Testing device and method for critical hydraulic gradient of water inrush and sand collapse in sandy soil

Abstract

This application provides a testing device and method for the critical hydraulic gradient of sandy soil undergoing sudden water inrush and sand collapse. The testing device includes: a transparent seepage chamber, a rubber tube, a permeable plate, a rock fissure simulation plate, a pressurization unit, an inlet pipe, an outlet pipe, a pressure sensor, a flow meter, a microparticle concentration detector, and a differential pressure transmitter. The testing device and method for the critical hydraulic gradient of sandy soil undergoing sudden water inrush and sand collapse provided by this application are simple and convenient, and realize independent adjustment of the three-dimensional stress state and fluid dynamic water pressure. It can realistically simulate high ground stress and high water pressure environments, and can accurately capture the influence of the initial loss of fine clay particles on the porosity of the overall sandy soil skeleton, thereby accurately defining the critical hydraulic gradient of complex-graded silty sandy soil from "seepage" to "piping" to "overall sand collapse".

Description

Technical Field

[0001] This application relates to the field of geological engineering technology, and in particular to a testing device and method for the critical hydraulic gradient of sandy soil inrush and sand collapse. Background Technology

[0002] During coal seam mining, the overlying strata are fractured due to mining activities, forming water-conducting fracture zones. Once these fracture zones affect loose aquifers, they can easily trigger water inrush and sand bursting disasters. In some mining areas, the loose sandy soil layers (such as the fourth aquifer) have extremely complex lithology, composed of gravel, sand, clay gravel, coarse sand, medium sand, and clayey sand, with generally high clay content and significant differences in permeability. Existing permeability failure testing devices cannot realistically simulate the initiation mechanism and permeability evolution process of such loose sandy soil layers under the combined action of deep in-situ stress and high hydraulic gradients of groundwater. Furthermore, current theoretical analysis of the water inrush and sand collapse mechanism lacks precise means to define the evolution process of complex graded silty sandy soil from "seepage" to "piping" to "overall sand collapse," making it impossible to accurately determine the critical hydraulic gradient corresponding to each stage. In addition, existing methods do not systematically consider the influence of the coupling of three factors—mud content, gradation characteristics, and confining pressure—on the critical hydraulic gradient, and the obtained parameters are difficult to directly apply to the accurate calculation of coal and rock pillars for sand control in coal mines. There is also a lack of quantitative methods to determine the influence of the geometric characteristics of bottom rock fissures (such as fissure opening and angle) on the boundary conditions for initiating water inrush and sand collapse. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide a testing device and method for the critical hydraulic gradient of sandy soil inrush and sand collapse, so as to solve or partially solve the above-mentioned technical problems.

[0004] A first aspect of this application provides a testing device for the critical hydraulic gradient of sand inrush and sand collapse, comprising: a transparent seepage chamber with a rubber tube inside for holding sand samples, the rubber tube being spaced apart from the inner wall of the transparent seepage chamber; a permeable plate disposed at the top of the rubber tube and abutting against the inner wall of the transparent seepage chamber; a rock fracture simulation plate disposed at the bottom of the rubber tube and abutting against the inner wall of the transparent seepage chamber; a pressurization unit communicating with the outer wall of the transparent seepage chamber and disposed opposite to the rubber tube; an inlet pipe communicating with the top of the transparent seepage chamber and connected to a pressure sensor; an outlet pipe communicating with the bottom of the transparent seepage chamber and connected to a flow meter and a microparticle concentration detector; and a differential pressure transmitter disposed on the outside of the transparent seepage chamber and connected to both ends of the rubber tube.

[0005] Furthermore, the testing device for the critical hydraulic gradient of sand inrush and sand collapse also includes an imaging unit, which is disposed on the outside of the transparent seepage chamber and opposite to the rubber tube.

[0006] Furthermore, one end of the water inlet pipe is connected to a water storage tank, and a horizontal flow pump and a pressure stabilizing valve are connected between the water inlet pipe and the water storage tank; one end of the water outlet pipe is connected to a water collection tank.

[0007] Furthermore, the rock fracture simulation plate includes a top plate and a support grid stacked together, the top plate having fracture openings, and the bottom of the support grid having a filter screen.

[0008] A second aspect of this application provides a method for testing the critical hydraulic gradient of sand inrush and sand collapse, using the testing device for the critical hydraulic gradient of sand inrush and sand collapse as described in the first aspect above. The testing method includes: preparing a sand sample and installing it into the rubber tube; applying confining pressure to the sand sample through the pressurizing unit; applying a gradually increasing hydraulic gradient to the sand sample through the inlet pipe; and determining the critical hydraulic gradient using the flow meter, the microparticle concentration detector, or the differential pressure transmitter.

