Strip mine coal floor water inrush coefficient threshold determination method based on similar material simulation

Abstract

The invention provides a similar material simulation-based strip mine coal floor water inrush coefficient threshold determination method, and relates to the technical field of strip mine floor water inrush prevention and control. The method comprises the following steps: selecting similar parameters in a similar material simulation test, constructing a similar material simulation test device, and preparing a similar material; designing a monitoring equipment arrangement scheme, carrying out a physical model test, analyzing a pressure and deformation change rule in the strip mine floor water inrush process under the current working condition, recording a water pressure value at the water inrush moment, calculating a critical water inrush coefficient based on a water inrush coefficient method, determining a water inrush coefficient threshold value under the condition, and determining the water inrush coefficient threshold value by adjusting the thickness of a water-resisting layer and the lithology of the water-resisting layer. And critical water inrush pressure and water-resisting layer thickness of strip mine floor water inrush under different working conditions are determined respectively, and water inrush coefficient threshold values under different geological conditions are determined. According to the method, the water inrush process can be visually displayed, the water inrush coefficients under different geological conditions are determined, and theoretical support can be provided for water inrush prediction and prevention and control of the open pit coal mine.

Description

Technical Field

[0001] The present invention relates to the technical field of open-pit mine floor water inrush prevention and control, and in particular to a method for determining an open-pit mine coal floor water inrush coefficient threshold based on similar material simulation. Background Art

[0002] When an open-pit mine reaches the coal floor, if there is a pressurized aquifer at a certain distance below the coal floor, the pressurized water under the coal seam may break through the barrier of the coal seam floor rock layer during the coal mining process and rush into the open-pit mine with great water pressure and water flow, causing a sharp increase in the water volume in the mine, which in turn poses a serious threat to the safe production of the mine.

[0003] According to the calculation formula of water inrush coefficient in the Regulations on Coal Mine Water Prevention and Control (2009), , where T is the water inrush coefficient, P is the water pressure on the bottom plate aquiclude, and M is the thickness of the bottom plate aquiclude.

[0004] There are currently several main methods for determining the water inrush coefficient threshold:

[0005] (1) Empirical method:

[0006] Based on statistical analysis of extensive geological and hydrogeological data, my country proposed threshold values ​​for the water inrush coefficient in the 1960s. In normal geological zones, the threshold is typically 0.1 MPa / m; in tectonic damage zones, the threshold is 0.06 MPa / m. These empirical values ​​are based on the characteristics of floor water inrush during mining operations in major water-rich mining areas in North my country (such as Jiaozuo, Fengfeng, and Handan-Xingxing). The international reference value is the concept of relative aquiclude thickness proposed by Hungarian scholar Wegfrens, with a threshold of 1.5 m / atm. my country's water inrush coefficient threshold of 0.06 MPa / m is derived from this standard after converting and adjusting units.

[0007] (2) Theoretical analysis method:

[0008] The water inrush coefficient is calculated by establishing theoretical models of groundwater dynamics and rock mechanics, combined with actual geological and hydrogeological conditions. The model usually considers the motion equation of groundwater flow, the stress-strain relationship of the surrounding rock, and boundary conditions. For example, the water inrush coefficient is calculated as: , where T represents the water inrush coefficient, K is the permeability coefficient of the rock, h is the water head height, μ is the viscous resistance of the medium, and L is the length of the path through which the water flows.

[0009] (3) Statistical analysis method:

[0010] Through statistical analysis of a large number of water inrush cases, the distribution pattern and threshold of the water inrush coefficient were determined. For example, Yin Shangxian et al. classified the thickness of the aquiclude into five types: extremely thin, thin, moderately thick, thick, and extremely thick, and used the water resistance coefficient to modify the thickness of the different aquiclude thickness types.

[0011] (4) On-site monitoring test method:

[0012] In actual projects, parameters such as groundwater pressure and aquiclude thickness are obtained through drilling and water injection tests, the water inrush coefficient is calculated, and the threshold is verified and adjusted in combination with on-site monitoring data.

[0013] However, the above methods all have certain shortcomings, including the following aspects:

[0014] (1) The above methods are basically based on the published empirical values ​​and theoretical calculation formulas of water inrush coefficients, and are not applicable to the determination of the floor water inrush coefficient of open-pit mines;

[0015] (2) There are relatively few cases of water inrush in open-pit mines, and the amount of data available for statistical analysis is too small to be representative or universal.

[0016] (3) The on-site monitoring method can directly obtain the actual hydrogeological data of the mine and reflect the actual water inrush situation. However, the monitoring range and accuracy may be limited by equipment and environmental conditions, and long-term continuous monitoring is required to obtain reliable results. On-site implementation is also difficult and inefficient. Summary of the Invention

[0017] In response to the shortcomings of the existing technology, the present invention provides a method for determining the threshold value of the water inrush coefficient of the coal floor in an open-pit mine based on similar material simulation. The method simulates the floor water inrush process under different working conditions, analyzes the influencing factors of the water inrush in the open-pit mine floor, identifies the critical pressure water pressure and the thickness of the impermeable layer at the moment of water inrush, and determines the water inrush coefficient threshold under complex conditions based on the water inrush coefficient method, providing theoretical and technical support for solving the technical difficulties of accurately evaluating and preventing the danger of water inrush in open-pit mines.

