A two-dimensional simulation method for omnidirectional stress state of coal seam roof and floor

Abstract

The application provides a coal seam roof and floor omnidirectional stress state two-dimensional simulation method, and belongs to the technical field of coal seam mining simulation. The method sequentially comprises a coal seam bottom surface water pressure simulation method, a surrounding rock additional stress and surrounding rock self resistance to extrusion force simulation method, a coal seam mining simulation method and a determination method of experimental starting conditions. The four methods are sequentially used to simulate the upward pore water pressure of an aquifer and the self resistance to extrusion force of the aquifer rock mass, simulate the additional stress and self resistance to extrusion force of the surrounding rock of the coal seam roof and side surface under omnidirectional stress state, simulate the mining process of the coal seam under omnidirectional stress state, and determine the conditions before the experiment starts. The coal seam roof and floor omnidirectional stress state two-dimensional simulation method has the technical effect that the stress and displacement change of the actual coal seam roof and floor under omnidirectional stress state can be simulated, and the change of the surrounding rock of the coal seam under actual conditions can be studied.

Description

Technical Field

[0001] This invention belongs to the field of coal seam mining simulation technology, and more specifically, it relates to a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam. Background Technology

[0002] Pressurized mining of coal seams refers to mining operations where the coal seam is subjected to upward water pressure from the aquifer beneath it, posing a risk of water inrush. Two-dimensional physical simulation studies of pressurized mining conditions are of great significance for understanding crack formation and propagation, roof and floor deformation and failure, and water inrush mechanisms. They offer advantages such as precise and intuitive observation of phenomena and high fissure reproduction of actual rock masses, making them an important research method.

[0003] Currently, there is limited or immature research on two-dimensional physical simulation of coal seam mining under pressure, or the simulation research on pressure mining is insufficient, especially the simulation methods for pressurizing the surrounding rock and simulating the water pressure at the bottom of the surrounding rock. Summary of the Invention

[0004] The purpose of this invention is to provide a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam, aiming to solve the technical problem of insufficient research on two-dimensional physical simulation methods for pressurized mining in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam, comprising:

[0006] The coal seam bottom water pressure simulation method is used to simulate the upward force of the aquifer on the overlying rock mass, which is divided into two types: the upward water pressure of the water in the aquifer and the force of the aquifer rock mass itself resisting compression.

[0007] The simulation method for the additional stress of the surrounding rock and the force of the surrounding rock resisting compression is suitable for simulating the additional stress of the surrounding rock on the top and sides of the coal seam and the force of the surrounding rock resisting compression under omnidirectional stress.

[0008] The coal seam mining simulation method is suitable for simulating the mining process of coal seams under omnidirectional stress.

[0009] The method for determining the start conditions of the experiment is suitable for determining the conditions before the start of the experiment, such as the water pressure at the bottom of the coal seam, the additional stress of the surrounding rock, the force of the surrounding rock itself resisting compression, and the coal seam mining simulation. The experiment is carried out when the conditions are met.

[0010] In one possible implementation, the coal seam bottom water pressure simulation method includes the following steps:

[0011] Model making: Use similar materials to make experimental models, including simulated coal seams and simulated rock strata surrounding the coal seams;

[0012] During the model making process, pressure sensors and displacement sensors are placed inside the model and connected to monitoring equipment.

[0013] A bottom pressure module is set up to simulate the force exerted by the aquifer on the overlying rock mass. The bottom pressure module is located at the bottom of the model.

[0014] Using a pressurized water device, pressurized water is introduced into the bottom pressurization module, and the pressurized water flows through the bottom pressurization module and into the model. The pressure of the pressurized water is reasonably controlled to simulate the upward pore water pressure of the aquifer.

[0015] In one possible implementation, the bottom pressure module includes:

[0016] Multiple steel columns are arranged vertically and evenly spaced, and the multiple steel columns together form a cuboid structure. Steel plates are welded around the perimeter and bottom of the cuboid structure to form a cavity structure with an open top.

[0017] The first layer of steel plate is located on the upper end of the multiple steel columns and forms a closed cavity with the cavity structure. The first layer of steel plate is provided with multiple first holes for water to flow through. The first layer of steel plate is used to rigidly support the model.

[0018] The second steel plate is located at the top of the first steel plate and has multiple second holes. The diameter of the second holes is smaller than that of the first holes, which is suitable for simulating the pore environment of the actual aquifer. The pressurized water acts on the bottom surface of the model through the second holes to simulate the state of the contact surface between the aquifer and the overlying rock mass.

[0019] The inlet valve is connected at one end to the rear steel plate of the cuboid structure and at the other end to the pressurized water equipment. Opening the inlet valve allows water to be introduced into the cuboid structure.

[0020] The outlet valve is connected at one end to the rear steel plate of the cuboid structure. Opening the outlet valve is used to discharge the water inside the cuboid structure.

[0021] A fiberglass pipe, connected to the rear steel plate of the cuboid structure, is vertically upward-facing, with graduated lines on its outer surface. Water level values ​​are read through this fiberglass pipe, converted to calculate the water pressure at the bottom of the model, and the actual water pressure P exerted by the bottom pressurization module on the bottom of the model is obtained.

[0022] P = ρ × g × h

[0023] In the formula, ρ is the density of the experimental water, and h is the height difference between the water level in the fiberglass pipe and the bottom surface of the model; when the water pressure reaches the set water pressure, the bottom surface water pressure simulation requirement is met.

[0024] In one possible implementation, the first hole has a diameter of 3cm, the first steel plate has a thickness of 2cm, the steel column has a diameter of 3cm, the second steel plate has a thickness of 1cm, and the second hole has a diameter of 1mm.

[0025] In one possible implementation, the method for simulating the additional stress of the surrounding rock and the resistance of the aquifer rock mass to compression includes the following steps:

[0026] The finished model is rectangular in shape, including six sides: front, back, left, right, top, and bottom.