[0009] Furthermore, the critical hydraulic gradient includes the critical hydraulic gradient for leakage initiation. ,satisfy ,in, This represents the average concentration of microparticles under the background hydraulic gradient.

[0010] Furthermore, the critical hydraulic gradient includes the critical hydraulic gradient for piping. ,satisfy ,in, This is the coefficient for sudden increase in piping volume. This is the moving average of the rate of increase in microparticle concentration.

[0011] Furthermore, the critical hydraulic gradient includes the overall critical hydraulic gradient for sand erosion. , This refers to the hydraulic gradient when the flow meter reading increases abruptly, the differential pressure transmitter reading drops sharply, or the sand sample deforms or collapses.

[0012] Furthermore, the test method for the critical hydraulic gradient of sandy soil inrush and sand collapse also includes: replacing different rock fracture simulation plates and determining the critical hydraulic gradient; changing the mud content, non-uniformity coefficient or confining pressure of the sandy soil sample to determine the critical hydraulic gradient under different conditions, and constructing a critical hydraulic gradient prediction model.

[0013] Furthermore, the critical hydraulic gradient prediction model is as follows: ,in, The critical hydraulic gradient, Mud content, The coefficient of non-uniformity, For confining pressure, The fracture opening of the simulated rock fracture plate. is the regression coefficient.

[0014] A third aspect of this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the test method for the critical hydraulic gradient of sand bursting due to water inrush as described in the first aspect above.

[0015] A fourth aspect of this application provides a non-transitory computer-readable storage medium storing computer instructions for causing the computer to execute the test method for the critical hydraulic gradient of sand bursting due to water inrush as described in the first aspect above.

[0016] A fifth aspect of this application provides a computer program product, including computer program instructions that, when executed on a computer, cause the computer to perform the test method for the critical hydraulic gradient of sand bursting due to sudden water intrusion as described in the first aspect above.

[0017] As can be seen from the above, this application provides a testing device and method for the critical hydraulic gradient of sand inrush and sand collapse. The testing device includes: a transparent seepage chamber with a rubber tube inside for holding sand samples, the rubber tube being spaced apart from the inner wall of the transparent seepage chamber; a permeable plate disposed on top of the rubber tube and abutting against the inner wall of the transparent seepage chamber; a rock fracture simulation plate disposed at the bottom of the rubber tube and abutting against the inner wall of the transparent seepage chamber; a pressurization unit connected to the outer wall of the transparent seepage chamber and disposed opposite to the rubber tube; an inlet pipe connected to the top of the transparent seepage chamber and connected to a pressure sensor; an outlet pipe connected to the bottom of the transparent seepage chamber and connected to a flow meter and a microparticle concentration detector; and a differential pressure transmitter disposed on the outside of the transparent seepage chamber and connected to both ends of the rubber tube. This device, through the installation of a pressurization unit, inlet pipe, permeable plate, rock fissure simulation plate, and outlet pipe, achieves independent adjustment of three-dimensional stress state (confining pressure control) and fluid dynamic water pressure (hydraulic gradient control), realistically simulating high ground stress and high water pressure environments. The introduction of a microparticle concentration detector accurately captures the impact of the initial loss of fine clay particles on the overall porosity of the sandy soil skeleton, thus precisely defining the critical hydraulic gradient for the three stages from "seepage" to "piping" and then to "overall sand collapse." It can obtain precise parameters for seepage failure in sandy soils with different clay contents, directly serving the accurate calculation of the height of anti-sand coal and rock pillars in coal mines and the parameter optimization of grouting modification processes. This testing device and method for the critical hydraulic gradient of sandy soil inrush and sand collapse is simple, convenient, and can accurately and reliably measure the critical hydraulic gradient. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a test device for the critical hydraulic gradient of sandy soil inrush and sand collapse in an embodiment of this application.

[0020] Figure 2 This is a flowchart illustrating a method for testing the critical hydraulic gradient of sandy soil in the event of sudden water inrush and sand collapse, as described in an embodiment of this application.

[0021] Figure 3 This is a schematic diagram of the structure of an electronic device according to an embodiment of this application.

