Column and filling body interaction loading test device and method under variable stiffness condition

Abstract

The invention provides an ore pillar and filling body interaction loading test device and method under the variable stiffness condition, and belongs to the technical field of mining engineering.The device comprises a loading device, a lateral confinement cylinder, a load conduction column, an elastic energy storage device and a monitoring system, and a sample is placed in the lateral confinement cylinder; the elastic energy storage device comprises a first structure, a disc spring, a mandrel and a second structure, and the sample is a single pillar-filling body sample or a multi-pillar-filling body sample. The device has the advantages of simple operation and low cost, and can realize the flexible loading function of quantifiable rigidity of the testing machine. The device can be used in cooperation with an existing rock mechanical testing machine, so that the interaction process of the jambs and the cemented filling body under the loading conditions of top plates and bottom plates with different rigidities is simulated, a testing means and method can be provided for studying the reinforcing mechanism of the filling body on the jambs, and the influence mechanism of the filling body on the stress load transfer process between the jambs is clarified.

Description

Technical Field

[0001] The present invention relates to the technical field of mining engineering, and more particularly, to a loading test device and method for the interaction between a pillar and a filling body under variable stiffness conditions. Background Art

[0002] Most current studies mainly emphasize the lateral support effect of the filling body on a single pillar, but ignore the influence of the filling body on the load transfer behavior in the pillar system. As a key support structural unit, the extraction of pillars will inevitably lead to the redistribution of loads in the system, but the presence of the filling body will surely fundamentally change the process of load transfer. In structural mechanics, the number of alternative load transfer paths determines the anti-progressive collapse ability of the structure. The alternative load transfer paths can disperse and transfer the load to other components when a local failure occurs in the structure, thus maintaining the overall balance of the system. In the interaction between the filling body and the pillar, the filling body not only serves as a load transfer path, but also can strengthen the strength of the pillar during the loading process, and this strengthening effect gradually appears as the number of unstable pillars increases. Therefore, the passive support effect of the filling body is fully exerted, continuously improving the stability of the system and ultimately effectively preventing large-scale progressive instability of the pillars. Therefore, in the process of using the filling method to recover residual pillars, it is not only necessary to deeply study how to exert the passive support ability of the filling body, but also to clarify the mechanical action mechanism of the filling body on the load transfer process between pillars, which can provide a new theoretical basis for the design of filling mining methods. Currently, the research results lack test equipment and methods for studying the influence of the filling body on the load transfer behavior in the pillar system. Summary of the Invention

[0003] In view of the above-mentioned technical problems, a loading test device and method for the interaction between a pillar and a filling body under variable stiffness conditions are provided.

[0004] The technical means adopted by the present invention are as follows:

[0005] A loading test device for the interaction between a pillar and a filling body under variable stiffness conditions, located in a distributed optical fiber and acoustic emission monitoring environment, includes: a loading device, a lateral confinement cylinder, a load conduction column, an elastic energy storage device, and a monitoring system. The specimen is placed inside the lateral confinement cylinder. The loading device is located above the lateral confinement cylinder. The top of the loading device is in contact connection with the top plate of the testing machine, and the bottom is in contact connection with the top end of the rock specimen in the specimen. The bottom end of the rock specimen is in contact with the top end of the load conduction column, and the rock specimen and the load conduction column are axially centered.

[0006] The elastic energy storage device includes a first structure, a disc spring, a mandrel, and a second structure. The lower part of the second structure is fixed on the loading platform of the testing machine. The lower end of the mandrel is installed on the second structure, and the upper end is slidably connected to the first structure. The disc spring is sleeved outside the mandrel and is located between the first structure and the second structure. The lateral confinement cylinder is placed on the top of the first structure, and the load conduction column is arranged inside the first structure above and below the lateral confinement cylinder.

[0007] The monitoring system is arranged in the specimen and the first structure. The specimen is a single ore pillar - filling body specimen or a multi - ore pillar - filling body specimen.

[0008] Furthermore, the loading device includes a loading pad, a spherical socket indenter, and a spherical head pressure column. The top of the loading pad is in contact with the top plate of the testing machine. The spherical socket indenter is in contact with the loading pad. One end of the spherical head pressure column is connected to the spherical socket indenter, and the other end is in contact with the top end of the rock specimen. Wherein, the spherical socket indenter is provided with a spherical groove structure, and one end of the spherical head pressure column is a spherical structure, and the spherical structure is connected in cooperation with the spherical groove structure.

[0009] Furthermore, the first structure includes an upper pressure plate, a cover plate, and a lower pressure plate connected in sequence. The top of the upper pressure plate is in contact with the bottom end of the lateral confinement cylinder. The load conduction column is installed inside the upper pressure plate and the lateral confinement cylinder. The lower pressure plate is provided with a groove, which is centrosymmetric with the mandrel. The upper end of the mandrel is slidably connected in the groove.

[0010] Furthermore, the upper pressure plate is provided with a circular groove matching the size of the rock specimen. The center of the circular groove is aligned with the center of the rock specimen. The load conduction column is installed in the circular groove, and a load sensor is arranged in the circular groove. The load sensor is placed below the load conduction column. The upper pressure plate is provided with a load sensor wire outlet groove.

[0011] The cover plate is provided with threaded holes and is fixedly connected to the lower pressure plate by bolts.

[0012] The inner diameter of the groove of the lower pressure plate is equal to the outer diameter of the upper end of the mandrel and is nested on the upper end of the mandrel.

[0013] Furthermore, the second structure includes an upper bottom plate and a lower bottom plate. The upper bottom plate is connected to the lower bottom plate. The lower bottom plate is fixed on the loading platform of the testing machine. The lower end of the mandrel is inserted and connected in the upper bottom plate and the lower bottom plate.

[0014] Furthermore, a wrench is connected to the upper bottom plate and the mandrel. Wherein, the longitudinal side wall of the upper bottom plate is provided with a first guiding hole. The position of the mandrel in contact with the upper bottom plate is provided with a second guiding hole. The second guiding hole is communicated with the first guiding hole and is perpendicular to the axial direction of the mandrel. The wrench is embedded inside the upper bottom plate and the mandrel through the first guiding hole and the second guiding hole.

[0015] Threaded holes are provided on the upper bottom plate and are fixedly connected to the lower bottom plate through bolts;

[0016] The lower bottom plate is fixedly mounted on the loading platform of the testing machine through bolts.

[0017] Furthermore, an optical fiber outlet hole is provided on the outer shell of the lateral confinement cylinder, and a groove communicating with the circular groove is provided at the bottom of the lateral confinement cylinder. The diameter of this groove is the same as the diameter of the rock specimen.

