A three-dimensional similar simulation experiment system and method for super-long working face scale effect

Abstract

This invention relates to the field of physical simulation experiments in mining engineering, and discloses a three-dimensional similarity simulation experimental system and method for the scale effect of ultra-long working faces. The system includes a rigid bearing model box frame, a variable-scale model box body, a stepless adjustment system for the working face strike length, a simulated floor assembly, and a multi-field collaborative monitoring system. The variable-scale model box body contains a fixed reaction wall and a strike-sliding adjustable reaction wall. The adjustment system drives the reaction wall to move and lock via a screw-connected X-shaped rigid pressure equalization component mechanism. The floor assembly includes a detachable floor platform, a coal pillar bearing platform, filling similar materials, and a flexible isolation membrane. This invention achieves continuous stepless adjustment and single-variable control of the working face length within the same system by adjusting the position of the reaction wall in conjunction with floor reconstruction. The pressure equalization mechanism ensures the stability of the active boundary, and the flexible membrane and bottom observation equipment enable full-field visual monitoring of the floor deformation caused by mining.

Description

Technical Field

[0001] This invention relates to the field of physical simulation experiment technology in mining engineering, specifically a three-dimensional similarity simulation experiment system and method for the scale effect of ultra-long working faces. Background Technology

[0002] With the increasing intensity of coal mining, extending the working face length has become a major technical approach to achieve high yield and efficiency. The overburden migration patterns, bearing pressure distribution, and floor failure characteristics of ultra-long working faces exhibit unique scale effects, fundamentally different from conventional working faces. Physical similarity simulation experiments are an important means of revealing the mechanical behavior of such deep rock masses.

[0003] Existing three-dimensional similarity simulation experimental devices generally employ rigid box structures with fixed geometric dimensions. When conducting comparative experimental studies on the working face length effect, it is typically necessary to construct physical models in model boxes of different specifications, and to perform repeated filling and dismantling within the same experimental system. Due to the presence of proportioning errors and differences in curing environments in artificially prepared similar materials, the physical and mechanical properties of different batches of model bodies cannot be completely consistent. This leads to interference from fluctuations in the properties of doped materials in the experimental results, making it impossible to achieve precise control over the single variable of working face length.

[0004] In terms of boundary control for large-scale models, existing devices that use movable sidewalls for spatial adjustment often cannot adapt to high-tonnage lateral earth pressures due to the simple design of the propulsion mechanism. Single-point drive methods are prone to causing unbalanced forces on the movable wall panels, leading to wall attitude deflection and failing to guarantee the verticality and stability of the model boundary.

[0005] Furthermore, traditional 3D model boxes primarily rely on enclosed thick steel plates for passive support at the bottom. While this structure ensures the model's load-bearing capacity, it obstructs the optical observation path at the bottom. During coal seam excavation, the dynamic deformation, crack initiation, and propagation processes of the floor strata remain invisible. Even with internally embedded sensors, only localized discrete data can be acquired, making it impossible to intuitively analyze the spatiotemporal evolution characteristics of the mining floor using non-contact, full-field measurement technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a three-dimensional similarity simulation experimental system and method for the scale effect of ultra-long working faces. It solves the problems of existing three-dimensional similarity simulation experimental devices being unable to flexibly adjust the length of the working face within the same physical system, making it difficult to achieve precise control of a single variable; large-size active boundaries experiencing uneven stress, which can easily lead to deflection and instability; and traditional closed base plate structures hindering full-field visualization monitoring of base plate rock deformation.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of this invention provides a three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces.

[0009] The system includes a rigid load-bearing model box frame, a variable-scale model box body set inside the frame, a stepless adjustment system for the working surface direction length, a simulation base plate assembly, and a multi-field collaborative monitoring system.

[0010] The variable-scale model box body defines an adjustable-length simulated rock strata filling space through the cooperation of fixed reaction walls and strike-slip adjustable reaction walls. The fixed reaction walls are fixedly connected to one side of the rigid load-bearing model box frame, while the strike-slip adjustable reaction walls are located inside the frame and can slide along the strike, thereby changing the effective experimental length of the model box. Inside the variable-scale model box body, rock strata-like materials and loading layer materials are filled layer by layer from bottom to top to simulate the physical and mechanical properties of the overlying rock strata and the vertical load environment of deep strata.

[0011] The stepless adjustment system for the working face length connects the sliding adjustment reaction wall to the rigid bearing model box frame, and is used to drive the reaction wall to move and establish a rigid boundary. The system uses an axial transmission screw in conjunction with a manually driven adjustment handle to achieve power input. To ensure the smooth movement and uniform force distribution of the large-sized reaction wall, an X-shaped rigid pressure equalization mechanism is installed on the back of the sliding adjustment reaction wall. This mechanism is connected to the four corners of the wall through multi-directional hinged anchor seats, converting the axial thrust of the screw into a uniformly distributed surface load, preventing the wall from deflecting or tilting during movement. A double-nut self-locking assembly is sleeved on the axial transmission screw, locking the reaction wall in a predetermined position by eliminating thread backlash to resist the lateral pressure generated inside the model.

[0012] The simulated base plate assembly is designed as a composite structure adaptable to variable-scale adjustments. It includes two coal pillar support platforms rigidly installed on the inner bottom of the fixed reaction wall and the directional sliding adjustment reaction wall, respectively. These two platforms extend in a cantilever shape to support the solid coal pillars at both ends of the model. A detachable base plate platform is arranged through the bottom of the rigid support model box frame. This platform is assembled from several long strip support plates that can be pulled out individually, and its upper surface remains in non-contact with the lower surface of the coal pillar support platform. The gap between the two coal pillar support platforms is filled with a similar filling material. This material automatically adapts to the bottom space after the reaction wall moves due to its bulk flow properties, and after compaction, forms a support surface flush with the coal pillar support platform. A flexible isolation membrane covers the similar filling material and overlaps the coal pillar support platform to support the rock strata similar material above and prevent particulate matter from entering the model's interior.

[0013] The multi-field collaborative monitoring system is used to capture physical parameters during the experiment. Displacement and stress monitoring elements are embedded within the rock strata-like materials and the loading layer materials, forming a three-dimensional monitoring array. Digital image correlation acquisition terminals and supplementary lighting are arranged below the rigid bearing model box frame, acquiring surface deformation images of the bottom rock strata through a flexible isolation membrane. The intelligent analysis system receives image data and calculates the overall displacement and strain distribution. Acoustic emission signal capture probes are arranged on the side wall of the frame to monitor rock strata fracture signals. In addition, the system is also equipped with a similar material slurry mixer and slurry pumping pipeline for auxiliary material transportation.

[0014] A second aspect of the present invention provides a three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces.

[0015] Based on the aforementioned system, this method enables comparative studies of conventional working face length conditions and ultra-long working face length conditions, while maintaining consistency in geological conditions and boundary constraints.