[0022] Reference numerals: 1. Transparent seepage chamber; 2. Rubber tube; 3. Sand sample; 4. Rock fissure simulation plate; 5. Permeable plate; 6. Pressurization unit; 7. Pressure sensor; 8. Pressure stabilizing valve; 9. Flow pump; 10. Water storage tank; 11. Flow meter; 12. Differential pressure transmitter; 13. Microparticle concentration detector; 14. Water collection tank; 15. Imaging unit; 16. Inlet pipe; 17. Outlet pipe. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0024] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0025] The following describes specific embodiments in conjunction with... Figures 1 to 3 The technical solution of this application will be described in detail below.

[0026] Some embodiments of this application provide a testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse, such as... Figure 1As shown, it includes: a transparent infiltration chamber 1, with a rubber tube 2 inside, the rubber tube 2 being used to hold a sand sample 3, the rubber tube 2 being spaced apart from the inner wall of the transparent infiltration chamber 1; a permeable plate 5, disposed on top of the rubber tube 2, abutting against the inner wall of the transparent infiltration chamber 1; a rock fracture simulation plate 4, disposed at the bottom of the rubber tube 2, abutting against the inner wall of the transparent infiltration chamber 1; a pressurization unit 6, communicating with the outer wall of the transparent infiltration chamber 1, and disposed opposite to the rubber tube 2; an inlet pipe 16, communicating with the top of the transparent infiltration chamber 1, the inlet pipe 16 being connected to a pressure sensor 7; an outlet pipe 17, communicating with the bottom of the transparent infiltration chamber 1, the outlet pipe 17 being connected to a flow meter 11 and a microparticle concentration detector 13; and a differential pressure transmitter 12, disposed on the outside of the transparent infiltration chamber 1, connected to both ends of the rubber tube 2.

[0027] The transparent seepage chamber 1 is a cylindrical or square chamber made of transparent, high-pressure resistant plexiglass or acrylic sheet, allowing real-time observation of the seepage evolution process. Inside the chamber is a rubber tube 2 (a transparent rubber membrane mold) for placing a sand sample 3 (referencing complex gradations of sand from actual fields). The rubber tube 2 flexibly confines the sides of the sand sample 3 without affecting lateral pressure transmission. An external water pressure loading interface connects to a pressurization unit 6 to provide flexible confining pressure simulating deep geostress. The pressurization unit 6, for example, is a pressure pump that applies pressure to the outer wall of the rubber tube 2 between the permeable plate 5 and the rock fissure simulation plate 4. The permeable plate 5 restricts the top of the sand sample 3 while allowing water from the inlet pipe 16 to enter the sand sample 3 to simulate seepage. The rock fissure simulation plate 4 restricts the bottom of the sand sample 3 and simulates the effect of fissures on seepage.

[0028] The differential pressure transmitter 12 is connected to the upper and lower ends of the sand sample 3 to monitor the head difference between the two ends of the sand sample 3 in real time, so as to adjust the hydraulic gradient. The microparticle concentration detector 13 is installed at the outlet pipe 17 at the bottom of the transparent seepage chamber 1 to record the mud content and fine sand loss rate in the overflow water in real time, so as to determine the initiation point of piping. The pressure sensor 7 can monitor the inlet water pressure, and the flow meter 11 can monitor the outlet water flow rate.

[0029] This testing device for the critical hydraulic gradient of sand inrush and sand collapse can effectively control the confining pressure and hydraulic gradient of the test based on the physical characteristics of loose sand layers. It can accurately and quantitatively measure the critical hydraulic gradient of sand under different mud contents and complex gradation conditions that cause seepage failure (including piping, soil erosion and sand collapse), providing data support for safe mining under water-bearing sand layers in coal mines and prevention and control of water inrush and sand collapse disasters.

[0030] In some embodiments, such as Figure 1As shown, the testing device for the critical hydraulic slope of sand inrush and sand collapse also includes: an imaging unit 15, which is set on the outside of the transparent seepage chamber 1 and is positioned opposite to the rubber tube 2.

[0031] A high-speed camera can be installed outside the transparent seepage chamber 1 to dynamically capture the evolution process of fine particle transport, skeleton reorganization, and eventual penetrating failure (sand collapse) inside the sand sample 3 as the hydraulic gradient increases.

[0032] In some embodiments, such as Figure 1 As shown, one end of the water inlet pipe 16 is connected to a water storage tank 10, and a horizontal flow pump 9 and a pressure stabilizing valve 8 are connected between the water inlet pipe 16 and the water storage tank 10; one end of the water outlet pipe 17 is connected to a water collection tank 14.

