Research On Data Processing Method Of Directional Borehole Radar For Tunnel Ahead Prospecting

With the development of tunnel construction in China towards complex environments such as difficult and dangerous mountainous areas in the west part of China,crossing rivers and seas,new requirements for more sophisticated geological prediction of tunnels are also proposed.Under the action of high confining pressure in deep buried tunnels,especially under the recharge of infinite water bodies overlying river-crossing and sea-crossing tunnels,small scale abnormal bodies can form sources of disasters,requiring appropriate means to detect and treat them in advance.The borehole radar detection method has the advantages of proximity detection,low external electromagnetic interference,and high detection accuracy,which can achieve the detection of small scale abnormal bodies at sub-meter level.However,the single borehole radar detection method can only detect the distance between the abnormal body and the borehole,making it difficult to detect the azimuth angle of the abnormal body.The cross-borehole radar detection method is only sensitive to the abnormal response between two holes,and often needs to drill multiple groups of boreholes for detection,which is time-consuming and laborious.In contrast,the single-borehole directional borehole radar detection method is a more ideal detection method,and it can obtain the three-dimensional position and shape of surrounding abnormal bodies through a single measurement of a single borehole,which has good potential of engineering application.However,the data processing method of directional borehole radar detection is still in the initial stage at present,and it is urgent to carry out specific research.In response to the above problems,this paper relies on the reflector-type directional radar detection system developed by the research team,and bases on theoretical analysis,numerical simulation,and laboratory experiments,a research on the data processing method of directional borehole radar detection is conducted.The focus is on the fast forward modeling method of directional borehole radar by Gaussian beam and the analysis of detection response characteristics,the azimuth orientation and 3D imaging algorithm of directional borehole radar detection of abnormal bodies,etc.A complete set of methods for directional borehole radar detection data processing has been formed,which has laid a good theoretical foundation for practical engineering applications to be carried out in the future.On the other hand,aiming at the requirement of directional detection using conventional borehole radar in engineering practice,the borehole-tunnel radar detection mode and its tomographic inversion and migration imaging algorithms are also studied,which provides a possible way for the directional detection of abnormal bodies based on conventional detection instruments.The main research work and results of this thesis are as follows:(1)Fast forward modeling method of Gaussian beam for directional borehole radar and analysis of detection response characteristics.Aiming at the problem that the conventional finite difference method and finite element method are difficult to realize the rapid simulation of reflector-type directional borehole radar detection,a fast simulation method for directional borehole radar detection based on Gaussian beam is proposed.On this basis,the characteristics of several detection methods commonly used by directional borehole radar and the response characteristics of typical anomalies are analyzed.(2)Azimuth estimation and 3D imaging algorithm for detection of abnormal bodies by directional borehole radar.Aiming at the problem that the azimuth estimation algorithm of abnormal bodies by the reflector-type directional borehole radar are currently immature,which is difficult to deal with the problem of complex detection scenarios,this paper refers to the air radar target recognition algorithm,and proposes a positioning scheme suitable for directional detection in the tunnel’s ahead prospecting borehole.And based on this,the multi-target abnormal body positioning method is studied,and the applicable scenarios of the directional borehole radar detection method are expanded.Furthermore,the abnormal body azimuth estimation algorithm and the back projection migration imaging method are combined to form a three-dimensional migration imaging algorithm for directional borehole radar detection.The three-dimensional orientation and imaging of abnormal bodies around the borehole has been realized,which has laid foundation for practical engineering applications.(3)A new detection mode for borehole-tunnel radar and its tomographic inversion and migration imaging algorithm.In addition to the data processing method of the dedicated directional radar detection system,this article also explores a hole tunnel radar detection method based on the existing conventional omnidirectional hole radar,and proposes a dedicated tomography inversion and migration imaging algorithm.This method adds borehole-tunnel transmission detection information to traditional omnidirectional reflection detection,which can indirectly achieve directional detection of abnormal bodies.It provides a possible approach for directional detection of abnormal bodies based on conventional detection instruments.On the basis of the research above,based on the reflector-type directional borehole radar prototype initially developed by the research team,the physical model test of abnormal body directional detection was carried out,and the indoor test of data collection and abnormal body azimuth estimation and migration imaging algorithm was conducted and the data acquisition and verification of the abnormal body azimuth estimation and migration imaging algorithm are carried out.The results are basically consistent with the position of the abnormal body,which verifies the effectiveness of the method proposed by this paper.