[0018] Furthermore, the disc springs are combined in different ways of superposition, opposition and combination, and a lubricating fluid is applied between the disc springs.

[0019] Furthermore, the monitoring system includes a load sensor, a fiber Bragg grating sensor, an acoustic emission probe and a strain gauge. The load sensor is embedded in the circular groove of the upper pressure plate of the first structure for detecting the axial load; the fiber Bragg grating sensor is buried inside the specimen for monitoring the lateral deformation of the filling body; the acoustic emission probe is attached to the surface of a single ore pillar or multiple ore pillars for monitoring the joint surface damage of a single ore pillar or multiple ore pillars; the strain gauge is attached to the surface of a single ore pillar or multiple ore pillars for monitoring the local strain of a single ore pillar or multiple ore pillars.

[0020] Furthermore, the device of the present invention is used in cooperation with a uniaxial compression testing machine to conduct a flexible loading test on rocks under the constraint of a cemented filling body.

[0021] The present invention also provides a method for testing the instability of rocks under the constraint of a cemented filling body. Using the loading test device for the interaction between ore pillars and filling bodies under variable stiffness conditions as described above, the method includes the following steps:

[0022] S1. Prepare the specimen, and arrange strain gauges, distributed fiber Bragg grating sensors and acoustic emission probes in the specimen. Among them, the strain gauges are connected to an external strain gauge, the distributed fiber Bragg grating sensors are connected to an external distributed fiber Bragg grating demodulator, and the acoustic emission probes are connected to an external acoustic emission instrument;

[0023] S2. According to the post-peak weakening characteristics in the complete stress-strain / displacement curve of the rock specimen and the loading stiffness of the testing machine, determine the instability conditions of the rock specimen, and then determine the stiffness selection range of the variable stiffness elastic energy storage device. For example, if the post-peak weakening modulus of a certain rock specimen during failure is m, at this time, adjust the disc spring group in the elastic energy storage device, and combine the disc springs in a combination way of superposition, opposition or combination to make its stiffness around m, so as to verify the Cook stiffness criterion, and complete the assembly work of the variable stiffness elastic energy storage device with the upper pressure plate, lower pressure plate, cover plate, upper bottom plate, lower bottom plate and mandrel, ensuring that the device can accurately simulate the required stiffness conditions;

[0024] S3. The stiffness of the variable-stiffness elastic energy storage device is calculated as follows:

[0025] When the disc springs are combined by the superposed combination method, they are assembled into a variable-stiffness elastic energy storage device of "superposed combined disc springs". The stiffness k of the variable-stiffness elastic energy storage device of "superposed combined disc springs" 1 satisfies the following formula:

[0026]

[0027] When the disc springs are combined by the opposed combination method, they are assembled into a variable-stiffness elastic energy storage device of "opposed combined disc springs". The stiffness k of the variable-stiffness elastic energy storage device of "opposed combined disc springs" 2 satisfies the following formula:

[0028]

[0029] When the disc springs are combined by the composite combination method, they are assembled into a variable-stiffness elastic energy storage device of "composite combined disc springs". The stiffness k of the variable-stiffness elastic energy storage device of "composite combined disc springs" 3 satisfies the following formula:

[0030]

[0031] In the formula, E is the elastic modulus of the spring material, f is the deformation of a single spring, μ is the Poisson's ratio, t is the thickness of a single disc spring, K 1 and K 4 are calculation coefficients, D is the outer diameter of the disc spring, h 0 is the calculated value of the deformation when the disc spring is flattened, n is the number of disc springs in the same direction, and i is the number of disc springs facing each other;

[0032] S4. For the uniaxial compression test, place the specimen and the variable-stiffness elastic energy storage device overlappingly, ensure that their axis centers are aligned, and install a load sensor at the bottom of a single ore pillar or multiple ore pillars. Then adjust the uniaxial compression testing machine so that the spherical socket indenter is in close contact with the loading platen;

[0033] S5. Set the monitoring parameters of the strain gauge, distributed fiber optic grating demodulator, and acoustic emission instrument, as well as the parameters of the uniaxial compression testing machine according to the test requirements;

[0034] S6. At the same time, turn on the switch button of the uniaxial compression testing machine, the acquisition start button of the strain gauge and the acoustic emission instrument, and the start button of the distributed fiber optic grating demodulator to start the test and collect data in real time;

[0035] S7. After the test is completed, unload the applied load, take out the lateral confinement cylinder, take out the damaged specimen from the lateral confinement cylinder, and clean the residual debris of the specimen. The test is over.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] 1. Multi-scenario applicability: The present invention can be used in combination with a variety of rock mechanics testing machines, which greatly broadens its application scope. It can simulate different test conditions, thereby testing the instability characteristics of pillar-fill bodies under various working conditions. Whether it is studying the flexible loading deformation instability of single pillar specimens, the support response characteristics of fill bodies, or the load transfer and transfer mechanism between pillars under the constraint of cemented fill bodies, it can be accurately realized, providing a powerful research tool for different needs in the mining process.

[0038] 2. Space and cost advantages: The present invention has the characteristics of small occupied space. In environments with limited space such as laboratories or mine sites, it can still be conveniently installed and used without occupying too much site resources. At the same time, its processing and manufacturing are simple, without the need for complex and expensive manufacturing processes and equipment, reducing the upfront investment cost. Moreover, the maintenance and repair costs are low. During the subsequent use process, even if component failures and other problems occur, they can be quickly repaired at a low cost, reducing the test stagnation time caused by equipment maintenance and improving the overall work efficiency.

[0039] 3. The distributed optical fiber and acoustic emission monitoring environment of the present invention has comprehensiveness and timeliness. Comprehensiveness: Through the distributed optical fiber, the lateral deformation of the fill body can be monitored in real time and continuously, accurately capturing the subtle changes in the fill body during the stress process, and timely discovering potential stability problems, such as the expansion and cracking of the fill body, providing key information for mine safety assessment. Timeliness: The acoustic emission probe is attached to the surface of the pillar, and can sensitively capture the damage of the pillar joint surface. Once there are initial damage signs such as cracking and dislocation on the joint surface, it can immediately send out a signal, enabling researchers to know in advance and take corresponding measures to effectively prevent further damage to the pillar and ensure the safety of mine production.

[0040] 4. The loading device of the present invention (including the loading cushion plate, spherical socket indenter, and spherical head indenter post) has stability and adaptability. Stability: The loading cushion plate is in close contact with the top plate of the testing machine, ensuring stable pressure transmission and providing a reliable loading foundation for the entire test, avoiding uneven loading force caused by poor contact. Adaptability: The spherical socket indenter and the spherical head indenter post cooperate to adapt to the small angular changes that may occur at the top of the rock specimen at the initial stage of stress, ensuring that the force acts vertically and uniformly on the specimen during the loading process, reducing the impact on the test results caused by slight deviation in the specimen placement, and improving the accuracy of test data.

