Mining slope stability evaluation method based on surface gas detection

Abstract

The invention relates to the technical field of geotechnical engineering, and provides a mining slope stability evaluation method based on surface gas detection, which comprises the following steps: step 1, slope field investigation and monitoring point layout; 2, continuous gas dissipation monitoring; 3, gas dissipation data processing and abnormity identification are carried out; 4, quantitatively evaluating the fracture development state; step 5, slope stability evaluation; and step 6, carrying out real-time risk early warning. According to the method, rapid, accurate, continuous, economical and effective evaluation on the slope stability condition is realized, and the reliability and practicability of slope crack monitoring and stability evaluation are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and in particular to a method for evaluating the stability of a mining slope based on surface gas detection. Background Art

[0002] With the increasing intensity of coal resource development, many coal mining areas are experiencing frequent slope geological disasters caused by mining activities in gently dipping layered strata. These disasters manifest as the development of cracks on mining-induced slopes, slope instability, and even collapse and landslide accidents. This poses a significant threat to coal mine production and the safety of the geological environment in mountainous areas. During underground coal mining, the rock mass is disturbed by mining, and the original equilibrium state of the overburden strata in the mining area changes, leading to stress redistribution and the generation of numerous cracks within the overburden. The formation, expansion, and penetration of these cracks are key factors controlling slope stability. However, surface cracks on slopes do not fully reflect the true extent of internal cracks within the slope. Sometimes surface cracks are relatively small, while internal cracks have already penetrated to the surface, posing a serious threat to slope stability.

[0003] Many coal seams mined in coal mining areas are rich in methane. After mining, gas accumulates in the goaf, including gas desorbed from the coal seam itself and gas escaping from fractures in adjacent coal seams and surrounding rock. As overburden fractures develop within the goaf, the gas accumulated there will escape to the surface through the rock mass fracture network. Therefore, monitoring surface gas emission patterns to infer the extent of overburden fracture development is a promising approach for fracture assessment and monitoring.

[0004] Existing detection and monitoring methods for internal cracks in mining slopes are mainly divided into two categories: contact detection and non-contact detection:

[0005] (1) Contact detection methods include borehole peek technology, core drilling method, geological caving method, etc. Although these methods can obtain relatively accurate information on fracture development, they have the problems of high detection cost, complex operation process, large disturbance to the slope, and monitoring results that can only reflect the fracture characteristics of local areas but are difficult to reflect the overall fracture development status.

[0006] (2) Non-contact detection methods such as radar detection and geophysical (electrical, transient electromagnetic, etc.) detection can achieve non-invasive monitoring. However, these methods are susceptible to interference from the physical properties of the rock mass and the environment under complex geological conditions of the slope, resulting in poor accuracy of the detection results and the inability to accurately identify the continuity of the fracture.

[0007] In addition, current research on gas monitoring technology focuses on the gas outburst patterns in underground goafs, gas concentration monitoring in ventilation systems, and detection of air leakage channels in goafs. However, there is still a lack of research and technology on directly using surface escaped gas detection to deduce the development of overburden cracks and then evaluate slope stability.

[0008] In summary, existing methods suffer from significant drawbacks, including high detection costs, poor monitoring accuracy, low monitoring efficiency, difficulty in continuous evaluation, and difficulty accurately reflecting the state of fracture continuity. These shortcomings severely restrict the reliability and efficiency of slope stability monitoring and assessment. Therefore, there is an urgent need to develop a new, more economical, accurate, continuous, and real-time method for monitoring fracture development in overburden slopes and assessing their stability. Summary of the Invention

[0009] The content of the present invention is to provide a method for evaluating the stability of mining slopes based on surface gas detection, which can solve the problems in the existing technology of high drilling detection cost, poor monitoring accuracy of geophysical methods, difficulty in surface deformation monitoring methods to accurately reflect the state of internal crack penetration, and difficulty in existing gas monitoring methods to achieve continuous and comprehensive evaluation of the spatial distribution of cracks.

[0010] A method for evaluating the stability of a mining slope based on surface gas detection according to the present invention comprises the following steps:

[0011] Step 1: Slope site investigation and monitoring point layout;

[0012] Step 2: Continuous gas emission monitoring;

[0013] Step 3: Gas emission data processing and anomaly identification;

[0014] Step 4: Quantitative evaluation of fissure development status;

[0015] Step 5: Slope stability assessment;

[0016] Step 6: Real-time risk warning.

