Method for identifying and treating coal spontaneous combustion and gas symbiosis disasters in overlapped goaf

Abstract

The invention discloses an overlapped goaf coal spontaneous combustion and gas symbiosis disaster identification and treatment method, which can accurately obtain an approximate range of a front goaf by combining geological data, a result detected by a transient electromagnetic detection device and a borehole observation instrument, and calculate the pore dimension and the average porosity of the area through a specific algorithm. Then, by taking the grouting hole as the center, a plurality of detection holes with different angles are formed, the directions of the detection holes are different to form a distribution form of continuously diffusing outwards in a spherical shape, and a comprehensive monitoring device is arranged at the final hole position of each detection hole, so that whether data of an underground gas concentration field, a temperature field, a gas pressure field, an air leakage flow field and a crustal stress field are abnormal or not is obtained; according to the method, redundant or complementary information of a plurality of monitoring devices at different positions in space or time is comprehensively and consistently explained or described on the whole goaf, so that the disaster condition can be identified and judged more accurately, and the construction safety in the whole tunneling or stoping process can be guaranteed.

Description

Technical Field

[0001] The present invention relates to a method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas, specifically to a method for accurately identifying and efficiently controlling the spontaneous combustion of coal and gas disasters in goaf areas caused by air leakage due to cracks during tunnel excavation and working face recovery operations in areas near overlapping goaf areas, belonging to the technical field of coal mine disaster prevention and control. Background Art

[0002] Coal is an important fossil fuel. In recent years, with the increasing demand for coal resources, the scale and difficulty of coal mining have continued to expand, and safety production is facing huge challenges. Disasters such as gas explosions in coal mines frequently occur, greatly affecting the stable and healthy operation of coal mining enterprises, and are also the main factors restricting the development of the coal industry.

[0003] The spontaneous combustion of coal in goaf and the compound disaster of gas are the result of the intersection of multiple media such as the fissure field, CH4 volume fraction field, O2 volume fraction field and temperature field in the goaf. In the intersection of multiple fields in the fissure space, disasters such as spontaneous combustion of coal, gas combustion and gas explosion coexist and influence each other, showing a strong dynamic coupling effect. For overlapping goafs or goafs where thick coal seams require multi-layer mining, after the upper layer coal mining is completed, there is less coal left in the goaf, the degree of coal fragmentation is low, and the probability of coal spontaneous combustion is low; however, when the lower layer mining is completed, it is actually equivalent to intervening in the lower part of the goaf. Due to the influence of factors such as inclination or pressure, the coal seam is re-exposed, causing the upper and lower layer goafs to be connected. The floating coal and the remaining coal in the goaf of the coal mine accelerate the temperature and oxidation under the condition of continuous air leakage, and the spontaneous combustion of coal caused by the suitable oxygen supply and heat storage environment becomes a high-temperature "ignition source" that triggers gas disasters. In addition, the goaf of the mining face is a semi-closed space, which is composed of a large amount of broken rocks and residual coal. If the working face advances slower due to factors such as faults and tunnel impact ground pressure during coal mining, the gas pressure in the upper and lower layers will be different. At the moment the upper and lower layers are connected, a large amount of gas will flow into the upper layer, causing the residual gas in the upper layer to continuously desorb and diffuse from the cracks in the bottom plate to the working face of the lower layer coal seam being mined, resulting in an increase in the gas and oxygen concentration in the lower layer, which ultimately accelerates the oxidation rate of the residual coal in the goaf, making it easy for coal spontaneous combustion and gas symbiosis disasters to occur.