[0016] This method first determines the geometric similarity ratio, bulk density similarity ratio, and stress similarity ratio of the physical model based on the second similarity theorem. Then, the strike-slip adjustment reaction wall is moved to the position of the conventional working face length and locked. Simulated floor components are laid and filled with rock strata similarity materials and loading layer materials to construct the initial physical model. After completing the simulated mining and monitoring under conventional working conditions, the model materials are cleaned, the locking is released, and the strike-slip adjustment reaction wall is moved to the position of the ultra-long working face length. During this process, the flowability of the filling similarity materials is utilized to increase the filling volume to adapt to the expanded coal pillar spacing and maintain the continuity of the floor support surface. Subsequently, the model is reconstructed with the same parameters for a second experiment.

[0017] In the simulated mining process, this method employs a two-step process. The first step involves extracting the load-bearing plate of the detachable base platform corresponding to the current mining location and removing the bottom rigid support. The second step involves clearing away any remaining filling material in the area, creating a free space beneath the flexible isolation membrane. The flexible isolation membrane bends and deforms under the load of the overlying rock strata. A digital image acquisition terminal captures deformation images of the flexible isolation membrane surface through this free space. Combined with internally embedded components and acoustic emission probes, this enables multi-field collaborative monitoring of mine pressure data.

[0018] Finally, by extracting monitoring data under conventional working face length and ultra-long working face length conditions, comparing the periodic pressure step distance, peak support pressure and roof subsidence under the two conditions, and reconstructing the rock fracture evolution coordinates based on acoustic emission data, the influence of working face length on the mine pressure manifestation law and the expansion range of overburden failure field can be quantitatively analyzed.

[0019] This invention provides a three-dimensional similarity simulation experimental system and method for the scale effect of ultra-long working surfaces. It has the following beneficial effects: 1. This invention achieves continuous, stepless adjustment of the working face length by setting up a variable-scale model box body inside a rigid bearing model box frame, and using an axial transmission screw in conjunction with a double-nut self-locking positioning component to drive and lock the sliding adjustment reaction wall. This structure can construct simulated working faces of different lengths within the same physical experimental system, ensuring the consistency of boundary constraints and geological parameters under different working conditions. This effectively isolates the single variable of working face length, facilitating precise analysis of the specific impact of ultra-long working face scale effects on the manifestation of mineral pressure and the characteristics of overburden migration.

[0020] 2. This invention, by setting an X-shaped rigid equalizing force component mechanism and a multi-directional hinged anchor seat on the back of the sliding adjustment reaction wall, transforms the single-point thrust input by the axial transmission screw into a uniformly distributed surface load acting on the four corners of the wall. This design effectively overcomes the deflection and tilting problems that easily occur in large-sized reaction walls during displacement and load-bearing processes, ensuring the verticality and stability of the model boundary when subjected to high-intensity lateral pressure from internal rock strata, and improving the accuracy and data reliability of boundary condition control in physical simulation experiments.

[0021] 3. This invention constructs a simulated floor assembly adaptable to variable-scale adjustments by employing a detachable floor platform that can be individually extracted, combined with a flexible isolation membrane supporting similar filling materials. This is further integrated with a digital image acquisition terminal located below, forming a non-contact observation window. This configuration, while simulating the coal seam excavation and unloading process, utilizes the characteristic of the flexible isolation membrane deforming synchronously with the rock strata, solving the problem of intuitive, full-field monitoring of floor strata deformation in traditional three-dimensional similarity simulation experiments. It achieves real-time capture and quantitative analysis of the displacement and strain fields of the mining-induced floor. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the front view cross-sectional structure of the three-dimensional similarity simulation experimental system and method for studying the scale effect of ultra-long working surfaces according to the present invention. Figure 2 This is a schematic diagram of the main structure of the variable-scale model box of the present invention; Figure 3 This is a side view cross-sectional structural diagram of the three-dimensional similarity simulation test bench excavation process according to the present invention; Figure 4 This is a flowchart of the three-dimensional similarity simulation experimental method for studying the scale effect of ultra-long working surfaces according to the present invention.

[0023] The components include: 1. Rigid bearing model box frame; 2. Fixed reaction wall; 3. Horizontal sliding adjustment reaction wall; 4. Axial transmission screw; 5. X-type rigid equalizing force component mechanism; 6. Multi-directional hinged anchor seat; 7. Double nut self-locking positioning assembly; 8. Manually driven adjustment handle; 9. Rock stratum similar material; 10. Loading layer material; 11. Displacement stress monitoring element; 12. Digital image correlation acquisition terminal; 13. Intelligent analysis system; 14. Supplementary lighting; 15. Similar material slurry mixer; 16. Slurry pumping pipeline; 17. Acoustic emission signal capture probe; 18. Coal pillar bearing platform; 19. Demountable base plate platform; 20. Filling with similar material; 21. Flexible isolation membrane. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] See attached document Figure 1 This invention provides a three-dimensional similarity simulation experimental system for studying the scale effect of ultra-long working surfaces. The three-dimensional similarity simulation experimental system for studying the scale effect of ultra-long working surfaces mainly includes: a rigid bearing model box frame 1, a variable scale model box body set inside the rigid bearing model box frame 1, a simulation base plate assembly laid at the bottom of the variable scale model box body, and a multi-field collaborative monitoring system.

[0026] The rigid bearing model box frame 1 constitutes the basic support structure of the entire experimental system. The variable-scale model box body is located above and inside the rigid bearing model box frame 1, and is configured to define the filling space of the simulated rock strata. The variable-scale model box body includes a fixed reaction wall 2 and a strike-sliding adjustable reaction wall 3. The fixed reaction wall 2 is fixedly connected to one side of the rigid bearing model box frame 1. The strike-sliding adjustable reaction wall 3 is located inside the rigid bearing model box frame 1 and is configured to slide horizontally along the strike direction of the working surface, thereby changing the effective experimental length of the model box.

[0027] The system also includes a stepless adjustment system for the working face length, configured to drive the sliding adjustment reaction wall 3 to move and lock its position. The stepless adjustment system for the working face length includes: an axial drive screw 4, an X-type rigid equalizing force mechanism 5, a multi-directional hinged anchor 6, a double-nut self-locking assembly 7, and a manually driven adjustment handle 8. The axial drive screw 4 passes through the center of the side wall of the rigid bearing model box frame 1. One end of the axial drive screw 4 is located outside the rigid bearing model box frame 1 and connected to the manually driven adjustment handle 8. The other end of the axial drive screw 4 extends into the interior of the rigid bearing model box frame 1. The X-type rigid equalizing force mechanism 5 is located on the back of the sliding adjustment reaction wall 3, and its cross center is hinged to the inner end of the axial drive screw 4. The four endpoints of the X-type rigid equalizing force mechanism 5 are anchored to the four corner areas of the back of the sliding adjustment reaction wall 3 via the multi-directional hinged anchor 6. The double-nut self-locking assembly 7 is sleeved on the axial transmission screw 4 and located on the inner and outer sides of the side wall of the rigid bearing model box frame 1.

