' in the front-to-back direction unchanged, directly remove the lateral baffle 13 on the right side to make the pressure in the right direction zero, and form a free unloading surface on the right side of the sample. At the same time, control the pressure relief of the lateral loading cylinder 7 on the left side to reduce the pressure σ3 in the left side to the residual stress σ3', simulate the working condition of radial stress reduction after unloading in the lower layer mining, and realize the stress path and boundary condition transformation process of the rock mass near the excavation boundary under the action of tangential stress. S42: Create artificial speckle patterns on the unloading surface to form multiple independently distributed spots; Step 5: Destruction Simulation; While keeping the lateral pressure σ2' and residual stress σ3' constant in the front-to-back direction, the axial pressure is continuously increased until the specimen fails. Simultaneously, the load and displacement data of the specimen during the failure process are collected by the loading monitoring system; the acoustic emission data of the specimen during the failure process is collected by the acoustic emission monitoring system; and the dynamic image data of the spots on the unloading surface during the failure process are collected by the high-speed camera. Step Six: Evolutionary Pattern Analysis; Based on the obtained experimental data, the stress-strain response, crack propagation and dynamic deformation were analyzed to obtain the dynamic evolution law of stress-strain, and the relationship equation between mechanical parameters and gangue particle size distribution was established.

[0038] To ensure that the high-definition camera can accurately identify the speckles, the artificial speckle pattern is created in step four, S42, as follows: S42-1: First, spray a layer of white paint evenly on the unloading surface to form a uniform background color; S42-2: After the background color has dried, spray black paint evenly onto the unloading surface to form multiple black spots that are randomly and independently distributed.

[0039] As a preferred option, static image data with nanometer-resolution is acquired using a SEM monitoring system after the sample is damaged.

[0040] As a preferred option, in step five, a high-definition camera is used to acquire dynamic image data of the spots in real time during the destruction simulation process.

[0041] Figure 3 The stress-strain curves of the gangue lateral confined compression-mining unloading test are shown. It is clear from the figure that the compression-unloading process is continuous. Figure 3 The curve on the left represents the compaction characteristics of gangue with different particle sizes (unit: mm). Figure 3The curve on the right represents the stress-strain curves of five groups of cemented bodies with different particle sizes during the decompression stage of mining. This effectively demonstrates that the test process conforms to the actual field conditions of lower-level mining. Furthermore, it shows that the present invention can realistically simulate the continuous damage evolution process of gangue compression consolidation and regenerated roof decompression. By analyzing the dynamic evolution law of stress-strain during the test, the present invention can accurately establish an equivalent mechanical constitutive model of mechanical parameters and gangue particle size distribution. This can realistically reveal how gangue particle size distribution affects its compression characteristics and effectively reveal the damage and failure mechanism of the regenerated roof.

[0042] This invention provides a method for testing the compression consolidation of gangue in goaf-regenerated rock mass during mining-induced unloading. First, gangue particles are manually filled before the sample is prepared, which helps preserve its natural gradation and pore structure, avoiding the heterogeneity errors of traditional pre-prepared samples. Next, vertical loading compresses the loose gangue into a cubic cemented mass, simulating the natural compaction process and ensuring the stability of the sample's mechanical properties. After compaction, pressure is stabilized in a set temperature and humidity environment, which helps eliminate stress concentration within the sample and improves the reliability of the test results. Subsequently, while maintaining constant axial pressure, lateral pressure is simultaneously applied under hydrostatic pressure conditions, accurately reproducing the initial triaxial stress state of the regenerated roof. The stress is increased from σ2 to σ2', matching the actual stress distribution conditions in the stope and enhancing the engineering applicability of the test. Furthermore, by combining a load monitoring system, an acoustic emission monitoring system, and a high-speed camera, synchronous recording of load-displacement, acoustic emission signals, and dynamic images can be achieved. Multi-source data can be cross-verified through multi-parameter synchronous acquisition, which is beneficial for accurately analyzing brittle / ductile failure modes and crack propagation patterns. Finally, stress-strain response, crack propagation, and dynamic deformation analysis can reveal the spatiotemporal evolution characteristics of gangue failure. Combining particle size distribution data to establish a quantitative relationship between mechanical parameters (such as strength and modulus) and gangue properties can provide a reliable theoretical basis for engineering optimization.

[0043] Compared with the prior art, the advantages of the present invention are as follows: 1. Full-process digital closed-loop control: Digital closed-loop control is realized from loading to unloading, which greatly improves the accuracy of the test and ensures repeatability.