[0018] A method for determining a threshold value of water inrush coefficient of an open-pit mine floor based on similar material simulation includes the following steps:

[0019] Step 1: Selection of similar parameters in similar material simulation tests;

[0020] The similarity parameters specifically include geometric similarity ratio, bulk density similarity ratio and stress similarity ratio;

[0021] The geometric similarity ratio is specifically: ;

[0022] Where: C L is the geometric similarity ratio, L p For prototype size, Lm is the model size;

[0023] The bulk density similarity ratio is specifically: ;

[0024] Where: C γ is the bulk density similarity ratio, γ p is the bulk density of the prototype material, γ m is the bulk density of the model material;

[0025] The stress similarity ratio is specifically: ;

[0026] Where: C σ is the stress similarity ratio, σ p is the prototype stress, σ m is the model stress.

[0027] Step 2: Construction of similar material simulation test device;

[0028] It specifically includes a bracket, a box body, an open-pit mine similar material model and a water supply mechanism; the box body includes a transparent glass test box and a water pressure control box, both of which are fixedly installed on the bracket; the open-pit mine similar material model is located inside the transparent glass test box; the water pressure control box includes a first water pressure control box and a second water pressure control box, which are symmetrically arranged on both sides of the transparent glass test box, the first water pressure control box and the transparent glass test box are connected through a water inlet window, and the second water pressure control box and the transparent glass test box are connected through a drainage window; the water supply mechanism is distributed in parallel with the box body, the water outlet of the water supply mechanism is connected to the water pressure control box, and the return water outlet of the water supply mechanism is connected to the second water pressure control box.

[0029] The transparent glass test box and the water pressure control box both adopt transparent structures.

[0030] A water inlet orifice plate is fixedly installed at the water inlet window between the water pressure control box and the transparent glass test box, and a filter screen is fixedly mounted on the surface of the water inlet orifice plate.

[0031] A water level observation tube is installed outside the transparent glass test box, a water level scale is provided on the surface of the water level observation tube, and the bottom end of the water level observation tube is connected to the middle and lower part of the transparent glass test box.

[0032] The open-pit mine similar material model includes an aquifer, an aquiclude and a slope layer; the aquifer, aquiclude and slope layer are distributed sequentially from bottom to top.

[0033] The water supply mechanism includes a water tank, a water pump, a water injection pipe, a return water main pipe and a return water branch pipe; the water pump is fixedly arranged on the top of the water tank, the water outlet of the water pump is connected to the water inlet of the water injection pipe, and the water outlet of the water injection pipe extends to the inside of the water pressure control box; a drain port is opened at the bottom of the water pressure control box, and each drain port is connected to a return water branch pipe; one end of the return water main pipe is connected to the water tank, and the return water branch pipe is connected to the return water main pipe.

[0034] A water injection control valve and a water injection flow sensor are respectively provided on the water injection pipe; and a return water control valve is provided on the return water main pipe.

[0035] Step 3: Preparation of similar materials;

[0036] Step 3.1: Determine similarity criteria and performance requirements;

[0037] The similarity criterion is specifically as follows: if two phenomena are similar, then the dimensionless equations and single-valued conditions of the two phenomena are the same, that is, they have the same dimensionless solutions; if all dimensionless combinations of the dimensionless equations and single-valued conditions of the two phenomena are equal, then these dimensionless combinations become the similarity criterion, and the performance requirements to be achieved by similar materials are determined by the similarity criterion;

[0038] Step 3.2: Select raw materials;

[0039] Select appropriate base materials according to performance requirements;

[0040] Step 3.3: Determine the optimal ratio;

[0041] Determine the optimal ratio of raw materials through experiments and theoretical analysis;

[0042] Step 3.4: Preparation and molding;

[0043] Weigh the raw materials according to the optimal ratio; first stir the dry materials thoroughly, then add the liquid medium and continue stirring to form a uniform mixture; select the appropriate molding method based on the required shape and size.

[0044] Step 3.5: Maintenance and post-processing;

[0045] The curing specifically includes: curing the formed similar materials under corresponding environmental conditions;

[0046] The post-processing specifically includes: after the curing is completed, the performance of similar materials must be tested and evaluated through experiments to ensure that their performance is similar to that of the prototype material and meets the requirements of actual application.

[0047] Step 4: Design of monitoring equipment layout;

[0048] Step 4.1: Design of the layout of the earth pressure gauge sensor monitoring equipment;

[0049] Earth pressure gauge sensors are evenly distributed on the contact surface between the simulated mudstone aquifer bottom plate and the aquifer. Horizontal directional burial technology is used during burial to ensure that the pressure sensing surface is perpendicular to the force direction. Fine sand is then filled around the earth pressure gauge sensors for compaction.

[0050] Step 4.2: Design of distributed fiber optic monitoring equipment layout;

[0051] Distributed optical fiber is used to measure the strain inside the model. By monitoring and measuring the change in Brillouin frequency shift, the degree of strain on the optical fiber can be reversely calculated.

