WO2016074510A1

WO2016074510A1 - Method for determining earth surface interpenetrated crack distribution and air leakage characteristics in shallow burial coal mining

Info

Publication number: WO2016074510A1
Application number: PCT/CN2015/086602
Authority: WO
Inventors: 秦波涛; 王奇奇; 申宏敏; 马立强; 鲁义
Original assignee: 中国矿业大学
Priority date: 2014-11-11
Filing date: 2015-08-11
Publication date: 2016-05-19
Also published as: CN104462654B; AU2015345707B2; CN104462654A; ZA201606183B; AU2015345707A1

Abstract

A method for determining earth surface interpenetrated crack distribution and air leakage characteristics in shallow burial coal mining. The method comprises the following steps: determining the similar experimental material ratio according to actual stratum data of a mine; laying a similar material model according to the geometric similarity and the power similarity; conducting coal bed excavation after the material strength and the raw rock strength are similar, and taking fracture development pictures after the model excavation is stable; conducting graying and vectorizing on the pictures by means of image processing software; importing the vectorized fracture images to numerical simulation software, and conducting calculation; and comparing the obtained result with measured data, and obtaining an accurate numerical model by means of continuous modification. By means of the method, the overlaying strata fracture distribution and air leakage characteristics under the shallow burial coal bed condition can be disclosed, and the beneficial reference is provided for the on-site situations such as the blockage of air leakage passageways.

Description

Ground fracture fissure distribution and air leakage characteristics determination method for shallow buried coal seam mining

Technical field

The invention relates to a method for judging the distribution of surface through cracks and the characteristics of air leakage in shallow buried coal seam mining, and belongs to the experimental research on fractured rock mass in the field of underground geotechnical engineering and the method for judging the characteristics of surface fissure leakage.

Background technique

China's coal mining strategy is moving westward. Most of the western mining areas are shallow buried coal seams. The shallow buried coal seams have serious surface leakage, which is easy to trigger coal spontaneous combustion in the goaf. Coal spontaneous combustion will not only affect the normal production of the mine, but also may cause serious fire or gas explosion accidents. Due to the shallow burial of the western coal seam, a large number of fissures penetrating the surface of the earth are formed under the action of mining stress. These fissures constitute the main channel for oxygen supply from coal spontaneous combustion. When using anti-fire-extinguishing materials such as yellow mud (fly ash) pulp, mortar, and three-phase foam to prevent fire and cool down the spontaneous combustion danger zone and air leakage point of the goaf, it is difficult to detect cracks due to traditional technical means. The distribution position causes the fire-extinguishing material to be unable to be transported to the vicinity of the air leakage point in time to complete the sealing of the air leakage passage. Therefore, it is important to study the distribution of cracks in shallow coal seams and the characteristics of air leakage to seal the air leakage passage and prevent coal spontaneous combustion.

At present, the methods for determining the surface fissure distribution and air leakage characteristics of shallow buried coal seams are mainly tracer gas method and numerical simulation method. The tracer gas method is to release the SF ₆ tracer gas at the air leakage source, collect the gas sample at the air leakage, and qualitatively determine the air leakage channel by analyzing the concentration of the gas sample. Due to the limitations of the site environment and measurement methods, the crack distribution and air leakage characteristics of the entire goaf can only be reflected by monitoring some points, and the judgment results are susceptible to factors such as the release amount. In the numerical simulation of the shallow coal seam fissure leakage, the equivalent continuous medium model is generally used to make the fissure and the surrounding rock mass equivalent to a continuous medium with a certain permeability tensor, which is solved by the porous medium theory. However, it ignores the influence of the longitudinal cracks of the shallow buried coal seams on the surface leakage, and the simulation results often have large deviations from the actual conditions when dealing with such large-scale fractures.

Summary of the invention

OBJECT OF THE INVENTION: In view of the deficiencies of existing numerical simulation methods, the present invention introduces the development of fractures into a numerical model by combining similar material simulation experiments with numerical simulations, thereby overcoming the difficulty in detecting fractures in the rock and over-exaggerating the numerical model. Simplification and other problems; at the same time, the correction of the model can effectively improve the accuracy and reliability of the model, and provide a useful reference for the determination of surface through-fracture distribution and air leakage characteristics after mining in shallow buried mining areas.