[0027] The front and rear sides of the model are enclosed with fiberglass, and the upper left and right sides of the model are pressed against the model with pressure modules. The pressure modules are used to push and squeeze the model towards the upper left and right sides of the model, so that the model is under omnidirectional force.

[0028] By using multiple pressurization modules to squeeze and push the model, the pressure and displacement of the coal seam under omnidirectional stress can be simulated.

[0029] In one possible implementation, the pressurization module includes:

[0030] An airbag, filled with gas and with adjustable inflation volume;

[0031] A baffle is placed between the airbag and the model. A stress box is provided on the side of the baffle near the airbag. The stress box is used to monitor the pushing force of the airbag on the baffle.

[0032] A pressure valve is provided on the side of the baffle closer to the model to limit the movement of the baffle closer to the model. The pressure valve is suitable for simulating the additional stress of the surrounding rock mass to ensure that the boundary pressure reaches the set value. The pressure valve is opened after the pressure reaches the set value.

[0033] A stop valve is provided on the side of the airbag away from the model to limit the movement of the airbag away from the model. The stop valve is suitable for simulating the effective stress of the surrounding rock mass itself.

[0034] By filling the air bladder with gas, the air bladder can expand or contract. When the pressure reaches a set value, the pressure valve is disassembled to apply pressure to the model. When the stress on the model increases and the air bladder is further compressed, the pressure stops when the model wall reaches the stop valve position, and the air bladder cannot be compressed further. This is used to simulate the force of the surrounding rock mass resisting compression.

[0035] In one possible implementation, the coal seam recovery simulation method includes the following steps:

[0036] A coal seam mining mold is buried at the pre-mining location of the coal seam, with the width of the coal seam mining mold being the same as the width of the model and the length being the same as the length of a single mining operation of the simulated coal seam, so that the mining cycle of the simulated coal seam is consistent with the actual coal seam mining cycle.

[0037] A coal seam mining mold is manufactured, comprising a mold body and a similar material disposed inside the mold body. The mold body includes a basin-shaped structure formed by the combination of a front movable baffle, a rear movable baffle, a left baffle, a right baffle, and a bottom plate. The similar material is located inside the basin-shaped structure. The front movable baffle and the rear movable baffle are detachably connected to the front and rear sides of the bottom plate, and the left baffle and the right baffle are respectively disposed on the left and right sides of the bottom plate.

[0038] Based on the actual compressive strength of the coal seam and the stress similarity ratio, the coal seam similarity material of the model is configured.

[0039] The prepared similar material is placed into the mold body. During the placement process, a pressure sensor is placed to create multiple coal seam mining molds. The multiple coal seam mining molds are connected end to end to form a simulated coal seam.

[0040] Place the coal seam mining mold in the pre-mining position of the model. After the coal seam mining mold is placed, remove the front movable baffle and the rear movable baffle to maintain the integrity of the model.

[0041] Four fiberglass strips are used to replace the front movable baffle and the rear movable baffle. Two fiberglass strips are provided on the front and rear sides of the mold body. The two fiberglass strips can be translated and can move closer to or further away from each other.

[0042] By simultaneously translating one of the fiberglass strips on the front and back sides of the coal seam similar material, a gap is formed between the two fiberglass strips on the same side, and the gap length is the same as the simulated coal seam single mining distance and also the same as the length of a coal seam mining mold.

[0043] Remove one exposed coal seam mining mold, and move another fiberglass strip to make the gap between the two fiberglass strips disappear and form a docking state. The area of ​​the exposed coal seam inside the mold body is defined as the goaf.

[0044] Continue moving the fiberglass strip that was moved the first time, so that a gap is formed between the two fiberglass strips;

[0045] Remove the exposed coal seam mining mold, move another fiberglass strip horizontally, and connect the two fiberglass strips. Then the length of the goaf is twice the length of the goaf formed in the first goaf.

[0046] By repeating the above steps, the pressure data collected by the pressure sensor is used to record the entire process of the coal seam from its original stress to the increase of its supporting stress, thus simulating the coal seam mining process under omnidirectional stress.

[0047] In one possible implementation, a through hole is provided on the rear movable baffle, and the signal output end of the pressure sensor installed inside the similar material is led out to the outside of the mold body through the through hole via a signal line; the inner side of the fiberglass strip is treated with a sliding effect.

[0048] In one possible implementation, the method for determining the experiment start condition includes:

[0049] Multiple test blocks with the same properties as the similar material used in the experiment are prepared, such that the properties of each test block represent the properties of different locations along the height direction in the similar material; wherein the similar material is formed into a model after being prepared.

[0050] Multiple test blocks were placed in the same environment as similar materials and air-dried.

[0051] Take out multiple test blocks, test the moisture content of the multiple test blocks, and obtain the average moisture content of the multiple test blocks;

[0052] Compressive strength tests were performed on multiple test blocks, and a compressive strength set value was set on the testing equipment;

[0053] When the average moisture content is as low as 3% and the compressive strength reaches the set value, the test block is deemed to meet the experimental conditions. Then, similar materials with the same physical and mechanical properties as the test block can also meet the experimental conditions so that experiments can be conducted.

[0054] In one possible implementation, after the similar material used in the experiment reaches the experimental conditions, the mold used to make the similar material is removed to expose the similar material. An impermeable coating is then applied evenly to the surface of the similar material or model to maintain the stability of the model's moisture content and compressive strength.

