Research On Fracture Characteristic Of Surrounding Rock And The Relationship With Microseismic Actibity In Synclinal Axis Region

In China,the proportion of underground mining is increasing,with the gradual disappearance of shalow mineral resources.In the process of coal mining,due to the influence of high tectonic stress,the strong mining-induced earthquake,rock burst and other dynamic disasters occur more frequently in synclinal axis region,which seriously restrict mining safely and efficiently.At present,the development law of strong mining-induced earthquake and the rule of rock burst are still not clear in synclinal axis region.Due to horizontal tectonic stress,the stress distribution characteristics,the fracture characteristic and the overburden strata movement law of surrounding rock are different from normal.It is the reason why strong mining-induced earthquake and rock burst occur more frequently in synclinal axis region.The regional geological structure of Yanbei coal mine in Gansu province is complicated,and the phenomenon of rock burst is significant.The 250202 working face is located in the synclinal axis of Yanbei coal mine,and many strong mine earthquakes and rock burst events are induced in the mining process.This thesis focused on the correlation between microseismic activity and regional stress field in synclinal axis region.Through the technical means of in-situ stress measurement,inversion of in-situ stress,similar simulation experiment,theoretical analysis and Rock mechanical test,the fracture characteristic of surrounding rock and the relationship with seismic actibity in synclinal axis region are revealed.1.The characteristic of stress field and its evolution during mining in synclinal axis region are clarified.The synclinal axis region is the area with high degree of stress concentration,and it has high horizontal tectonic stress,it is the reason why strong mining-induced earthquake and rock burst occur more frequently.Under the influence of high horizontal tectonic stress,the maximum principal stress in surrounding rock increases with higher stress gradient as it gets closer to the axial part of syncline.In contrast,it has little influence on vertical stress,which is mainly affected by the buried depth of rock.2.Fracture laws of surrounding rock in characteristic zones during mining in synclinal axis region were obtained.The surrounding rock was classified into different characteristic zones,according to the deformation and fracture characteristics of the surrounding rock in the synclinal axis region during mining.With analysing the frequency and energy of microseismic event which occurrend in different characteristic zones of surrounding rock,which was proved that the influence of strong mining-induced earthquake is various in different characteristic zones of surrounding rock.3.Based on the theoretical calculations and sensitivity analysis with the theoretical model,which was proved that the law of overburden strata movement and the stress distribution law of surrounding rock in characteristic zones have changed during mining in synclinal axis region.The result of similar simulation experiment and the monitoring data during mining which also proved this conclusion is convincing.4.Microseismic events were classified according to the fracture mechanism of surrounding rock in characteristic zones.Based on above,The relationship between the characteristics of microseismic enents and the stress states of surrounding rock in characteristic zones was obtained.On this basis,According to the microseismic parameter b and its physical meaning in G-R relation,the characteristics of microseismic activity in surrounding rock of different characteristic zones were obtained and the relationship between fracture characteristic of surrounding rock and seismic activity in synclinal axis region was found.The result of monitoring during mining also proved this conclusion is convincing.