Numerical simulation and exploration test for water from the floor strata of coal mining face using dual frequency induced polarization method

Deep coal seam mining is often threatened by water damage under the floor，which seriously affects the safe and efficient production of coal mines. Using mine electrical method to detect the water abundance of floor strata is an important way in the prevention and control of water disasters in coal mines，but this method faces the problems of strong multi solution of measured resistivity and inaccurate positioning of anomalies. In order to further improve the detection accuracy of the water rich area of the rock strata，an all around dual frequency induced polarization (IP) method for the coal mining face was proposed. Combined with the geological and geoelectric conditions of the roof and floor of deep group A coal seams in the Huainan mining area，the geoelectric models of the water rich cylinders in different directions were constructed. Based on the Cole-Cole model，the numerical simulation for the dual frequency induced polarization field was carried out by using the finite element method，and the response characteristics of IP parameters of different anomaly models were analyzed theoretically. The results show that ① The apparent parameters of IP in a single roadway show low resistivity and high frequency dispersity. The intersection point of the curves can accurately locate the strike position of the abnormal models，but is unable to determine its orientation exactly. ② The curves of apparent parameters of IP corresponding to each transmitting point in the double roadway are focused near the abnormal model，and also show the abnormal characteristics of low resistivity and high frequency dispersity. The position relationship between the transmitting points and the abnormal models determines the shape and properties of the apparent parameter curves，and the position relationship between the receiving points and the abnormal models determines the amplitude of apparent parameters. In which，the apparent parameters amplitude responded by the abnormal model lied in the working face or roadway floor is larger than that lied outside of the working face. In order to further evaluate the imaging accuracy of the apparent parameters of IP，the three dimensional inversion results of perspective and all around data in the double roadways were compared and analyzed. The results show that the sounding data obtained in single roadway and perspective data obtained in the double roadways can be mutually constrained，and the inversion parameters of IP obtained by the all around method can be used for positioning the abnormal models accurately，which demonstrates the superiority of this method. The engineering practice further shows that this method can effectively reduce the multiple solutions of electrical anomalies，and greatly improve the spatial positioning accuracy of anomalies and the accurate determination effect of water rich areas of coal floor strata，which provides a strong technical support for the accurate prevention and control of coal mine water disaster.