[0055] The beneficial effects of the two-dimensional simulation method for the omnidirectional stress state of coal seam roof and floor provided by this invention are as follows: Compared with the prior art, this invention's two-dimensional simulation method for the omnidirectional stress state of coal seam roof and floor simulates the upward pore water pressure of the aquifer and the resistance of the aquifer rock mass to compression by using a coal seam bottom water pressure simulation method; it simulates the additional stress of the surrounding rock and the resistance of the surrounding rock to compression by using a surrounding rock additional stress and surrounding rock resistance to compression by using a surrounding rock resistance to compression simulation method; it simulates the coal seam mining process under omnidirectional stress by using a coal seam mining simulation method; and it uses an experimental start condition determination method suitable for determining the conditions before starting the experiment for coal seam bottom water pressure, surrounding rock additional stress and surrounding rock resistance to compression, and coal seam mining simulation. If the conditions are met, the experiment is carried out. This method can realize the study of coal seam surrounding rock under omnidirectional stress under actual conditions, and has the technical effect of simulating the stress and displacement changes of the actual coal seam roof and floor under omnidirectional stress, and predicting the changes of coal seam surrounding rock under actual conditions. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 A block diagram of a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam provided in an embodiment of the present invention;

[0058] Figure 2 This is a schematic diagram of the structure of the pressurization module before compression in a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam provided in an embodiment of the present invention (the square frame in the middle represents the model);

[0059] Figure 3 This is a schematic diagram of the structure of the pressurization module before compression in a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam provided in an embodiment of the present invention (position diagram of the test block and the model corresponding to the positions).

[0060] Figure 4 A schematic diagram of the pressurization module in the extrusion process of a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam provided in an embodiment of the present invention (schematic diagram of the relationship between the fiberglass strip and the excavated coal seam, in which the horizontal black rectangular structure represents the coal seam);

[0061] Figure 5A schematic diagram of the pressurization module structure located on the upper left and right sides of the model, which is provided in an embodiment of the present invention for a two-dimensional simulation method of the omnidirectional stress state of the roof and floor of a coal seam;

[0062] Figure 6 for Figure 5 At the start of the experiment, the airbag pressure reaches the set value, the pressurization valve is opened, the airbag pressure acts on the model, and the state diagram shows the state of the model being pushed up.

[0063] Figure 7 for Figure 5 During the experiment, when the airbag was further compressed, the model wall reached the stop valve position and the airbag was stopped, which is a schematic diagram of the state where the airbag could not be compressed further.

[0064] Figure 8 for Figure 5 A schematic diagram showing the deflated state of the airbag inside the pressurization module before the experiment began;

[0065] Figure 9 A schematic diagram of the bottom pressure module structure located on the lower side of the model in a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam provided in an embodiment of the present invention;

[0066] Figure 10 for Figure 9 A top view of the first layer of steel plate in the structure;

[0067] Figure 11 for Figure 9 A top view of the second layer of steel plate;

[0068] Figure 12 for Figure 9 Rear view of the bottom pressure module;

[0069] Figure 13 This is a schematic diagram of the first stage of the coal seam excavation process, provided by an embodiment of the present invention, for a two-dimensional simulation method of the omnidirectional stress state of the coal seam roof and floor.

[0070] Figure 14 This is a schematic diagram of the second stage structure during coal seam excavation, provided by an embodiment of the present invention, for a two-dimensional simulation method of the omnidirectional stress state of the coal seam roof and floor.

[0071] Figure 15 This is a schematic diagram of the third stage of the coal seam excavation process, provided by a two-dimensional simulation method for the omnidirectional stress state of the top and bottom plates of a coal seam according to an embodiment of the present invention.

[0072] Explanation of reference numerals in the attached figures:

[0073] 1. Model; 2. Pressurization module; 21. Airbag; 22. Baffle; 23. Pressurization valve; 24. Stop valve; 25. Stress box; 26. Steel column; 27. First layer steel plate; 28. Second layer steel plate; 29. ​​Inlet valve; 210. Outlet valve; 211. Fiberglass pipe; 212. Steel plate; 213. First hole; 214. Second hole; 3. Monitoring equipment; 4. Test block; 5. Fiberglass strip; 5A. Left fiberglass strip; 5B. Right fiberglass strip; 6. Bottom pressurization module. Detailed Implementation

[0074] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0075] Please refer to the following: Figures 1 to 15 The present invention will now describe a two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam. The two-dimensional simulation method for the omnidirectional stress state of coal seam roof and floor includes a coal seam bottom surface water pressure simulation method, a simulation method for additional stress of surrounding rock and the force of surrounding rock resisting compression, a coal seam mining simulation method, and a method for determining the experimental start conditions. The upward force of the aquifer at the bottom of the coal seam on the overlying rock mass is divided into two types: one is the upward water pressure of the water body in the aquifer, and the other is the force of the aquifer rock mass resisting compression. The coal seam bottom surface water pressure simulation method is used to simulate the upward pore water pressure of the aquifer and the force of the aquifer rock mass resisting compression. The simulation method for additional stress of surrounding rock and the force of the surrounding rock resisting compression are suitable for simulating the additional stress of the surrounding rock on the top and sides of the coal seam under omnidirectional stress. The coal seam mining simulation method is suitable for simulating the mining process of the coal seam under omnidirectional stress. The method for determining the experimental start conditions is suitable for determining the conditions before the start of the experiment for the coal seam bottom surface water pressure, the additional stress of surrounding rock and the force of the surrounding rock resisting compression, and the coal seam mining simulation. When the conditions are met, the experiment is carried out.

[0076] The beneficial effects of the two-dimensional simulation method for the omnidirectional stress state of coal seam roof and floor provided by this invention are as follows: Compared with the prior art, the two-dimensional simulation method for the omnidirectional stress state of coal seam roof and floor of this invention simulates the upward pore water pressure of the aquifer and the resistance of the aquifer rock mass to compression by using the coal seam bottom water pressure simulation method; simulates the additional stress of the surrounding rock and the resistance of the surrounding rock to compression by using the surrounding rock additional stress and the surrounding rock itself to compression by using the surrounding rock itself to compression by using the surrounding rock additional stress and the surrounding rock itself to compression by using the coal seam mining simulation method; and simulates the coal seam mining process under omnidirectional stress by using the experimental start condition determination method. The experimental start condition determination method is suitable for determining the conditions before the start of the experiment for coal seam bottom water pressure, surrounding rock additional stress and the surrounding rock itself to compression by using the surrounding rock itself to compression, and coal seam mining simulation. If the conditions are met, the experiment is carried out. It can realize the study of the surrounding rock of coal seam under omnidirectional stress under actual conditions, and has the technical effect of simulating the stress and displacement changes of the actual coal seam roof and floor under omnidirectional stress, and simulating the changes of the surrounding rock of coal seam under actual conditions.

