Study On Failure Law Of Overlying Strata In Stope Based On Seismic-Electrical Coupling Monitoring

As one of the main energy sources in China,coal mining has always been plagued by the problem of overlying strata deformation and failure during coal mining and backfilling,which poses a significant threat to coal mine safety.Accurate detection of such deformation and failure is necessary,but current technologies still have room for improvement.To overcome the limitations of single geophysical methods,this thesis proposes the use of a seismic-electric coupling monitoring technique to study the deformation and failure of overlying strata in the mining area.This method combines the use of parallel electric and microseismic signals,especially the conversion of passive microseismic sources into active seismic sources for analyzing the overlying strata conditions.The main research results are as follows:(1)Three numerical models of overlying strata electrical resistivity were established for mining faces using different backfilling methods.The response characteristics of electrical resistivity during the development stages of the two bands were compared under different observation systems,and design schemes for observation systems with different detection requirements were obtained.Compared with the bi-longitudinal borehole-tunnel observation system and the bi-oblique borehole-tunnel observation system,the bi-oblique measurement line observation system has a finer judgment of the development height of the two bands and a simpler on-site layout.The bi-longitudinal borehole-tunnel observation system and the bioblique borehole-tunnel observation system,compared with the bi-oblique measurement line observation system,can conduct high-precision exploration of the development size,morphology,and other aspects of the two bands.Numerical verification demonstrated the feasibility of using electrical resistivity monitoring systems to explore the deformation and failure patterns of overlying strata during coal mining and backfilling.(2)Three numerical models of different lengths were established,and an oblique monitoring system was installed.Based on the characteristics of the microseismic method,different positions of the source were set up for stimulation,and microseismic signals were calculated.By comparing the propagation characteristics of the source signal in different models,the wave velocity curve under the conditions of single stimulation and multiple receptions,as well as multiple stimulations and single reception,were studied,and it was found that microseismic signals have significant speed differences when passing through different overlying strata media.Based on this,the development height of the two bands can be determined,and numerical verification demonstrated the feasibility of converting passive microseismic signals into active seismic signals to analyze the development height of the two bands.(3)A 2D mining face model was constructed based on the similar criteria according to the actual field conditions.The seismic-electric coupling monitoring technology was used to monitor the entire process of advancing the mining face.The model’s electrical resistivity response characteristics and microseismic event locations were obtained.The microseismic signals were converted into active seismic signals for analysis.The calculated results were compared with the actual deformation and failure of the model’s mining face overburden.The study found that the electrical resistivity in the collapse zone and water-conducting fracture zone increased from the background value of 440 Ω·m to about 900Ω·m and 700Ω·m,respectively.When the microseismic signals crossed the two zones,the velocity change range was between 50m/s to 100m/s.The physical experiments verified the effectiveness of the seismic-electric coupling monitoring technology in calculating the height of the two zones.(4)At the 1W402 coal mine in Xinjiang,the deformation and failure patterns of the overlying strata during the mining of B4 coal were monitored on site using the seismic-electric coupling technique.The analysis showed that the electrical resistivity increased significantly at the locations of the two zones.Microseismic events were more frequent in the water-conducting fracture zone at a depth of 35-45 meters,and microseismic events were also observed in the caving zone at a depth of 0-20 meters.When converted into active-source seismic signals,the analysis showed that the microseismic signals exhibited significant velocity changes at the interface of the two zones,which was consistent with the analysis of the electrical resistivity response characteristics.The on-site application of the seismic-electric coupling monitoring technique validated its effectiveness in detecting the deformation and failure patterns of the overlying strata and the development heights of the two zones in the mining area.The thesis has 58 pictures,12 tables and 100 references.