[0041] 5. The lateral confinement cylinder of the present invention has simulation authenticity and monitoring convenience. Simulation authenticity: The lateral confinement cylinder is cylindrical, and there are grooves inside and at the bottom with the same diameter as the rock specimen, which can provide lateral restraint for the specimen, highly simulating the actual confined environment of the ore pillar in mine mining, making the test results closer to the actual working conditions, and helping to accurately study the interaction between the ore pillar and the filling body under confinement conditions. Monitoring convenience: The outer shell of the lateral confinement cylinder is provided with an optical fiber outlet hole, which facilitates the connection between the distributed optical fiber and the external demodulator, realizes the real-time monitoring of the transverse deformation of the filling body, does not affect the overall device structure, and ensures the smooth realization of the monitoring function.

[0042] 6. The elastic energy storage device of the present invention (including the upper pressure plate, cover plate, lower pressure plate, disc spring, upper bottom plate, lower bottom plate and core shaft) has adjustable stiffness, convenient assembly, and guidance and coordination. Adjustable stiffness: The disc springs are combined in different ways of stacking, butting and compounding, which can flexibly adjust the stiffness of the loading device, easily simulate the variable stress environments faced by the ore pillar at different stages and under different geological conditions during mine mining, and provide diverse loading conditions for comprehensively studying the interaction between the ore pillar and the filling body. Convenient assembly: The connection methods of each component are simple and stable. The upper pressure plate contacts the bottom end of the lateral confinement cylinder, the lower pressure plate is fixedly connected to the cover plate by bolts, the upper bottom plate and the lower bottom plate are bolted and sleeved on the core shaft, and the lower bottom plate is fixed on the loading platform of the testing machine. This design makes the device assembly convenient and fast, and can be efficiently completed whether in the laboratory setup or the temporary modification at the mine site, saving time costs. Guidance and coordination: The upper bottom plate is provided with a guiding hole, and the contact position between the core shaft and the upper bottom plate is also provided with a guiding hole. The wrench is inserted into the upper bottom plate and the inside of the core shaft through the guiding hole, ensuring the orderly relative movement of the components during the force application process. The lower pressure plate and the core shaft can slide relative to each other, and each component works in coordination, not only realizing the stiffness adjustment function, but also ensuring the stability and reliability of the entire loading process.

[0043] Based on the above reasons, the present invention can be widely promoted in the fields of mining engineering, etc. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 It is a schematic structural diagram of the loading test device of the present invention.

[0046] Figure 2 It is a longitudinal sectional schematic diagram of the preparation of a single ore pillar - filling body specimen and the sensor arrangement of the present invention.

[0047] Figure 3 It is a cross-sectional schematic diagram of the preparation of a single ore pillar-backfill specimen of the present invention and the arrangement of sensors.

[0048] Figure 4 It is a longitudinal-sectional schematic diagram of the preparation of a multi-ore pillar-backfill specimen of the present invention and the arrangement of sensors.

[0049] Figure 5 It is a longitudinal-sectional schematic diagram of the preparation of a multi-ore pillar-backfill specimen of the present invention and the arrangement of sensors.

[0050] Figure 6 It is a schematic diagram of the application of the loading test device of the present invention on a conventional uniaxial compression testing machine.

[0051] Figure 7 It is a schematic diagram of the combination of disc springs in the form of superposition, butt joint or compound combination of the present invention, where (a) is superposition, (b) is butt joint, and (c) is compound.

[0052] In the figure: 1. Loading backing plate; 2. Ball socket indenter; 3. Ball head compression column; 4. Lateral confinement cylinder; 5. Load conduction column; 6. Upper pressure plate; 7. Load sensor; 8. Cover plate; 9. Lower pressure plate; 10. Disc spring; 11. Mandrel; 12. Upper bottom plate; 13. Lower bottom plate; 14. Wrench. Detailed implementation manners

[0053] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0054] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way restrictive of the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0055] It should be noted that the terms used here are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used here, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0056] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for the sake of convenience in description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the description. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0057] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by orientation words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal", and "top, bottom" are generally based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description. Without contrary statements, these orientation words 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. Therefore, they should not be construed as limiting the protection scope of the present invention: the orientation words "inside, outside" refer to the inside and outside relative to the contour of each component itself.

[0058] For the convenience of description, spatial relative terms such as "above...", "over...", "on the upper surface of...", "above" can be used here to describe the spatial positional relationships between a device or feature shown in the drawings and other devices or features. It should be understood that the spatial relative terms are intended to cover different orientations in use or operation in addition to the orientation described in the drawings for the device. For example, if the device in the drawing is inverted, the device described as "above other devices or structures" or "over other devices or structures" will then be positioned as "below other devices or structures" or "under other devices or structures". Thus, the exemplary term "above..." can include both the orientations of "above..." and "below...". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and corresponding interpretations should be made for the spatial relative descriptions used here.

[0059] In addition, it should be noted that the use of words such as "first", "second" to limit components is only for the convenience of differentiating the corresponding components. Without additional statements, the above words have no special meanings. Therefore, they should not be construed as limiting the protection scope of the present invention.

[0060] Embodiment 1

[0061] In the existing technology, when studying the interaction between ore pillars and backfill under variable stiffness loading conditions, a conventional uniaxial compression testing machine may be used for simple loading, relying only on some basic mechanical sensors, such as a single pressure sensor, to monitor the axial load. There is a lack of comprehensive and refined monitoring means for the lateral deformation of the backfill, the damage of the joint surface of the ore pillar, and the local strain of the ore pillar. And there may be no integrated device specifically designed for the variable stiffness loading requirement, but rather adjust the loading stiffness in a relatively scattered and temporary way, such as simple methods like replacing gaskets with different stiffnesses.

[0062] In terms of monitoring: Only using conventional mechanical sensors cannot comprehensively capture the multi-dimensional physical information in the interaction process between the ore pillar and the backfill. For example, the lateral deformation of the backfill cannot be monitored in real time, making it difficult to judge the stability change of the backfill during the stress process. Once problems such as lateral expansion and cracking of the backfill occur, it is difficult to detect in time, affecting the assessment of the overall structural stability.

[0063] There is a lack of effective monitoring of the damage of the joint surface of the ore pillar. Since the joint surface of the ore pillar is a key part of stress concentration and potential failure, without monitoring means such as acoustic emission probes, it is impossible to know in advance the damage signs such as cracking and dislocation of the joint surface, increasing the safety hazards in mine exploitation.