[0033] The horizontal flow pump 9 is connected to the water inlet pipe 16 at the top of the seepage chamber. The pressure is continuously adjusted by the pressure stabilizing valve 8 to precisely control the hydraulic gradient that evolves through seepage.

[0034] In some embodiments, the rock fracture simulation plate 4 includes a top plate and a support grid stacked together, and the top plate is provided with fracture openings.

[0035] The top plate directly contacts the sand sample 3. The top plate has specifically shaped fissure openings to simulate various water-conducting channels, including single fissures, intersecting fissures, and irregular rock cross-sections. By adjusting the fissure opening and angle, the simulation of the initiation boundary conditions for water inrush and sand collapse under different geological conditions is achieved. The support grid provides support to ensure the smooth drainage of the water-sand mixture while withstanding the axial pressure and confining pressure from above.

[0036] The testing methods of this device include, for example, the following: Preparation of sand sample 3: Extract original sand samples of the "four-content" type from the study area and determine their original gradation and mud content. According to the experimental plan, prepare sand samples 3 with specific mud content and gradation, compact them in layers inside the rubber tube 2, and install them in the multi-field coupled transparent seepage chamber 1. Apply confining pressure: Inject water into the transparent seepage chamber 1 through the pressurization unit 6 to pressurize the sand sample 3 to reach the preset lateral confining pressure value, simulating its in-situ stress state. Gradually apply hydraulic gradient: Start the horizontal flow pump 9 to slowly and stepwise increase the water pressure from the top of the sand sample 3. Data acquisition and failure determination: Stay at each hydraulic gradient step for a certain period of time and record the water pressure difference between the upper and lower ends and the flow rate through the sand sample 3 in real time. Observe the data of the microparticle concentration detector 13. When the mud content and fine particle concentration in the water flow show a sudden increase in inflection point, it is determined as the initial starting point of seepage failure (piping). Continue increasing the water head until the flow rate of sand sample 3 increases sharply, causing macroscopic deformation or collapse of the skeleton. Record the water pressure difference at this point. Calculate the critical hydraulic gradient for ultimate soil erosion or sand runoff by using the pressure difference and the height of sand sample 3. Parameter analysis: Change the mud content, gradation, and confining pressure of sand sample 3, repeat the above steps, and plot the nonlinear relationship curve between the critical hydraulic gradient and factors such as mud content and confining pressure to provide accurate parameters for the prevention and control of sudden water inrush and sand runoff.

[0037] Some embodiments of this application provide a method for testing the critical hydraulic gradient of sandy soil inrush and sand collapse, using the testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse as described in the first aspect above, such as... Figure 2 As shown, the test method includes the following steps:

[0038] S1. Prepare a sand sample and install it into the rubber tube.

[0039] S1.1. Loose sand samples were extracted from the study area, and the original gradation curve and mud content (mass percentage of particles with a diameter less than 0.075 mm) of the samples were determined by a combination of sieving and densitometer methods.

[0040] S1.2. Based on the test results, set the mud content levels (usually four levels: 5%, 10%, 15%, and 20%) and gradation characteristics (such as uniformity coefficient). =5~30, curvature coefficient =1~3), prepare sand samples. The mud content is adjusted by adding or washing away fine particles on the basis of the original sample, and the gradation is achieved by adjusting the mass ratio of each particle group.

[0041] S1.3. The prepared sand sample is compacted in layers inside a rubber tube. Each layer is 30mm to 50mm thick. The number of compactions is determined according to the target porosity. This produces a standard cylindrical sand sample with a diameter of 50mm to 100mm and a height of 100mm to 200mm.

[0042] S1.4. Install the rubber tube containing the sand sample into the transparent permeation chamber, install the rock fracture simulation plate at the bottom of the sand sample, and install the permeable plate at the top to complete the installation of the sand sample.

[0043] S2. Apply confining pressure to the sand sample through the pressurization unit.

[0044] S2.1. Water is injected into the transparent permeation chamber through the pressurization unit to pressurize it, so that the flexible water pressure is applied evenly to the side of the sand sample wrapped by the rubber tube, and the preset lateral confining pressure σ3 is applied.

[0045] S2.2 and confining pressure σ3 range from 0.5MPa to 5.0MPa. Multiple confining pressure levels can be set with a gradient of 0.5MPa or 1.0MPa to simulate the in-situ stress state of loose layers under different burial depths.

[0046] S2.3 After applying the confining pressure, stabilize for 5 to 10 minutes to ensure uniform stress distribution within the sand sample.