[0004] In order to effectively prevent and control the combined disaster of spontaneous combustion of coal and gas in goaf, relevant scholars at home and abroad have carried out coordinated prevention and control from the aspects of controlling oxygen, gas, temperature, time, etc. Mainly through the implementation of gas extraction and injection of non-combustible materials and other "extraction-sealing-injection-injection" related measures, to ensure the safe mining of coal resources with the symbiotic disaster of spontaneous combustion of gas and coal. At present, the Chinese invention patent with publication number CN117005911A discloses a method and device for monitoring and early warning of combined disasters in deep mining of coal mines. It mainly combines the preset evaluation system to dynamically couple the physical quantity data of disaster monitoring geospatial space and the time measurement data of disaster monitoring geospatial space within the range of disaster monitoring geospatial geometric data to obtain real-time early warning information, but only considers the relevant geological factors, which is not comprehensive. The Chinese invention patent with publication number CN111425245A discloses a method for preventing and controlling the symbiotic disasters of coal and gas based on the optimization of the air leakage field in the goaf. The method mainly determines the reasonable negative pressure of extraction of the coal seam, optimizes the air leakage field in the goaf, and then ensures the gas extraction effect while realizing the prevention and control of the symbiotic disasters of coal and gas. The Chinese invention patent with publication number CN108959691A discloses a method for determining the dynamic isolation parameters of the coupled disasters of the high-gas self-igniting goaf. The method mainly simulates the flow field by obtaining the distribution law of the porosity behind the goaf, so as to determine the optimal isolation parameters. However, since the symbiotic disasters of coal spontaneous combustion and gas are hidden, coupled, dynamic and complex, the above-mentioned prevention and control of the symbiotic disasters only monitors and controls some of the problems, and the research system is still imperfect.

[0005] In summary, the existing methods for identifying and controlling the combined disaster of spontaneous combustion of coal and gas are not systematic enough. In order to prevent the mutual influence between various disaster types, the dynamic changes in the coexisting environment of the goaf, the disaster-causing evolution caused by nonlinear temperature rise in the goaf, and the inability to accurately observe the changes in fire inside the goaf, which jointly lead to the continuous deterioration of the disaster accidents caused by spontaneous combustion of coal and gas, it is necessary to adopt a multidisciplinary and multi-means integration approach to achieve accurate prediction and assessment of the disaster risk of spontaneous combustion of coal and gas in the goaf, accurate acquisition of disaster information, reasonable selection of closed areas, and accurate positioning and intelligent directional disposal of disaster areas, so as to provide key technical support for effectively avoiding the occurrence of compound disaster accidents.

[0006] Therefore, the present invention proposes a method that can accurately judge whether the surrounding gas concentration field, temperature field, gas pressure field, leakage flow field, and ground stress field are abnormal through multiple factors such as the concentration of harmful gases, gas pressure, temperature, ground stress, and air leakage conditions, and take different solutions to the abnormal phenomena, thereby providing technical support for the accurate identification and efficient control of coal spontaneous combustion and gas disasters in goafs, which is the research direction of the present invention. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for identifying and controlling disasters caused by spontaneous combustion of coal and gas co-existence in overlapping goaf areas, which can effectively solve the above-mentioned technical problems.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is: a method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas, the specific steps of which are:

[0009] A. Before tunnel excavation, advance drilling is performed in front of the tunnel according to the construction design drawings to determine whether there is a goaf in front. If no goaf is found, the tunnel starts to be excavated to the detection distance of the advance drilling and stops, and continues to construct advance drilling forward from the current position to determine whether there is a goaf. This cycle is repeated until it is determined that there is a goaf, and then step B is entered;

[0010] B. Use a transient electromagnetic detection device to extend into the advance borehole to determine the specific location and shape of the goaf, and determine the porosity in the goaf, and then determine the scope that needs to be reinforced and the water-cement ratio and dosage of the paste quick-setting material;

[0011] C. Use the advanced drilling hole as the grouting hole, and grout different areas of the front goaf according to the water-cement ratio and dosage of the paste quick-setting material calculated in step B;

[0012] D. After the slurry solidifies, multiple detection holes are arranged around the grouting hole with the grouting hole as the center, and a comprehensive monitoring device is placed at the end hole position of each detection hole to obtain the monitoring data around the end hole of each detection hole in real time;