[0052] Step 5: Specific process of physical model test operation;

[0053] Step 5.1: Mix and stir similar materials to complete the preliminary preparations for the experiment;

[0054] Step 5.2: Complete the laying of anti-seepage cloth and aquifer inside the transparent glass test chamber. The upper surface of the aquifer should not be lower than the upper edge of the water inlet and drain holes in the vertical direction. The contact between the aquifer and the circular hole should be isolated with a filter mesh.

[0055] Step 5.3: Complete the laying of an aquiclude of the set thickness above the aquifer, ensuring close contact between the four sides of the aquiclude and the four walls of the model chamber. During the laying of the aquiclude, complete the placement of the earth pressure gauge and optical fiber.

[0056] Step 5.4: Leave a set area of ​​exposed aquiclude in the middle of the aquiclude. Cover the exposed aquiclude with a set slope and height. Ensure that the upper surface of the pit slope does not exceed the upper edge of the model chamber in height. Use weights instead of backfill on the upper part of the slope.

[0057] Step 5.5: Open the water injection control valve, start the water pump, and pump tap water from the water storage tank into the water pressure control box through the water injection pipe. The water flows through the water inlet orifice plate and the water inlet filter into the transparent glass test box and seeps into the aquifer.

[0058] Step 5.6: Observe the water level changes in the transparent glass test chamber in real time through the water level observation tube until the water level in the water level observation tube reaches the bottom plate of the waterproof layer, then turn off the water pump;

[0059] Step 5.7: Collect the fiber optic data for the first time. After the collection is completed, water is injected into the two water pressure control boxes at the same speed. At the same time, the soil pressure gauge data is recorded.

[0060] Step 5.8: When water inrush occurs in the aquitard, stop water injection, shut down the monitoring equipment, and record and store the real-time pressure data measured by the earth pressure gauge in the aquitard and the real-time water level data displayed by the water level observation tube. Simultaneously, record and store the fiber optic monitoring data in the aquitard.

[0061] Step 5.9: Summarize all collected data, analyze the pressure and deformation changes during water inrush in the open-pit mine floor under the current working conditions, record the water pressure value at the time of water inrush, calculate the critical water inrush coefficient based on the water inrush coefficient method, determine the water inrush coefficient threshold under these conditions, and complete the test.

[0062] Step 5.10: Adjust the thickness and lithology of the aquiclude and repeat steps 5.1 to 5.9 to determine the critical water inrush pressure and aquiclude thickness for water inrush from the open-pit mine floor under different working conditions, and calculate the water inrush coefficient threshold under different geological conditions.

[0063] The beneficial effects of adopting the above technical solution are:

[0064] The present invention provides a method for determining the threshold value of the water inrush coefficient of the coal floor of an open-pit mine based on similar material simulation. Specifically, a similar material simulation test device is used to conduct simulation tests on the water inrush process under different mining conditions in the open-pit mine. The deformation and destruction process of the coal floor aquiclude under different geological conditions is simulated. By analyzing the test simulation results, the water pressure value and the thickness of the aquiclude corresponding to the critical water inrush moment are found, and the water inrush coefficient threshold value is determined. This method can intuitively display the water inrush process, is easy to implement, and is flexible to operate. The water inrush coefficient threshold value under complex conditions can be determined through experiments, providing a scientific basis for water inrush hazard assessment and the formulation of prevention and control measures for open-pit mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a flow chart of a method for determining a threshold value of water inrush coefficient of an open-pit coal floor based on similar material simulation according to the present invention;

[0066] Figure 2 This is a schematic diagram of a similar material simulation test device;

[0067] Among them, 1 is a fixed bracket, 2 is a transparent glass test box, 3 is the first water pressure control box, 4 is the second water pressure control box, 5 is the second water inlet orifice plate, 6 is the first water inlet orifice plate, 7 is a water level observation tube, 8 is aquifer, 9 is aquiclude, 10 is slope layer, 11 is a water storage tank, 12 is a water pump, 13 is water injection pipeline, 14 is return water main pipe, 15 is return water branch pipe, 16 is water injection control valve, 17 is water injection flow sensor, 18 is return water control valve;

[0068] Figure 3 This is a mining status map of the first mining area in the example of the present invention;

[0069] Figure 4 This is a simplified schematic diagram of the hydrogeological model of the mining area in the example of the present invention;

[0070] Figure 5 This is a diagram showing the arrangement of the soil pressure gauge monitoring equipment of the present invention;

[0071] Figure 6 This is a diagram showing the layout of the distributed optical fiber monitoring equipment of the present invention;

[0072] Figure 7 Schematic diagram of the location of the water burst point in the example of the present invention;

[0073] Figure 8 This is a data analysis diagram of each soil pressure monitoring point in the example of the present invention;

[0074] Among them, (a) - T1 soil pressure gauge monitoring data, (b) - T2 soil pressure gauge monitoring data, (c) - T3 soil pressure gauge monitoring data, (d) - T4 soil pressure gauge monitoring data, (e) - T5 soil pressure gauge monitoring data, (f) - T6 soil pressure gauge monitoring data, (g) - T7 soil pressure gauge monitoring data, (h) - T8 soil pressure gauge monitoring data, (i) - T9 soil pressure gauge monitoring data;

[0075] Figure 9 This is an analysis diagram of optical fiber monitoring data in an example of the present invention. DETAILED DESCRIPTION

[0076] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0077] The open-pit mine in a certain area of ​​Pakistan's Thar coalfield has a gentle stratum dip and no faults. The main mining seams are C1 and C2. As the C2 seam is mined, the coal floor aquifer is exposed. 2m below the aquifer lies a confined aquifer, posing a risk of water inrush. The slope angle of the inner dump is 16°, the slope angle of the working side is 12°, and the slope height is 210m. Figure 3 As shown in the figure, the rock layer distribution is simplified into slope body layer, aquiclude and aquifer, and the following is established: Figure 4 The experimental model.

