Simulation method for water inrush in coal seam with concealed structure

Abstract

The application discloses a simulation method for water inrush in coal seam mining with concealed structure, and belongs to the technical field of underground space mining simulation, and comprises the following steps: S1, providing a confining pressure for a rectangular test block, the rectangular test block is sequentially divided into a roof simulation layer, a coal seam simulation layer and a floor simulation layer from top to bottom, the floor simulation layer contains a concealed structure, and the coal seam simulation layer comprises a plurality of sections of test paste bodies containing air bags which are poured along a preset cutting depth direction; S2, cutting the test paste bodies along the cutting depth direction and according to a preset cutting interval time, and the air bags are punctured and extracted in the cutting process; S3, recording crack propagation phenomena through acoustic emission; S4, reconstructing crack distribution rules; and S5, obtaining damage space and time characteristics of the roof simulation layer and the floor simulation layer by comprehensively analyzing test results. In the process of excavating the coal seam simulation layer, the confining pressure can be matched to realize similar simulation of crack change rules under water inrush conditions, and the method is reasonable in three-dimensional stress, fast in cutting rate and low in workload.

Description

Technical Field

[0001] This invention relates to the field of underground space mining simulation technology, and in particular to a simulation method for water inrush during mining of coal seams with concealed structures. Background Technology

[0002] Due to the concealed nature of underground mining activities, the impact of mining coal seams containing concealed structures (including concealed faults, concealed folds, concealed uplifts, concealed depressions, and concealed rock masses) is often difficult to monitor. In order to intuitively obtain the rock strata crack failure law after the destruction of underground coal seams with concealed structures, researchers often use similar simulation experiments. For example, the patent number "201610301582.6" and the patent name "Similar Test Device and Visualization Method for the Activation of Confined Faults and the Formation of Water Inrush Channels" includes the following steps: (1) Making a similar model; the material ratio of the similar model is determined according to the hydrogeological conditions of the working face of the fault-containing coal seam to be simulated and the properties of the coal seam, roof and floor strata; (2) Model loading: a uniformly distributed vertical load is applied to the roof of the coal seam of the similar model, a horizontal load that increases linearly with the burial depth is applied to the side of the similar model, and a certain uniformly distributed pressure of confined water is applied to the bottom of the similar model using a water pressure loading system; (3) Model excavation: the excavation size of each step of the model is calculated according to the model similarity ratio, and the working is simulated. The normal advancement of the face until it is excavated to a certain distance through the fault; (4) Signal acquisition and processing: During the simulated excavation, the deformation and destruction of the top and bottom strata of the coal seam, the generation, expansion and connection of fault surrounding rock fissures and the process of sudden change in seepage of fault surrounding rock forming a water inrush channel are observed through a transparent glass baffle. At the same time, the evolution law of information such as stress, displacement, seepage and temperature of the bottom fault surrounding rock during the working face advancement, the energy distribution characteristics of fault activation fissures and the sudden change characteristics of seepage of confined water in the fissures are collected by the corresponding processing system. However, the current similar simulation test has many problems: First, the workload is large. When excavating the simulated coal seam, the coal seam cutting takes a long time, which is not conducive to the experimental simulation efficiency; Second, the application of three-dimensional stress is not reasonable enough. Only the stress in the upper and lower and left and right directions is given; Third, the properties of the similar simulation material are quite different from those of the original rock material. The degree of restoration is not high and the simulation effect needs to be discussed. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned technical problems and provide a simulation method for water inrush during the mining of coal seams with concealed structures. In the process of excavating the simulated coal seam, the method can achieve a similar simulation of the crack change law under water inrush conditions by combining it with the confining pressure on the rectangular test block. The method has reasonable three-dimensional stress, fast cutting rate and low workload.