Technical Solution: In order to achieve the above object, the technical solution adopted by the present invention is:

A method for judging the distribution of surface through cracks and the characteristics of air leakage in shallow buried coal seam mining, comprising the following steps:

(1) Determine the ratio of the model to the original rock, calculate the ratio and amount of different materials in the simulation of each layer of rock formation according to the lithology, thickness and physical and mechanical parameters of the buried rock layer in the mining area;

(2) According to the ratio and amount of the obtained materials, the experimental rock formation model is laid in order according to the stratigraphic relationship and inclination angle of the original rock, and the model is placed, and the resistance strain gauge is arranged in the adjacent rock layer;

(3) When the difference between the strength of the model and the strength of the original rock is within the threshold range, simulate the actual mining conditions of the prototype, and prepare to excavate the coal seam in the model;

(4) According to the advancing speed at the time of actual excavation of the prototype and the length of each excavation, set the advancing speed of the excavation of the model and the length of each excavation, and after each excavation, place 40~ Continue to excavate after 80 minutes;

(5) During the process of excavation of the model, the detection data of the strain gauges are recorded. When the data of each strain gauge is no longer changed or the variation range is within the threshold range, the model reaches the stress balance and the model is excavated. Photograph of the development of the fracture after stress balance of the model using the camera after completion;

(6) processing the photograph of the fracture development obtained as a vector graphic;

(7) Import the vector graphics into the COMSOL numerical simulation software and set it as the initial geometric model, adjust the geometric model size, and set the geometric model material properties and boundary conditions;

(8) Perform meshing on the set geometric model and solve the calculation to obtain the wind leakage velocity and pressure distribution of the fracture;

(9) Compare and analyze the obtained wind leakage wind speed and pressure distribution with the air leakage data of each point of the prototype for on-site measurement, and continuously adjust the design parameters of the geometric model to obtain the fracture air leakage wind speed which is consistent with the field measurement. The law of pressure distribution provides a reference for sealing the air leakage passage.

Specifically, in the step (2), the resistance strain gauge is disposed between two adjacent rock layers, and the resistance strain gauges in the same horizontal detection plane are arranged in a mesh shape to collect detection data; for example, designing the same level The strain gauges in the detection plane are arranged in a grid pattern of a rectangular array, and the horizontal distance between two adjacent strain gauges on the same lateral or longitudinal straight line is generally designed to be 30 cm.

Specifically, in the step (3), it is determined whether the difference between the model strength and the original rock strength is within a threshold range, and the specific method is: before the laying of the model, the mechanical property test is performed to determine that the simulated material reaches a difference between the mechanical properties of the original rock and the threshold value. The water content w ₀ in the range; after the model is laid and allowed to stand for a period of time, the water content w of the model material is measured, and when w=w ₀ , the difference between the model strength and the original rock strength is considered to be within the threshold range.

More specifically, in the step (3), the method for determining the water content of the material is a weighing method, specifically: taking a certain amount of material as a sample, and weighing the sample using a balance of 0.1 g precision, As the wet weight m of the sample, the sample was baked to a constant weight in an oven at 105 ° C, and the weight of the sample was weighed again using a balance of 0.1 g precision, and the wet weight m _{s of the} sample was recorded to calculate the water content. w=m _s /m.

Specifically, in the step (6), the method for processing the photographed fissure development photograph into a vector graph is: using computer graphics processing technology, including image filtering, sharpening enhancement, image segmentation, noise filtering, and detection refinement. After the internal processing, vectorized fracture data is generated, and the vectorized fracture data is used as a vector graphic.

Specifically, in the step (7), the material properties include a fluid density ρ, a hydrodynamic viscosity μ, a coal rock permeability k around the fracture, and a coal rock porosity ε; the boundary condition is specifically set as: an upper crack inlet The pressure p _{0 is} set to atmospheric pressure, the lower fracture outlet pressure is set to the goaf side pressure, and the left and right boundaries are set to no flow boundary.