[0078] The embodiment of the present invention specifically realizes the determination of the water inrush coefficient threshold of the coal floor of the open-pit mine.

[0079] A method for determining the threshold value of water inrush coefficient of open-pit mine floor based on similar material simulation, the process is as follows Figure 1 As shown, the following steps are included:

[0080] Step 1: Selection of similar parameters in similar material simulation tests;

[0081] The similarity parameters specifically include geometric similarity ratio, bulk density similarity ratio and stress similarity ratio;

[0082] The test model should take into account the test bench specifications and on-site conditions, and select reasonable geometric similarity ratios, bulk density similarity ratios, and stress similarity ratios;

[0083] The geometric similarity ratio is specifically: ;

[0084] Where: C L is the geometric similarity ratio, L p The prototype size of the open pit mine, m, L m is the model size, m;

[0085] The bulk density similarity ratio is specifically: ;

[0086] Where: C γ is the bulk density similarity ratio, γ p is the bulk density of the prototype material, kN / m 3 , γ m is the bulk density of the model material, kN / m 3 ;

[0087] The stress similarity ratio is specifically: ;

[0088] Where: C σ is the stress similarity ratio, σ p is the prototype stress, Kpa, σ m is the model stress, KPa;

[0089] In this embodiment, the similar material model is designed based on the similarity theory according to the physical and mechanical properties of the actual rock formation and the geometric shape of the mine. The geometric similarity ratio is determined as ; Bulk density similarity ratio is , the stress similarity ratio is .

[0090] Step 2: Construction of similar material simulation device;

[0091] Construct a 3m×3m similar material simulation test device, as shown in the schematic diagram Figure 2 As shown. It includes: a fixing bracket 1, a transparent glass test box 2, a first water pressure control box 3, a second water pressure control box 4, a second water inlet orifice plate 5, a first water inlet orifice plate 6, a water level observation tube 7, a water storage tank 11, a water pump 12, a water injection pipeline 13, a return water main pipe 14, a return water branch pipe 15, a water injection control valve 16, a water injection flow sensor 17, and a return water control valve 18.

[0092] The open pit mine similar material model includes an aquifer 8, an aquiclude 9 and a slope layer 10; the aquifer, aquiclude and slope layer are sequentially distributed from bottom to top.

[0093] Step 3: Preparation of similar materials;

[0094] Similar materials refer to materials that are similar to the original materials in physical, mechanical and other properties. Their preparation methods vary depending on the specific application and similarity requirements. The preparation steps are as follows:

[0095] Step 3.1: Determine similarity criteria and performance requirements;

[0096] The similarity criterion is specifically: if two phenomena are similar, then the dimensionless equations and single-valued conditions for the two phenomena are identical, meaning they have the same dimensionless solutions. If all dimensionless combinations of the dimensionless equations and single-valued conditions for the two phenomena are equal, then these dimensionless combinations become the similarity criterion, specifically defining the key performance indicators of the prototype material, such as mechanical and physical properties. The similarity criterion is determined based on the specific application, and the performance requirements to be achieved by similar materials are determined through the similarity criterion.

[0097] Step 3.2: Select raw materials;

[0098] Select appropriate base materials based on performance requirements; there are many common similar material simulation raw materials. Aggregates such as quartz sand, fly ash, and loess serve as the skeleton, determining basic properties such as density and strength; binders such as lime and gypsum are used to bond aggregates, affecting material strength and modulus; regulators such as bentonite and vaseline can adjust moisture content, friction coefficient and other properties; additives such as fibers, metal powders, and chemicals are used to enhance toughness, adjust density, or control setting time.

[0099] Step 3.3: Determine the optimal ratio;

[0100] Determine the optimal ratio of raw materials through experiments and theoretical analysis;

[0101] In this embodiment, an orthogonal test method is used to study the performance variation of similar materials under different ratios to find the optimal combination that meets the similarity criterion;

[0102] Step 3.4: Preparation and molding;

[0103] Weigh the raw materials according to the optimal ratio; first stir the dry materials thoroughly, then add an appropriate amount of water or other liquid medium and continue stirring to form a uniform mixture; select the appropriate molding method according to the required shape and size.

[0104] Step 3.5: Maintenance and post-processing;

[0105] Curing specifically involves curing the formed similar materials under appropriate environmental conditions to ensure stable performance. For example, cement-based similar materials generally require curing in a humid environment for a certain period of time. If needed, similar materials can be treated with surface treatments such as polishing and coating to meet specific testing or application requirements.