[0013] E. During the excavation and mining process, the staff regularly records the monitoring data of each detection hole and uploads it to the data terminal in a timely manner; the data terminal analyzes the monitoring data to determine whether there are any abnormalities around the end holes of each detection hole. If it is determined that there are abnormalities, an early warning prompt is issued to stop construction. At the same time, the abnormal area is quickly located according to the location of the abnormal detection hole, and the degree of danger is determined in combination with the monitoring data. Then, corresponding treatment measures are taken according to the degree of danger, so as to reduce the probability of disasters;

[0014] F. After the disaster is dealt with, continue to use each detection hole to obtain the corresponding monitoring data. After monitoring for a period of time, if no abnormality is found during this period, continue to excavate the tunnel for a certain distance, and repeat steps A to E to continue the next section of the advance detection process; if an abnormality is found during this period, repeat step E to determine the degree of danger of the abnormality, and adopt corresponding treatment measures until the monitoring data returns to normal, then continue to excavate the tunnel.

[0015] Furthermore, the specific process of determining the goaf in step A is as follows: during the advance drilling process, a comprehensive determination is made as to whether there is a goaf ahead based on multiple factors, including the water inflow from the drill bit, the advancement speed, and the resistance encountered during advancement.

[0016] Furthermore, the specific process of determining the porosity in step B is as follows: according to the specific position and shape of the goaf, multiple borehole peeps are sent into the goaf to take images, and the images obtained by each borehole peep are unfolded to obtain a panoramic image, and the images are processed by binarization and grayscale methods respectively, and different side lengths δ are used to process the images. k The boxes cover the matrix area in the image, and the number of boxes N required for counting δk ; Then use the least squares method to calculate the series of data points (-lgδ k ,lgN δk ) to perform linear fitting and obtain the fitting straight line equation: lgN δk =D B ×(-lg δk )+b, and then calculate the pore fractal dimension D B ; So the porosity is expressed as: where r min and r max are the minimum and maximum radii of the pore channel, D B is the pore fractal dimension, 0<D in two-dimensional space B <2,0<D B <3.

[0017] Furthermore, the water-cement ratio and the amount of the paste quick-setting material are determined in step B as follows: the porosity of the goaf is not uniformly distributed, and the porosity of similar goafs is classified. By dividing the porosity of different regions, combining the size of the porosity, and the fluidity and mechanical strength of the paste quick-setting material, the amount of the paste quick-setting material is calculated using the following formula;

[0018] Slurry diffusion radius:

[0019]

[0020] Where P1 is the grouting pressure, P0 is the groundwater pressure, μ is the ratio of the viscosity of the slurry to the viscosity of water, and θ is the angle between the central axis of the grouting hole and the vertical line. is the porosity of the porous medium, is the starting pressure gradient, t is the grouting time, K is the permeability coefficient, R is the slurry diffusion radius after time t, and r is the grouting hole radius;

[0021] Grouting volume:

[0022] Q=A·L·π·R 2 ·e c β

[0023] Where A is the slurry loss coefficient; L is the length of the grouting hole; R is the slurry diffusion radius; e c is the average porosity of rock; β is the slurry filling coefficient.

[0024] Furthermore, in step D, each detection hole is centered on the grouting hole, and its distribution is spherical at different angles and continuously spreads outward from the grouting hole, which is used to monitor the situation during the entire excavation or mining process; the comprehensive monitoring device includes a bundle tube monitor, a thermocouple or a high-sensitivity optical fiber, a ground stress sheet, a U-tube or a micromanometer and a hot wire wind speed monitor, which are used to obtain gas concentration field, temperature field, gas pressure field, leakage air flow field and ground stress field data.

[0025] Further, the step E specifically includes: observing whether the data of gas concentration field, temperature field, gas pressure field, air leakage flow field and ground stress field are abnormal; and taking corresponding treatment measures by combining various data, as follows:

[0026] (1) When the temperature field and gas concentration field are abnormal, the following countermeasures are adopted:

[0027]

[0028] (2) When the local stress field is abnormal, that is, the stress detected by the pressure plate after grouting is less than the stress borne by the rock mass itself, it indicates that the grouting material is still likely to break, and the interior should continue to be filled with paste quick-setting materials with stronger bearing strength;

