Research On Transient Electromagnetic Detection Method Under Special Detection Environment

In recent years,with the increasingly complex terrain,geological conditions and working environment,the precision of geophysical exploration is required to be higher and higher.For example: 1.In the complex tunnel environment under the construction of TBM machine,the investigation of water-filled faults,broken zones,isolated water bodies and other adverse geological conditions in the construction area;2.Fine investigation of the poor geological body of the isolated stone in the construction area under the complex detection environment of the subway shield tunneling machine;3.In the complex urban environment of Jinan,detailed detection of baotu Spring and Hehu Spring underground hydraulic connection channels.The influence of TBM machine on each component of electromagnetic field excited by electric source is analyzed,and the distribution characteristics of each component of electromagnetic field in space are studied,and it is illustrated from the aspects of field distribution and single-point attenuation curve that the interference of TBM machine can be effectively reduced by adopting the device form based on electric source excitation and observing electric field Ex component.The effects of different distributions of multi-source transient electromagnetic fields are discussed.In order to prove that the multi-source transient electromagnetic device can effectively improve the signal-to-noise ratio,resolution and detection depth of detection,a tunnel model constructed by TBM machine is specifically designed.The finite element method(FEM)is used to analyze the three-dimensional transient electromagnetic field induced by single and multi-source devices.The different characteristics of transient electromagnetic field induced by sources with different distribution modes are analyzed from the attenuation curve of single point,relative anomaly,distribution characteristics of field,apparent resistivity profile and imaging results.At the same time,to achieve more accurate electromagnetic sounding and more accurate positioning for small-scale karst caves,a detection method based on TBM in complex detection environment for isolated small-scale karst caves is also explored.A borehole was drilled in the center point of the tunnel face toward the tunnel construction direction,the electrical source was excited into the hole,and array data was collected on the tunnel face.Electromagnetic sounding is carried out through the movement of the source,and the plane position of the defective geological body is determined through the distribution characteristics of the electromagnetic field on the tunnel face,so as to complete the accurate exploration of the defective geological body of the smallscale karst cave,and solve the difficult problem of transient electromagnetic tunnel advance prediction under the construction condition of TBM to some extent.The tunnel model constructed by shield tunneling machine is designed,and the model with isolated stone in front of the tunnel face is designed.The finite element method(FEM)is used to analyze the 3D transient electromagnetic field induced by single and multi-source devices.The different characteristics of transient electromagnetic field induced by different sources with different distribution modes are analyzed from the attenuation curve of single point,relative anomaly,distribution characteristics of field and apparent resistivity profile.At the same time,to achieve more accurate electromagnetic sounding and more accurate location for small scale isolated stone,a detection method for isolated small-scale stone under complex detection environment based on shield machine is also explored.A borehole was drilled in the center point of the tunnel face toward the tunnel construction direction,the electrical source was excited into the hole,and array data was collected on the tunnel face.Electromagnetic sounding is carried out through the movement of the source,and the plane position of the defective geological body is determined through the distribution characteristics of the electromagnetic field on the tunnel face,so as to complete the accurate exploration of the defective geological body of the small scale isolated stone,and solve the problem of transient electromagnetic tunnel advance prediction under the construction condition of shield tunneling to a certain extent.A new detection method was explored for the delicate exploration demand of underground hydraulic connection channels of Baotu Spring and Hehu Spring.The semi-airborn transient electromagnetic device of the electric power source is used to survey the underground hydraulic connection in Jinan,the source is distributed outside the city,and the 3D data collection is carried out in the urban area of Jinan by uav.This method can complete the exploration of the hydraulic connection channel without affecting the normal life of the citizens.Based on the geological structure and groundwater system theory,constructs the 3D geological model,and use the vector finite element method(FEM)for 3D simulation of the transient electromagnetic,this provides a possible means to detect hydraulic connections in complex urban detection environments.In the process of building the subway in Jinan,it is of certain guiding significance to protect the spring channel effectively.