[0004] To achieve the above objectives, the present invention provides the following solution: The present invention discloses a method for simulating water inrush during mining of coal seams containing concealed geological structures, comprising the following steps: S1. Provide confining pressure to the rectangular test block according to the preset loading rate. The rectangular test block is divided into a roof simulation layer, a coal seam simulation layer and a bottom simulation layer from top to bottom. The bottom simulation layer contains a hidden structure. The coal seam simulation layer includes several sections of test paste containing air bladders that are cast sequentially along the preset cutting depth direction. S2. Cut the test paste sequentially along the cutting depth direction at preset cutting intervals. During the cutting process, when the air bladder of each section of the test paste is exposed, puncture the air bladder to release the pressure and extract it. S3. Record the crack propagation phenomenon of the top plate simulation layer and the bottom plate simulation layer during the test by acoustic emission; S4. Reconstruct the crack distribution pattern after the test; S5. Based on the test results of combined steps S3 and S4, obtain the spatial and temporal characteristics of the damage to the roof and floor simulated layers caused by the mining of the coal seam simulation layer.

[0005] Preferably, the concealed structure is a double-layered sheet-like sponge sand.

[0006] Preferably, the airbag is cylindrical, the diameter of the airbag is equal to the cutting size of each advance, the length of the airbag is 1 / 3 of the cutting size of each advance, and the cutting size of the advance is 2 / 3 of the thickness of the test paste.

[0007] Preferably, the test paste is a colored paste, and the colors of two adjacent test pastes are different.

[0008] Preferably, the roof simulation layer includes a basic roof simulation layer and a direct roof simulation layer. The direct roof simulation layer is located between the basic roof simulation layer and the coal seam simulation layer. The basic roof simulation layer, the direct roof simulation layer, the coal seam simulation layer, and the floor simulation layer are derived from the actual basic roof, direct roof, coal seam, and floor by scaling down the scale.

[0009] Preferably, the mass ratio of casting materials is similar to that of the basic roof, immediate roof, coal seam, and floor, based on the rock mechanics properties of the material. The mass ratio of the casting material for the basic roof simulation layer is gypsum:silica powder:water = 170:2:70; the mass ratio of the casting material for the immediate roof simulation layer is gypsum:silica powder:water = 165:2:70; the mass ratio of the casting material for the test paste is gypsum:silica powder:water = 160:2:70; and the mass ratio of the casting material for the floor simulation layer is gypsum:silica powder:water = 175:2:70.

[0010] Preferably, the rock mass mechanical properties and stress distribution of the rock strata within the immediate roof, main roof, coal seam, and floor failure zone are obtained through on-site in-situ stress testing, core drilling, and high-density electrical resistivity tomography, thereby obtaining the true height of the roof, coal seam, and floor failure zone and determining the size and location of the concealed structures.

[0011] Preferably, the confining pressure loading rate is 1 kN / s.

[0012] Preferably, a triaxial pressurization system is used to pressurize the rectangular test block in the vertical, horizontal, and front-back directions. The triaxial pressurization system includes a top pressurization head, a base for placing the rectangular test block, and four peripheral pressurization heads disposed on the four sides of the rectangular test block. The loading end of the top pressurization head is provided with a top pressurization plate, and the loading end of the peripheral pressurization heads is provided with a peripheral pressurization plate. The peripheral pressurization plates are provided with cutting slots for cutting equipment to cut the coal seam simulation layer.

[0013] Preferably, the crack distribution pattern after the experiment is reconstructed by CT scanning and slice inversion methods.

[0014] The present invention achieves the following technical effects compared to the prior art: 1. This invention, through the excavation of a simulated coal seam layer and the application of confining pressure to a rectangular test block, can achieve a similar simulation of the crack change pattern caused by water inrush. The confining pressure can achieve all-round stress in the vertical, horizontal, and front-back directions, and the three-dimensional stress is reasonable. The simulated coal seam layer is composed of several test pastes containing air bladders. When the cutting equipment cuts the test paste, the air bladders are punctured to release the pressure and become suffocated, which can accelerate the cutting speed of the test paste, thereby increasing the efficiency of each cut in the test and reducing the workload of the experiment.