[0106] The post-processing is specifically as follows: after the curing is completed, the performance of similar materials must be tested and evaluated through experiments, such as compressive strength test, shear strength test, density test and moisture content test, to ensure that its performance is similar to that of the prototype material and meets the requirements of actual application.

[0107] The basic aggregate of the aquifer analog material is a mixture of sand and gravel. Based on the analog ratio, the physical and mechanical parameters of the mudstone in the coal floor aquiclude were calculated. The corresponding prototype and model physical parameters are shown in Table 1.

[0108] Table 1 Comparison of physical and mechanical parameters between model mudstone and prototype mudstone;

[0109] mudstone <![CDATA[Unit weight (KN / m 3 )]]> Compressive strength (MPa) Cohesion (KPa) Internal friction angle (°) prototype 15.58~20.29 0.135~1.99 9~89 29.9~54.1 Model 15.58~20.29 0.0027~0.0398 0.18~1.78 29.9~54.1

[0110] The basic aggregates selected for the raw material ratio are fine sand and loess with a particle size of 0~2mm, the binder materials are gypsum and lime, and the regulator is bentonite.

[0111] An orthogonal experiment was designed to determine the optimal ratio that meets the physical and mechanical requirements of the model mudstone. Many factors can influence experimental results in a single study, but due to experimental limitations, a comprehensive consideration is not possible. Generally, 3 to 7 factors are appropriate. When determining the number of levels for a factor, factors with a significant impact on the experimental results can have more levels, while maintaining a reasonable spacing between levels to facilitate analysis of the experimental results. The four factors in this orthogonal experiment were: cementitious ratio (A), lime-gypsum ratio (B), bentonite content (C), and moisture content (D). Each factor had four levels: cementitious ratios of 8:1, 10:1, 12:1, and 14:1; lime-gypsum ratios of 2:1, 1:2, 3:1, and 1:3; bentonite content of 6%, 8%, 10%, and 12%; and moisture content of 8%, 10%, 12%, and 14%. The ranges for each factor are shown in Table 2.

[0112] Table 2. Orthogonal test level factor table;

[0113] serial number A-bone glue ratio B-lime-gypsum ratio C-bentonite content% D-moisture content% 1 8：1 2：1 6 8 2 10：1 1：2 8 10 3 12：1 3：1 10 12 4 14：1 1：3 12 14

[0114] Note: Bentonite content is the percentage of bone glue mass; water content is the percentage of bone glue mass + bentonite mass;

[0115] Table 3 Orthogonal test plan table;

[0116] serial number A-bone glue ratio B-lime-gypsum ratio C-bentonite content% D-moisture content% 1 8：1 2：1 6 8 2 8：1 1：2 8 10 3 8：1 3：1 10 12 4 8：1 1：3 12 14 5 10：1 2：1 8 12 6 10：1 1：2 6 14 7 10：1 3：1 12 8 8 10：1 1：3 10 10 9 12：1 2：1 10 14 10 12：1 1：2 12 12 11 12：1 3：1 6 10 12 12：1 1：3 8 8 13 14：1 2：1 12 10 14 14：1 1：2 10 8 15 14：1 3：1 8 14 16 14：1 1：3 6 12

[0117] An orthogonal experimental scheme was designed, as shown in Table 3. Test samples were prepared and tested. According to the test results, the material ratio that meets the physical and mechanical parameters of the aquiclude model is: bone glue ratio of 8:1, lime gypsum ratio of 3:1, bentonite content of 10%, and moisture content of 12%.

[0118] Step 4: Design of monitoring equipment layout;

[0119] Step 4.1: Design of the layout of the earth pressure gauge sensor monitoring equipment;

[0120] In order to monitor the stress changes of the mudstone aquiclude under the action of bottom plate pressure water, the DMTY series vibrating string soil pressure gauge is used as the soil pressure gauge. The soil pressure gauge sensors are evenly distributed on the contact surface between the simulated mudstone aquiclude bottom plate and the aquifer. The deformation and damage positions of the aquiclude are mainly concentrated in the exposed area, so monitoring points are evenly set in the exposed area of ​​the bottom plate. During the burial process, a horizontal directional burial process is adopted to ensure that the pressure sensing surface is perpendicular to the force direction, and fine sand is filled around the soil pressure gauge sensor for compaction to avoid stress transmission distortion. The DH3816N static stress and strain test analysis system produced by Jiangsu Donghua Testing Technology Co., Ltd. is used for data collection. The system is based on the high-precision resistance strain principle and is equipped with a multi-channel synchronous acquisition module. The sampling frequency range is: 0.1Hz~10kHz, the range is: ±5000με, the accuracy level is: 0.1%FS, and it can accurately capture the transient response characteristics of soil pressure during dynamic loading. Data is recorded every 10s during the test. The DMTY series strain type soil pressure gauge layout monitoring plan is as follows Figure 5 shown.