[0029] (3) When the gas pressure field and the air leakage flow field are abnormal, the drilling excavation will cause stress redistribution, and the coal body around the borehole will be subjected to stress changes similar to those caused by tunnel excavation. The dual disturbance will aggravate the damage to the coal body, the development of the cracks will reach maturity, and the air flow in the field will be abnormal, providing a continuous oxygen supply to the coal seam, which will make coal spontaneous combustion more likely to occur. At this time, SF6 gas is used for tracer marking, and new boreholes are drilled around the current abnormal detection hole or adjacent detection holes to release SF6 at a constant flow rate. Under negative pressure extraction conditions, the tracer gas is mixed with the negative pressure drainage tunnel air and diffused to the extraction borehole. After a period of time, the tracer gas will be evenly distributed in the abnormal detection hole. Then, a portable gas detector is used to detect whether there is air leakage. The borehole air leakage rate is calculated by the distance between the release point and the receiving point and the time difference between the release of SF6 and the detection of SF6. When the air leakage rate is greater than the threshold, the grouting process is carried out in time.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] ① The present invention can combine the geological data, the results of the transient electromagnetic detection device and the borehole peep instrument to accurately obtain the approximate range of the goaf ahead, and observe the change of resistivity in the terrain ahead through the detection of the transient electromagnetic detection device and accurately obtain the morphological characteristics of the underground geological anomaly; and use the borehole peep instrument to explore forward until it reaches the goaf, then it can combine the binarization method, grayscale regulation method and difference algorithm to process the picture taken by the borehole peep instrument, convert the three-dimensional image into a one-dimensional plane, and then better calculate the pore dimension and average porosity of the area; effectively avoid the omissions and heavy workload in manual excavation, and ensure safe mining.

[0032] ② The present invention takes the grouting hole as the center and arranges multiple detection holes at different angles, and each detection hole is oriented in different directions to form a distribution form that continuously diffuses outward in a spherical shape. A comprehensive monitoring device is arranged at the end hole position of each detection hole to obtain whether the underground gas concentration field, temperature field, gas pressure field, leakage flow field, and ground stress field data are abnormal. The redundant or complementary information of multiple monitoring devices at different positions in space or time is used to provide a relatively complete and consistent interpretation or description of the goaf as a whole, thereby achieving more accurate identification and judgment of disaster situations, and ensuring construction safety during the entire excavation or mining process.

[0033] ③ The present invention adopts a prevention and control method of first identifying and then controlling in view of the complexity, suddenness, dynamism and coupling of coal spontaneous combustion and gas symbiosis disasters in overlapping goaf areas. The data processing center integrates the geological data during mining in the upper goaf area of ​​the coal mine, the sensing data of the buried monitoring device in the detection hole, and the detection situation of the borehole peep instrument, and can obtain the distribution of the fracture field, gas concentration field, temperature field, gas pressure field, and ground stress distribution field in front of and above the excavation. Finally, the changes in the abnormal field are comprehensively considered and analyzed, and the corresponding control method is selected according to the situation to achieve more accurate prevention of symbiotic disasters after grouting.

[0034] ④ The present invention combines underground equipment and software monitoring systems, theories and actual on-site conditions, reducing the shortcomings of many blind spots, poor timeliness, and high missed reporting rates in the traditional goaf coal spontaneous combustion monitoring process, greatly improving the underground proactive disaster prevention and disaster resistance capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the overall flow chart of the present invention;

[0036] Figure 2 It is a drilling schematic diagram of the present invention;

[0037] Figure 3 This is a schematic diagram of the placement angle of the transient electromagnetic detection construction wire frame in the present invention;

[0038] Figure 4 It is a schematic diagram of drilling in the horizontal direction of the detection hole in the present invention;

[0039] Figure 5 It is a schematic diagram of drilling in the vertical direction of the detection hole in the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below.