[0028] The simulated floor assembly is configured as a bearing model to simulate the mining process. The simulated floor assembly includes: a coal pillar bearing platform 18, a detachable floor platform 19, a similar filling material 20, and a flexible isolation membrane 21. The coal pillar bearing platform 18 is rigidly installed on the inner bottom of the fixed reaction wall 2 and the inner bottom of the directional sliding adjustment reaction wall 3, extending cantileveredly into the box. The detachable floor platform 19 is arranged through the bottom of the rigid bearing model box frame 1 and is located directly below the coal pillar bearing platform 18. The similar filling material 20 is laid on the detachable floor platform 19 between the two coal pillar bearing platforms 18. The flexible isolation membrane 21 covers the similar filling material 20, with both ends of the flexible isolation membrane 21 overlapping the coal pillar bearing platform 18.

[0029] The system is filled with rock-like material 9 and loading layer material 10. A multi-field collaborative monitoring system is configured to monitor physical parameters during the experiment. The multi-field collaborative monitoring system includes: displacement and stress monitoring elements 11 embedded in the rock-like material 9 and loading layer material 10; a digital image correlation acquisition terminal 12 arranged below the rigid bearing model box frame 1; an intelligent analysis system 13 connected to the digital image correlation acquisition terminal 12; a supplementary light 14 providing illumination for the digital image correlation acquisition terminal 12; and an acoustic emission signal capture probe 17 arranged on the side wall of the rigid bearing model box frame 1. The system is also equipped with a similar material slurry mixer 15 and a slurry pumping pipeline 16 for transporting the rock-like material 9.

[0030] The system's physical model parameters are determined based on the second similarity theorem. The system is based on geometric similarity ratio. Similarity ratio of bulk density and stress similarity ratio Build.

[0031] Geometric similarity ratio Defined as: ; In the formula, Indicates the geometric length of the model; This represents the geometric length of the prototype. In this embodiment, Set to 1:400.

[0032] Bulk density similarity ratio Defined as: ; In the formula, Indicates the density of the model material; This represents the unit weight of the prototype rock stratum. In this embodiment, Set to 1:1.6.

[0033] Stress similarity ratio By geometric similarity ratio Similarity to bulk density Export, defined as: ; In this embodiment, The calculated value is 1:640.

[0034] See attached document Figure 1 and attached Figure 2 The present invention provides a three-dimensional similarity simulation experimental system for studying the scale effect of ultra-long working surfaces. The system includes a variable-scale model box main structure, which is configured to provide a visualized, length-adjustable experimental space.

[0035] The main structure of the variable-scale model box is constructed based on a rigid load-bearing model box frame 1. The rigid load-bearing model box frame 1 is assembled by welding high-strength channel steel, and its bottom is fixedly installed on a support base. The left side wall of the rigid load-bearing model box frame 1 is set as a closed fixed reaction wall 2, while the right side of the rigid load-bearing model box frame 1 is set as an open structure.

[0036] The main structure of the variable-scale model box includes a sliding adjustment reaction wall 3 located inside the rigid load-bearing model box frame 1. The sliding adjustment reaction wall 3 is configured as the right movable boundary of the model box. The external dimensions of the sliding adjustment reaction wall 3 are adapted to the internal cross-sectional dimensions of the rigid load-bearing model box frame 1. The sliding adjustment reaction wall 3 can slide horizontally along the length direction of the rigid load-bearing model box frame 1, i.e., the direction of the simulated working surface.

[0037] The system also includes a stepless adjustment system for the working face length, which connects the sliding adjustment reaction wall 3 to the rigid bearing model box frame 1. The stepless adjustment system for the working face length includes: an axial transmission screw 4, an X-type rigid equalizing force component mechanism 5, a multi-directional hinged anchor seat 6, a double-nut self-locking positioning assembly 7, and a manually driven adjustment handle 8.

[0038] The axial drive screw 4 adopts a T-shaped trapezoidal thread structure. The axial drive screw 4 passes through the central through hole of the right side panel of the rigid load-bearing model box frame 1. The first end of the axial drive screw 4 is located outside the rigid load-bearing model box frame 1 and is fixedly connected to the manually driven adjustment handle 8. The second end of the axial drive screw 4 extends into the internal space of the rigid load-bearing model box frame 1.

[0039] The X-type rigid equalizing force mechanism 5 is arranged on the side of the sliding adjustment reaction wall 3 away from the model filling area. The X-type rigid equalizing force mechanism 5 includes cross-connected rigid links. The cross center node of the X-type rigid equalizing force mechanism 5 is hinged to the second end of the axial drive screw 4 via a bearing component. The bearing component is configured to allow the axial drive screw 4 to rotate relative to the X-type rigid equalizing force mechanism 5 while transmitting axial thrust or tension.

[0040] There are four multi-directional hinged anchor seats 6. The four multi-directional hinged anchor seats 6 are fixedly installed at the four corner points of the rectangular area on the back of the sliding adjustment reaction wall 3. The four ends of the X-type rigid equalizing force component mechanism 5 are respectively connected to the four multi-directional hinged anchor seats 6 through multi-directional hinges.

[0041] The double-nut self-locking assembly 7 includes a first locking nut and a second locking nut. Both the first and second locking nuts are threaded onto the axial transmission screw 4. The first locking nut is located on the inner surface of the right side panel of the rigid load-bearing model box frame 1. The second locking nut is located on the outer surface of the right side panel of the rigid load-bearing model box frame 1.

[0042] During operation, the axial drive screw 4 is rotated by rotating the manually driven adjusting handle 8. The axial force generated by the axial drive screw 4 is transmitted to the center of the X-type rigid equalizing force mechanism 5. The X-type rigid equalizing force mechanism 5 decomposes the received single-point axial force into four component forces. The four component forces act synchronously on the four corner points of the directional sliding adjustment reaction wall 3 through four multi-directional hinged anchor seats 6. This force transmission structure ensures that the directional sliding adjustment reaction wall 3 remains vertical during sliding, preventing tilting or jamming.

[0043] After the sliding adjustment reaction wall 3 is adjusted to the predetermined position, tighten the first locking nut to make it press against the inner wall of the rigid bearing model box frame 1, and tighten the second locking nut to make it press against the outer wall of the rigid bearing model box frame 1. Utilizing the mechanical self-locking characteristics of the threaded pair and the clamping effect of the double nuts on the sidewalls, the gap between the axial transmission screw 4 and the mating hole is eliminated, thereby constructing a rigid lateral experimental boundary to resist the lateral earth pressure generated inside the model.

[0044] See attached document Figure 2 and attached Figure 3 The present invention provides a composite base plate and lateral bearing structure, the structure being configured to maintain the stability of the coal pillar boundary under variable scale conditions and to simulate the mining process.

[0045] The composite base plate and lateral bearing structure mainly consist of a coal pillar bearing platform 18, a detachable base plate platform 19, a similar filling material 20, and a flexible isolation membrane 21. The structure is located in the bottom area of ​​the rigid bearing model box frame 1 and inside the variable-scale model box body.