[0064] The monitoring of the local strain of the ore pillar is insufficient, and it is impossible to accurately locate the strain change in the local weak area of the ore pillar under complex stress, which is not conducive to taking targeted reinforcement and optimization measures.

[0065] In terms of loading: The method of temporarily adjusting the stiffness by scattered replacement of gaskets is cumbersome to operate and difficult to guarantee the accuracy. Each time a gasket is replaced, the loading device needs to be recalibrated, consuming a lot of time and manpower, and it is difficult to achieve continuous and accurate stiffness changes, unable to simulate the complex and variable actual stress environment in the mine exploitation process, resulting in a large deviation between the test results and the actual working conditions, and it is difficult to effectively guide the mine exploitation design and safe production.

[0066] The loading device and the monitoring system are not organically combined, and each part is relatively independent, making it difficult to synchronize and coordinate the data acquisition and loading process, affecting the test efficiency and data accuracy, and not conducive to in-depth study of the interaction mechanism between the ore pillar and the backfill.

[0067] To solve the existing problems, such as Figures 1-6As shown in the figure, the present invention provides a loading test device for the interaction between ore pillars and backfill under variable stiffness conditions, that is, a device for studying the interaction between ore pillars and backfill under variable stiffness loading conditions. This device is located in a distributed optical fiber and acoustic emission monitoring environment, and it includes a loading device, a lateral confinement cylinder 4, a load conduction column 5, an elastic energy storage device, and a monitoring system and other structures. The specimen is placed inside the lateral confinement cylinder 4, the loading device is located above the lateral confinement cylinder 4, and the elastic energy storage device is placed below the lateral confinement cylinder 4. The specimen is a single ore pillar-backfill specimen or a multi-ore pillar-backfill specimen. The present invention has the advantages of simple operation and low cost, and can realize the flexible loading function with quantifiable stiffness of the testing machine. It can be used in conjunction with existing rock mechanics testing machines to simulate the interaction process between ore pillars and cemented backfill under different stiffness roof and floor loading conditions, and can provide experimental means and methods for studying the reinforcement mechanism of backfill on ore pillars, and clarify the influence mechanism of the backfill on the stress load transfer process between ore pillars.

[0068] The loading device includes a loading cushion plate 1, a ball socket indenter 2, and a ball head indenter column 3. The top of the loading cushion plate 1 is in contact with the top plate of the testing machine. The ball socket indenter 2 is in contact with the loading cushion plate 1. The upper end of the ball head indenter column 3 is connected to the ball socket indenter 2, and the lower end is in contact with the top of the rock specimen in the specimen (single ore pillar-backfill specimen or multi-ore pillar-backfill specimen). The loading device is used to apply a load to the rock specimen. The ball socket indenter 2 and the ball head indenter column 3 can adapt to the fine displacement and angular changes of the specimen to ensure stable loading. Specifically, the loading cushion plate 1 is plate-shaped and is used to contact the top plate of the testing machine to transfer pressure. The ball socket indenter 2 has a spherical groove structure, and one end of the ball head indenter column 3 is a spherical structure. The two cooperate to adapt to a certain angular change of the specimen.

[0069] The bottom end of the rock specimen in the lateral confinement cylinder 4 is in contact with the top end of the load conduction column 5, and the rock specimen and the load conduction column 5 are axially centered. The outer shell of the lateral confinement cylinder 4 is provided with an optical fiber outlet hole. The bottom of the lateral confinement cylinder 4 is provided with a groove communicating with the circular groove, and its diameter is the same as the diameter of the rock specimen. The lateral confinement cylinder 4 provides lateral restraint for the specimen to simulate the actual working conditions of the mine. Specifically, the lateral confinement cylinder 4 is cylindrical, and the groove at the bottom with the same diameter as the rock specimen is used to place the load conduction column 5.

[0070] The elastic energy storage device (variable stiffness loading device) includes an upper pressure plate 6, a cover plate 8, a lower pressure plate 9, disc springs 10, an upper bottom plate 12, a lower bottom plate 13 and a core shaft 11. The upper pressure plate 6, the cover plate 8 and the lower pressure plate 9 are connected in sequence from top to bottom. The top of the upper pressure plate 6 is in contact with the bottom end of the lateral confinement cylinder 4. The load conduction column 5 is installed inside the upper pressure plate 6 and the lateral confinement cylinder 4. The upper pressure plate 6 has a circular groove matching the size of the rock specimen for placing the load conduction column 5 and the load sensor 7. The setting of the load conduction column 5 can ensure the stable placement and uniform stress of the specimen. The load conduction column 5 is installed in the circular groove, and the load sensor 7 is arranged in the circular groove. The load sensor 7 is placed below the load conduction column 5. The center of the circular groove of the upper pressure plate 6 is aligned with the center of the rock specimen, and it is provided with a wire outlet groove for the load sensor. The cover plate 8 is provided with threaded holes and is fixedly connected to the lower pressure plate 9 by bolts. The lower pressure plate 9 is provided with a groove, which is centrosymmetric with the core shaft 11 and can slide relative to each other. In addition, the inner diameter of the groove in the center of the lower pressure plate 9 is equal to the outer diameter of the core shaft 11, and it is nested on the upper end of the core shaft 11. The disc springs 10 are disc-shaped and are combined in different ways of stacking, butting and compounding. Lubricating fluid is applied between the disc springs 10. The disc springs 10 and the upper bottom plate 12 are sleeved on the core shaft 11 together. Among them, the disc springs 10 are sleeved outside the core shaft 11 and are connected between the lower pressure plate 9 and the upper bottom plate 12. The lower end of the core shaft 11 is inserted and connected to the centers of the upper bottom plate 12 and the lower bottom plate 13. The upper bottom plate 12 is provided with threaded holes, and the lower bottom plate 13 is fixedly connected to the upper bottom plate 12 by bolts. In addition, the longitudinal side wall of the upper bottom plate 12 is provided with a guiding hole, and the contact position of the core shaft 11 with the upper bottom plate 12 is provided with a guiding hole. The two guiding holes are communicated and perpendicular to the axial direction of the core shaft 11. The wrench 14 is embedded into the upper bottom plate 12 and the inside of the core shaft 11 through the two guiding holes. The lower bottom plate 13 is fixed on the loading platform of the testing machine by bolts. The variable stiffness loading device realizes stiffness adjustment through different combination methods of the disc springs 10 to meet different test requirements, studies the interaction between the ore pillar and the filling body under variable stiffness loading conditions, and each monitoring component collects data in real time to provide comprehensive and accurate information for the research.