[0041] like Figure 1 As shown, the specific steps of the present invention are:

[0042] A. Before tunnel excavation, advance drilling is performed in front of the tunnel according to the construction design drawings. During the advance drilling process, the water inflow of the drill bit, the advancement speed, and the resistance encountered during advancement are comprehensively judged to determine whether there is a goaf in front. If no goaf is found, the tunnel starts to be excavated to the detection distance of the advance drilling and stops, and continues to construct advance drilling forward from the current position to determine whether there is a goaf. This cycle is repeated until it is determined that there is a goaf, and then step B is entered;

[0043] B. Use a transient electromagnetic detection device to extend into the advance borehole to determine the specific location and shape of the goaf and determine the porosity of the goaf. Figure 2 and 3 As shown in the figure, the specific process is as follows: according to the specific position and shape of the goaf, multiple borehole peeps are sent into the goaf to take images, and the images obtained by each borehole peep are unfolded to obtain a panoramic image. The images are processed by binarization and grayscale methods respectively, and different side lengths δ k The boxes cover the matrix area in the image, and the number of boxes N required for counting δk ; Then use the least squares method to calculate the series of data points (-lgδ k ,lgN δk ) to perform linear fitting and obtain the fitting straight line equation: lgN δk =D B ×(-lg δk )+b, and then calculate the pore fractal dimension D B , so the porosity is expressed as: where r min and r max are the minimum and maximum radii of the pore channel, D B is the pore fractal dimension, 0<D in two-dimensional space B <2,0<D B <3;

[0044] Determine the scope that needs to be reinforced and the water-cement ratio and dosage of the paste quick-setting material. Specifically, the porosity of the goaf is not evenly distributed. The porosity of similar goafs is classified. By dividing the porosity of different areas, combined with the size of the porosity, the fluidity and mechanical strength of the paste quick-setting material, the dosage of the paste quick-setting material is calculated using the following formula;

[0045] Slurry diffusion radius:

[0046]

[0047] Where P1 is the grouting pressure, P0 is the groundwater pressure, μ is the ratio of the viscosity of the slurry to the viscosity of water, and θ is the angle between the central axis of the grouting hole and the vertical line. is the porosity of the porous medium, is the starting pressure gradient, t is the grouting time, K is the permeability coefficient, R is the slurry diffusion radius after time t, and r is the grouting hole radius;

[0048] Grouting volume:

[0049] Q=A·L·π·R 2 ·e c β

[0050] Where A is the slurry loss coefficient; L is the length of the grouting hole; R is the slurry diffusion radius; e c is the average porosity of rock; β is the slurry filling coefficient.

[0051] C. Use the advanced drilling hole as the grouting hole, and grout different areas of the front goaf according to the water-cement ratio and dosage of the paste quick-setting material calculated in step B;

[0052] D. After the slurry solidifies, each detection hole is centered on the grouting hole. Its distribution is spherical at different angles and continuously spreads outward from the grouting hole. The horizontal distance between adjacent detection holes is 1-2m, and each detection hole faces different directions. Figure 4 and 5 As shown, a comprehensive monitoring device is placed at the end position of each detection hole to monitor the situation during the entire excavation or mining process; the comprehensive monitoring device includes a bundle tube monitor, a thermocouple or a high-sensitivity optical fiber, a ground stress sheet, a U-tube or a micromanometer and a hot wire wind speed monitor, which are used to obtain gas concentration field, temperature field, gas pressure field, leakage air flow field and ground stress field data.

[0053] E. During the excavation and mining process, the staff regularly records the monitoring data of each detection hole and uploads it to the data terminal in a timely manner; the data terminal analyzes the monitoring data to determine whether there are any abnormalities around the end holes of each detection hole. If it is determined that there are abnormalities, an early warning prompt will be issued to stop construction. At the same time, the abnormal area is quickly located according to the location of the abnormal detection hole, and the degree of danger is determined in combination with the monitoring data. Then, corresponding treatment measures are taken according to the degree of danger to reduce the probability of disasters. Specifically, observe whether the gas concentration field, temperature field, gas pressure field, leakage flow field and ground stress field data are abnormal; at the same time, through the combination of various data, corresponding treatment measures are taken, as follows:

[0054] (1) When the temperature field and gas concentration field are abnormal, the following countermeasures are adopted:

[0055]