More specifically, in the step (7), the method for solving the permeability k and the porosity ε of the coal rock surrounding the crack is: taking four displacement monitoring points adjacent to each other on the model plane to form a quadrilateral ABCD, the coal seam Mining, when the overburden collapses, the area of the quadrilateral ABCD changes from S to S':

Calculate the coefficient of expansion of coal rock mass: K _p =S'/S;

Calculate the porosity according to the coefficient of expansion of coal and rock mass:

The permeability and porosity ε of the coal and rock mass are satisfied:

Where d is the particle size of the broken coal rock mass, and C is the coefficient, generally taking C=172.8.

Specifically, in the step (7), the geometric model is described as follows:

1) The free flow of fluid inside the fracture zone is described by the Navier-Stokes equation:

Where ρ represents fluid density, u represents fluid velocity, μ represents hydrodynamic viscosity, p represents unit fluid pressure difference, F unit fluid volume force;

2) The coal and rock mass around the fissure area is treated as a porous medium, which belongs to seepage, and is described by Darcy's law:

Where μ denotes hydrodynamic viscosity, k is the permeability of the coal rock mass, q fluid flow rate, p is the unit fluid pressure difference, and Z is the height change amount.

Advantageous Effects: The method for judging the distribution of surface through cracks and the characteristics of air leakage in shallow buried coal seams provided by the present invention has the following advantages:

1. A method for determining the strength of similar materials by measuring the water content is proposed, which has the advantages of simplicity, convenience, and the like;

2. Through the similar material simulation experiment, the distribution map of overburden fractures in the model after simulated coal seam mining can be obtained, and the distribution of cracks in different regions after coal seam mining can be visually observed, which can be used for numerical simulation analysis of the characteristics of overburden fractures;

3. By combining similar material simulation experiments with numerical simulations, the fracture treatment can be reduced to equivalent The error caused by the continuous medium or fracture network model makes the numerical simulation results more consistent with the actual situation.

DRAWINGS

Figure 1 is a flow chart of the method of the present invention;

Figure 2 is a schematic diagram of calculation of the coefficient of expansion of the goaf;

Figure 3 is a distribution diagram of the resistance strain gauge and the displacement monitoring point;

Figure 4 is a fracture distribution map after simulated coal seam mining;

Figure 5 is a vector graphic;

Figure 6 is a distribution diagram of the fracture air leakage velocity.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

FIG. 1 is a flow chart showing an implementation method for determining the surface through-fracture distribution and air leakage characteristics of a shallow buried coal seam, and the present invention will be further described below with reference to examples.

A coal mine in Shendong mining area is a shallow buried mine. The ground fissures are developed after coal seam mining, and the air leakage in the goaf is serious, causing spontaneous combustion of coal. The air leakage channel sealing scheme is given by the method of the present invention. The specific steps are as follows:

(1) Determine the ratio of the model to the original rock to be 1:100, the model length is 2.5m, and the width is 0.5m. According to the rock lithology, thickness and physical and mechanical parameters provided by the mine, the calculation model simulates each layer of rock layers differently. The ratio and dosage of the materials are shown in Table 1:

Table 1 Model similar material simulation ratio (1:100)

(2) According to the ratio and amount of the obtained materials, the experimental rock formation model is laid down from the bottom to the top according to the stratigraphic relationship and inclination angle of the original rock, and the strain gauge is placed in the adjacent rock layer; The arrangement of the strain gauges is as follows: the strain gauges are arranged in a mesh shape in the same detection plane, and the spacing between adjacent strain gauges in the same detection plane is 30 cm, and the arrangement of the strain gauges is as shown in FIG.

(3) After the model is laid, it is allowed to stand for 10 days, then a small sample is taken from the upper edge of the model, and the water content is measured by the weighing method. When compared with the original rock, the water content of the same layer is compared. The difference in water content is less than 5%. Within the difference range, the strength of the model material is considered to be similar to that of the original rock, and excavation can be performed.