[0071] The monitoring system includes monitoring components such as the equipped load sensor 7, fiber Bragg grating sensor, acoustic emission probe, strain gauge, etc. Each monitoring component is distributed at the corresponding key positions. The axial load is monitored by the load sensor 7 embedded in the circular groove of the upper pressure plate 6. The lateral deformation condition of the filling body is monitored by the fiber Bragg grating sensor buried inside the ore pillar - filling body specimen. The damage and failure condition of the ore pillar joint surface is monitored by the acoustic emission probe attached to the surface of the ore pillar. The local strain of the ore pillar is monitored by the strain gauge attached to the surface of the ore pillar. Each component cooperates with each other and works together.

[0072] Usage method:

[0073] The device of the present invention is used in cooperation with a uniaxial compression testing machine to conduct a flexible loading test on rocks under the constraint of cemented filling bodies.

[0074] A method for testing the instability of rocks under the constraint of cemented backfill, including arranging strain gauges, distributed fiber optic grating sensors and acoustic emission probes in the pillar-backfill specimen, preparing the specimen, determining the instability condition of the specimen according to the complete stress-strain / displacement curve of the rock specimen, combining with the loading stiffness of the testing machine, and then determining the selection range of the stiffness of the variable stiffness loading device. Select a suitable disc spring group to assemble the variable stiffness loading device, place the pillar-backfill specimen and the variable stiffness loading device overlappingly and install a load sensor, adjust the uniaxial compression testing machine, set relevant monitoring and testing machine parameters, and turn on the test equipment at the same time. After the test is completed, a series of steps such as unloading and cleaning the specimen are carried out.

[0075] By cooperating the loading device of the present invention with a uniaxial compression testing machine, a test environment simulating the actual working conditions of a mine is constructed. In this environment, the loading test of the pillar-backfill specimen can be accurately carried out to study their mechanical responses under different stiffness loading conditions. For example, by adjusting the combination mode of the disc springs to change the stiffness of the loading device, it is possible to simulate the different stress states applied to the pillar and the backfill during the mine exploitation process due to factors such as the mining depth and the change of the ore body structure.

[0076] With the help of monitoring means such as the distributed optical fiber, acoustic emission monitoring system and strain gauges in the device, various physical parameter changes of the pillar and the backfill during the test can be comprehensively and real-time obtained. For example, the fiber optic grating sensor monitors the lateral deformation of the backfill, the acoustic emission probe monitors the damage of the joint surface of the pillar, and the strain gauge monitors the local strain of the pillar. These data provide detailed basis for deeply understanding the interaction mechanism between the pillar and the backfill.

[0077] The present invention can be combined with a variety of rock mechanics testing machines, and can test the instability characteristics of the pillar-backfill under different test conditions, study the flexible loading deformation instability of a single pillar specimen and the support response characteristics of the backfill, and the load transfer and transfer mechanism between pillars under the constraint of cemented backfill. The present invention has the characteristics of small occupied space, large stiffness adjustment range, simple processing and production, and low maintenance and repair costs.

[0078] Example 2

[0079] The present invention also provides a method for testing the instability of rocks under the constraint of cemented backfill. Applying the loading test device for the interaction between a pillar and a backfill under variable stiffness conditions of the present invention, the method includes the following steps:

[0080] S1. Prepare the specimen to ensure that it meets the test requirements and can truly simulate the actual structure of ore pillars and backfill in the mine. Strain gauges, distributed fiber optic grating sensors, and acoustic emission probes are arranged in the specimen. These monitoring components will collect various data of the specimen during the test in real time. Among them, the strain gauges are connected to an external strain gauge, the distributed fiber optic grating sensors are connected to an external distributed fiber optic grating demodulator, and the acoustic emission probes are connected to an external acoustic emission instrument.

[0081] S2. According to the post-peak weakening characteristics in the complete stress-strain / displacement curve of the rock specimen (conduct a uniaxial test on the rock specimen before the test to obtain the complete stress-strain / displacement curve), and the loading stiffness of the testing machine, determine the instability condition of the rock specimen (uniaxial compressive strength of the rock), and then determine the stiffness selection range of the variable stiffness elastic energy storage device. For example, if the post-peak weakening modulus of a certain rock specimen failure is m, at this time, adjust the disc spring group in the elastic energy storage device, and combine the disc springs 10 in a superposed, opposed, or composite combination method to make its stiffness around m, which can verify the Cook stiffness criterion, and complete the assembly of the variable stiffness elastic energy storage device with the upper platen 6, lower platen 9, cover plate 8, upper base plate 12, lower base plate 13, and mandrel 11 to ensure that the device can accurately simulate the required stiffness condition.

[0082] S3. According to the "National Standard of the People's Republic of China" GB / T 1972 - 20058, the stiffness calculation formula of the variable stiffness elastic energy storage device is as follows:

[0083] Calculate the stiffness k of the "superposed combination disc spring" variable stiffness elastic energy storage device according to formula (1) 1 . When the disc springs 10 are combined in an opposed combination method, they are assembled into an "opposed combination disc spring" variable stiffness elastic energy storage device.

[0084]

[0085] Calculate the stiffness k of the "opposed combination disc spring" variable stiffness elastic energy storage device according to formula (2) 2 . When the disc springs 10 are combined in an opposed combination method, they are assembled into an "opposed combination disc spring" variable stiffness elastic energy storage device.

[0086]

[0087] Calculate the stiffness k of the "composite combination disc spring" variable stiffness elastic energy storage device according to formula (3) 3 . When the disc springs 10 are combined in a composite combination method, they are assembled into a "composite combination disc spring" variable stiffness elastic energy storage device.

[0088]

[0089] Wherein, E is the elastic modulus of the spring material, f is the deformation of a single-piece spring, μ is the Poisson's ratio, t is the thickness of a single-piece disc spring, K 1 and K 4 are calculation coefficients, D is the outer diameter of the disc spring, h 0 is the calculated value of the deformation when the disc spring is flattened, n is the number of disc springs in the same direction, and i is the number of disc springs facing each other. Specific different disc spring combination forms are as shown in Figure 7 (a), (b), and (c) of

[0090] S4. For the uniaxial compression test, place the specimen and the variable stiffness elastic energy storage device overlappingly, ensure that their axis centers are aligned, and install a load sensor 7 at the bottom of a single ore pillar or multiple ore pillars. Then adjust the uniaxial compression testing machine so that the spherical socket indenter 2 is in close contact with the loading pad 1 to prepare for the start of the test;

[0091] S5. Set the monitoring parameters of the strain gauge, distributed fiber optic grating demodulator, and acoustic emission instrument according to the test requirements, as well as the parameters of the uniaxial compression testing machine, to ensure that each monitoring device and test device can accurately collect data and apply corresponding forces;

[0092] S6. At the same time, turn on the switch button of the uniaxial compression testing machine, the acquisition start button of the strain gauge and the acoustic emission instrument, and the start button of the distributed fiber optic grating demodulator to start the test. Each device works synchronously and collects data in real time;

[0093] S7. After the test is completed, unload the applied load, take out the confining cylinder 4, take out the damaged specimen from the confining cylinder 4, and clean the residual debris of the specimen. The test is over.