[0077] In some embodiments, please refer to Figures 1 to 15 The method for simulating water pressure at the bottom of a coal seam includes the following steps: constructing a model 1, setting up a bottom pressure module 6, and introducing pressurized water. Model 1 is constructed using similar materials and includes a simulated coal seam and surrounding rock strata. During model 1 construction, pressure and displacement sensors are placed inside the model 1 and connected to a monitoring device 3. The bottom pressure module 6 is set up to simulate the force exerted by the aquifer on the overlying rock mass; it is located at the bottom of model 1. Pressurized water is introduced into the bottom pressure module 6 using a pressurized water device, allowing the water to pass through the module and flow into the model 1. The pressure of the pressurized water is appropriately controlled to simulate the upward pore water pressure from the aquifer and the resistance of the aquifer rock mass to compression. The pressurized water device inputs water pressure into model 1 to simulate the upward pore water pressure from the aquifer and the resistance of the aquifer rock mass to compression; the applied water pressure is adjustable. The method of water injection can refer to existing technology, and the method of water pressure adjustment can also refer to existing technology.

[0078] Specifically, the stress and displacement sensors are located inside Model 1 (made of similar materials) (simulating the interior of coal seams and rock masses), and are evenly distributed in multiple layers, each layer arranged in a matrix. This allows for the monitoring of stress and displacement changes at different locations within Model 1. The specific locations of the stress and displacement sensors are not limited in this embodiment and are not shown in the figures.

[0079] Multiple stress sensors are installed inside Model 1 to monitor the stress changes in the original rock caused by coal seam excavation in Model 1; multiple displacement sensors are installed inside Model 1 to monitor the displacement changes and damage of the rock mass in Model 1; monitoring device 3 is communicatively connected to multiple stress sensors and multiple displacement sensors and receives the monitored stress and displacement signals respectively.

[0080] In some embodiments, please refer to Figures 1 to 15 The bottom pressure module 6 includes multiple steel columns 26, a first layer steel plate 27, a second layer steel plate 28, an inlet valve 29, an outlet valve 210, and a fiberglass pipe 211. The multiple steel columns 26 are vertically spaced and evenly distributed, forming a cuboid structure. Steel plates 212 are welded around the perimeter and bottom of the cuboid structure to form a chamber structure with an open top. The first layer steel plate 27 is located on top of the multiple steel columns 26, forming a closed chamber with the chamber structure. Multiple first holes 213 are provided on the first layer steel plate 27, with the diameter of each hole larger than the outer diameter of the steel column 26. The first holes 213 allow water to flow through, and the first layer steel plate 27 provides rigid support for the model 1. The second layer steel plate 28 is located on top of the first layer steel plate 27 and has multiple... The second hole 214 has a smaller diameter than the first hole 213, which is suitable for simulating the pore environment of an actual aquifer. Pressurized water acts on the bottom surface of the model 1 through the second hole 214 to simulate the contact surface between the aquifer and the overlying rock mass. One end of the inlet valve 29 is connected to the rear steel plate 212 of the cuboid structure, and the other end is connected to a pressurized water device. Opening the inlet valve 29 is used to input water into the cuboid structure. The water enters the model 1 after passing through the first hole 213 and the second hole 214 in sequence. One end of the outlet valve 210 is connected to the rear steel plate 212 of the cuboid structure. Opening the outlet valve 210 is used to discharge the water inside the cuboid structure. The fiberglass pipe 211 is connected to the rear steel plate 212 of the cuboid structure, is set vertically upward, and has scale lines on its outer surface. The steel column 26 provides a certain supporting force to Model 1. Through this simulated water pressure method, the upward force exerted by the aquifer at the bottom of Model 1 on the overlying rock mass is twofold: one is the force of the aquifer rock mass itself resisting compression, and the other is the upward water pressure within the aquifer. By applying water pressure, the changes in aquifer and pore water pressure can be simulated.

[0081] In this embodiment, the water pressure is increased by opening the inlet valve 29 and injecting water into the cuboid structure. After the structure is filled with water, the water pressure rises. The actual water pressure P at the bottom of model 1 is calculated by reading the water level on the fiberglass pipe 211. Therefore, P = ρ × g × h, where ρ is the density of the experimental water and h is the height difference between the water level in the fiberglass pipe 211 and the bottom of model 1. This method simulates the upward pore water pressure of the aquifer and the resistance of the aquifer rock mass to compression. It precisely controls the water pressure, accurately recreates the actual pore environment and water state within the aquifer, and recreates the actual water-rock interaction environment at the bottom of the coal seam under pressure threat. It can simulate the actual process of water inrush at the bottom of the coal seam to the greatest extent possible.

[0082] In some embodiments, please refer to Figures 1 to 15 The first hole 213 has a diameter of 3cm, the first steel plate 27 has a thickness of 2cm, the steel column 26 has a diameter of 3cm, the second steel plate 28 has a thickness of 1cm, and the second hole 214 has a diameter of 1mm. At least one first hole 213 and at least one second hole 214 are aligned vertically. Pressurized water can act on the bottom surface of model 1 through the second hole 214, replicating the contact state between the aquifer and the overlying rock mass. The first and second steel plates 27 and 28, the inlet valve 29 and outlet valve 210, and the fiberglass pipe 211 on the bottom surface of model 1 can simulate the application of water pressure to model 1, which is consistent with actual conditions and meets experimental requirements. The experimental results obtained have high reference value.