[0015] 2. The concealed structure of this invention uses double-layered sheet-like sponge sand, which can effectively simulate the surface roughness and high water permeability of concealed structures, thereby improving the realism of the simulation.

[0016] 3. This invention configures similar casting material mass ratios based on the rock mechanical properties of the basic roof, immediate roof, coal seam, and floor, which can approximate the real rock mass properties, thereby improving the degree of reproduction and simulation realism. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0018] Figure 1A schematic diagram of the structure used in fabricating a rectangular test block for an experimental kit; Figure 2 This is a schematic diagram of the triaxial pressurization system; Figure 3 This is a cross-sectional view of the test paste; Figure 4 A schematic diagram of the three-dimensional structure of the box used in the experiment; Figure 5 This is a schematic diagram of the excavation process for the first cutting of the rectangular test block at the depth. Figure 6 This is a schematic diagram of the excavation process for the second cutting of the rectangular test block. Figure 7 This is a schematic diagram of the excavation process for the third cutting of the rectangular test block. Figure 8 This is a schematic diagram of a small direct mill. Figure 9 This is a schematic diagram of the cutting head of a small straight mill.

[0019] Explanation of reference numerals in the attached figures: 1. Rectangular test block; 2. Experimental preparation box; 3. Triaxial pressure system; 4. Small direct mill; 101. Basic roof simulation layer; 102. Immediate roof simulation layer; 103. Coal seam simulation layer; 104. Floor simulation layer; 105. Concealed structure; 106. Experimental paste; 107. Airbag; 201. First metal sheet; 202. Second metal sheet; 203. Third metal sheet; 204. Separating metal strip; 205. Slide rail; 301. Top pressure head; 302. Base; 303. Peripheral pressure head; 304. Top pressure plate; 305. Peripheral pressure plate; 306. Cutting and grooving; 401. Cutting head; 402. Air blower hole. Detailed Implementation

[0020] The technical solutions of 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 one embodiment 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.

[0021] This embodiment provides a simulation method for water inrush during mining of coal seams with concealed geological structures, such as... Figures 1 to 8 As shown, it includes the following steps: S1. Provide confining pressure to rectangular test block 1 according to the preset loading rate. Rectangular test block 1 is divided into a roof simulation layer, a coal seam simulation layer 103 and a bottom simulation layer 104 from top to bottom. The bottom simulation layer 104 contains a hidden structure 105. The coal seam simulation layer 103 includes several sections of test paste 106 that are poured sequentially along the preset cutting depth direction. The test paste 106 contains an airbag 107. S2. Along the cutting depth direction, the test paste 106 is cut sequentially at the preset cutting interval. That is, after cutting a section of test paste 106, a certain time interval is required. Cutting one section of test paste 106 represents one cutting depth to simulate one cut of coal mining machine on site. During the cutting process, when the air bladder of each section of test paste 106 is exposed, the air bladder 107 is punctured to release the pressure and be extracted, thereby saving the cutting time of test paste 106 and greatly improving the cutting simulation efficiency. S3. The crack propagation phenomenon of the top plate simulation layer and the bottom plate simulation layer 104 during the test is recorded in real time using acoustic emission technology. S4. Reconstruct the crack distribution pattern after the test; S5. Combining the experimental results of steps S3 and S4, the spatial and temporal characteristics of the damage to the simulated roof layer and simulated floor layer 104 caused by the mining of the simulated coal seam 103 are obtained. This leads to the spatial and temporal characteristics of the damage to the roof and floor during actual coal seam mining, providing a basis for the mechanism of roof and floor failure in coal mines and for predicting disasters such as water inrush from hidden structures in the roof and floor. It also provides confining pressure for the rectangular test block 1, solving the problem that traditional similarity experiments only provide stress in the vertical and horizontal directions, and the application of three-dimensional stress is not reasonable enough. The test paste 106 contains air bladders 107. During the cutting process, the air bladders 107 are punctured, which can save the cutting time of the test paste 106 and greatly improve the cutting simulation efficiency. This experimental method is simple, has a small workload, and has a high repeatability.