[0046] The coal pillar support platform 18 is constructed as a rigid cantilever structure. There are two coal pillar support platforms 18. One coal pillar support platform 18 is rigidly fixed to the inner bottom surface of the fixed reaction wall 2. The other coal pillar support platform 18 is rigidly fixed to the inner bottom surface of the sliding adjustment reaction wall 3. Both coal pillar support platforms 18 extend horizontally into the interior space of the model box. The vertical position of the coal pillar support platform 18 is higher than the bottom reference plane of the rigid support model box frame 1, creating a predetermined accommodating space between the lower surface of the coal pillar support platform 18 and the bottom of the box. The coal pillar support platform 18 is configured to support the solid coal pillars at both ends of the model, ensuring that the solid coal pillars remain relatively stationary relative to the reaction walls to which they are attached during the experiment, and do not shift with the movement of the bottom components.

[0047] A detachable base platform 19 is positioned directly beneath the coal pillar support platform 18. The detachable base platform 19 is composed of several long, strip-shaped support plates closely arranged and assembled along the model's orientation. The length of each long, strip-shaped support plate exceeds the maximum design length of the rigid support model box frame 1. The detachable base platform 19 extends along the entire bottom length of the rigid support model box frame 1. Horizontal passages for the detachable base platform 19 are provided at the bottom of both the fixed reaction wall 2 and the orientation-sliding adjustment reaction wall 3.

[0048] The detachable base platform 19 is configured to be pulled out horizontally. The upper surface of the detachable base platform 19 maintains a non-contact or sliding contact with the lower surface of the coal pillar support platform 18, so that the removal of the detachable base platform 19 will not cause the coal pillar support platform 18 to move due to friction.

[0049] A similar filling material 20 is laid on the upper surface of the removable base platform 19. Specifically, the laying area is located in the interval between the fixed-side coal pillar support platform 18 and the movable-side coal pillar support platform 18. The similar filling material 20 is a free-flowing granular material.

[0050] The filling material 20 is compacted and leveled. The thickness of the filling material 20 is controlled so that the upper surface of the compacted filling material 20 is in the same horizontal geometric plane as the upper surface of the coal pillar support platforms 18 on both sides. The filling material 20 uses the fluidity of bulk materials to fill the height difference between the detachable bottom plate platform 19 and the coal pillar support platform 18, and automatically adapts to the horizontal distance between the two platforms changed by the movement of the reaction wall 3 adjusted by the directional sliding.

[0051] A flexible isolation film 21 is laid flat over the filling similar material 20. The two sides of the flexible isolation film 21 overlap and support the upper surfaces of the coal pillar support platforms 18 on both sides. The flexible isolation film 21 is configured to support the rock stratum similar material 9 above and prevent the filling similar material 20 particles from entering the interior of the model rock stratum.

[0052] During the simulated mining experiment, a single strip plate in the detachable bottom plate platform 19 was extracted and the corresponding filling material 20 above the strip plate was cleaned up, forming a free space under the flexible isolation film 21, thereby simulating the bending, delamination and collapse behavior of the roof rock strata of the working face after losing support.

[0053] See attached document Figure 1 and attached Figure 3 This invention provides a multi-field collaborative monitoring and assisted loading system, which is configured to capture the physical parameters of the interior and surface of simulated rock strata in real time, and to prepare and transport model materials.

[0054] The multi-field collaborative monitoring and auxiliary loading system includes a displacement stress monitoring element 11. The displacement stress monitoring element 11 is pre-embedded in specific strata within the rock-similar material 9 and the loading layer material 10. The displacement stress monitoring element 11 is connected to an external data acquisition instrument via a signal transmission cable. The displacement stress monitoring element 11 is configured to directly measure the vertical stress changes and internal displacement settlement values ​​of rock strata at different depths within the model during the mining process.

[0055] The system includes a non-contact optical monitoring component based on digital image correlation technology. The component includes a digital image correlation acquisition terminal 12, an intelligent analysis system 13, and a supplementary light 14. The digital image correlation acquisition terminal 12 is disposed in the space below the bottom of the rigid load-bearing model box frame 1, with its lens optical axis vertically upward aligned with the bottom surface of the flexible isolation film 21. The supplementary light 14 is arranged adjacent to the digital image correlation acquisition terminal 12 and configured to provide a uniform illumination field to the bottom surface of the flexible isolation film 21.

[0056] The digital image correlation acquisition terminal 12 is configured to continuously acquire speckle images of the surface of the bottom rock strata through a transparent or semi-transparent flexible isolation film 21. The intelligent analysis system 13 is signal-connected to the digital image correlation acquisition terminal 12 and is configured to receive image data and calculate the full-field displacement and strain distribution cloud map, thereby monitoring the fracture and migration characteristics of the bottom rock strata of the working face.

[0057] The system includes an acoustic emission monitoring component. This component consists of several acoustic emission signal capturing probes 17. These probes 17 are coupled to the metal surface of the side wall of the rigid load-bearing model box frame 1, or extend into the interior of the rock-like material 9 via waveguide rods. The acoustic emission signal capturing probes 17 are configured to capture the elastic wave signals released during the fracture of the rock material, used to analyze the energy release pattern of the model rock fracture and to locate the seismic source in three dimensions.

[0058] The system also includes auxiliary loading and material delivery components, mainly consisting of a similar material slurry mixer 15 and a slurry pumping pipeline 16. The similar material slurry mixer 15 is configured to mix aggregates, binders, and water in a predetermined ratio to form a slurry-like similar material. One end of the slurry pumping pipeline 16 is connected to the outlet of the similar material slurry mixer 15, and the other end extends to the upper interior of the variable-scale model box body. The slurry pumping pipeline 16 is configured to transport the uniformly mixed slurry into the box body for layered casting to construct the rock strata similar material 9.

[0059] See attached document Figure 4 This invention provides a method for determining similarity parameters and planning operating conditions, which is executed as the basic step S1 of the entire experimental process. The method includes determining the key parameters of the physical model based on the second similarity theorem and planning different working surface lengths for comparative experiments.

[0060] Key parameters include geometric similarity ratio Similarity ratio of bulk density and stress similarity ratio The process of determining the parameters follows the mathematical definitions below: Geometric similarity ratio Defined as the ratio of the model's geometric length to the prototype's geometric length, the formula is as follows: ; In the formula, Indicates the geometric length of the model; This indicates the geometric length of the prototype. This scale determines the scaling relationship between the laboratory model dimensions and the actual engineering dimensions.

[0061] Bulk density similarity ratio Defined as the ratio of the unit weight of the model material to the unit weight of the prototype rock layer, the formula is as follows: ; In the formula, Indicates the density of the model material; This indicates the unit weight of the prototype rock layer. This ratio guides the selection of proportions for similar materials.

[0062] Stress similarity ratio According to the second theorem of similarity, by geometric similarity ratio Similarity to bulk density The product is derived from the following formula: ; This ratio is used to convert the load applied by the model to the actual formation stress.

[0063] Based on the determined similarity ratio parameter, the method plans two experimental conditions with significant scale differences: the conventional working face length condition L1 and the ultra-long working face length condition L2.