[0017] Preferably, in step 1, based on the geological structure of the mining slope, the location of the mining area and the historical mining situation, the fissure areas where gas may escape are determined through on-site investigation; based on the surface crack location, the location of the goaf and the deformation characteristics of the slope, the slope is divided into several monitoring areas, and a gas monitoring point is set in each monitoring area; a fixed gas monitoring probe is installed at each monitoring point. The probe must have the function of continuously monitoring the gas concentration and escape flow, and the installation depth is 0.3m-0.5m below the surface fissure to ensure the collection of escaped gas.

[0018] Preferably, in step 2, gas concentration and flow monitoring equipment is used to continuously record the gas escape data of each monitoring point. The recording period is 24 hours of uninterrupted monitoring, and the data recording interval is once every 5 minutes. The real-time monitoring range of gas concentration changes is 0.001% to 5%, and the escape flow monitoring accuracy is 0.01L / min.

[0019] Preferably, in step 3, the gas concentration and escape flow data collected at the monitoring point are sorted, and time-gas concentration and time-escape flow change curves are drawn; and the judgment criteria for gas escape anomaly are set as follows:

[0020] (3.1) The gas concentration suddenly rises to more than 2 times the daily average concentration and lasts for more than 30 minutes;

[0021] (3.2) The gas flow rate suddenly increases by more than 2 times the daily average flow rate and lasts for more than 30 minutes;

[0022] Any situation that meets any of the above conditions will be judged as an abnormal gas leakage event, and the marked cracks may penetrate the goaf to the surface.

[0023] Preferably, in step 4, specifically:

[0024] (4.1) Collect and compile statistics on the gas concentration and escape flow peak data of the abnormal events identified in step 3;

[0025] (4.2) Use industrial CT scanning and 3D reconstruction technology to extract fracture characteristics of the sampled rock mass and obtain fracture opening, density, and fracture trace length parameters;

[0026] (4.3) The permeability k of the rock mass is calculated using Darcy's law of seepage, and the equivalent permeability k under the combined effect of fracture aperture and fracture density is calculated using the cubic law. f , establish k f Statistical mathematical model between monitoring gas escape amount;

[0027] (4.4) Based on the model, quantitative evaluation is conducted on the spatial distribution, development degree and continuity of cracks in the monitoring area.

[0028] Preferably, in step 5, specifically:

[0029] (5.1) Based on the fracture development parameters obtained in step 4 and the abnormal gas emission monitoring data, a 3D numerical model including the fracture network and slope geological structure is constructed using 3D geological modeling software FLAC3D or COMSOL;

[0030] (5.2) Input mining stress field parameters, rock mass physical and mechanical parameters, and fracture network distribution parameters into the model and perform multi-condition numerical simulations to simulate slope deformation and instability processes at different fracture development stages;

[0031] (5.3) Through simulation analysis, the influence of crack parameters on slope stability is analyzed to identify the distribution areas of key unstable cracks and potential instability modes of the slope.

[0032] Preferably, in step 6, the crack parameters and gas escape data obtained through continuous monitoring are input into the slope stability early warning platform, risk warning thresholds are set, and slope instability risk warning signals are analyzed and issued in real time to provide a basis for slope safety control.

[0033] The beneficial effects of the present invention are as follows:

[0034] By monitoring the amount of gas escaped from the slope surface and its changing patterns, the present invention establishes a quantitative relationship between the development state of overburden cracks and the characteristics of gas escape, thereby achieving a rapid, accurate, continuous and cost-effective evaluation of the slope stability, and improving the reliability and practicality of slope crack monitoring and stability evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a flow chart of a method for evaluating the stability of a mining slope based on surface gas detection in an embodiment. DETAILED DESCRIPTION

[0036] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments. It should be understood that the embodiments are merely for explaining the present invention and are not intended to limit the present invention.

[0037] Example

[0038] like Figure 1 As shown, this embodiment provides a method for evaluating the stability of a mining slope based on surface gas detection, which includes the following steps:

[0039] Step 1: Slope site investigation and monitoring point layout;

[0040] Based on the geological structure of the mining slope, the location of the mining area and the historical mining situation, the fissure areas where gas may escape are determined through on-site investigation; based on the location of surface cracks, the location of the goaf and the deformation characteristics of the slope, the slope is divided into several monitoring areas, and gas monitoring points are set up in each monitoring area; a fixed gas monitoring probe is installed at each monitoring point. The probe must have the function of continuously monitoring gas concentration and escape flow, and the installation depth must be 0.3m-0.5m below the surface fissures to ensure the collection of escaped gas.