[0047] S3. Apply a gradually increasing hydraulic gradient to the sand sample through the water inlet pipe.

[0048] S3.1 Start the horizontal flow pump and apply a downward permeation flow of water to the sand sample through the top water inlet pipe. Gradually increase the inlet pressure using a step-by-step pressurization method.

[0049] S3.2, hydraulic gradient Calculate using the following formula: In the formula The difference in water head (m) between the upper and lower ends of the sand sample is measured in real time by a differential pressure transmitter. The height of the sand sample is shown in meters.

[0050] S3.3 The increment of each hydraulic gradient step is 0.05~0.2, and the settling time of each step is 3min~5min; during the settling period of each step, the following parameters are collected simultaneously: the difference in hydraulic head between the upper and lower ends of the sand sample. and traffic The concentration of microparticles in the effluent is recorded in real time by a differential pressure transmitter and a flow meter, with a sampling frequency of not less than 1 Hz; (Unit: mg / L), recorded in real time by a microparticle concentration detector, with a sampling frequency of not less than 1 Hz; changes in the appearance of sand samples were continuously captured by a high-speed camera at a frame rate of not less than 50 frames per second.

[0051] S4. Determine the critical hydraulic gradient using the flow meter, the microparticle concentration detector, or the differential pressure transmitter.

[0052] S4.1 Calculate the concentration of microparticles With hydraulic gradient change curve .definition The hydraulic gradient corresponding to the first occurrence of a value exceeding three times the background value and showing a continuous upward trend is the critical hydraulic gradient for leakage initiation. Right now, ,in, The average concentration of microparticles under the background hydraulic gradient (<0.2) is given.

[0053] As an early warning threshold, it represents the lowest hydraulic gradient at which fine particles begin to migrate. It can serve as a baseline for abnormal water inflow at the mining face; when the hydraulic gradient is detected to be approaching... Therefore, patrols should be strengthened. When the hydraulic gradient of the aquifer exceeds... But not achieved This is the optimal window for grouting reinforcement, as the sandy soil skeleton remains intact, allowing the grout to evenly penetrate and fill the pores. For impermeable layers with high clay content, if the actual hydraulic gradient is < The impermeable layer can be considered intact in terms of seepage; exceeding This indicates that fine particles have begun to be lost, and the water-resistant performance is deteriorating. For projects with extremely high safety requirements (such as underwater coal mining), [the following can be taken]: Alternative As a design parameter, a greater safety margin is allowed.

[0054] S4.2, in The hydraulic gradient is then increased further. When the concentration of microparticles shows a sudden, inflection-point increase, piping is identified as the initiation of piping. The critical hydraulic gradient includes the critical hydraulic gradient for piping. ,satisfy ,in, The piping surge coefficient is set to 3-5. This is the moving average of the rate of increase in microparticle concentration.

[0055] S4.3, Critical hydraulic gradient includes overall critical hydraulic gradient for sand erosion. , The hydraulic gradient is defined as the flow meter reading increasing abruptly, the differential pressure transmitter reading dropping sharply, or the sand sample deforming or collapsing.

[0056] The hydraulic gradient corresponding to the loss of large amounts of microparticles and the macroscopic deformation or collapse of the sand skeleton is the critical hydraulic gradient for overall sand collapse. The judgment criterion is that any of the following conditions are met: flow rate A step increase occurred. The flow rate exceeded three times the stable flow rate of the previous step; the differential pressure transmitter reading dropped suddenly (indicating the formation of a through-flow channel inside the sand sample); and high-speed camera images showed that the sand sample underwent significant macroscopic deformation or collapse.

[0057] The test method for the critical hydraulic gradient of sandy soil inrush and sand collapse truly reproduces the deep geological environment, realizes independent control and coupled loading of confining pressure and hydraulic gradient, and can truly simulate the sandy soil seepage failure process under high ground stress and high water pressure environment. The test results are closer to the actual engineering situation.

[0058] Precisely defining the critical hydraulic gradient for three stages: By integrating online monitoring of microparticle concentration with multi-source information such as flow rate, pressure difference, and images, a quantitative judgment criterion for three stages from "leakage" to "piping" and then to "overall sand collapse" is proposed, and precise values ​​of the critical hydraulic gradient for each stage are given, which solves the problem that existing methods can only give a single failure gradient.

