Propagation Of Borehole Radar's Electromagnetic Wave And Detection To Abnormal Geo-bodies

Borehole radar is a new geological exploration tool introduced into China in the 1990 s.It is a kind of well detection mode for ground penetrating radar.Borehole radars rely on the transmitted electromagnetic signals to detect deep underground fractures and abnormal geo-bodies.Because of its superiority to the underground depth of detection and its higher resolution with respect to surface radar,it is considered to have a better application prospect.In recent years,there have been relatively successful applications in the design of site selection for major projects and the investigation of potential safety hazards in mine projects,which has improved the economic performance in engineering activities.This paper first introduces the measurement modes of borehole radars: single-hole measurement,borehole-surface measurement and cross-hole measurement,and explaining its measurement principle.The propagation of electromagnetic waves was analyzed from the Maxwell equations,electromagnetic wave fluctuating,attenuation,and electrical parameters of the medium?Make sure to study single-hole reflection rules of anomalous geological bodies in the formation.Based on the YEE algorithm,the differential format of the two-dimensional TM wave magnetic field component and the electric field component is deduced from Maxwell's equations.Forward modeling of two-dimensional TM wave propagation was performed using the FDTD-based Gprmax method.Establishing physical models of underground space and anomalous bodies,and assigning electromagnetic wave propagation influencing factors: dielectric conductivity(?),dielectric constant(?),and borehole radar center frequency(f)to do forward simulations to obtain corresponding radar profiles illustration.From the profile,the same radar,when the conductivity remains unchanged,with the increase of the dielectric constant,the reflected intensity of the radar wave gradually increases and the detection distance increases;the same radar,when the dielectric constant does not change,with the conductance With the increase of the rate,the reflected signal intensity of radar waves gradually weakens and the detection distance decreases.The reflected signal intensity of different center frequency radars in the same geological environment gradually increases but the number of redundant signals increases greatly,and the detection distance gradually decreases.In the simulation of many radar profiles,the information is more dispersed and difficult to extract in practical applications.To solve this problem,this paper introduces the concept of grayscale and extracts gray values from radar profile images.Corresponding to the response signal strength(Q)and detection distance(S)of the electromagnetic wave to the abnormal geologic body,the propagation law of the electromagnetic wave is quantified from the point of data,which a highly uniform law curve is fitted,and specifically analyzed how the three major factors do effects to electromagnetic wave propagation.Using the laws summarized in this paper,in the Shuangyashan and Changchun Jingyue project examples,selected the type of borehole radar based on the parameters such as site electrical parameters and rock types that have been obtained,and the borehole radar is judged by the regularity curve to its anomaly bodies detection signal strength and detection distance,evaluating the feasibility of the radar in the detection.After obtaining the on-site detection data,the radar cross-section of the stratum is obtained through filtering and noise reduction,and compared with the stratum data and sample analysis results in this area,and the accuracy of the borehole radar detection data is verified.