[0022] Preferably, the coal seam simulation layer 103 can be set horizontally or inclined, depending on the actual situation. Figure 1 , Figure 5 , Figure 6 as well as Figure 7 The airbag 107 can be made of vulcanized rubber, or other materials. The cutting interval is 1 hour.

[0023] In this embodiment, as Figures 1 to 9As shown, the concealed structure 105 is a double-layered sheet-like sponge sand. The sponge sand can be used to simulate the rough surface and high permeability of the concealed structure, improving the realism of the simulation. Specifically, when casting the rectangular test block 1, the double-layered sheet-like sponge sand can be sewn into a shape similar to a knife sheath, and then it can be placed on one end of a rectangular sheet. Then, the end of the rectangular sheath is cast together with the casting material, and then the rectangular sheet is removed, leaving the double-layered sheet-like sponge sand in the predetermined position of the rectangular test block 1.

[0024] In this embodiment, as Figures 1 to 9 As shown, the airbag 107 is cylindrical, with a diameter equal to the cutting size for each advance, and a length that is 1 / 3 of the cutting size for each advance. The cutting size is 2 / 3 of the thickness of the test paste 106.

[0025] Furthermore, in this embodiment, as Figures 1 to 9 As shown, the test paste 106 is a colored paste, with adjacent test pastes 106 of different colors, used to indicate the excavation progress. For example, black test paste 106 and red test paste 106 may appear alternately; alternatively, several sections of test paste 106 can all be of different colors, depending on actual needs. The specific preparation method involves adding a colored liquid, such as alternating between black and red liquid, to the casting material of the test paste 106.

[0026] Furthermore, in this embodiment, as Figures 1 to 9 As shown, the roof simulation layer includes a basic roof simulation layer 101 and an immediate roof simulation layer 102, with the immediate roof simulation layer 102 located between the basic roof simulation layer 101 and the coal seam simulation layer 103. The basic roof simulation layer 101, immediate roof simulation layer 102, coal seam simulation layer 103, and floor simulation layer 104 are derived from the actual basic roof, immediate roof, coal seam, and floor by scaling down. Typically, the scaling down ratio is 1:100 or 1:200.

[0027] To improve the mechanical properties of rectangular test block 1 and its resemblance to real rock and coal seams, and to enhance the realism of the experimental simulation, in this embodiment, as follows: Figures 1 to 9 As shown, the mass ratio of pouring materials should be similar based on the rock mechanical properties of the basic roof, immediate roof, coal seam, and floor.

[0028] Specifically, the mass ratio of the casting material for the basic top simulation layer 101 is model gypsum: microsilica powder: water = 170:2:70; the mass ratio of the casting material for the direct top simulation layer 102 is model gypsum: microsilica powder: water = 165:2:70; the mass ratio of the casting material for the test paste 106 is model gypsum: microsilica powder: water = 160:2:70; and the mass ratio of the casting material for the bottom plate simulation layer 104 is model gypsum: microsilica powder: water = 175:2:70.

[0029] During fabrication, a rectangular test block 1 is fabricated using an experimental fabrication box 2. The experimental fabrication box 2 is a rectangular box. Based on the thicknesses of the basic roof simulation layer 101, the direct roof simulation layer 102, the coal seam simulation layer 103, and the floor simulation layer 104, three sliding tracks 205 are set on the edge of the experimental fabrication box 2. A first metal sheet 201, a second metal sheet 202, and a third metal sheet 203 are inserted sequentially. The first metal sheet 201 and the short side of the experimental fabrication box 2 form a first area for casting the basic roof simulation layer 101. The area between the first metal sheet 201 and the second metal sheet 202 forms a second area for casting the direct roof simulation layer 102. The area between the second metal sheet 202 and the third metal sheet 203 forms a third area for casting the coal seam simulation layer 103. The third metal sheet 203 and the other short side of the experimental fabrication box 2 form a fourth area for casting the floor simulation layer 104. Then, several dividing metal strips 204 are placed along the depth direction in the third region to divide the third region into several small areas for pouring test paste 106.

