Study On Geo-electrical Response Characteristics Of Overburden Strata Induced By Mining

Caving zones could be caused due to destruction of roof of coal seam by mining, which could lead to sudden water inflow to the roof, so it is of important significance to carry out dynamic monitoring towards the collapsed zones. Experiments has indicated electrical resistivity of rocks can change remarkably while enduring destruction, which has become physical basis for applying DC current method to monitor dynamic collapsed zones. In this thesis, geophysical monitoring method for roof destructed will be put forward by analyzing the changing characteristics of electrical resistivity of roof rocks, in order to effectively prevent water inflow accident.In this thesis, based on studies of destruction characteristics and the changing principles of electrical resistivity in destructed roof rocks and the hydrogeological features of mines, different geo-electricity models for roof rock destruction have been established which have different geological structures, different face advances and different distances, and DC current method 3-D forward modeling is carried out towards the geo-electricity model, then the apparent resistivity cross-section diagrams are obtained by inversion which reflect the dynamic changes of collapsed zones of coal seam roof in the process of face advance. The numerical modeling results indicate: DC current method can effectively detect the fissure zones, isograms for apparent resistivity for different structures present large discrepancies, and the distribution law of apparent resistivity matches with the development scope for the collapsed zones and fissure zones under different advance periods, which has laid theoretical foundation for monitoring of collapsed zones and fissure zones by DC current method.Based on similar law with the physical modeling, the physical modeling is adopted in the laboratory to simulate the filed geo-electrical detection, results show: with progressing of advance face, distribution of apparent resistivity agrees with the scope of collapsed zones and fissure zones within the model while the destruction scope of roof will grow gradually, and the changing characteristics of apparent resistivity for the physical model is basically identical with the numerical modeling results generally, which further proves the DC current method can be adopted for monitoring roof destruction.Combining with results of numerical simulation and physical modeling, explanations are made towards destructions dynamic monitoring triggered by mining to the roof of a coal mine in Erdos, and corresponding conclusion has been drawn: the destruction scope of roof of this coal mine have been enlarged gradually with progressing of advance face, the maximum depths for the collapsed zones and fissure zones are respectively 20 m and 50 m, and the apparent resistivity changing features for the destruction scope basically agree with the numerical and physical modeling results.The DC current electrical resistivity method can accurately reflect the resistivity changing features of and geological structures in the roof, and determine scopes of collapsed zones and fissure zones. By studies and applications of numerical simulation, physical modeling and engineering cases, the DC current resistivity method for monitoring destruction by mining of roof has been proved to be feasible and reliable and has potential application significance.