Study On Electrical Characteristics Of Coal Mining Cracks In Yubei Mining Area

The ground fissures caused by coal mining and the upward fissures formed by the deformation and destruction of the overlying strata affect human production activities.Studying the electrical characteristics of ground fissures caused by mining has certain theoretical and practical significance.The thesis carried out a research on the electrical characteristics of ground fissure development in coal mining by selecting direct current method and geological radar,and the research obtained the following results:(1)The numerical simulation of the DC method found that the Wenner array has low lateral resolution but accurately locates the anomaly in the vertical direction,the Schlumberger array has poor vertical resolution,the intermediate gradient array has a large detection abnormality range,and the bilateral pole-dipole array pairs anomalies.The reflection of the body is sensitive and the lateral resolution is high.(2)The apparent resistivity contours of the coal seam are distributed horizontally before mining;with the excavation of the coal face,the range of caving and fissure zones is further expanded,and the resistivity changes drastically at the goaf location,far away from the goaf,etc.The value lines are still distributed in layers.(3)The center frequency of the radar antenna increases and the image resolution increases.The moving speed of the antenna increases and the image resolution decreases.As the crack depth increases,the position of the hyperbolic diffracted wave at the bottom of the crack decreases,and at the same time,the two wings of the diffracted wave at the bottom gradually become gentle and the energy weakens.When the dielectric constant difference between the media becomes smaller,the reflected signal strength becomes weaker,and the response of the bottom diffracted wave appears downward on the time axis.(4)The geological radar response of several common surface cracks was studied.A strong energy reflection zone appears in the center of the vertical crack,and curve characteristics appear at both ends of the reflection zone.V-shaped cracks reflect the strongest energy in the center and present a horizontal state.As the depth increases,the energy decreases.Inclined cracks are a series of hyperbolic diffraction along the oblique direction.Split cracks form a series of hyperbolic diffraction wave groups in the development direction.Multi-form fractures will have more events superimposed on the side where they develop and extend,and the overall response corresponds to the direction of fracture extension.(5)The development height of upward fractures in the overlying strata caused by the stoping at 112201 working face of Xiaobaodang No.1 Well is limited.Analysis shows that the maximum development depth of downward fractures on the surface is only 3.25m,and the two are not connected.