[0064] The working face length corresponding to the standard working face length condition L1 is set as follows: Based on geometric similarity ratio ,when When the value is set to 1000mm, the corresponding simulated prototype working surface length is 400m. This working condition serves as the benchmark reference group for scale effect analysis.

[0065] The working face length corresponding to the L2 working condition with an ultra-long working face length is set as follows: Based on geometric similarity ratio ,when When the value is set to 2250 mm, the corresponding simulated prototype working surface length is 900 m. This working condition is used as the experimental group of variables for scale effect analysis.

[0066] The working condition planning clearly defines two specific target positions that need to be adjusted in the main body of the variable-scale model box during the experiment. The conventional working face length working condition L1 and the ultra-long working face length working condition L2 will be realized sequentially within the same rigid bearing model box frame 1 by adjusting the reaction wall 3 by moving the direction of sliding. At the same time, other geological condition parameters (including the friction coefficient of the bottom plate, the physical and mechanical properties of the rock strata, and the boundary constraint conditions) will be kept consistent except for the working face length, so as to ensure the principle of single variable and provide comparable basic data for subsequent analysis of the influence of working face length on the manifestation law of mine pressure.

[0067] See attached document Figure 1 Appendix Figure 2 and attached Figure 4 This invention provides a three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces, which corresponds to step S2 in the experimental process.

[0068] Step S2 first performs a mechanical adjustment operation to set the effective experimental length of the model box. The operator rotates the manual drive adjustment handle 8, driving the axial transmission screw 4 to rotate. The axial transmission screw 4 transmits the axial thrust to the sliding adjustment reaction wall 3 through the X-shaped rigid equalizing force mechanism 5. After being subjected to force, the sliding adjustment reaction wall 3 translates along the internal guide rail of the rigid bearing model box frame 1. When the sliding adjustment reaction wall 3 moves to the pre-planned conventional working surface length condition L1 position, that is, the working surface length of the model... When in this situation, stop rotating the manually driven adjustment handle 8.

[0069] Subsequently, a boundary locking operation is performed. The first locking nut located on the inner side of the rigid load-bearing model box frame 1 and the second locking nut located on the outer side are rotated, causing the double-nut self-locking assembly 7 to tightly clamp the side wall plate of the rigid load-bearing model box frame 1. Through the mechanical self-locking action of the double nuts, the axial movement backlash of the axial transmission screw 4 is eliminated, and the sliding adjustment reaction wall 3 is rigidly fixed to the boundary. The location was used to construct a closed and stable lateral boundary for the experimental space.

[0070] After determining the boundary positions, the composite base plate laying operation is performed. Several long strip-shaped bearing plates of the detachable base plate platform 19 are passed one by one through the reserved channel at the bottom of the rigid bearing model box frame 1, and tightly spliced ​​on the horizontal plane to form a continuous bearing surface that runs through the bottom of the model box. In the area between the coal pillar bearing platform 18 connected to the fixed reaction wall 2 and the coal pillar bearing platform 18 connected to the directional sliding adjustment reaction wall 3, a similar filling material 20 is laid on top of the detachable base plate platform 19.

[0071] The laid similar filling material 20 is compacted and leveled. A leveling tool is used to smooth the upper surface of the similar filling material 20, ensuring it is at the same level as the upper surfaces of the coal pillar support platforms 18 on both sides, forming a continuous and flat reference surface. Next, a flexible isolation film 21 is laid above the reference surface. The flexible isolation film 21 is ensured to completely cover the similar filling material 20, with both ends extending and flattened on the upper surfaces of the coal pillar support platforms 18 on both sides, thereby establishing a flexible isolation interface between the model rock layer and the bottom mechanical structure.

[0072] Finally, the model material filling and sensor installation operations were performed. The similar material mixing machine 15 was started to prepare the slurry, which was then pumped to the top of the flexible isolation membrane 21 via the slurry pumping pipeline 16. Following the designed rock strata sequence, the rock strata similar material 9 was poured layer by layer from bottom to top. During the pouring process, the displacement stress monitoring element 11 was embedded into the rock strata similar material 9 according to predetermined coordinates. Simultaneously, the acoustic emission signal capture probe 17 was installed at the predetermined monitoring position. After the rock strata similar material 9 had cured and dried, the loading layer material 10 was laid on top, completing the physical model construction of the initial working condition L1.

[0073] See attached document Figure 3 and attached Figure 4 This invention provides a two-step mining and monitoring method, which corresponds to step S3 in the experimental process and is configured to simulate the coal seam excavation process and simultaneously record the rock strata response characteristics.

[0074] The three-dimensional similarity simulation experimental method for the scale effect of ultra-long working faces advances the simulated working face sequentially step by step according to a predetermined excavation step. The simulation operation of each excavation step includes two consecutive physical steps: the step of extracting the rigid bottom plate strip and the step of cleaning the flexible backfill material.

[0075] In the step of removing the rigid base plate strip, the operator selects the strip bearing plate of the single detachable base plate platform 19 corresponding to the current simulated mining position. Force is applied horizontally outwards to completely remove the strip bearing plate from the bottom of the rigid bearing model box frame 1. This operation removes the rigid vertical support boundary at the bottom of the current mining area, but the space above is still occupied by similar filling material 20.

[0076] Immediately afterwards, the flexible backfill material was removed. Within the channel space created after the strip support plate was removed, the remaining backfill material 20 above the original support plate was cleared. By physically removing these loose particles, a suspended free space was created below the flexible isolation membrane 21. At this point, the flexible isolation membrane 21 lost its bottom support in this area and, under the weight and load of the upper rock stratum similar material 9, bent downwards, thus simulating the change in mechanical boundary conditions after the working face roof loses coal seam support during actual mining.

[0077] While performing the aforementioned two-step mining operation, the multi-field collaborative monitoring system operates synchronously. The digital image correlation acquisition terminal 12, through the opening exposed at the bottom of the rigid bearing model box frame 1 due to the removal of the plates, and with the illumination aid of the supplementary light 14, continuously captures a sequence of speckle images of the bottom surface of the flexible isolation film 21. Since the flexible isolation film 21 is in close contact with the bottom surface of the rock-similar material 9, this image sequence reflects the real-time displacement and strain field evolution of the simulated rock stratum floor.

[0078] The intelligent analysis system 13 receives image data from the digital image correlation acquisition terminal 12, uses digital image correlation algorithms to calculate the full-field displacement and strain distribution cloud map, and quantitatively analyzes the settlement and deformation characteristics of the rock stratum floor. At the same time, the displacement stress monitoring element 11 embedded in the model outputs the vertical stress value and internal displacement value of each measuring point in real time, and records the distribution range and peak position of the advance support pressure.

[0079] Acoustic emission signal capture probe 17 continuously monitors the elastic wave signals generated inside the similar rock material 9 throughout the mining process. By analyzing the ring count, energy rate, and three-dimensional positioning coordinates of the acoustic emission signals, the spatiotemporal evolution law of fracture initiation, propagation, and penetration within the model rock strata is determined. The system summarizes the monitoring data from the above different physical fields along a unified time axis to complete the mining simulation and data recording under the current working conditions.