[0030] During casting, the pastes are prepared sequentially according to the specified proportions and stirred evenly before casting in the first, second, third, and fourth zones. When preparing the test paste 106, two different colored pastes are made: one is mixed with black water, and the other with red water. When casting the third zone, airbags 107 are placed into several small zones, and then the black and red pastes are cast alternately. When casting the fourth zone, a concealed structure 105, such as double-layered sheet-like sponge sand or other double-layered sheet-like materials, is placed in advance. After all zones are cast, the first metal sheet 201, second metal sheet 202, third metal sheet 203, and separating metal strip 204 are removed, and the specially designed grouped test box is vibrated again. To facilitate the removal of the metal sheets and separating metal strip 204, they can be coated with lubricating oil before casting. The first metal sheet 201, second metal sheet 202, and third metal sheet 203 can have a certain angle to simulate the dip angle of a coal seam. The thickness of the test paste 106 can be the same or different.

[0031] In this embodiment, as Figures 1 to 9 As shown, the rock mass mechanical properties, stress distribution, and true height of the roof, coal seam, and floor failure zones within the range of the direct roof, main roof, coal seam, and floor failure zones are obtained through on-site in-situ stress testing, core drilling, and high-density electrical resistivity tomography, thereby determining the size and location of the concealed structure 105.

[0032] In this embodiment, as Figures 1 to 9 As shown, the confining pressure loading rate is 1 kN / s.

[0033] Furthermore, in this embodiment, as Figures 1 to 9As shown, a triaxial pressurization system 3 is used to pressurize the rectangular test block 1 in the vertical, horizontal, and front-back directions. The triaxial pressurization system 3 includes a top pressurization head 301, a base 302 for placing the rectangular test block 1, and four peripheral pressurization heads 303 respectively disposed on the four sides of the rectangular test block 1. The loading end of the top pressurization head 301 is provided with a top pressurization plate 304, and the loading end of the peripheral pressurization head 303 is provided with a peripheral pressurization plate 305. The peripheral pressurization plate 305 is provided with a cutting slot 306 for a cutting device to cut the coal seam simulation layer 103. Preferably, the size and angle of the cutting slot 306 are variable to accommodate changes in the size and inclination angle of the coal seam simulation layer 103, and the size and shape of the peripheral pressurization plate 305 are variable to accommodate changes in the size and inclination angle of the coal seam.

[0034] In step S1, the rectangular test block 1 is placed on the base 302 of the triaxial testing system. Pressure is applied to the rectangular test block 1 vertically, horizontally, and back-and-forthly at a loading rate of 1 kN / s. Simultaneously, a cutting device, such as a small direct-fired mill 4, is used. The small direct-fired mill 4 has air holes 402 at its cutting head 401. Along the depth direction, the simulated coal seam 103 is cut through the cutting slot 306. The mining interval is 1 hour. During the cutting process, air is blown while cutting to remove the broken particles after cutting.

[0035] In this embodiment, as Figures 1 to 9 As shown, the crack distribution pattern after the experiment was reconstructed using CT scanning and slice inversion methods. Color injection inversion involves injecting colored water under pressure after rock strata failure. The water enters the fractured cracks, and the rock is sliced ​​to construct a coordinate system, thus roughly reconstructing the crack propagation process and distribution. CT scanning requires immediately stopping the mechanical loading test when the excavation process attracts the experimenter's attention, focusing on crack development phenomena such as crack initiation and propagation, rock cracking sounds, or even the spalling and ejection of rock fragments. After CT, the loading path is repeated until the previous stopping point, and observation continues. Alternatively, identical rectangular specimens can be prepared and reloaded along the same path to continue the experiment.