[0044] 2. Multi-parameter synchronous monitoring: Integrating mechanical, acoustic emission, and image acquisition technologies, it achieves multi-dimensional data fusion analysis, effectively improving monitoring accuracy. Simultaneously, through multi-parameter synchronous monitoring, it can obtain extremely rich and mutually corroborating data on the failure process of rock samples, comprehensively and accurately revealing the mechanical behavior, damage evolution, and fracture mechanism of the samples.

[0045] 3. Highly realistic engineering scenario: During the test, by removing the lateral baffle on one side, the sample can be continuously transformed from a six-sided stress state to a single-sided unloading and five-sided stress state. Combined with dynamic unloading and stress field adjustment, the complete process of gangue compression and consolidation and regenerated roof mining unloading can be perfectly simulated. This ensures that the process of obtaining multi-source information such as stress and strain is continuous and can truly reflect the continuous change process of gangue compression and consolidation in the upper layer goaf and roof fracture in the lower layer remining.

[0046] 4. Quantification of the influence of particle size distribution: By establishing the relationship equation between mechanical parameters and gangue characteristics, a scientific basis can be provided for engineering material selection and design.

[0047] 5. Balance between cost and efficiency: The adoption of a detachable confining pressure loading frame and a digital closed-loop system reduces equipment costs while improving test efficiency.

[0048] This method is simple to implement and has low implementation costs. It enables continuous and accurate reproduction of the entire process of gangue compression and consolidation-regenerated roof mining and unloading, providing reliable technical support for stability analysis and support design in deep rock mass engineering. The research results using this method can be directly used for stability assessment and support design of the regenerated roof.

Claims

1. A test device for unloading mining-regenerated rock mass compression consolidation in goaf areas, comprising an external bearing frame (1), characterized in that, It also includes a vertical loading cylinder (6), an internal confining pressure loading frame (2), a horizontal loading cylinder (7), a hydraulic pumping mechanism, an acoustic emission monitoring system, a loading monitoring system, and a control unit; The external load-bearing frame (1) includes a support base plate (3), support columns (4) and a support top plate (5). The support top plate (5) is fixedly connected above the support base plate (3) by multiple support columns (4), forming a load-bearing space between the support base plate (3), support columns (4) and support top plate (5). The vertical loading cylinder (6) is fixedly installed in the upper mounting hole at the center of the support top plate (5), and its telescopic end is fixedly installed with an upper loading plate (8). The internal confining pressure loading frame (2) is located at the bottom of the load-bearing space and is fixedly installed on the upper end of the support base plate (3). The internal confining pressure loading frame (2) is formed by four side baffles (13) that are detachably enclosed. It has a pressure relief chamber (12) in the center for accommodating the sample and four side mounting holes are provided in the center of the four side baffles (13). Four transverse loading cylinders (7) are respectively installed in four side mounting holes, and side loading plates (9) are fixedly installed on their telescopic ends; a probe mounting groove (11) is opened on the inner side of the side loading plate (9). The hydraulic pumping mechanism includes an oil pump and a multi-way directional valve. The oil pump is connected to the vertical loading cylinder (6) and four horizontal loading cylinders (7) respectively through the multi-way directional valve. The acoustic emission probe of the acoustic emission monitoring system is installed in the probe mounting slot (11) and is used to collect acoustic emission data during the test. The loading monitoring system includes a pressure sensor 1, a displacement sensor 1, a pressure sensor 2, and a data logger; the pressure sensor 1, displacement sensor 1, and pressure sensor 2 are all high-precision sensors; the pressure sensor 1 and displacement sensor 1 are installed on the vertical loading cylinder (6); the four pressure sensors 2 are respectively installed on the four horizontal loading cylinders (7); the data logger is respectively connected to the pressure sensor 1, displacement sensor 1, and pressure sensor 2; The control unit is connected to the data logger, the load monitoring system, the acoustic emission monitoring system, and the hydraulic pumping mechanism, respectively.

2. The test device for unloading mining-regenerated rock mass compression consolidation-regeneration of gangue in a goaf according to claim 1, characterized in that, It also includes a SEM monitoring system and a high-speed camera connected to the controller. The SEM monitoring system is used to acquire static image data with nanometer resolution, and the high-speed camera is set on one side outside the external support frame (1) to acquire dynamic image data during the side failure process of the sample.

3. A test device for unloading mining-regenerated rock mass compression consolidation-regeneration of gangue in a goaf, as described in claim 1 or 2, is characterized in that... The two adjacent side baffles (13) in the internal confining pressure loading frame (2) are fixedly connected by connecting bolts.