[0056] (2) When the local stress field is abnormal, that is, the stress detected by the pressure plate after grouting is less than the stress borne by the rock mass itself, it indicates that the grouting material is still likely to break, and the interior should continue to be filled with paste quick-setting materials with stronger bearing strength;

[0057] (3) When the gas pressure field and the air leakage flow field are abnormal, the drilling excavation will cause stress redistribution, and the coal body around the borehole will be subjected to stress changes similar to those caused by tunnel excavation. The dual disturbance will aggravate the damage to the coal body, the development of the cracks will reach maturity, and the air flow in the field will be abnormal, providing a continuous oxygen supply to the coal seam, which will make coal spontaneous combustion more likely to occur. At this time, SF6 gas is used for tracer marking, and new boreholes are drilled around the current abnormal detection hole or adjacent detection holes to release SF6 at a constant flow rate. Under negative pressure extraction conditions, the tracer gas is mixed with the negative pressure drainage tunnel air and diffused to the extraction borehole. After a period of time, the tracer gas will be evenly distributed in the abnormal detection hole. Then, a portable gas detector is used to detect whether there is air leakage. The borehole air leakage rate is calculated by the distance between the release point and the receiving point and the time difference between the release of SF6 and the detection of SF6. When the air leakage rate is greater than the threshold, the grouting process is carried out in time.

[0058] F. After the disaster is dealt with, continue to use each detection hole to obtain the corresponding monitoring data. After monitoring for a period of time, if no abnormality is found during this period, continue to excavate the tunnel for a certain distance, and repeat steps A to E to continue the next section of the advance detection process; if an abnormality is found during this period, repeat step E to determine the degree of danger of the abnormality, and adopt corresponding treatment measures until the monitoring data returns to normal, then continue to excavate the tunnel.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas, characterized in that: The specific steps are: A. Before tunnel excavation, advance drilling is performed in front of the tunnel according to the construction design drawings to determine whether there is a goaf in the front. If no goaf is found, the tunnel starts to be excavated to the detection distance of the advance drilling and stops, and continues to construct advance drilling forward from the current position to determine whether there is a goaf. This cycle is repeated until it is determined that there is a goaf, and then step B is entered; B. Use a transient electromagnetic detection device to extend into the advance borehole to determine the specific location and shape of the goaf, and determine the porosity in the goaf, and then determine the scope that needs to be reinforced and the water-cement ratio and dosage of the paste quick-setting material; C. Use the advanced drilling hole as the grouting hole, and grout different areas of the front goaf according to the water-cement ratio and dosage of the paste quick-setting material calculated in step B; D. After the slurry solidifies, multiple detection holes are arranged around the grouting hole with the grouting hole as the center, and a comprehensive monitoring device is placed at the end hole position of each detection hole to obtain the monitoring data around the end hole of each detection hole in real time; E. During the excavation and mining process, the staff regularly records the monitoring data of each detection hole and uploads it to the data terminal in a timely manner; the data terminal analyzes the monitoring data to determine whether there are any abnormalities around the end holes of each detection hole. If it is determined that there are abnormalities, an early warning prompt is issued to stop construction. At the same time, the abnormal area is quickly located according to the location of the abnormal detection hole, and the degree of danger is determined in combination with the monitoring data. Then, corresponding treatment measures are taken according to the degree of danger, so as to reduce the probability of disasters; F. After the disaster is dealt with, continue to use each detection hole to obtain the corresponding monitoring data. After monitoring for a period of time, if no abnormality is found during this period, continue to excavate the tunnel for a certain distance, and repeat steps A to E to continue the next section of the advance detection process; if an abnormality is found during this period, repeat step E to determine the degree of danger of the abnormality, and adopt corresponding treatment measures until the monitoring data returns to normal, then continue to excavate the tunnel.

2. The method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas according to claim 1 is characterized in that: The specific process of determining the goaf in step A is as follows: during the advance drilling process, a comprehensive determination is made as to whether there is a goaf ahead based on multiple factors, including the water inflow from the drill bit, the advancement speed, and the resistance encountered during advancement.