[0083] In some embodiments, please refer to Figures 1 to 15 The simulation method for the additional stress of the surrounding rock and the resistance of the surrounding rock itself to compression includes the following steps: enclosing the front and rear sides of model 1 with fiberglass and using pressure modules 2 to push and compress model 1; the prepared model 1 is rectangular and includes six sides: front, back, left, right, top, and bottom; enclosing the front and rear sides of model 1 with fiberglass, and using pressure modules 2 to abut against model 1 on the upper left and right sides of model 1, the pressure modules 2 being used to push and compress model 1 towards the upper left and right sides of model 1, so that model 1 is under omnidirectional stress; by using multiple pressure modules 2 to compress and push model 1, the pressure and displacement of the coal seam under omnidirectional stress are simulated.

[0084] In some embodiments, please refer to Figures 1 to 15The pressurization module 2 includes an airbag 21, a baffle 22, a pressurization valve 23, and a stop valve 24. The airbag 21 is filled with gas, and the inflation volume is adjustable. The baffle 22 is placed between the airbag 21 and the model 1. A stress box 25 is provided on the side of the baffle 22 near the airbag 21. The stress box 25 is used to monitor the pushing force of the airbag 21 on the baffle 22. The pressurization valve 23 is located on the side of the baffle 22 near the model 1 and is used to limit the movement of the baffle 22 towards the side closer to the model 1. The pressurization valve 23 is suitable for simulating the additional stress of the surrounding rock mass to ensure that the boundary pressure reaches a set value. After the pressure reaches the set value, Open the pressurization valve 23; the stop valve 24 is located on the side of the airbag 21 away from the model 1, and is used to limit the movement of the airbag 21 away from the model 1. The stop valve 24 is suitable for simulating the effective stress of the surrounding rock mass itself; by filling the airbag 21 with gas, the airbag 21 increases or decreases. When the pressure reaches a set value, the pressurization valve 23 is disassembled to allow the pressure to act on the model 1; when the stress of the model increases and the airbag 21 is further compressed, the pressure stops when the wall of the model 1 reaches the position of the stop valve 24. The airbag 21 cannot be further compressed, which is used to simulate the force of the surrounding rock mass itself resisting compression.

[0085] By disassembling the pressure valve 23 to move the baffle 22 and apply it to the model 1, the airbag 21, when compressed into a collapsed state, can be limited by the stop valve 24 to move away from the model 1. A preset pressure value for the airbag 21 (which can be manually set) is established. By setting the pressure valve 23, the boundary pressure is ensured to reach the preset pressure value, simulating the additional stress of the surrounding rock mass (horizontal stress is mainly tectonic stress, while the rock mass on the top surface of model 1 is mainly subjected to self-weight stress (vertically downward)). When the pressure of the airbag 21 reaches the preset pressure value, the pressure valve 23 is opened (i.e., the pressure valve 23 is disassembled), allowing the airbag 21 to push and compress the model 1. By setting the stop valve 24, the resistance of the surrounding rock mass to compression can be simulated. This method accurately and comprehensively simulates the stress state of the surrounding rock mass, achieving precise loading control.

[0086] In this embodiment, the airbag 21 is blocked by a baffle 22, and the pressure valve 23 prevents the airbag 21 from further expanding. For ease of explanation, the plug that blocks the baffle 22 is called the "pressure valve 23". A stress box 25 (a stress sensor that can monitor the stress or pressure of the airbag 21) is installed on one side of the baffle 22, and the pressure value can be monitored during the pressurization process. At the beginning of the experiment, the airbag 21 is first inflated. When the pressure of the airbag 21 on the baffle 22 reaches the set pressure value, the "pressure valve 23" is opened, so that the pressure of the airbag 21 acts on the model 1. Another plug is set on the other side of the airbag 21. For ease of explanation, this plug is called the "stop valve 24". The setting of the "stop valve 24" can simulate the force of the rock mass resisting compression.

[0087] Prior to this invention, in existing technology, pressure was applied directly to model 1 during experiments. As model 1 deformed, the pressure value changed, making it impossible to determine whether the pressure applied to model 1 reached the set pressure value. However, with this invention, the pressure of airbag 21 is precisely controlled. When the set pressure value is reached, the "pressurization valve 23" is opened, allowing the pressure of airbag 21 to act on the surface of model 1.

[0088] Notes on this invention: The pressure exerted on Model 1 by the surrounding rock mass includes two parts: firstly, the effective pressure inherent in the surrounding rock mass itself (equivalent to the resistance of the surrounding rock mass itself when Model 1 expands and compresses it); secondly, the potential additional stress exerted on Model 1 by the surrounding rock mass (the force actively applied to Model 1 by the surrounding rock mass). In the horizontal direction, tectonic stress predominates; on the top surface of Model 1, self-weight stress predominates (vertically downwards); and on the bottom surface, aquifer water pressure predominates (pore water pressure). Taking the horizontal tectonic stress as an example: When the tectonic stress decreases, the baffle 22 reaches its lowest position, and the effective stress between the rock masses comes into play. Conversely, when the tectonic pressure increases, the effective stress between the rock masses decreases, the baffle 22 is lifted by the airbag 21, and the pressure on the surface of Model 1 increases. This method effectively prevents the uncontrollable compressive force of Model 1 on the airbag 21 during the experiment. If the compressive pressure is too low, it cannot simulate reality; if the compressive pressure is too high, the load exceeds the simulated additional stress, and the pressure is excessively released after the working face is mined, resulting in severe deformation or damage. Accurate simulation of the stress state of Model 1 was achieved.