[0094] Embodiment 3

[0095] As shown in Figure 6 , a rock uniaxial compression instability testing machine is used to carry out a flexible loading test on an ore pillar under the constraint of a cemented filling body, and study the characteristics of flexible loading deformation instability and filling body support response of the ore pillar specimen. This testing machine is an application of a device for studying the interaction between an ore pillar and a filling body under flexible loading conditions on a conventional uniaxial compression testing machine, and is composed of a conventional rock uniaxial compression testing machine and a loading test device for the interaction between an ore pillar and a filling body under variable stiffness conditions of the present invention.

[0096] Applying a loading test device for the interaction between an ore pillar and a filling body under variable stiffness conditions, the present invention discloses a method for testing the instability of a rock under the constraint of a cemented filling body. The specific implementation scheme is as follows:

[0097] Step 1: Prepare an ore pillar - filling body specimen

[0098] (1) Prepare different numbers of rocks (ore pillars) with a size of Φ50×100 mm according to the test objectives, and place them in the circular grooves at the bottom of the lateral confinement cylinder 4;

[0099] (2) Paste strain gauges and acoustic emission probes on the rock surface, embed fiber Bragg gratings at the bottom of the mold, and there are two fiber optic outlets on the side of the mold for fiber optic extraction. See Figure 3 and Figure 5 shown;

[0100] (3) Weigh according to the ash-sand ratio and mass concentration designed in the test. Put the weighed quantitative tailings and cement into the mixer. After fully stirring the two evenly, add quantitative deionized water until evenly stirred to prepare the cemented filling slurry;

[0101] (4) Pour the prepared cemented filling slurry into the groove of the lateral confinement cylinder 4 blocked by special pads. Then use a stirring rod to vibrate and fully tamp it to ensure the homogeneity of the ore pillar - filling body sample;

[0102] (5) Cover the prepared ore pillar - filling body sample with plastic film for sealing treatment. Grind the sample after curing in the curing box for 24 hours to ensure that there is no eccentricity in the ore pillar. Then put it into the curing box for curing according to the curing age designed in the test, and thus complete the preparation of the ore pillar - filling body sample.

[0103] According to the complete stress - strain / displacement curve of the rock sample, combined with the loading stiffness of the testing machine, determine the conditions for the sample to become unstable, and then determine the stiffness selection range of the variable stiffness elastic energy storage device. This step provides a basis for selecting a suitable disc spring group later.

[0104] Step 2: Assemble the experimental instruments

[0105] Assemble a loading test device for the interaction between an ore pillar and a filling body under variable stiffness conditions. Calculate the number and combination method of the required disc springs 10 according to the stiffness requirements of the simulated roof and floor to be simulated in the test, and complete the assembly of the variable stiffness elastic energy storage device with the upper pressure plate 6, lower pressure plate 9, cover plate 8, upper bottom plate 12, lower bottom plate 13 and core shaft 11 to ensure that the device can accurately simulate the required stiffness conditions. Fix a loading test device for the interaction between an ore pillar and a filling body under variable stiffness conditions on the loading platform of the testing machine with bolts. Among them, select a suitable disc spring group according to the stiffness requirements for instability, and combine the disc springs 10 in a combination of stacking, butting or compounding. Place the prepared ore pillar - filling body on the load conduction column 5.

[0106] Step 3: Adjust the stiffness of the loading test device for the interaction between the ore pillar and the filling under a variable stiffness condition according to the requirements, and conduct uniaxial compression tests under different loads; the principle for selecting the stiffness of the interaction device between the ore pillar and the filling under the flexible loading condition is determined based on the post-peak weakening characteristics of the rock sample under uniaxial compression and the loading stiffness of the testing machine.

[0107] Step 4: For the uniaxial compression test, place the ore pillar - filling specimen and the variable stiffness elastic energy storage device overlappingly (i.e., stacked up and down as shown in Figure 6 ), ensure that their axial centers are aligned, install a load sensor 7 at the bottom of the ore pillar, and then adjust the uniaxial compression testing machine to make the spherical socket indenter 2 in close contact with the loading pad 1 to prepare for the start of the test.

[0108] Step 5: After all the preparatory work is ready, set the monitoring parameters of the strain gauge, distributed fiber optic grating demodulator, and acoustic emission instrument, as well as the parameters of the uniaxial compression testing machine according to the test requirements, to ensure that each monitoring device and test device can accurately collect data and apply the corresponding force.

[0109] Step 6: Simultaneously turn on the switch button of the uniaxial compression testing machine, the acquisition start button of the strain gauge and the acoustic emission instrument, and the start button of the distributed fiber optic grating demodulator to start the formal test. Each device works synchronously to collect data in real time.

[0110] Step 7: After the test is completed, unload the applied load, remove the lateral confinement cylinder 4, take out the damaged ore pillar - filling specimen from the lateral confinement cylinder 4, and clean the residual debris of the specimen.

[0111] Step 8: Use strain gauges to monitor the local stress - strain data of a single ore pillar, and at the same time analyze the damage and failure conditions of the ore pillar joint surface in combination with acoustic emission data; fiber optic grating sensors are buried inside the ore pillar - filling specimen to measure the total lateral deformation of the filling; based on the test results, conduct a comparative analysis of the test results of different stiffness configurations of the interaction device between the ore pillar and the filling under the flexible loading condition and the passive support effects provided by fillings with different strengths, qualitatively and quantitatively analyze the influence of different stiffness ratios, filling rates, and pillar diameters on instability, and further analyze the instability and failure characteristics of the ore pillar under the passive support of the filling.

[0112] Advantages of the present invention:

[0113] I. Overall advantages

[0114] Multi-scenario applicability: The present invention can be used in combination with a variety of rock mechanics testing machines, which greatly broadens its application scope and can simulate different test conditions, thereby testing the instability characteristics of ore pillars - backfill under various working conditions. Whether it is studying the flexible loading deformation instability of single ore pillar specimens, or the support response characteristics of backfill, as well as the load transfer and transfer mechanism between ore pillars under the constraint of cemented backfill, it can be accurately achieved, providing a powerful research tool for different needs in the mining process.