3. The method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas according to claim 1 is characterized in that: The specific process of determining the porosity in step B is as follows: according to the specific position and shape of the goaf, multiple borehole peeps are sent into the goaf to take images, and the images obtained by each borehole peep are unfolded to obtain a panoramic image, and the images are processed by binarization and grayscale methods respectively, and different side lengths δ are used to process the images. k The boxes cover the matrix area in the image, and the number of boxes N required for counting δk ; Then use the least squares method to calculate the series of data points (-lgδ k ,lgN δk ) to perform linear fitting and obtain the fitting straight line equation: lgN δk =D B ×(-lg δk )+b, and then calculate the pore fractal dimension D B ; So the porosity is expressed as: where r min and r max are the minimum and maximum radii of the pore channel, D B is the pore fractal dimension.

4. The method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas according to claim 1 is characterized in that: The water-cement ratio and the amount of the paste quick-setting material are determined in step B as follows: the porosity of the goaf is not uniformly distributed, and the porosity of similar goafs is classified. By dividing the porosity of different regions, combining the porosity, the fluidity and mechanical strength of the paste quick-setting material, the amount of the paste quick-setting material is calculated using the following formula; Slurry diffusion radius: Where P1 is the grouting pressure, P0 is the groundwater pressure, μ is the ratio of the viscosity of the slurry to the viscosity of water, and θ is the angle between the central axis of the grouting hole and the vertical line. is the porosity of the porous medium, is the starting pressure gradient, t is the grouting time, K is the permeability coefficient, R is the slurry diffusion radius after time t, and r is the grouting hole radius; Grouting volume: Q=A·L·π·R 2 ·e c ·b Where A is the slurry loss coefficient; L is the length of the grouting hole; R is the slurry diffusion radius; e c is the average porosity of rock; β is the slurry filling coefficient.

5. The method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas according to claim 1 is characterized in that: In step D, each detection hole is centered on the grouting hole, and its distribution is spherical at different angles and continuously spreads outward from the grouting hole, which is used to monitor the situation during the entire excavation or mining process; the comprehensive monitoring device includes a bundle tube monitor, a thermocouple or a high-sensitivity optical fiber, a ground stress sheet, a U-tube or a micromanometer and a hot wire wind speed monitor, which is used to obtain gas concentration field, temperature field, gas pressure field, leakage air flow field and ground stress field data.

6. The method for identifying and controlling the disaster of spontaneous combustion of coal and gas co-existence in overlapping goaf areas according to claim 5 is characterized in that: The step E specifically includes: observing whether the data of gas concentration field, temperature field, gas pressure field, air leakage flow field and ground stress field are abnormal; and taking corresponding treatment measures by combining various data, as follows: (1) When the temperature field and gas concentration field are abnormal, the following countermeasures are adopted: (2) When the local stress field is abnormal, that is, the stress detected by the pressure plate after grouting is less than the stress borne by the rock mass itself, it indicates that the grouting material is still likely to break, and the interior should continue to be filled with paste quick-setting materials with stronger bearing strength; (3) When the gas pressure field and the air leakage flow field are abnormal, the drilling excavation will cause stress redistribution, and the coal body around the borehole will be subjected to stress changes similar to those caused by tunnel excavation. The dual disturbance will aggravate the damage to the coal body, the development of the cracks will reach maturity, and the air flow in the field will be abnormal, providing a continuous oxygen supply to the coal seam, which will make coal spontaneous combustion more likely to occur. At this time, SF6 gas is used for tracer marking, and new boreholes are drilled around the current abnormal detection hole or adjacent detection holes to release SF6 at a constant flow rate. Under negative pressure extraction conditions, the tracer gas is mixed with the negative pressure drainage tunnel air and diffused to the extraction borehole. After a period of time, the tracer gas will be evenly distributed in the abnormal detection hole. Then, a portable gas detector is used to detect whether there is air leakage. The borehole air leakage rate is calculated by the distance between the release point and the receiving point and the time difference between the release of SF6 and the detection of SF6. When the air leakage rate is greater than the threshold, the grouting process is carried out in time.

Images