| Frequency selection method for telluric electricity field(FSM)is an alternating current exploration method based on the difference of electrical conductivity between underground rock and ore.The method studies the electrical changes of underground geoelectric section by measuring the variation law of electric field horizontal components of several different frequencies produced by "natural" alternating electromagnetic fields on the ground,so as to solve geological problems.This method can measure very reliable low potential anomaly above the low resistance body,and its method is easy to operate,low cost,fast detection speed and wide application range,so it gradually get everyone's approval.It has good application effect,especially in finding groundwater resources and mine water hazard investigation.In this paper,the source and influencing factors of primary field of FSM are studied experimentally.Then,considering the relationship between alternating electric field component and alternating magnetic field component,the causes of abnormal frequency selection method are discussed theoretically.The feasibility of frequency selection method in hardened pavement observation is analyzed by experiment and practical application.The daily variation law of natural electric field frequency selection method is tested in different environments,and the daily variation data are analyzed and processed by wavelet analysis and denoising method.The experimental data are used to compare and study the daily variation of the geomagnetic field in industrial parks,urban areas and mountainous areas far from the city.According to the measured data,we found that the diurnal variation of the geomagnetic field in industrial parks and towns is closely related to the working time of residents,and the mountainous areas are mainly affected by thunder and lightning.In practical work,we can suppress the interference caused by environmental noise in daily life by digital filtering method.The geomagnetic field in mountainous areas and urban areas is relatively stable from 8:00 a.m.to 17:30 p.m.,so we can work during this period.However,when we work in industrial parks,the observation results are seriously disturbed by mechanical operation during the day,so we consider to carry out the construction at night.Based on the derivation of the abnormal formula of the frequency selection method of the sphere excited by the three-dimensional electromagnetic field,the forward simulation of the abnormal sphere in the alternating electromagnetic field is carried out to analyze the influence of different parameters on the anomaly of the frequency selection method.In view of the shortcomings in the past,the coupling relationship between the alternating electric field component and the alternating magnetic field component is considered in this simulation.The results show that the value of the electric field component produced by the alternating magnetic field is small,so the influence on the electric field component of the abnormal body on the ground is small,which is similar to the forward not consider the relationship between electric field component and magnetic field component before.The comparative experiment between the frequency section observation of hardened pavement and the conventional soil observation is taken by FSM observation.The experimental results show that the profile curves of hardened cement pavement and soil are basically the same,and the feasibility of observation and collection in hardened cement pavement is verified by practical application examples.In this paper,we have studied the field source composition and the cause for anomaly based on FSM,and we have explored the practical application of frequency selection method.This is of great practical significance to the theory and application of FSM.It can further instruct field work and provide a theoretical basis for the interpretation of abnormal reactions,so it can improve the accuracy of the results. |
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