[0089] In particular, the water injection test conducted on the bottom surface of Model 1 in this invention can simulate the pore environment of the aquifer and the actual state of water-rock interaction, precisely control the water pressure, and realize the reproduction of the water discharge process. The interior of Model 1 has a key layer, similar to the key layer in actual coal mining.

[0090] In some embodiments, please refer to Figures 1 to 15The coal seam mining simulation method includes the following steps: embedding a coal seam mining mold at the pre-mining location of the coal seam, ensuring the width of the mold is equal to the model width and the length is equal to the single mining length of the simulated coal seam, so that the mining cycle of the simulated coal seam is consistent with the actual coal seam mining cycle; fabricating the coal seam mining mold, which includes a mold body and a similar material disposed inside the mold body, the mold body including a basin-shaped structure formed by the combination of a front movable baffle, a rear movable baffle, a left baffle, a right baffle, and a bottom plate, with the similar material located inside the basin-shaped structure; the front movable baffle and the rear movable baffle can... The front and rear sides of the base plate are disassembled, and the left and right baffles are respectively set on the left and right sides of the base plate; based on the actual compressive strength of the coal seam and combined with the stress similarity ratio, coal seam similar materials for the model are configured; the configured similar materials are placed into the mold body, and pressure sensors are placed during the placement process to create multiple coal seam mining molds, which are connected end to end to form a simulated coal seam; the coal seam mining molds are placed in the pre-mining position of the model, and after the coal seam mining molds are placed, the front and rear movable baffles are removed to maintain the integrity of the model; use Four fiberglass strips 5 replace the front and rear movable baffles. Two fiberglass strips 5 are provided on each of the front and rear sides of the mold body. The two fiberglass strips 5 can be translated and can move closer or further apart. By simultaneously translating one of the opposing fiberglass strips 5 on the front and rear sides of the coal seam-like material, a gap is formed between the two fiberglass strips 5 on the same side. The length of the gap is the same as the simulated single mining distance of the coal seam and also the same as the length of a coal seam mining mold. After removing one exposed coal seam mining mold, the other fiberglass strip 5 is translated, forming a gap between the two fiberglass strips 5. The gap disappears, forming a docking state. The area of ​​the exposed coal seam inside the mold body is defined as the goaf. Continue moving the first-moved fiberglass strip 5, forming a gap between the two fiberglass strips 5. Remove one exposed coal seam mining mold, translate the other fiberglass strip 5, and dock the two fiberglass strips 5. The length of the goaf is then twice the length of the first goaf. Repeat the above steps, and record the entire process of the coal seam from the original stress to the supporting stress increase through the pressure data collected by the pressure sensor, simulating the coal seam mining process under omnidirectional stress.

[0091] In some embodiments, please refer to Figures 1 to 15The rear movable baffle has a through hole, through which the signal output of a pressure sensor installed inside a similar material is led out to the outside of the mold body via a signal line; the inner surface of the fiberglass strip is treated with a sliding effect. One movement represents the completion of a single mining operation of the actual coal seam. Repeated cyclic movement can realize the entire mining process of the coal seam, ensuring both similarity to coal seam mining and convenience of the mining process, minimizing the time of exposed parts, and ensuring the overall omnidirectional stress environment of Model 1.

[0092] The inner sides of the fiberglass on both the front and rear sides of the model 1 of the present invention are treated with a sliding mechanism, which does not affect the deformation of the surface of the model 1, that is, the friction between the model 1 and the model 1 is reduced. Vertical grooves are provided on the sides of the multiple steel columns 26. In the experiment, the fiberglass on both sides is inserted vertically into the vertical grooves, so that the pressure module 2 on the lower side of the model 1 body is combined with the model 1 into a whole.

[0093] During the simulated mining process, the exposed portion of the excavated section is achieved by moving the fiberglass strips 5. After the coal seam is hollowed out, the surface is promptly sealed to observe deformation, damage, and stress. Model 1 has fiberglass strips 5 connected end-to-end on both the front and rear sides, defined as left fiberglass strip 5A and right fiberglass strip 5B. In the diagram, the right end of left fiberglass strip 5A and the left end of right fiberglass strip 5B are connected. During the simulated coal seam mining, the horizontal movement of the fiberglass strips 5 simulates the mining process. One movement represents one mining operation, and this process is repeated to achieve the entire mining process. The advantages of this invention are that it can simulate omnidirectional stress states, provides a clear visual representation of experimental phenomena, and allows for precise control of experimental conditions.

[0094] The specific operational steps for mining are as follows: 1) Please refer to Figure 13 1) Move the right fiberglass strip 5B to the right, the distance of which is the distance of a single mining operation; 2) Install the front movable baffle 22 and the rear movable baffle 22 on the front and rear sides of the exposed simulated coal seam, respectively; 3) Remove the exposed simulated coal seam, thus completing this mining operation; 4) Move the left fiberglass strip 5A to the right to ensure that the left fiberglass strip 5A and the right fiberglass strip 5B are connected, forming a closed environment inside model 1; 5) The stress sensor inside model 1 records the entire process of the coal seam from the original rock stress state to the increase of the supporting stress. In this way, mining is realized and the omnidirectional stress environment is simulated.

[0095] Preferably, during the simulated mining process, the aforementioned pressurizing module 2 and bottom pressurizing module 6 can be used to apply pressure or pushing force to model 1 on its left, right, top, and bottom sides, so that the coal seam mining in the model is under omnidirectional stress. Please refer to [link / reference]. Figures 13 to 15 .