[0121] Step 4.2: Design of distributed fiber optic monitoring equipment layout;

[0122] Distributed optical fiber is used to measure the strain inside the model; when light propagates in the optical fiber, it interacts with the acoustic wave field in the optical fiber to generate Brillouin scattered light. When strain acts on the optical fiber, its refractive index and acoustic wave propagation speed will change, and this change will further cause the Brillouin frequency shift to change. By monitoring and measuring the change in the Brillouin frequency shift, the degree of strain borne by the optical fiber can be reversely calculated. In this experiment, a polyurethane optical fiber with a diameter of 2mm was selected, model NZS-DSS-C07, which can minimize the resistance within the slope model. A double-ended high-precision distributed optical fiber strain demodulator, model fTB2505, was used for data acquisition. Considering that the distributed optical fiber strain demodulator can only measure one closed optical fiber, in order to monitor the strain pattern of the exposed area of ​​the aquiclude, the optical fiber is divided into several monitoring lines, which are evenly laid in an S shape on the simulated mudstone aquiclude. The two ends are connected to the BOFDA demodulator through optical fiber jumpers to collect test data. The optical fiber data is set to be recorded once every 1 minute until the bottom plate damage stops. See the distributed optical fiber equipment layout plan. Figure 6 .

[0123] Step 5: Specific process of physical model test operation;

[0124] Step 5.1: Mix and stir similar materials to complete the preliminary preparations for the experiment;

[0125] Step 5.2: Complete the installation of the impermeable cloth and aquifer inside the transparent glass test chamber. Lay a 30cm thick layer of river sand and gravel mixture on top of the waterproof plastic film at the bottom as the aquifer, ensuring a smooth surface. Ensure the upper surface of the aquifer is at least as high as the upper edges of the inlet and outlet orifices. Use gauze to isolate the contact area between the aquifer and the circular holes to prevent sand from entering the hydraulic pressure control box. Place the earth pressure gauge in the designated location according to the installation plan.

[0126] Step 5.3: Lay the aquiclude above the aquifer. Lay a 2 cm thick layer of prepared mudstone on top of the aquifer and compact it with hammering to serve as a simulated mudstone aquiclude. Ensure close contact between the four sides of the aquiclude and the four walls of the transparent glass test chamber to achieve a seal. During the aquiclude installation, complete the placement of the earth pressure gauge and fiber optic sensor.

[0127] Step 5.4: Leave a 1.8m x 0.9m exposed aquiclude in the center of the aquiclude. Cover the surrounding area with a slope of a certain slope and height. Use sand to create the slope shape and weight it, simulating the load on the mudstone aquiclude. Ensure that the upper surface of the pit slope does not exceed the upper edge of the transparent glass test box in height. The working side (west side) slope angle is 12°, the inner dump (east side) slope angle is 16°, and the south and north side slope angles are 22°.

[0128] Step 5.5: Open the water injection control valve, start the water pump, and pump tap water from the water storage tank into the water pressure control box through the water injection pipe. The water flows through the water inlet orifice plate and the water inlet filter into the transparent glass test box and seeps into the aquifer.

[0129] Step 5.6: Observe the water level changes in the transparent glass test chamber in real time through the water level observation tube until the water level in the water level observation tube reaches the level of the waterproof layer bottom plate, then turn off the water pump;

[0130] Step 5.7: After collecting the fiber optic data for the first time, connect the water injection pipes to the water tanks on both sides and inject water into the water tanks at the same speed. At the same time, start recording the earth pressure gauge data.

[0131] Step 5.8: When water inrush occurs in the aquitard, stop water injection, shut down the monitoring equipment, and record and store the real-time pressure data measured by the earth pressure gauge sensor in the aquitard and the real-time water level data displayed by the water level observation tube. Simultaneously, record and store the fiber optic monitoring data in the aquitard.

[0132] Step 5.9: Summarize all collected data, analyze the changing patterns of various parameters during the water inrush process in the open-pit mine floor under the current working conditions, record the water pressure at the time of water inrush, calculate the water inrush coefficient, determine the water inrush coefficient threshold under these conditions, and complete the test.

[0133] This embodiment also includes the analysis of test results, which is as follows:

[0134] Step 6: Test results analysis:

[0135] Step 6.1: Macro deformation and failure characteristics analysis;

[0136] (1) After the test began, as the water level in the water tanks on both sides rose, the exposed middle part of the aquiclude gradually bulged upward and deformed. Until the end of the test, no crack water inrush occurred in this part.

[0137] (2) A crack appeared near the north slope corner, and water gushed out. The location of the water burst point is as follows: Figure 7 shown.

[0138] Step 6.2: Analysis of soil pressure monitoring results;

[0139] The soil pressure gauge data at each point measured in the test are as follows Figure 8As shown. Among them, (a) is the monitoring data of the soil pressure gauge T1, (b) is the monitoring data of the soil pressure gauge T2, (c) is the monitoring data of the soil pressure gauge T3, (d) is the monitoring data of the soil pressure gauge T4, (e) is the monitoring data of the soil pressure gauge T5, (f) is the monitoring data of the soil pressure gauge T6, (g) is the monitoring data of the soil pressure gauge T7, (h) is the monitoring data of the soil pressure gauge T8, and (i) is the monitoring data of the soil pressure gauge T9;