[0080] See attached document Figure 4 This invention provides a three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces. The method corresponds to steps S4 and S5 in the experimental process. It is configured to realize the conversion from the conventional working surface length condition L1 to the ultra-long working surface length condition L2 within the same experimental system, and to ensure the effectiveness of the comparative experiment.

[0081] After completing all mining and monitoring tasks for the conventional working face length L1, the first step was to clean up the experimental waste and reposition the bottom plate. The experimentally removed fractured rock strata similar material 9, loading layer material 10, and used flexible isolation membrane 21 were completely removed from the variable-scale model box body. The remaining filling similar material 20 at the bottom was cleaned up. Subsequently, the long strip bearing plate of the previously removed detachable bottom plate platform 19 was reinserted and laid flat at the bottom of the rigid bearing model box frame 1, restoring its full-length continuity and constructing a continuous bottom boundary for the next experiment.

[0082] Next, perform the dimensional adjustment operation. Loosen the double-nut self-locking assembly 7 located on the inner and outer sides of the rigid load-bearing model box frame 1 to release the axial lock on the axial transmission screw 4. The operator rotates the manual drive adjustment handle 8, driving the sliding adjustment reaction wall 3 to move away from the fixed reaction wall 2 along the guide rail. Continue adjusting until the sliding adjustment reaction wall 3 reaches the predetermined ultra-long working surface length L2 position, i.e., the working surface length of the model. At this point, tighten the double-nut self-locking assembly 7 again to lock the sliding adjustment reaction wall 3 into the new position.

[0083] After completing the scaling adjustment, a model reconstruction operation under single-variable control is performed. Between the fixed reaction wall 2 and the shift-adjustment reaction wall 3, which has been moved to a new position, a similar filling material 20 is re-laid above the detachable base platform 19. During this process, the total amount of similar filling material 20 is increased to accommodate the expanded coal pillar spacing due to the increased working face length. The similar filling material 20 is compacted and leveled so that its upper surface is once again at the same horizontal reference plane as the upper surfaces of the coal pillar bearing platforms 18 on both sides.

[0084] The variable-scale reconstruction process follows a strict single-variable control principle. During the transition from working condition L1 to working condition L2, the foundation position of the rigid bearing model box frame 1, the material and surface friction coefficient of the detachable base platform 19, the installation position of the coal pillar bearing platform 18 relative to its respective reaction wall, and the monitoring geometry of the multi-field collaborative monitoring system all remain unchanged. The unchanged physical parameters are the position of the directional sliding adjustment reaction wall 3 and the filling volume of the similar material 20. This control method ensures the consistency of the base plate boundary conditions and eliminates systematic errors introduced by replacing the experimental platform or rebuilding the base plate.

[0085] Finally, within the adjusted experimental space, following the exact same material ratio, layer thickness, and process flow as working condition L1, similar rock strata material 9 was refilled and displacement stress monitoring elements 11 were installed to construct a physical model suitable for working condition L2. Subsequently, the experiment was repeated according to the two-step mining process and monitoring flow to obtain mine pressure manifestation data under ultra-long working face conditions.

[0086] See attached document Figure 4 This invention provides a three-dimensional similarity simulation experimental method for the scale effect of ultra-long working faces. The three-dimensional similarity simulation experimental method for the scale effect of ultra-long working faces corresponds to step S6 in the experimental process. It is configured to quantitatively analyze the influence of working face length on the mine pressure manifestation law based on the monitoring data of conventional working face length condition L1 and ultra-long working face length condition L2.

[0087] The three-dimensional similarity simulation experiment method for the scale effect of ultra-long working faces first performs data extraction and feature recognition operations. The full-process monitoring records of the conventional working face length condition L1 and the ultra-long working face length condition L2 are retrieved from the database stored in the intelligent analysis system 13. Based on the stress-time curve output by the displacement stress monitoring element 11 and the roof collapse image sequence recorded by the digital image correlation acquisition terminal 12, the specific time of each period of pressure and the corresponding excavation advance distance are identified. According to the identification results, the average periodic pressure step distance, average peak support pressure, and maximum roof subsidence are statistically obtained for both working conditions.

[0088] A three-dimensional similarity simulation experiment method for the scale effect of ultra-long working faces was used to calculate the dynamic load factor to assess the risk of rockburst. For each periodic rockburst event, the dynamic load factor was calculated based on the vertical stress data recorded by the displacement stress monitoring element 11. Dynamic load factor The calculation formula is defined as follows: ; In the formula, This represents the peak vertical stress recorded at the monitoring point during the period of cyclic pressure application; This represents the average vertical stress recorded at monitoring points during the non-pressure stabilization phase. By comparing the two operating conditions... The distribution characteristics of the values ​​are used to determine whether an increase in the length of the working face leads to an aggravation of the dynamic load manifestation.

[0089] A three-dimensional similarity simulation experiment method for the scale effect of ultra-long working faces was used to calculate the rate of change of the scale effect to quantify parameter differences. The periodic pressure step distance, peak bearing pressure, and cumulative acoustic emission energy were selected as key evaluation indicators, and the rate of change of each indicator when transitioning from a conventional scale to an ultra-long scale was calculated. Rate of change The calculation formula is defined as follows: ; In the formula, This represents the value of a certain physical and mechanical property under the working condition L2 with an ultra-long working face; This represents the value of the corresponding physical and mechanical properties under the conventional working face length condition L1. If... A positive value indicates that the index increases with the length of the working face; if... A negative value indicates that the index decreases as the working face length increases.

[0090] A three-dimensional similarity simulation experiment method for the scale effect of ultra-long working faces was used to comprehensively analyze acoustic emission three-dimensional localization data. Source coordinate data recorded by acoustic emission signal capture probe 17 were used to reconstruct the evolution trajectory of rock fractures in three-dimensional space. By comparing the distribution height and concentration area of ​​high-energy source events in the overlying strata of the goaf under two working conditions, the differences in the strike and dip extent of the overlying strata failure field under ultra-long working face conditions were determined.

[0091] The three-dimensional similarity simulation experiment method for the scale effect of ultra-long working faces ultimately generates a scale effect analysis report based on the above calculation results. The report establishes the mapping relationship between the length of the working face and the mine pressure parameters, clarifies the special motion form of the roof structure and the variation law of stress field distribution under ultra-long working face mining conditions, and provides quantitative experimental basis for the selection of supports and the design of roadway support in actual engineering ultra-long working faces.

[0092] See attached document Figure 1 - Appendix Figure 4 This invention provides a specific application scenario parameter example, which demonstrates the specific parameter settings for simulating coal seam mining at a depth of 600 meters using the system.

[0093] The application scenario is based on a defined physical simulation similarity criterion. A geometric similarity ratio is set. The ratio is 1:400. The bulk density similarity ratio is set. The ratio is 1:1.6. The stress similarity ratio is set as follows: The ratio is 1:640. The time similarity ratio is set. The ratio is 1 to 20.