(4) Calculate the length of each simulated excavation from the actual propulsion speed of the mine to 10 cm, place it for 1 hour after excavation, and excavate again.

(5) Each excavation uses a static strain measurement processor to record relevant data through a computer. After the entire model is excavated, when the data recorded by the computer does not change, the model reaches stress balance, and the professional camera is used after the model is excavated. A photograph of the development of the fracture of the model is shown in Figure 4.

(6) Using the graphics processing software to process the photographed fissure development photos into vector graphics, as shown in FIG.

(7) The vector graphics obtained in step (6) are imported into COMSOL numerical simulation software and set as initial geometric figures. Adjust the size of the geometric model, set the fluid density ρ=1.29kg/m ³ , the hydrodynamic viscosity μ=17.9×10 ^-6 Pa·s, the permeability of coal rock mass k and the porosity of coal rock mass ε; Specifically, the upper crack inlet pressure p ₀ =1 atm, the lower crack outlet pressure is set to 101.12 kPa of the goaf side pressure, and the left and right boundaries are set to have no flow boundary.

(8) The method for solving the permeability k and porosity ε of the coal and rock mass around the fissure is: taking four displacement monitoring points adjacent to each other on the model plane to form a quadrilateral ABCD, coal seam mining, when the overburden layer collapses, The area of the quadrilateral ABCD changes from S to S':

Calculate the coefficient of expansion of coal rock mass: K _p =S'/S;

The permeability and porosity ε of the coal and rock mass are satisfied:

According to the data provided by the mine, the original porosity and permeability of the coal and rock mass are brought into the above formula to obtain the porosity and permeability of the coal and rock mass around the fracture.

(9) Due to the free flow of fluid in the fracture zone, the Navier-Stokes equation is used to describe:

Where ρ represents the fluid density, u represents the fluid velocity, μ represents the hydrodynamic viscosity, p represents the unit fluid pressure difference, and F unit fluid volume force.

The coal rock mass around the fracture zone is treated as a porous medium, which belongs to seepage, and is described by Darcy's law:

(10) Perform mesh meshing on the model, solve the system equations, and obtain the fracture air velocity and pressure distribution map, as shown in Figure 6.

(11) According to the position of the on-site detection point, the corresponding point is taken from the numerical model. By comparing the wind speed and wind pressure of the on-site monitoring points with the wind speed and wind pressure of the corresponding points in the numerical model, it is found that the difference between the two is less than 20%. The simulation data is in good agreement with the actual data, and the model does not need to be corrected. The simulation results can reflect the crack distribution and air leakage characteristics of shallow coal seams, and are used to guide the sealing of the air leakage passages in the goaf, thus preventing the coal spontaneous combustion in the mine.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It should be considered as the scope of protection of the present invention.

Claims

A method for judging the distribution of surface through cracks and the characteristics of air leakage in shallow buried coal seam mining, characterized in that the method comprises the following steps:

(1) Determine the ratio of the model to the original rock, calculate the ratio and amount of different materials in the simulation of each layer of rock formation according to the lithology, thickness and physical and mechanical parameters of the buried rock layer in the mining area;

(2) According to the ratio and amount of the obtained materials, the experimental rock formation model is laid in order according to the stratigraphic relationship and inclination angle of the original rock, and the model is placed, and the resistance strain gauge is arranged in the adjacent rock layer;

(3) When the difference between the strength of the model and the strength of the original rock is within the threshold range, simulate the actual mining conditions of the prototype, and prepare to excavate the coal seam in the model;

(4) According to the advancing speed at the time of actual excavation of the prototype and the length of each excavation, set the advancing speed of the excavation of the model and the length of each excavation, and after each excavation, place 40~ Continue to excavate after 80 minutes;

(5) During the process of excavation of the model, the detection data of the strain gauges are recorded. When the data of each strain gauge is no longer changed or the variation range is within the threshold range, the model reaches the stress balance and the model is excavated. Photograph of the development of the fracture after stress balance of the model using the camera after completion;