[0140] According to relevant regulations and provisions on coal mine water prevention and control in my country, the water inrush coefficient method is generally used to evaluate the degree of water inrush danger in coal mine floors: Where: T is the water inrush coefficient, MPa / m, P is the water pressure on the bottom plate aquiclude, MPa, and M is the thickness of the bottom plate aquiclude, m. The water inrush coefficients at each point of the earth pressure gauge are shown in Table 4:

[0141] Table 4 Water inrush coefficient at each point of earth pressure gauge;

[0142] Earth pressure gauge number Confined water pressure P (MPa) Thickness of water barrier M(m) Water inrush coefficient T (MPa / m) T1 0.003 0.02 0.15 T2 0.00337 0.02 0.1685 T3 0.00328 0.02 0.164 T4 0.00364 0.02 0.182 T5 0.00376 0.02 0.188 T6 0.00279 0.02 0.1395 T7 0.00393 0.02 0.198 T8 0.00334 0.02 0.167 T9 0.00342 0.02 0.171

[0143] The water pressure at the time of water inrush collected by soil pressure gauges T1 to T9 ranged from 0.00279 to 0.00393 MPa. The location where the water inrush occurred was closest to the T7 monitoring point, and the water inrush coefficient at this location was 0.198 MPa / m. Therefore, the water inrush coefficient threshold under this condition was determined to be 0.198 MPa / m.

[0144] Step 6.3: Fiber optic monitoring results analysis;

[0145] Draw an analysis chart based on the optical fiber monitoring data at the time of water inrush, as shown in the following figure Figure 9 As shown in the figure, the exposed middle portion of the simulated mudstone aquiclude in the model experiences significant strain due to the aquifer water pressure, with an average strain ranging from 300με to 360με and a maximum strain of 490.791με. The test results indicate that a water inrush occurred between fiber-optic monitoring lines JC1 and JC2. Analysis of the fiber-optic data collected in the figure above indicates that, due to the slope load, the strain difference between monitoring lines JC2 and JC1 is significant, leading to shear failure and cracks at this location, which in turn causes a water inrush. The fiber-optic monitoring results can be used to analyze the mechanism of the water inrush.

[0146] The monitoring data analysis results from this example clearly define the water inrush coefficient threshold under a specific operating condition in this open-pit mine. The water inrush point occurs at the toe of the slope, primarily due to shear failure in the rock mass, which creates cracks and provides a channel for water flow. This example only illustrates a water inrush test under one operating condition. Based on the research objectives, test models for different operating conditions can be constructed to determine the water inrush coefficient threshold under different conditions.

[0147] The above description is merely an illustration of the preferred embodiments of the present disclosure and the technical principles employed. Those skilled in the art should understand that the scope of the invention encompassed by the embodiments of the present disclosure is not limited to technical solutions formed by specific combinations of the aforementioned technical features. It also encompasses other technical solutions formed by any combination of the aforementioned technical features or their equivalents, without departing from the aforementioned inventive concept. For example, a technical solution formed by replacing the aforementioned features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. A method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation, characterized in that: The following steps are involved: Step 1: Selection of similar parameters in similar material simulation tests; Step 2: Construction of similar material simulation test device; Step 3: Preparation of similar materials; Step 4: Design the monitoring equipment layout plan; Step 5: Conduct physical model test operations to determine the threshold value of water inrush coefficient under different geological conditions.

2. The method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation according to claim 1 is characterized in that: The similarity parameters in step 1 specifically include geometric similarity ratio, bulk density similarity ratio and stress similarity ratio; The geometric similarity ratio is specifically: ; Where: C L is the geometric similarity ratio, L p For prototype size, L m is the model size; The bulk density similarity ratio is specifically: ; Where: C γ is the bulk density similarity ratio, γ p is the bulk density of the prototype material, γ m is the bulk density of the model material; The stress similarity ratio is specifically: ; Where: C σ is the stress similarity ratio, σ p is the prototype stress, σ m is the model stress.

3. The method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation according to claim 1, characterized in that: The similar material simulation test device described in step 2 specifically includes a bracket, a box, an open-pit mine similar material model and a water supply mechanism; the box includes a transparent glass test box and a water pressure control box, both of which are fixedly installed on the bracket; the open-pit mine similar material model is located inside the transparent glass test box; the water pressure control box includes a first water pressure control box and a second water pressure control box, which are symmetrically arranged on both sides of the transparent glass test box, the first water pressure control box and the transparent glass test box are connected through a water inlet window, and the second water pressure control box and the transparent glass test box are connected through a drainage window; the water supply mechanism is distributed in parallel with the box, the water outlet of the water supply mechanism is connected to the water pressure control box, and the return water port of the water supply mechanism is connected to the second water pressure control box; The transparent glass test box and the water pressure control box both adopt transparent structures; A water inlet orifice plate is fixedly installed at the water inlet window between the water pressure control box and the transparent glass test box, and a water inlet filter is fixedly mounted on the surface of the water inlet orifice plate; A water level observation tube is installed on the outside of the transparent glass test box, a water level scale is provided on the surface of the water level observation tube, and the bottom end of the water level observation tube is connected to the middle and lower part of the transparent glass test box; The open pit mine similar material model includes an aquifer, an aquiclude and a slope layer; the aquifer, aquiclude and slope layer are sequentially distributed from bottom to top; The water supply mechanism includes a water storage tank, a water pump, a water injection pipe, a return water main pipe and a return water branch pipe; the water pump is fixedly installed on the top of the water storage tank, the water outlet of the water pump is connected to the water inlet of the water injection pipe, and the water outlet of the water injection pipe extends to the inside of the water pressure control box; a drainage port is opened at the bottom of the water pressure control box, and each drainage port is connected to a return water branch pipe; one end of the return water main pipe is connected to the water storage tank, and the return water branch pipe is connected to the return water main pipe; A water injection control valve and a water injection flow sensor are respectively provided on the water injection pipe; and a return water control valve is provided on the return water main pipe.