[0094] The physical dimensions of the main structure of the variable-scale model box are set to meet the requirements for boundary effect elimination. The internal net width of the rigid load-bearing model box frame 1 is set to 1000 mm. The maximum internal net height of the rigid load-bearing model box frame 1 is set to 1500 mm. For the standard working face length L1, the sliding adjustment reaction wall 3 is locked at a horizontal distance of 1000 mm from the fixed reaction wall 2, corresponding to a simulated prototype working face length of 400 meters. For the ultra-long working face length L2, the sliding adjustment reaction wall 3 is locked at a horizontal distance of 2250 mm from the fixed reaction wall 2, corresponding to a simulated prototype working face length of 900 meters.

[0095] The proportions of the rock strata similarity material 9 are determined based on the physical and mechanical properties of the target rock strata. For fine sandstone strata, a mixture of aggregate and cementitious agent in a mass ratio of 7:3 is used, where the aggregate is river sand with a particle size of 0.5 mm to 1.0 mm, and the cementitious agent consists of gypsum and calcium carbonate in a mass ratio of 2:1. For sandy mudstone strata, a mixture of aggregate and cementitious agent in a mass ratio of 6:4 is used, where the cementitious agent consists of gypsum and calcium carbonate in a mass ratio of 1:1. The filling similarity material 20 uses dry quartz sand with a particle size of 2 mm to 5 mm, and its loose bulk density is controlled at 1.5 g / cm³.

[0096] The displacement stress monitoring elements 11 are arranged according to the principle of high-density array. Horizontal monitoring lines are arranged at three layers with vertical heights of 100 mm, 300 mm, and 500 mm from the coal seam roof. On each horizontal monitoring line, a displacement stress monitoring element 11 is buried every 100 mm along the strike direction. The number of acoustic emission signal capturing probes 17 is set to 16, of which 8 are installed on the front and rear side walls of the rigid bearing model box frame 1, and the other 8 are installed below the loading layer on the top of the model, forming a spatial array surrounding the monitoring area.

[0097] Vertical load applied by loading layer material 10 Calculations are based on the weight of the unsimulated overlying strata. The calculation formula is as follows: ; In the formula, This represents the average unit weight of the prototype rock strata, taken as 0.025 MN per cubic meter; This indicates the burial depth of the prototype coal seam, taken as 600 meters; This represents the total height of the rock layers laid in the model, and is taken as 1200 mm. This represents the geometric similarity ratio, with a value of 1 to 400. This represents the stress similarity ratio, with a value of 1:640. Substituting these values ​​into the formula, the compensation load applied to the top of the model is calculated. It is 0.0125 MPa.

[0098] During the excavation simulation phase, the continuously adjustable working face length system and the detachable base platform 19 work together to perform fixed-distance excavation. The single excavation step distance is set to 50 mm, corresponding to a prototype advancement distance of 20 meters. After each excavation operation, the settling time is set to 30 minutes to ensure sufficient stress adjustment within the rock stratum similar material 9, and at least 100 speckle images are acquired by the digital image correlation acquisition terminal 12 for subsequent analysis.

[0099] See attached document Figure 2 and attached Figure 3This invention provides a key technology mechanism analysis, including a mechanical transmission and locking mechanism for variable scale adjustment, an adaptive filling mechanism for composite base plates, and a mining simulation mechanism based on flexible interfaces.

[0100] The mechanical transmission and locking mechanism of the variable-scale adjustment relies on the synergistic effect of the axial transmission screw 4 and the sliding adjustment reaction wall 3. When the adjustment handle 8 is manually driven to input a rotational torque, the axial transmission screw 4 converts the rotational motion into axial linear motion. The displacement of the sliding adjustment reaction wall 3... The number of rotations of the manually driven adjustment handle 8 They satisfy a precise linear mechanical relationship, as shown in the following formula: ; In the formula, This indicates the horizontal distance that the sliding reaction wall 3 moves along the guide rail, in millimeters. Indicates the number of rotations of the axial drive screw 4; The thread lead of the axial drive screw 4 is expressed in millimeters per turn. This mechanism ensures the accuracy of the experiment on the working surface length of the model. The control precision reaches the millimeter level.

[0101] During the movement of the sliding adjustment reaction wall 3, the X-type rigid equalizing force mechanism 5 utilizes its force transmission and balancing mechanism. The X-type rigid equalizing force mechanism 5 is connected between the end of the axial transmission screw 4 and the back of the sliding adjustment reaction wall 3, configured to transfer the concentrated axial thrust generated by the screw. Distributed as a uniformly distributed surface load Applying to the back of the wall, the formula is as follows: ; In the formula, This represents the total axial thrust applied by the leadscrew. This indicates the contact area between the X-type rigid equalizing force component mechanism 5 and the sliding adjustment reaction wall 3. This mechanism prevents the wall from deflecting or undergoing local deformation during movement or compression. Once the predetermined position is reached, the double-nut self-locking assembly 7 eliminates the axial backlash of the lead screw through the frictional self-locking characteristics of the threaded pair, transforming the movable adjustment mechanism into a rigid physical boundary.

[0102] The adaptive filling mechanism of the composite floor slab is configured to address the technical challenge of continuous floor slab reconstruction under variable-scale conditions. When the position of the sliding adjustment reaction wall 3 changes, the horizontal distance between the two coal pillar bearing platforms 18... The change occurs. A similar filling material 20 utilizes its granular flowability to fill the gap, with the required filling volume... The formula is as follows: Automatically adjusted based on boundary position: ; In the formula, This represents the internal net width of the rigid load-bearing model box frame 1; This indicates the horizontal distance between the edges of the two coal pillar support platforms 18 on the fixed and moving sides; This indicates the thickness of the filling similar material 20. This mechanism ensures that regardless of changes in the model scale, there is always a continuous, uniformly high support medium beneath the rock stratum similar material 9, eliminating the bottom step effect caused by equipment adjustments.

[0103] The mining simulation mechanism based on a flexible interface involves the conversion process of load transfer and displacement release. In the unexcavated state, the self-weight of the rock stratum similar material 9 and the overlying load are transferred to the filling similar material 20 through the flexible isolation membrane 21, and are ultimately borne by the detachable bottom platform 19. When performing two-step mining, removing the detachable bottom platform 19 eliminates the vertical support force, but the flexible isolation membrane 21 temporarily maintains the stability of the loose particles through its tension. Subsequently, the filling similar material 20 is cleared, creating free space. At this time, the flexible isolation membrane 21 deforms synchronously with the bottom surface of the rock stratum, and its light transmittance, combined with the digital image correlation acquisition terminal 12, enables the full-field displacement of the rock stratum bottom plate under non-contact conditions. Non-destructive monitoring.

