CSAMT response regularity of double-layer goaf in coal mine

China is not only a major coal-producing country，but also one of the countries most seriously affected by water disasters. With the increase and expansion of coal mining depth，mining intensity，mining speed and mining scale，as well as the large-scale development of new coalfields，the threat of coal mine water disaster is becoming more and more serious. Accurate geophysical exploration of the distribution of coal mine goaf is the main way to reduce coal mine water disaster. CSAMT method is an important electromagnetic exploration method for the detection of multi-layer goaf water accumulation area in coal mines. In order to study the electromagnetic response law of double-layer goaf in a coal mine of Yang Coal Group，the CSAMT responses of different types of double-layer goaf were simulated based on finite element method. The results show that：① when there is a double-layer abnormal body，when the electrical properties of the two abnormal bodies are both high-resistance or low-resistance，the layer interval of the abnormal body affects the longitudinal resolution of the abnormal body，and when the interval is small，it is difficult to distinguish the boundary of the double-layer anomaly. When the interval between the two abnormal bodies is more than 50 m，it can be divided into the response of two abnormal bodies，the larger the interval between the abnormal bodies，the more obvious the response. ② when the upper layer of the double-layer goaf is high resistivity and the lower layer is low resistivity，the abnormal response of the two layers can be distinguished when the interval between the two layers reaches 10m. The larger the interval between the layers，the better the resolution. ③ when the upper layer of the double-layer goaf is low resistance and the lower layer is high resistance，only when the interval between the two layers is more than 50 m，can we distinguish the anomalies caused by the two layers of abnormal bodies，indicating that the upper low resistivity bodies have shielding effect on the lower abnormal bodies. ④ finally，according to the forward simulation results，the experimental area similar to the electrical property of the model is selected for the experiment，and the test results are basically consistent with the response law of the forward simulation，which shows that the forward simulation results are more reliable. The CSAMT response law of the above-mentioned multi-layer abnormal bodies can provide a basis for the selection of electromagnetic exploration methods in double-layer goaf under different electrical conditions.