[0059] The system considers the influence of complex gradation and mud content: In view of the prominent characteristics of complex gradation and high mud content of loose sandy soil, the system studies the influence of mud content, non-uniformity coefficient and confining pressure on critical hydraulic gradient and establishes a multi-factor nonlinear prediction model.

[0060] Quantitative assessment of the bottom fracture effect: Through a replaceable rock fracture simulation plate, the quantitative determination of the boundary conditions for water inrush and sand burst initiation under different fracture configurations and opening degrees was realized, providing direct parameters for the risk assessment of water inrush and sand burst in fault or fracture development areas.

[0061] In some embodiments, the method for testing the critical hydraulic gradient of sandy soil inrush and sand collapse further includes: S5. Replace the rock fracture simulation plate with a different one and determine the critical hydraulic gradient.

[0062] S5.1 Replace the rock fracture simulation plate at the bottom of the sand sample and install the top plate with fractures of different geometric configurations, including: single straight fractures, cross fractures (angle 30°~90°) and irregular sawtooth fractures.

[0063] S5.2 Adjusting the crack opening by replacing the top plate with one of different thicknesses. (Values ​​range from 0.5mm to 5.0mm).

[0064] S5.3 For each fracture configuration and opening combination, repeat steps S1 to S4 to determine the critical hydraulic gradient of each stage of sand seepage failure under different bottom fracture conditions.

[0065] S6. By changing the mud content, non-uniformity coefficient, or confining pressure of sand samples, the critical hydraulic gradient under different conditions is determined, and a critical hydraulic gradient prediction model is constructed.

[0066] S6.1, Change the mud content of the sand sample (5%~20%), coefficient of uniformity (5~30) and confining pressure (0.5MPa~5.0MPa), repeat steps S1~S5 according to orthogonal experimental design or full experimental design.

[0067] S6.2. Based on the experimental data, plot the following relationship curves: Critical hydraulic gradient and confining pressure under different mud contents. Relationship curves; Critical hydraulic gradient and mud content under different confining pressures. The relationship curve; contour plots of critical hydraulic gradient with mud content and confining pressure under different non-uniformity coefficients.

[0068] S6.3. Based on the above experimental data, a critical hydraulic gradient prediction model is constructed using a multivariate nonlinear regression algorithm. ,in, The critical hydraulic gradient can be specifically defined as follows: , or , Mud content (%) The coefficient of non-uniformity, The confining pressure is (MPa). The crack opening (mm) of the rock fracture simulation plate. The values ​​are regression coefficients, and the units are shown in Table 1.

[0069] Table 1. Units of Regression Coefficients

[0070] S6.4 The established prediction model will be applied to the calculation of the height of coal and rock pillars for sand control in coal mines and the optimization of grouting modification parameters.

[0071] For example, the height of sand-control coal and rock pillars Determine using the following formula: In the formula: The water head (m) acting on the aquifer; This refers to the critical hydraulic gradient for overall sand collapse under the corresponding mud content and confining pressure conditions. For safety factors, a value of 1.5 to 2.0 is used.

[0072] The established critical hydraulic gradient prediction model can be directly applied to the accurate calculation of the height of coal and rock pillars for sand control in coal mines and the parameter optimization of grouting modification processes, thereby improving the pertinence and scientific nature of water hazard prevention and control.

[0073] Example 1 Taking the sandy soil of the "four-aquifer" aquifer in a coal mine in northern Anhui as the research object, this method was used to determine its critical hydraulic gradient.

[0074] Sand Sample Preparation and Installation Core samples of sand and soil were obtained from boreholes in the "four-aquifer" aquifer of the mine. The original gradation characteristics were determined using a combination of sieve analysis and densitometer methods: [Information on the non-uniformity coefficient is missing]. =12.3, curvature coefficient =1.8, mud content =12.5%. According to the experimental plan, four groups were set with mud content levels of 5%, 10%, 15%, and 20%, and six groups with uniformity coefficient levels of 5, 10, 15, 20, 25, and 30. Taking a mud content of 10% and a uniformity coefficient of 15 as an example, 500g of mixed sand sample was prepared and compacted in five layers inside a 61.8mm diameter rubber tube, with each layer compacted 25 times, to prepare a standard sand sample with a diameter of 61.8mm and a height of 125mm. A rock fracture simulation plate with a single straight crack (fracture opening) was installed at the bottom of the sand sample. =1.0mm), with permeable stones installed on top. The rubber tube encasing the sand sample is then installed and sealed in the transparent seepage chamber.