4. The test device for unloading mining-regenerated rock mass compression consolidation-regeneration of gangue in a goaf according to claim 3, characterized in that, The size of the upper loading plate (8) is adapted to the size of the pressure relief chamber (12); the lower end of the inner confining pressure loading frame (2) is fixedly connected to the outer side of the connecting plate (10), and the connecting plate (10) is fixedly connected to the supporting base plate (3) by connecting bolt two, and the connecting plate (10) is fixedly connected to the side baffle (13) by connecting bolt three.

5. The test device for unloading mining-regenerated rock mass compression consolidation-regeneration of gangue in a goaf according to claim 2, characterized in that, The acoustic emission monitoring system uses a DS5-16B multi-channel full-information acoustic emission analyzer; the SEM monitoring system uses a FlexSEM1000 high and low vacuum scanning electron microscope; and the displacement sensor is a rope displacement sensor.

6. The test device for unloading mining-regenerated rock mass compression consolidation-regeneration of gangue in a goaf according to claim 4, characterized in that, It also includes a power supply mechanism, which comprises a trolley and a distribution box. The distribution box is mounted on the trolley and connected to a power source for supplying electricity.

7. A method for unloading mining-induced compression consolidation-regenerated rock mass in goaf areas, employing the unloading testing device for goaf area compression consolidation-regenerated rock mass as described in claim 4, characterized in that... Includes the following steps: Step 1: Installation of the acoustic emission probe and manual filling of the filler; Four acoustic emission probes were installed in four probe mounting slots (11) respectively; gangue particles were loaded into the pressure relief chamber (12) to form an initial sample; Step 2: Lateral compression; Control the vertical loading cylinder (6) to drive the upper loading plate (8) to press down, compress the initial sample to a cubic cement body of a set size, stop the pressing process, record the current axial pressure σ1, and then place it in a set temperature and humidity environment to stabilize the pressure for a set time. Step 3: Initial stress loading; S31: Keep the axial pressure σ1 constant, and start synchronously loading the lateral pressure in the front and rear directions and the lateral pressure in the left and right directions according to the hydrostatic pressure conditions until the lateral pressure in the front and rear directions reaches σ2 and the lateral pressure in the left and right directions reaches σ3, then keep the load to simulate the initial triaxial stress state of the regenerated top plate. S32: Based on the lateral pressure σ2, increase the lateral pressure in the front and rear directions to reach σ2', and establish a triaxial stress field that matches the actual mining area; Step 4: Dynamic unloading simulation; S41: Keep the lateral pressure σ2' in the front and rear directions unchanged, directly remove the lateral baffle (13) on the right side, set the pressure in the right direction to zero, and form a free unloading surface on the right side of the sample. At the same time, reduce the pressure σ3 in the left direction to the residual stress σ3', simulate the working condition of radial stress reduction after unloading in the lower layer mining, and realize the rock stress path and boundary condition transformation process near the excavation boundary under tangential stress. S42: Create artificial speckle patterns on the unloading surface to form multiple independently distributed spots; Step 5: Failure simulation; Maintaining the lateral pressure σ2' and residual stress σ3' in the front-to-back direction unchanged, continuously increase the axial pressure until the specimen fails; Simultaneously, the load and displacement data of the specimen during the failure process are collected by the loading monitoring system; the acoustic emission data of the specimen during the failure process is collected by the acoustic emission monitoring system; and the dynamic image data of the spots on the unloading surface during the failure process are collected by the high-speed camera. Step Six: Evolutionary Pattern Analysis; Based on the obtained experimental data, the stress-strain response, crack propagation and dynamic deformation were analyzed to obtain the dynamic evolution law of stress-strain, and the relationship equation between mechanical parameters and gangue particle size distribution was established.

8. The method for testing the compression consolidation-regenerated rock mass in a goaf according to claim 7, characterized in that, In step four, S42, the artificial speckle pattern is created as follows: S42-1: First, spray a layer of white paint evenly on the unloading surface to form a uniform background color; S42-2: After the background color has dried, spray black paint evenly onto the unloading surface to form multiple black spots that are randomly and independently distributed.

9. The method for testing the compression consolidation-regenerated rock mass in a goaf according to claim 7, characterized in that, In step five, after the sample is destroyed, static image data with nanometer-resolution is acquired using a SEM monitoring system.

10. The method for testing the compression consolidation-regenerated rock mass in a goaf according to claim 7, characterized in that, In step five, a high-definition camera is used to acquire dynamic image data of the spots in real time during the destruction simulation process.

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