[0041] Step 2: Continuous gas emission monitoring;

[0042] Gas concentration and flow monitoring equipment is used to continuously record the gas escape data of each monitoring point. The recording period is 24 hours of uninterrupted monitoring, and the data recording interval is once every 5 minutes. The real-time monitoring range of gas concentration changes is 0.001% to 5%, and the escape flow monitoring accuracy is 0.01L / min.

[0043] Step 3: Gas emission data processing and anomaly identification;

[0044] The gas concentration and escape flow data collected at the monitoring points are collated and time-gas concentration and time-escape flow curves are drawn. The criteria for determining abnormal gas escape are set as follows:

[0045] (3.1) The gas concentration suddenly rises to more than 2 times the daily average concentration and lasts for more than 30 minutes;

[0046] (3.2) The gas flow rate suddenly increases by more than 2 times the daily average flow rate and lasts for more than 30 minutes;

[0047] Any situation that meets any of the above conditions will be judged as an abnormal gas leakage event, and the marked cracks may penetrate the goaf to the surface.

[0048] Step 4: Quantitative evaluation of fissure development status;

[0049] Specifically:

[0050] (4.1) Collect and compile statistics on the gas concentration and escape flow peak data of the abnormal events identified in step 3;

[0051] (4.2) Use industrial CT scanning and 3D reconstruction technology to extract fracture characteristics of the sampled rock mass and obtain fracture opening, density, and fracture trace length parameters;

[0052] (4.3) The permeability k of the rock mass is calculated using Darcy's law of seepage, and the equivalent permeability k under the combined effect of fracture aperture and fracture density is calculated using the cubic law. f , establish k f Statistical mathematical model between monitoring gas escape amount;

[0053] (4.4) Based on the model, quantitative evaluation is conducted on the spatial distribution, development degree and continuity of cracks in the monitoring area.

[0054] Step 5: Slope stability assessment;

[0055] Specifically:

[0056] (5.1) Based on the fracture development parameters obtained in step 4 and the abnormal gas emission monitoring data, a 3D numerical model including the fracture network and slope geological structure is constructed using 3D geological modeling software FLAC3D or COMSOL;

[0057] (5.2) Input mining stress field parameters, rock mass physical and mechanical parameters, and fracture network distribution parameters into the model and perform multi-condition numerical simulations to simulate slope deformation and instability processes at different fracture development stages;

[0058] (5.3) Through simulation analysis, the influence of crack parameters on slope stability is analyzed to identify the distribution areas of key unstable cracks and potential instability modes of the slope.

[0059] Step 6: Real-time risk warning;

[0060] In step 6, the crack parameters and gas escape data obtained through continuous monitoring are input into the slope stability early warning platform, and risk warning thresholds are set (for example, the crack penetration rate exceeds 30%, the gas escape flow rate continuously increases and exceeds the preset threshold, etc.). The slope instability risk warning signal is analyzed and issued in real time to provide a basis for slope safety prevention and control.

[0061] This embodiment can realize real-time, continuous, and economical monitoring and evaluation of the development status of slope overburden cracks, and significantly improve the accuracy and efficiency of mining slope disaster risk prediction and prevention and control.

[0062] Taking a gently dipping layered slope in a coal mining area in Guizhou as an example, five typical fissure monitoring points were selected, targeting areas with surface cracks near the goaf. Fixed gas monitoring probes were installed for continuous monitoring. Over 30 days of on-site monitoring, gas emission levels at each monitoring point were determined. At two of these monitoring points, significant abnormalities in gas concentrations were observed when mining progressed to specific locations. The peak concentration reached 1.5%, and the flow rate reached a maximum of 0.2 L / min, persisting for over 30 minutes.

[0063] The collected abnormal data were used in industrial CT scanning experiments, and the crack parameters (the average crack opening was 2 mm, the density was 0.15 / cm) were extracted by combining 3D reconstruction technology. 2 , the average length of the crack trace is 0.5m), and the equivalent permeability k of the slope crack is calculated based on the established statistical model. f About 5×10 -12 m2, confirming that the cracks have penetrated to the surface.