[0075] Apply confining pressure Water is injected into the seepage chamber to pressurize it to the confining pressure. =2.0MPa (simulating ground stress at a burial depth of approximately 200m), stabilized for 8 minutes.

[0076] Hydraulic gradient loading and critical value determination Start the horizontal flow pump, using hydraulic gradient increments. =0.1 represents a step-by-step pressure increase, with each step stabilizing for 4 minutes. The collected data is as follows: When When =0.3, the concentration of microparticles The concentration increased from a background value of 2.3 mg / L to 7.8 mg / L, exceeding the background value by more than three times (6.9 mg / L), and showed a continuous upward trend. Therefore, the critical hydraulic gradient for initiating leakage was determined. =0.30; continue to increase the pressure to When =0.8, =28.6mg / L, while the previous steps The sliding average was 6.2 mg / L, exceeding the set value. Threshold, determining the critical hydraulic gradient for piping. =0.80; continue to increase the pressure to At a gradient of 1.4, the flow rate suddenly increased from 3.2 mL / s in the previous step to 11.5 mL / s, an increase of more than three times. Simultaneously, the differential pressure transmitter reading suddenly dropped from 12.3 kPa to 8.7 kPa. High-speed camera footage showed a clear through-crack in the center of the sand sample, indicating the critical hydraulic gradient for overall sand collapse. =1.40.

[0077] Crack simulation test Replace crack opening =3.0mm cross-crack top plate (angle 60°), repeat the above steps, and measure. =0.22, =0.58, =1.02. Compared with a single fracture, the critical hydraulic gradient at each stage is significantly reduced under the cross-fracture condition.

[0078] Multifactor analysis After completing all experimental schemes according to the orthogonal experimental design, the overall critical hydraulic slope prediction model for the "four-content" sandy soil in the mining area can be obtained by using a multivariate nonlinear regression algorithm. The above model was applied to the calculation of sand-control coal-rock pillars in a working face of the mine: the water head of the aquifer. =85m, corresponding to a mud content of 10%, a confining pressure of 2.0MPa, and a fracture opening of 1.0mm. =1.40, safety factor Taking 1.8, the height of the sand and rock prevention pillar is: This method provides a scientific basis for the precise placement of coal and rock pillars for sand control in mines.

[0079] Based on the same inventive concept, corresponding to the methods of any of the above embodiments, this application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the test method for the critical hydraulic slope of sand bursting due to water inrush in any of the above embodiments.

[0080] Figure 3 This embodiment illustrates a more specific hardware structure of an electronic device, which may include a processor 1010, a memory 1020, an input / output interface 1030, a communication interface 1040, and a bus 1050. The processor 1010, memory 1020, input / output interface 1030, and communication interface 1040 are interconnected internally via the bus 1050.

[0081] The processor 1010 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this specification.

[0082] The memory 1020 can be implemented in the form of ROM (Read Only Memory), RAM (Random Access Memory), static storage device, dynamic storage device, etc. The memory 1020 can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented by software or firmware, the relevant program code is stored in the memory 1020 and is called and executed by the processor 1010.

[0083] The input / output interface 1030 is used to connect input / output modules to realize information input and output. The input / output modules can be configured as components within the device (not shown in the figure) or externally connected to the device to provide corresponding functions. The input devices can include keyboards, mice, touchscreens, microphones, various sensors, etc., and the output devices can include displays, speakers, vibrators, indicator lights, etc.

[0084] The communication interface 1040 is used to connect a communication module (not shown in the figure) to enable communication between this device and other devices. The communication module can communicate via wired means (e.g., USB, Ethernet cable, etc.) or wireless means (e.g., mobile network, WIFI, Bluetooth, etc.).

[0085] Bus 1050 includes a pathway for transmitting information between various components of the device, such as processor 1010, memory 1020, input / output interface 1030, and communication interface 1040.

[0086] It should be noted that although the above-described device only shows the processor 1010, memory 1020, input / output interface 1030, communication interface 1040, and bus 1050, in specific implementations, the device may also include other components necessary for normal operation. Furthermore, those skilled in the art will understand that the above-described device may only include the components necessary for implementing the embodiments of this specification, and not necessarily all the components shown in the figures.

[0087] The electronic equipment described above is used to implement the test method for the critical hydraulic gradient of sand bursting due to sudden water in any of the foregoing embodiments, and has the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0088] Based on the same inventive concept, corresponding to the methods of any of the above embodiments, this application also provides a non-transitory computer-readable storage medium storing computer instructions for causing the computer to execute the test method for the critical hydraulic gradient of sand bursting and sand collapse as described in any of the above embodiments.

