Research On The Detection Of Abnormal Stress In Front Of Driving Work Based On Dc Method

Coal and gas outbursts are very serious in China.With the increasing depth of coal mining and the increase of ground stress and gas,the risk of coal and gas outburst is increasingly serious and complex.In recent years,coal and gas outbursts still occur frequently,especially on the tectonic belt and stress concentrated area.Therefore,to effectively detect the abnormal stress in front of the working faces and accurately identify the corresponding area is the key for disaster prevention and control.In this paper,direct current(DC)method is introduced to detect the abnormal stress distribution in front of a driving face.An experimental system for the synergetic monitoring of DC and acoustic emission(AE)signals is established,and the uniaxial loading experiments on coal samples are conducted.The responding laws of apparent resistivity and AE parameters with stress are analyzed,and the current conduction mechanisms of stresses coals are investigated from both macro and micro perspectives.Based on numerical simulation results,the method ideas and principles of the application of DC method to the detection of the abnormal stress distribution in front of driving faces are put forward.To verify the feasibility of this method,field tests are carried out in coal mines.(1)The temporal and spatial evolution law of apparent resistivity and AE response during the deformation and fracture of coal samples under step loadings are studied.Results show that the response characteristics of apparent resistivity and AE signals are both closely related to the mechanical behaviors of the coal samples.In the initial stage of loading,apparent resistivity decreases with the increasing stress and the high resistance area is getting smaller,while AE activity maintains at a low level.In the fracture developing process,the apparent resistivity increases with increasing load,and the AE activity becomes active and a sudden increase of AE count appears when the sample failure occurs.According to the experimental results,the electrical conductivity and the change mechanism of the resistivity of the loaded coal are analyzed from the macro and micro point of view.(2)Stress distribution of the coal and rock mass in front of the 11061 working face in Fangshan coal mine during driving by FLAC3 D,and obtains the distribution and evolution laws of "three zones"-rupture belt,stress concentration belt and original stress belt are obtained.(3)The method ideas and principles of the application of DC method to the detection of the abnormal stress distribution in front of driving faces are put forward.Coal stress in front of the 11061 driving face in Fangshan mine is detected using the proposed DC method.The apparent resistivity nephograms are obtained by inversion technology,and both the normal and abnormal distribution of stress are analyzed and compared.The DC method is verified by the drillings volume and the actual coal uncovering situation,which shows that the results from DC method corresponds well with the verification indexes.The research results will provide an efficient and comprehensive method for the detection of abnormal distribution of stress in front of a working face,which is significant for the prediction of coal and gas outburst.In addition,the method should also provide a reference for the detection of stress distribution in other areas of this coal mine or even other coal mines around China,which is of a great significance to further improve the system for coal and rock dynamic disasters prevention and control.In this paper,47 figures,7 tables and 104 references are included.