(6) processing the photograph of the fracture development obtained as a vector graphic;

(7) Import the vector graphics into the COMSOL numerical simulation software and set it as the initial geometric model, adjust the geometric model size, and set the geometric model material properties and boundary conditions;

(8) Perform meshing on the set geometric model and solve the calculation to obtain the wind leakage velocity and pressure distribution of the fracture;

(9) Compare and analyze the obtained wind leakage wind speed and pressure distribution with the air leakage data of each point of the prototype for on-site measurement, and continuously adjust the design parameters of the geometric model to obtain the fracture air leakage wind speed which is consistent with the field measurement. The law of pressure distribution provides a reference for sealing the air leakage passage.
The method for judging the surface through crack distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 1, wherein in the step (2), the resistance strain gauge is arranged between the adjacent two rock layers at the same level. The resistance strain gauges in the detection plane are arranged in a mesh shape, and the horizontal distance between the adjacent two strain gauges is 30 cm to collect the detection data.
The method for determining the surface through crack distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 1, wherein in the step (3), it is determined whether the difference between the model strength and the original rock strength is within a threshold range, and the specific method is Before the model is laid, the water content w 0 when the simulated material reaches the threshold value within the threshold range is determined by the mechanical property test; after the model is laid and allowed to stand for a period of time, the water content w of the model material is measured, When w=w 0 , the difference between the model strength and the original rock strength is considered to be within the threshold range.
The method for determining the surface through crack distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 3, wherein in the step (3), the method for determining the water content of the material is a weighing method, specifically: taking a certain amount The material was used as a sample, and the weight of the sample was weighed using a balance of 0.1 g precision, and the wet weight m of the sample was recorded. The sample was baked to a constant weight in an oven at 105 ° C, and a balance of 0.1 g precision was used again. The weight of the sample was weighed and recorded as the wet weight m s of the sample, and the water content w = m s / m was calculated.
The method for determining the surface through crack distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 1, wherein in the step (6), the method for processing the photographed fracture development photo into a vector graphic is: using a computer The graphics processing technology generates vectorized fracture data by using image filtering, sharpening enhancement, image segmentation, noise filtering, and detection refinement, and uses vectorized fracture data as a vector graphic.
The method for determining surface through crack distribution and air leakage characteristic of shallow buried coal seam mining according to claim 1, wherein in the step (7), the material property comprises a fluid density ρ, a hydrodynamic viscosity μ, and a coal rock mass around the crack. Permeability k and coal rock porosity ε; the boundary conditions are set as follows: the upper fracture inlet pressure p 0 is set to atmospheric pressure, the lower fracture outlet pressure is set to the goaf side pressure, and the left and right boundaries are set to no flow boundary.
The method for determining the surface through-fracture distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 6, wherein in the step (7), the solution method for the permeability k and the porosity ε of the coal rock mass around the fracture is: Four displacement monitoring points adjacent to each other on the model plane form a quadrilateral ABCD, coal seam mining. When the overburden strata collapses, the area of the quadrilateral ABCD changes from S to S':

Calculate the coefficient of expansion of coal rock mass: K p =S'/S;

Calculate the porosity according to the coefficient of expansion of coal and rock mass:

The permeability and porosity ε of the coal and rock mass are satisfied:

Where d is the particle size of the broken coal rock mass, and C is the coefficient, generally taking C=172.8.
The method for judging the surface through crack distribution and the air leakage characteristic of the shallow buried coal seam mining according to claim 7, wherein in the step (7), the geometric model is described as follows:

1) The free flow of fluid inside the fracture zone is described by the Navier-Stokes equation:

Where ρ represents fluid density, u represents fluid velocity, μ represents hydrodynamic viscosity, p represents unit fluid pressure difference, F unit fluid volume force;

2) The coal and rock mass around the fissure area is treated as a porous medium, which belongs to seepage, and is described by Darcy's law:

Where μ denotes hydrodynamic viscosity, k is the permeability of the coal rock mass, q fluid flow rate, p is the unit fluid pressure difference, and Z is the height change amount.