[0036] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for simulating water inrush during mining of coal seams with concealed geological structures, characterized in that, Includes the following steps: S1. Provide confining pressure to the rectangular test block according to the preset loading rate. The rectangular test block is divided into a roof simulation layer, a coal seam simulation layer and a bottom simulation layer from top to bottom. The bottom simulation layer contains a hidden structure. The coal seam simulation layer includes several sections of test paste containing air bladders, which are poured sequentially along the preset cutting depth direction. The several sections of the test paste are arranged side by side. S2. Along the cutting depth direction, the test paste is cut sequentially at preset cutting intervals. Each cut of the test paste represents one cutting depth to simulate one cut by a coal mining machine. During the cutting process, when the air bladder of each section of the test paste is exposed, the air bladder is punctured to release pressure and is extracted. The air bladder is cylindrical, and its diameter is equal to the cutting size of each advance. The length of the air bladder is 1 / 3 of the cutting size of each advance. The cutting size is 2 / 3 of the thickness of the test paste. S3. Record the crack propagation phenomenon of the top plate simulation layer and the bottom plate simulation layer during the test by acoustic emission; S4. Reconstruct the crack distribution pattern after the test; S5. Based on the test results of combined steps S3 and S4, obtain the spatial and temporal characteristics of the damage to the roof and floor simulated layers caused by the mining of the coal seam simulation layer.

2. The simulation method for water inrush during mining of coal seams with concealed geological structures according to claim 1, characterized in that, The concealed structure is a double-layered sheet-like sponge sand.

3. The simulation method for water inrush during mining of coal seams with concealed geological structures according to claim 1, characterized in that, The test paste is a colored paste, and the colors of two adjacent test pastes are different.

4. The simulation method for water inrush during mining of coal seams with concealed geological structures according to claim 3, characterized in that, The roof simulation layer includes a basic roof simulation layer and a direct roof simulation layer. The direct roof simulation layer is located between the basic roof simulation layer and the coal seam simulation layer. The basic roof simulation layer, direct roof simulation layer, coal seam simulation layer, and floor simulation layer are derived from the actual basic roof, direct roof, coal seam, and floor by scaling down the scale.

5. The simulation method for water inrush during mining of coal seams with concealed geological structures according to claim 4, characterized in that, Based on the rock mechanics properties of the basic roof, immediate roof, coal seam, and floor, similar mass ratios of casting materials are configured. The mass ratio of the casting material for the basic roof simulation layer is model gypsum: microsilica powder: water = 170:2:70; the mass ratio of the casting material for the immediate roof simulation layer is model gypsum: microsilica powder: water = 165:2:70; the mass ratio of the casting material for the test paste is model gypsum: microsilica powder: water = 160:2:70; and the mass ratio of the casting material for the floor simulation layer is model gypsum: microsilica powder: water = 175:2:

70.

6. The method for simulating water inrush during mining of coal seams with concealed geological structures according to claim 5, characterized in that, By using in-situ stress testing, core drilling, and high-density electrical resistivity tomography, the rock mechanics properties and stress distribution of the strata within the immediate roof, main roof, coal seam, and floor failure zones of the coal seam are obtained, the true height of the roof, coal seam, and floor failure zones is determined, and the size and location of the concealed structures are identified.

7. The simulation method for water inrush during mining of coal seams with concealed geological structures according to claim 1, characterized in that, The confining pressure loading rate is 1 kN / s.

8. The method for simulating water inrush during mining of coal seams with concealed geological structures according to claim 7, characterized in that, A triaxial pressurization system is used to pressurize the rectangular test block in the vertical, horizontal, and front-back directions. The triaxial pressurization system includes a top pressurization head, a base for placing the rectangular test block, and four peripheral pressurization heads located on the four sides of the rectangular test block. The loading end of the top pressurization head is provided with a top pressurization plate, and the loading end of the peripheral pressurization heads is provided with a peripheral pressurization plate. The peripheral pressurization plates are provided with cutting slots for cutting equipment to cut the coal seam simulation layer.

9. The method for simulating water inrush during mining of coal seams with concealed geological structures according to claim 8, characterized in that, The crack distribution pattern after the experiment was reconstructed using CT scanning and slice inversion methods.

Images