Claims

1. A three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces, characterized in that, include: Rigid load-bearing model box frame (1); The variable-scale model box body is set inside the rigid bearing model box frame (1). The variable-scale model box body includes a fixed reaction wall (2) fixedly connected to one side of the rigid bearing model box frame (1) and a directional sliding adjustment reaction wall (3) set inside the rigid bearing model box frame (1) and sliding along the direction. A stepless adjustment system for the working surface orientation length of the sliding reaction wall (3) connecting the rigid bearing model box frame (1); The simulated base plate assembly includes a coal pillar bearing platform (18) rigidly installed on the inner bottom of the fixed reaction wall (2) and the directional sliding adjustment reaction wall (3), a detachable base plate platform (19) arranged through the bottom of the rigid bearing model box frame (1), a filling similar material (20) laid on the detachable base plate platform (19), and a flexible isolation film (21) covering the filling similar material (20). The rock-like material (9) is filled in layers inside the main body of the variable-scale model box and the loading layer material (10) is located above the rock-like material (9). And a multi-field collaborative monitoring system set up inside and around the model.

2. The three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces according to claim 1, characterized in that, The continuously variable adjustment system for the working face length includes: An axial transmission screw (4) passes through the side wall of the rigid load-bearing model box frame (1) and is connected at one end to a manually driven adjustment handle (8) while the other end extends into the box body. An X-shaped rigid equalizing force distribution mechanism (5) is set on the back of the sliding adjustment reaction wall (3) and hinged at the center to the inner end of the axial transmission screw (4) to convert the axial thrust into a uniformly distributed surface load. The double-nut self-locking assembly (7), which is sleeved on the axial transmission screw (4) and located on the inner and outer sides of the rigid bearing model box frame (1), is used to lock the directional sliding adjustment reaction wall (3) in a predetermined position by eliminating thread clearance.

3. The three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces according to claim 1, characterized in that, In the simulated base plate assembly: The two coal pillar support platforms (18) extend into the box in a cantilever shape and their lower surfaces remain in a non-contact state with the detachable bottom plate platform (19); The detachable base plate platform (19) is assembled from several long strip-shaped support plates arranged along the direction of the model and capable of being pulled out individually, for removing the bottom support; The filling material (20) is filled in the gap between the two coal pillar support platforms (18) and its compacted upper surface is flush with the upper surface of the coal pillar support platform (18); The flexible isolation film (21) is attached at both ends to the coal pillar support platform (18) to support the rock stratum similar material (9) above and prevent the filling similar material (20) from entering the model.

4. The three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces according to claim 1, characterized in that, The stepless adjustment system for the working face direction length also includes four multi-directional hinged anchors (6) that are respectively fixedly installed in the four corner areas of the back of the direction sliding adjustment reaction wall (3). The four endpoints of the X-type rigid equalizing force component mechanism (5) are respectively connected to the four multi-directional hinged anchor seats (6) to prevent the directional sliding adjustment reaction wall (3) from deflecting during the movement.

5. The three-dimensional similarity simulation experimental system for the scale effect of ultra-long working surfaces according to claim 1, characterized in that, The multi-field collaborative monitoring system includes: Displacement stress monitoring element (11) pre-embedded inside the model; A digital image correlation acquisition terminal (12) is arranged below the rigid bearing model box frame (1) with its lens optical axis vertically upward aligned with the bottom surface of the flexible isolation film (21) for acquiring surface speckle images of the bottom rock layer through the flexible isolation film (21); A supplementary light (14) is arranged below the rigid load-bearing model box frame (1) to provide illumination; Intelligent analysis system that receives image data and calculates the displacement and strain distribution across the entire field (13); Acoustic emission signal capture probe (17) is arranged on the side wall of the rigid load-bearing model box frame (1).

6. The three-dimensional similarity simulation experimental system for the scale effect of an ultra-long working surface according to claim 5, characterized in that, The system also includes a similar material slurry mixer (15) and a slurry pumping pipeline (16) connected to the interior of the variable-scale model box body for transporting the rock strata similar material (9). The displacement stress monitoring element (11) is arranged at different layers and horizontal positions of the rock stratum similar material (9) and the loading layer material (10) to form a three-dimensional monitoring array.

7. A three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces, characterized in that, The method applied to the three-dimensional similarity simulation experimental system for the scale effect of an ultra-long working surface as described in any one of claims 1-6 includes the following steps: S1. Based on the second similarity theorem, determine the geometric similarity ratio, bulk density similarity ratio, and stress similarity ratio of the physical model, and plan the working conditions for conventional working face length and ultra-long working face length. S2, drive the sliding adjustment reaction wall (3) to move to the position corresponding to the length of the conventional working face and lock it, lay the simulated base plate assembly and fill the rock stratum similar material (9) and the loading layer material (10) to build the initial physical model; S3. Simulate mining using the initial physical model according to the predetermined excavation step distance, and simultaneously record the mine pressure data under the conventional working face length condition through the multi-field collaborative monitoring system. S4. Clean up the model material after the experiment, release the lock of the sliding adjustment reaction wall (3), drive the sliding adjustment reaction wall (3) to move to the position corresponding to the length of the ultra-long working surface and lock it again. S5. Under the new boundary conditions, the simulated base plate assembly is re-laid, the filling amount of the filling similar material (20) is increased to adapt to the expanded coal pillar spacing, and the physical model containing the rock stratum similar material (9) and the loading layer material (10) is reconstructed according to the same parameters before simulated mining and monitoring are carried out. S6. Extract monitoring data under the conventional working face length condition and the ultra-long working face length condition, compare the periodic pressure step distance, peak support pressure and roof subsidence under the two conditions, and generate analysis results on the influence of working face length on the mine pressure manifestation law.

8. The three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces according to claim 7, characterized in that, In steps S3 and S5, the simulated mining adopts a two-step process, including: The first step is to extract the detachable base plate platform (19) corresponding to the current mining location and remove the bottom rigid support; The second step is to clean up the remaining filling material (20) in the area, so that a free space is formed below the flexible isolation film (21); The flexible isolation film (21) bends and deforms under the load of the rock layer above, and the digital image correlation acquisition terminal (12) acquires the deformation image of the surface of the flexible isolation film (21) through the free space.

9. The three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces according to claim 7, characterized in that, In steps S4 and S5, the process of switching from the conventional working face length condition to the ultra-long working face length condition includes: Loosen the double-nut self-locking assembly (7), and rotate the manual drive adjustment handle (8) to push the sliding adjustment reaction wall (3) to translate through the axial transmission screw (4); Once the target position is reached, tighten the double-nut self-locking assembly (7) to establish a rigid boundary; Keeping the rigid bearing model box frame (1) in the same position, the gap between the bottom plate caused by the movement of the reaction wall is automatically filled by the loose flowability of the filling similar material (20), thus maintaining the continuity of the bottom plate support surface.

10. The three-dimensional similarity simulation experimental method for the scale effect of ultra-long working surfaces according to claim 7, characterized in that, The comparative analysis described in step S6 includes: Based on the data from the displacement stress monitoring element (11), the cycle pressure step distance, peak support pressure and dynamic load coefficient under the two working conditions are calculated. Based on the data from the acoustic emission signal capture probe (17), the three-dimensional source coordinates of the rock fracture evolution are reconstructed, and the extension range of the overlying failure field in the strike and dip direction under the two working conditions is determined. Based on the data from the digital image correlation acquisition terminal (12), the maximum subsidence of the top strata and the deformation characteristics of the bottom strata under the two working conditions are determined.

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