[0064] Substituting these parameters into the FLAC3D three-dimensional numerical model, a simulation analyzed the slope's stability under the current fracture parameters. The results showed that the safety factor in the critical area dropped from an initial 1.25 to 0.98, below the safety threshold of 1.0, indicating a potential risk of slope instability. Based on this analysis, the early warning platform immediately issued an alert, and the mining area implemented timely reinforcement measures, effectively preventing further deterioration of the slope.

[0065] This embodiment shows that the method proposed in this embodiment can accurately identify the state of crack penetration, effectively realize real-time evaluation of slope stability and risk warning, the method is highly feasible, and has significant economic and safety benefits.

[0066] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the stability of mining slopes based on surface gas detection, characterized by: The following steps are involved: Step 1: Slope site investigation and monitoring point layout; Step 2: Continuous gas emission monitoring; Step 3: Gas emission data processing and anomaly identification; Step 4: Quantitative evaluation of fissure development status; Step 5: Slope stability assessment; Step 6: Real-time risk warning.

2. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 1, characterized in that: In step 1, based on the geological structure of the mining slope, the location of the mining area and the historical mining situation, the fissure areas where gas may escape are determined through on-site investigation; based on the location of surface cracks, the location of the goaf and the deformation characteristics of the slope, the slope is divided into several monitoring areas, and gas monitoring points are set up in each monitoring area; a fixed gas monitoring probe is installed at each monitoring point. The probe must have the function of continuously monitoring gas concentration and escape flow, and the installation depth must be 0.3m-0.5m below the surface fissures to ensure the collection of escaped gas.

3. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 2, characterized in that: In step 2, gas concentration and flow monitoring equipment is used to continuously record the gas escape data of each monitoring point. The recording period is 24 hours of continuous monitoring, and the data recording interval is once every 5 minutes. The real-time monitoring range of gas concentration changes is 0.001% to 5%, and the escape flow monitoring accuracy is 0.01L / min.

4. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 3, characterized in that: In step 3, the gas concentration and escape flow data collected at the monitoring points are sorted and time-gas concentration and time-escape flow curves are drawn; the criteria for determining gas escape anomaly are set as follows: (3.1) The gas concentration suddenly rises to more than 2 times the daily average concentration and lasts for more than 30 minutes; (3.2) The gas flow rate suddenly increases by more than 2 times the daily average flow rate and lasts for more than 30 minutes; Any situation that meets any of the above conditions will be judged as an abnormal gas leakage event, and the marked cracks may penetrate the goaf to the surface.

5. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 4, characterized in that: In step 4, specifically: (4.1) Collect and compile statistics on the gas concentration and escape flow peak data of the abnormal events identified in step 3; (4.2) Use industrial CT scanning and 3D reconstruction technology to extract fracture characteristics of the sampled rock mass and obtain fracture opening, density, and fracture trace length parameters; (4.3) The permeability k of the rock mass is calculated using Darcy's law of seepage, and the equivalent permeability k under the combined effect of fracture aperture and fracture density is calculated using the cubic law. f , establish k f Statistical mathematical model between monitoring gas escape amount; (4.4) Based on the model, quantitative evaluation is conducted on the spatial distribution, development degree and continuity of cracks in the monitoring area.

6. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 5, characterized in that: In step 5, specifically: (5.1) Based on the fracture development parameters obtained in step 4 and the abnormal gas emission monitoring data, a 3D numerical model including the fracture network and slope geological structure is constructed using 3D geological modeling software FLAC3D or COMSOL; (5.2) Input mining stress field parameters, rock mass physical and mechanical parameters, and fracture network distribution parameters into the model and perform multi-condition numerical simulations to simulate slope deformation and instability processes at different fracture development stages; (5.3) Through simulation analysis, the influence of crack parameters on slope stability is analyzed to identify the distribution areas of key unstable cracks and potential instability modes of the slope.

7. The method for evaluating the stability of a mining-induced slope based on surface gas detection according to claim 6, characterized in that: In step 6, the crack parameters and gas escape data obtained through continuous monitoring are input into the slope stability early warning platform, the risk warning threshold is set, and the slope instability risk warning signal is analyzed and issued in real time to provide a basis for slope safety prevention and control.

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