[0096] In some embodiments, please refer to Figures 1 to 15The method for determining the start conditions of the experiment includes the following steps: preparing test block 4, drying test block 4, testing the moisture content and compressive strength of test block 4; preparing multiple test blocks 4 with the same properties as the similar material used in the experiment, such that the properties of each test block 4 represent the properties of different positions along the height direction in the similar material; wherein the similar material is formed into model 1 after preparation; placing multiple test blocks 4 in the same environment as the similar material for drying; taking out multiple test blocks 4, testing the moisture content of multiple test blocks 4, and obtaining the average moisture content of multiple test blocks 4; testing the compressive strength of multiple test blocks 4, and setting the compressive strength set value on the testing equipment; when the average moisture content is as low as 3% and the compressive strength reaches the set value, it is determined that the test block 4 meets the experimental conditions, and the similar material with the same physical and mechanical properties as the test block 4 can also meet the experimental conditions for conducting the experiment.

[0097] By testing the physical and mechanical properties of test block 4, it is determined that model 1 meets the test conditions (moisture content and compressive strength) before the simulation test can be conducted. In this invention, the air bladder 21 inside the pressurization module 2 is in a deflated state before the experiment begins. Test blocks 4 (using the same materials and proportions as model 1) are prepared for each key rock layer of model 1. After model 1 is stacked, it is ensured that test blocks 4 are in the exact same environment as model 1.

[0098] Two conditions must be met to begin the experiment. First, test the moisture content of specimen 4 and determine its average moisture content. When the average moisture content drops to 3%, condition one is met. Second, test the compressive strength of specimen 4. If the compressive strength reaches the set value, condition two is met. If both conditions are met, the experiment can begin. This precise understanding of the actual moisture content and physical and mechanical properties of Model 1 allows for accurate determination of the starting conditions for Model 1.

[0099] Previously, the drying days for Model 1 were based on empirical values, primarily observing the drying condition of the Model 1 surface. This approach failed to accurately reflect the overall moisture content of Model 1 and its physical and mechanical properties, resulting in simulation results that did not reflect actual conditions. This new method can simulate real-world conditions to the greatest extent possible.

[0100] In some embodiments, please refer to Figures 1 to 15 After the similar material used in the experiment reaches the experimental conditions, the mold for making the similar material is removed to expose the similar material. The surface of the similar material or model 1 is then evenly coated with an impermeable coating to maintain the stability of the moisture content and compressive strength of model 1.

[0101] The present invention provides a method for determining the condition before the start of the simulation experiment. Before the experiment begins, the moisture content of model 1 is tested. Model 1 is placed inside the space enclosed by multiple pressurization modules 2 to ensure that the environmental conditions are completely identical. When the moisture content of model 1 is as low as 3%, the compressive strength of model 1 is tested. The simulation experiment can only be carried out when both the moisture content and compressive strength of model 1 meet the standards.

[0102] The compressive strength setting value is the actual value of the compressive strength of the coal seam or rock mass. In other words, the compressive strength of Model 1 must be comparable to the actual compressive strength of the coal seam or surrounding rock so that the data obtained through simulation test can be close to the actual situation and meet the test conditions.

[0103] The method of the present invention can maximize the grasp of the parameters of the material in Model 1, reproduce the actual rock mass, and at the same time improve the convenience, operability and repeatability of the simulation.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam, characterized in that, include: The coal seam bottom water pressure simulation method is used to simulate the upward force of the aquifer on the overlying rock mass, which is divided into two types: the upward water pressure of the water in the aquifer and the force of the aquifer rock mass itself resisting compression. The simulation method for the additional stress of the surrounding rock and the force of the surrounding rock resisting compression is suitable for simulating the additional stress of the surrounding rock on the top and sides of the coal seam and the force of the surrounding rock resisting compression under omnidirectional stress. The coal seam mining simulation method is suitable for simulating the mining process of coal seams under omnidirectional stress. The method for determining the start conditions of the experiment is suitable for determining the conditions before the start of the experiment, such as the water pressure at the bottom of the coal seam, the additional stress of the surrounding rock and the force of the surrounding rock itself resisting compression, and the coal seam mining simulation. The experiment is carried out when the conditions are met. The method for simulating water pressure at the bottom of a coal seam includes the following steps: Model making: Use similar materials to make experimental models, including simulated coal seams and simulated rock strata surrounding the coal seams; During the model making process, pressure sensors and displacement sensors are placed inside the model and connected to monitoring equipment. A bottom pressure module is set up to simulate the force exerted by the aquifer on the overlying rock mass. The bottom pressure module is located at the bottom of the model. Using a pressurized water device, pressurized water is introduced into the bottom pressurization module, and the pressurized water flows through the bottom pressurization module and into the model. The pressure of the pressurized water is reasonably controlled to simulate the upward pore water pressure of the aquifer. The bottom pressure module includes: Multiple steel columns are arranged vertically and evenly spaced, and the multiple steel columns together form a cuboid structure. Steel plates are welded around the perimeter and bottom of the cuboid structure to form a cavity structure with an open top. The first layer of steel plate is located on the upper end of the multiple steel columns and forms a closed cavity with the cavity structure. The first layer of steel plate is provided with multiple first holes for water to flow through. The first layer of steel plate is used to rigidly support the model. The second steel plate is located at the top of the first steel plate and has multiple second holes. The diameter of the second holes is smaller than that of the first holes, which is suitable for simulating the pore environment of the actual aquifer. The pressurized water acts on the bottom surface of the model through the second holes to simulate the state of the contact surface between the aquifer and the overlying rock mass. The inlet valve is connected at one end to the rear steel plate of the cuboid structure and at the other end to the pressurized water equipment. Opening the inlet valve allows water to be introduced into the cuboid structure. The outlet valve is connected at one end to the rear steel plate of the cuboid structure. Opening the outlet valve is used to discharge the water inside the cuboid structure. A fiberglass pipe, connected to the rear steel plate of the cuboid structure, is vertically upward-facing, with graduated lines on its outer surface. Water level values ​​are read through this fiberglass pipe, converted to calculate the water pressure at the bottom of the model, and the actual water pressure P exerted by the bottom pressurization module on the bottom of the model is obtained. P=ρ×g×h In the formula, ρ is the density of the experimental water, and h is the height difference between the water level in the fiberglass pipe and the bottom surface of the model; when the water pressure reaches the set water pressure, the bottom surface water pressure simulation requirement is met.

2. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 1, characterized in that, The diameter of the first hole is 3cm, the thickness of the first layer of steel plate is 2cm, the diameter of the steel column is 3cm, the thickness of the second layer of steel plate is 1cm, and the diameter of the second hole is 1mm.

3. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 1, characterized in that, The simulation method for the additional stress of the surrounding rock and the resistance of the aquifer rock mass to compression includes the following steps: The finished model is rectangular in shape, including six sides: front, back, left, right, top, and bottom. The front and rear sides of the model are enclosed with fiberglass, and the upper left and right sides of the model are pressed against the model with pressure modules. The pressure modules are used to push and squeeze the model towards the upper left and right sides of the model, so that the model is under omnidirectional force. By using multiple pressurization modules to squeeze and push the model, the pressure and displacement of the coal seam under omnidirectional stress can be simulated.

4. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 3, characterized in that, The pressurization module includes: An airbag, filled with gas and with adjustable inflation volume; A baffle is placed between the airbag and the model. A stress box is provided on the side of the baffle near the airbag. The stress box is used to monitor the pushing force of the airbag on the baffle. A pressure valve is provided on the side of the baffle closer to the model to limit the movement of the baffle closer to the model. The pressure valve is suitable for simulating the additional stress of the surrounding rock mass to ensure that the boundary pressure reaches the set value. The pressure valve is opened after the pressure reaches the set value. A stop valve is provided on the side of the airbag away from the model to limit the movement of the airbag away from the model. The stop valve is suitable for simulating the effective stress of the surrounding rock mass itself. By filling the air bladder with gas, the air bladder can expand or contract. When the pressure reaches a set value, the pressure valve is disassembled to apply pressure to the model. When the stress on the model increases and the air bladder is further compressed, the pressure stops when the model wall reaches the stop valve position, and the air bladder cannot be compressed further. This is used to simulate the force of the surrounding rock mass resisting compression.

5. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 1, characterized in that, The coal seam mining simulation method includes the following steps: A coal seam mining mold is buried at the pre-mining location of the coal seam, with the width of the coal seam mining mold being the same as the width of the model and the length being the same as the length of a single mining operation of the simulated coal seam, so that the mining cycle of the simulated coal seam is consistent with the actual coal seam mining cycle. A coal seam mining mold is manufactured, comprising a mold body and a similar material disposed inside the mold body. The mold body includes a basin-shaped structure formed by the combination of a front movable baffle, a rear movable baffle, a left baffle, a right baffle, and a bottom plate. The similar material is located inside the basin-shaped structure. The front movable baffle and the rear movable baffle are detachably connected to the front and rear sides of the bottom plate, and the left baffle and the right baffle are respectively disposed on the left and right sides of the bottom plate. Based on the actual compressive strength of the coal seam and the stress similarity ratio, the coal seam similarity material of the model is configured. The prepared similar material is placed into the mold body. During the placement process, a pressure sensor is placed to create multiple coal seam mining molds. The multiple coal seam mining molds are connected end to end to form a simulated coal seam. Place the coal seam mining mold in the pre-mining position of the model. After the coal seam mining mold is placed, remove the front movable baffle and the rear movable baffle to maintain the integrity of the model. Four fiberglass strips are used to replace the front movable baffle and the rear movable baffle. Two fiberglass strips are provided on the front and rear sides of the mold body. The two fiberglass strips can be translated and can move closer to or further away from each other. By simultaneously translating one of the fiberglass strips on the front and back sides of the coal seam similar material, a gap is formed between the two fiberglass strips on the same side, and the gap length is the same as the simulated coal seam single mining distance and also the same as the length of a coal seam mining mold. Remove one exposed coal seam mining mold, and move another fiberglass strip to make the gap between the two fiberglass strips disappear and form a docking state. The area of ​​the exposed coal seam inside the mold body is defined as the goaf. Continue moving the fiberglass strip that was moved the first time, so that a gap is formed between the two fiberglass strips; Remove the exposed coal seam mining mold, move another fiberglass strip horizontally, and connect the two fiberglass strips. Then the length of the goaf is twice the length of the goaf formed in the first goaf. By repeating the above steps, the pressure data collected by the pressure sensor is used to record the entire process of the coal seam from its original stress to the increase of its supporting stress, thus simulating the coal seam mining process under omnidirectional stress.

6. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 5, characterized in that, A through hole is provided on the rear movable baffle, and the signal output end of the pressure sensor installed inside the similar material is led out to the outside of the mold body through the through hole via a signal line; the inner side of the fiberglass strip is treated with a sliding effect.

7. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 1, characterized in that, The methods for determining the start conditions of the experiment include: Multiple test blocks with the same properties as the similar material used in the experiment are prepared, such that the properties of each test block represent the properties of different locations along the height direction in the similar material; wherein the similar material is formed into a model after being prepared. Multiple test blocks were placed in the same environment as similar materials and air-dried. Take out multiple test blocks, test the moisture content of the multiple test blocks, and obtain the average moisture content of the multiple test blocks; Compressive strength tests were performed on multiple test blocks, and a compressive strength set value was set on the testing equipment; When the average moisture content is as low as 3% and the compressive strength reaches the set value, the test block is deemed to meet the experimental conditions. Then, similar materials with the same physical and mechanical properties as the test block can also meet the experimental conditions so that experiments can be conducted.

8. The two-dimensional simulation method for the omnidirectional stress state of the roof and floor of a coal seam as described in claim 7, characterized in that, After the similar material used in the experiment meets the experimental conditions, the mold used to make the similar material is removed to expose the similar material. The surface of the similar material or model is then evenly coated with an impermeable coating to maintain the stability of the model's moisture content and compressive strength.

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