4. The method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation according to claim 1, characterized in that: The step 3 specifically includes the following steps: Step 3.1: Determine similarity criteria and performance requirements; The similarity criterion is specifically as follows: if two phenomena are similar, then the dimensionless equations and single-valued conditions of the two phenomena are the same, that is, they have the same dimensionless solutions; if all dimensionless combinations of the dimensionless equations and single-valued conditions of the two phenomena are equal, then these dimensionless combinations become the similarity criterion, and the performance requirements to be achieved by similar materials are determined by the similarity criterion; Step 3.2: Select raw materials; Select appropriate base materials according to performance requirements; Step 3.3: Determine the optimal ratio; Determine the optimal ratio of raw materials through experiments and theoretical analysis; Step 3.4: Preparation and molding; Weigh all raw materials according to the optimal ratio; first stir the dry materials thoroughly, then add the liquid medium and continue stirring to form a uniform mixture; select the appropriate molding method based on the desired shape and size; Step 3.5: Maintenance and post-processing; The curing specifically includes: curing the formed similar materials under corresponding environmental conditions; The post-processing specifically includes: after the curing is completed, the performance of similar materials must be tested and evaluated through experiments to ensure that their performance is similar to that of the prototype material and meets the requirements of actual application.

5. The method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation according to claim 1, characterized in that: The step 4 specifically includes the following steps: Step 4.1: Design of the layout of the earth pressure gauge sensor monitoring equipment; Earth pressure gauge sensors are evenly distributed on the contact surface between the simulated mudstone aquifer bottom plate and the aquifer. Horizontal directional burial technology is used during burial to ensure that the pressure sensing surface is perpendicular to the force direction. Fine sand is then filled around the earth pressure gauge sensors for compaction. Step 4.2: Design of distributed fiber optic monitoring equipment layout; Distributed optical fiber is used to measure the strain inside the model; by monitoring and measuring the change in Brillouin frequency shift, the degree of strain on the optical fiber is reversely calculated.

6. The method for determining the threshold value of water inrush coefficient of open-pit coal floor based on similar material simulation according to claim 1, characterized in that: The step 6 specifically includes the following steps: Step 5.1: Mix and stir similar materials to complete the preliminary preparations for the experiment; Step 5.2: Complete the laying of anti-seepage cloth and aquifer inside the transparent glass test chamber. The upper surface of the aquifer should not be lower than the upper edge of the water inlet and drain holes in the vertical direction. The contact between the aquifer and the circular hole should be isolated with a filter mesh. Step 5.3: Complete the laying of an aquiclude of the set thickness above the aquifer, ensuring close contact between the four sides of the aquiclude and the four walls of the model chamber. During the laying of the aquiclude, complete the placement of the earth pressure gauge and optical fiber. Step 5.4: Leave a set area of ​​exposed aquiclude in the middle of the aquiclude. Cover the exposed aquiclude with a set slope and height. Ensure that the upper surface of the pit slope does not exceed the upper edge of the model chamber in height. Weights can be used instead of backfill on the upper part of the slope. Step 5.5: Open the water injection control valve, start the water pump, and pump tap water from the water storage tank into the water pressure control box through the water injection pipe. The water flows through the water inlet orifice plate and the water inlet filter into the transparent glass test box and seeps into the aquifer. Step 5.6: Observe the water level changes in the transparent glass test chamber in real time through the water level observation tube until the water level in the water level observation tube reaches the bottom plate of the waterproof layer, then turn off the water pump; Step 5.7: Collect the fiber optic data for the first time. After the collection is completed, water is injected into the two water pressure control boxes at the same speed. At the same time, the soil pressure gauge data is recorded. Step 5.8: When water inrush occurs in the aquitard, stop water injection, shut down the monitoring equipment, and record and store the real-time pressure data measured by the earth pressure gauge in the aquitard and the real-time water level data displayed by the water level observation tube. Simultaneously, record and store the fiber optic monitoring data in the aquitard. Step 5.9: Summarize all collected data, analyze the pressure and deformation changes during water inrush in the open-pit mine floor under the current working conditions, record the water pressure value at the time of water inrush, calculate the critical water inrush coefficient based on the water inrush coefficient method, determine the water inrush coefficient threshold under these conditions, and complete the test. Step 5.10: Adjust the thickness and lithology of the aquiclude and repeat steps 5.1 to 5.9 to determine the critical water inrush pressure and aquiclude thickness for water inrush from the open-pit mine floor under different working conditions, and calculate the water inrush coefficient threshold under different geological conditions.

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