[0115] Space and cost advantages: It has the characteristics of small occupied space. In environments with limited space such as laboratories or mine sites, it can still be conveniently installed and used without occupying too much site resources. At the same time, its processing and manufacturing are simple, without the need for complex and expensive manufacturing processes and equipment, reducing the upfront investment cost. Moreover, the maintenance and repair costs are low. During the subsequent use process, even if problems such as component failures occur, they can be quickly repaired at a low cost, reducing the test stagnation time caused by equipment maintenance and improving the overall work efficiency.

[0116] II. Design advantages or beneficial effects of each technical point

[0117] (1) Distributed optical fiber and acoustic emission monitoring environment:

[0118] Comprehensiveness: Through the distributed optical fiber, the lateral deformation of the backfill can be monitored in real time and continuously, accurately capturing the subtle changes in the backfill during the stress process, and timely discovering potential stability problems such as the expansion and cracking of the backfill, providing key information for mine safety assessment.

[0119] Timeliness: The acoustic emission probe is attached to the surface of the ore pillar, which can sensitively capture the damage of the ore pillar joint surface. Once there are initial damage signs such as cracking and dislocation on the joint surface, it can immediately send a signal, enabling researchers to know in advance and take corresponding measures to effectively prevent further damage to the ore pillar and ensure the safety of mine production.

[0120] (2) Loading device (including loading pad, spherical socket indenter and spherical head indenter column):

[0121] Stability: The loading pad is in close contact with the top plate of the testing machine, ensuring stable pressure transmission and providing a reliable loading basis for the entire test, avoiding uneven loading force caused by poor contact.

[0122] Adaptability: The spherical socket indenter and the spherical head indenter column cooperate to adapt to the small angular changes that may occur at the top of the rock specimen at the initial stage of stress, ensuring that the force acts vertically and evenly on the specimen during the loading process, reducing the impact on the test results caused by a slight deviation in the specimen placement, and improving the accuracy of the test data.

[0123] (3) Lateral confinement cylinder:

[0124] Simulation authenticity: The confined cylinder is cylindrical with a groove at the bottom that is the same diameter as the rock sample, which can provide lateral restraint for the pillar-backfill sample, and its height simulates the actual confined environment of the pillar in mine exploitation, making the test results closer to the real working conditions and helping to accurately study the interaction between the pillar and the backfill under restraint conditions.

[0125] Monitoring convenience: The outer shell of the confined cylinder is provided with an optical fiber outlet hole, which facilitates the connection between the distributed optical fiber and the external demodulator to realize real-time monitoring of the lateral deformation of the backfill, without affecting the overall device structure and ensuring the smooth realization of the monitoring function.

[0126] (4) Elastic energy storage device (including upper pressure plate, cover plate, lower pressure plate, disc spring, upper bottom plate, lower bottom plate and core shaft):

[0127] Stiffness adjustability: The disc springs are combined in different ways such as stacking, butting and compounding, which can flexibly adjust the stiffness of the loading device, easily simulate the variable stress environments faced by the pillar under different stages and different geological conditions during mine exploitation, and provide diverse loading conditions for comprehensively studying the interaction between the pillar and the backfill.

[0128] Assembly convenience: The connection methods of each component are simple and stable. The upper pressure plate contacts the bottom end of the confined cylinder, the lower pressure plate is fixedly connected to the cover plate by bolts, the upper bottom plate and the lower bottom plate are bolted and sleeved on the core shaft, and the lower bottom plate is fixed on the loading platform of the testing machine. This design makes the device assembly convenient and fast, and can be efficiently completed whether in the laboratory setup or on-site temporary modification in the mine, saving time costs.

[0129] Guidance and coordination: The upper bottom plate is provided with a guiding hole, and the contact position between the core shaft and the upper bottom plate is also provided with a guiding hole. The wrench is inserted into the upper bottom plate and the core shaft through the guiding hole, ensuring the orderly relative movement between components during the stress process. The lower pressure plate and the core shaft can slide relative to each other, and each component works in coordination, realizing both the stiffness adjustment function and ensuring the stability and reliability of the entire loading process.

[0130] In the research on the stability of underground engineering: In addition to mine exploitation, similar principles can be used in the research on the interaction between the lining and the surrounding rock of underground projects such as subways and tunnels. During tunnel construction, the stress changes between the filling layer behind the lining and the surrounding rock at different tunneling stages can be simulated. By adjusting the variable stiffness loading device to simulate the process of surrounding rock stress release, and using monitoring means to master the stability of the lining structure in real time, providing a basis for optimizing the tunnel support design and preventing collapse accidents.

[0131] In the field of slope reinforcement engineering simulation: it is used to simulate the interaction between slope reinforcement structures (such as anchor cables, anti-slide piles, etc.) and rock and soil masses. The filling body is analogized as the reinforcement material, and the ore pillar is regarded as the "skeleton" of natural rock and soil masses. Through this device, the influence of the change in the stiffness of the reinforcement structure on the slope stability under working conditions such as earthquakes and rainfall is studied to help determine the optimal reinforcement plan and improve the reliability of slope protection projects.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A loading test device for interaction between pillars and filling bodies under variable stiffness conditions, characterized in that: include: A loading device, a side confinement cylinder (4), a load transmission column (5), an elastic energy storage device and a monitoring system, wherein the sample is placed in the side confinement cylinder (4), the loading device is located above the side confinement cylinder (4), the top of the loading device is in contact with and connected to the top plate of the testing machine, and the bottom is in contact with and connected to the top of the rock sample in the sample; the bottom end of the rock sample is in contact with the top of the load transmission column (5), and the rock sample is aligned with the axial center of the load transmission column (5); The elastic energy storage device comprises a first structure, a disc spring (10), a core shaft (11) and a second structure, wherein the lower part of the second structure is fixed on the loading platform of the testing machine, the lower end of the core shaft (11) is mounted on the second structure, and the upper end is slidably connected to the first structure; the disc spring (10) is sleeved outside the core shaft (11) and is located between the first structure and the second structure, the side limit cylinder (4) is placed on the top of the first structure, and the load transfer column (5) is arranged inside the upper part of the first structure and the lower part of the side limit cylinder (4); The monitoring system is arranged in the sample and the first structure, and the sample is a single-pillar-filling sample or a multi-pillar-filling sample.

2. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1 is characterized in that: The loading device comprises a loading pad (1), a ball-socket pressure head (2) and a ball-head pressure column (3); the top of the loading pad (1) contacts the top plate of the testing machine; the ball-socket pressure head (2) contacts the loading pad (1); one end of the ball-head pressure column (3) is connected to the ball-socket pressure head (2) and the other end contacts the top of the rock sample; wherein the ball-socket pressure head (2) is provided with a spherical groove structure, one end of the ball-head pressure column (3) is a spherical structure, and the spherical structure is connected to the spherical groove structure in a matching manner.

3. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1 is characterized in that: The first structure comprises an upper pressure plate (6), a cover plate (8) and a lower pressure plate (9) which are connected in sequence, the top of the upper pressure plate (6) is in contact with the bottom end of the side limit cylinder (4), the load transfer column (5) is installed inside the upper pressure plate (6) and the side limit cylinder (4), and the lower pressure plate (9) is provided with a groove which is symmetrical with the center of the core shaft (11), and the upper end of the core shaft (11) is slidably connected in the groove.

4. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 3 is characterized in that: The upper pressing plate (6) is provided with a circular groove matching the size of the rock sample, the center of the circular groove is aligned with the center of the rock sample, the load transmission column (5) is installed in the circular groove, a load sensor (7) is arranged in the circular groove, and the load sensor (7) is placed below the load transmission column (5); the upper pressing plate (6) is provided with a load sensor outlet groove; The cover plate (8) is provided with a threaded hole and is fixedly connected to the lower pressing plate (9) by bolts; The inner diameter of the groove of the lower pressing plate (9) is equal to the outer diameter of the upper end of the core shaft (11), and is nested in the upper end of the core shaft (11).

5. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1 is characterized in that: The second structure comprises an upper base plate (12) and a lower base plate (13), wherein the upper base plate (12) is connected to the lower base plate (13), and the lower base plate (13) is fixed on a loading platform of a testing machine, and the lower end of the mandrel (11) is inserted and connected to the upper base plate (12) and the lower base plate (13).

6. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 5 is characterized in that: The upper base plate (12) and the mandrel (11) are connected with a wrench (14), wherein a first guide hole is provided on a longitudinal side wall of the upper base plate (12), and a second guide hole is provided on the mandrel (11) at a position in contact with the upper base plate (12), the second guide hole is communicated with the first guide hole and is perpendicular to the axial direction of the mandrel (11), and the wrench (14) is embedded in the upper base plate (12) and the mandrel (11) through the first guide hole and the second guide hole; The upper base plate (12) is provided with threaded holes and is fixedly connected to the lower base plate (13) by bolts; The lower base plate (13) is fixed on the loading platform of the testing machine by means of bolts.

7. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1 is characterized in that: The outer shell of the side limiting cylinder (4) is provided with an optical fiber outlet hole, and the bottom of the side limiting cylinder (4) is provided with a groove connected to the circular groove, and the diameter of the groove is the same as the diameter of the rock sample.

8. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1 is characterized in that: The disc springs (10) are combined in different ways, such as overlapping, matching and compounding, and lubricating liquid is applied between the disc springs (10).

9. The loading test device for interaction between pillars and filling bodies under variable stiffness conditions according to claim 1, characterized in that: The monitoring system comprises a load sensor (7), a fiber grating sensor, an acoustic emission probe and a strain gauge. The load sensor (7) is embedded in a circular groove of an upper pressure plate (6) of the first structure for detecting an axial load. The fiber grating sensor is buried inside a sample for monitoring the lateral deformation of a filling body. The acoustic emission probe is attached to the surface of a single pillar or multiple pillars for monitoring the damage and destruction of joint surfaces of the single pillar or multiple pillars. The strain gauge is attached to the surface of a single pillar or multiple pillars for monitoring the local strain of the single pillar or multiple pillars.

10. A method for testing the instability of rock under the constraint of cemented filling body, using the loading test device for interaction between pillar and filling body under variable stiffness condition as claimed in any one of claims 1 to 9, characterized in that: The steps include: S1. Prepare a sample and arrange a strain gauge, a distributed fiber Bragg grating sensor and an acoustic emission probe in the sample, wherein the strain gauge is connected to an external strain gauge, the distributed fiber Bragg grating sensor is connected to an external distributed fiber Bragg grating demodulator, and the acoustic emission probe is connected to an external acoustic emission instrument; S2. According to the post-peak weakening characteristics of the full stress-strain / displacement curve of the rock sample and the loading stiffness of the testing machine, the conditions for the instability of the rock sample are determined, and then the stiffness selection range of the variable stiffness elastic energy storage device is determined. By adjusting the disc spring group in the elastic energy storage device, the disc spring (10) is combined in a superimposed, matched or composite combination manner, and the assembly of the variable stiffness elastic energy storage device is completed with the upper pressure plate (6), the lower pressure plate (9), the cover plate (8), the upper bottom plate (12), the lower bottom plate (13) and the core shaft (11), so as to ensure that the device can accurately simulate the required stiffness conditions; S3. The stiffness of the variable stiffness elastic energy storage device is calculated as follows: When the disc springs (10) are combined in a stacking combination, they are assembled into a "stacked combined disc spring" variable stiffness elastic energy storage device. The stiffness k1 of the "stacked combined disc spring" variable stiffness elastic energy storage device satisfies the following formula: When the disc springs (10) are combined in a paired combination manner, they are assembled into a "paired combined disc spring" variable stiffness elastic energy storage device, and the stiffness k2 of the "paired combined disc spring" variable stiffness elastic energy storage device satisfies the following formula: When the disc springs (10) are combined in a composite combination manner, they are assembled into a "composite combined disc spring" variable stiffness elastic energy storage device, and the stiffness k3 of the "composite combined disc spring" variable stiffness elastic energy storage device satisfies the following formula: Where, E is the elastic modulus of the spring material, f is the deformation of the single disc spring, μ is the Poisson's ratio, t is the thickness of the single disc spring, K1 and K4 are calculation coefficients, D is the outer diameter of the disc spring, h0 is the calculated value of the deformation of the disc spring when it is flattened, n is the number of disc springs in the same direction, and i is the number of disc springs in opposite directions; S4. For the uniaxial compression test, the sample and the variable stiffness elastic energy storage device are placed overlappingly to ensure that the axis centers of the two are aligned, and a load sensor (7) is installed at the bottom of the single pillar or multiple pillars, and then the uniaxial compression testing machine is adjusted so that the ball socket pressure head (2) is in close contact with the loading pad (1); S5. Set the monitoring parameters of the strain gauge, distributed fiber Bragg grating demodulator and acoustic emission instrument, as well as the parameters of the uniaxial compression testing machine according to the test requirements; S6. Simultaneously turn on the switch button of the uniaxial compression testing machine, the collection start button of the strain gauge and acoustic emission instrument, and the start button of the distributed fiber Bragg grating demodulator to start the test and collect data in real time; S7. After the test is completed, the applied load is unloaded, the side confinement cylinder (4) is taken out, the damaged sample is taken out from the side confinement cylinder (4), and the residual debris of the sample is cleaned. The test is completed.

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