[0089] The non-transitory computer-readable medium of this embodiment includes both permanent and non-permanent, removable and non-removable media, and information storage can be implemented by any method or technology. Information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transfer medium that can be used to store information accessible by a computing device.

[0090] The computer instructions stored in the storage medium of the above embodiments are used to cause the computer to execute the test method for the critical hydraulic slope of sand bursting due to water inrush as described in any of the above embodiments, and have the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0091] Based on the same concept, corresponding to the methods of any of the above embodiments, this application also provides a computer program product, including computer program instructions, which, when the computer program instructions are run on a computer, cause the computer to execute the test method for the critical hydraulic slope of sand bursting due to water inrush as described in any of the above embodiments, and have the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0092] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.

[0093] Furthermore, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, the apparatus may be shown in block diagram form. This is to prevent the embodiments of this application from being difficult to understand, and it also takes into account the fact that the details of the implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be fully within the understanding of those skilled in the art). In setting forth specific details to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application may be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0094] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0095] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse, characterized in that, include: A transparent infiltration chamber is equipped with a rubber tube inside, which is used to hold sand samples. The rubber tube is spaced apart from the inner wall of the transparent infiltration chamber. A permeable plate is installed at the top of the rubber tube and abuts against the inner wall of the transparent infiltration chamber; A rock fracture simulation plate is placed at the bottom of the rubber tube and abuts against the inner wall of the transparent seepage chamber; The pressurization unit is connected to the outer wall of the transparent permeation chamber and is positioned opposite to the rubber tube. The water inlet pipe is connected to the top of the transparent seepage chamber, and a pressure sensor is connected to the water inlet pipe; The outlet pipe is connected to the bottom of the transparent seepage chamber, and the outlet pipe is connected to a flow meter and a microparticle concentration detector; A differential pressure transmitter is located on the outside of the transparent seepage chamber and connected to both ends of the rubber tube.

2. The testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 1, characterized in that, Also includes: The imaging unit is located on the outside of the transparent permeation chamber, opposite to the rubber tube.

3. The testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 1, characterized in that, One end of the inlet pipe is connected to a water storage tank, and a horizontal flow pump and a pressure stabilizing valve are connected between the inlet pipe and the water storage tank; one end of the outlet pipe is connected to a water collection tank.

4. The testing device for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 1, characterized in that, The rock fracture simulation plate includes a top plate and a support grid stacked together, and the top plate is provided with fracture openings.

5. A method for testing the critical hydraulic gradient of sandy soil during sudden water inrush and sand collapse, characterized in that, Using the testing apparatus for the critical hydraulic gradient of sandy soil inrush and sand collapse as described in any one of claims 1-4, the testing method includes: Prepare a sand sample and install it into the rubber tube; Confining pressure is applied to the sand sample through the pressurization unit; A gradually increasing hydraulic gradient is applied to the sand sample through the inlet pipe; The critical hydraulic gradient is determined by the flow meter, the microparticle concentration detector, or the differential pressure transmitter.

6. The test method for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 5, characterized in that, The critical hydraulic gradient includes the critical hydraulic gradient for leakage initiation. ,satisfy ,in, This represents the average concentration of microparticles under the background hydraulic gradient.

7. The test method for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 6, characterized in that, The critical hydraulic gradient includes the critical hydraulic gradient for piping. ,satisfy ,in, This is the coefficient for sudden increase in piping volume. This is the moving average of the rate of increase in microparticle concentration.

8. The test method for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 7, characterized in that, The critical hydraulic gradient includes the critical hydraulic gradient for overall sand erosion. , The hydraulic gradient is defined as the flow meter reading increasing abruptly, the differential pressure transmitter reading dropping sharply, or the sand sample deforming or collapsing.

9. The test method for the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 5, characterized in that, Also includes: Replace the rock fracture simulation plates with different ones and determine the critical hydraulic gradient; By changing the mud content, non-uniformity coefficient, or confining pressure of sand samples, the critical hydraulic gradient under different conditions was determined, and a critical hydraulic gradient prediction model was constructed.

10. The method for testing the critical hydraulic gradient of sandy soil inrush and sand collapse according to claim 9, characterized in that, The critical hydraulic gradient prediction model ,in, The critical hydraulic gradient, Mud content, The coefficient of non-uniformity, For confining pressure, The fracture opening of the simulated rock fracture plate. is the regression coefficient.

Images