Key Issues Of Dynamic Exploration Survey Based On The Borehole Radar And Digital Imaging

High stability of substructure is required in high-speed transit construction. The route with good engineering geological condition would be selected in project planning, but it still inevitably travels through some complicated or unfavorable sections in geological route selection, such as fracture zone, crush belt, karst region and underground river etc. In order to meet the requirement of the high stability of substructure, accurate and detailed geophysical data should be provided in stages of design and construction. Thereby, a novel effective technique named dynamic exploration survey is expected to prospect the fine geological structure with least possible boreholes in engineering construction by integratedly using the most advanced borehole radar and borehole imaging technology.It is the goal of this study to improve upon the current practice of using and interpreting borehole radar data and borehole imaging data and to establish the fundamental theory and methods of the dynamic exploration survey technology. There are some key issues in this study, including the geometrical-physical model of borehole radar wave, the numerical simulation of radar cross section (RCS) of unfavorable geologic bodies (UGB) and the comprehensive analysis method of borehole radar data and borehole imaging data. To deal with the key issues mentioned above, the important results of this paper include:1. The theory and technology of borehole radar in geological exploration and the principle of wave propagation and attenuation in rock mass are systematically studied. The methods of borehole radar data processing and interpretation are introduced, and the main feature of borehole RCS and several current estimate methods of dielectric constant are summarized.2. According to the typical UGB that meet in the actual exploration work, the radar response of different geological condition, i.e. different height, width, shape, buried depth, antenna interval, filling condition and surrounding rock etc, is simulated and analyzed by the method of finite-difference time-domain, and the resolution capability and application condition in real detection of different models are discussed to build up a direct and perceptual understanding of borehole radar applications.3. Through analyzing the geometrical-physical model of two kinds of geologic bodies, i.e. discontinuities and cavities, the propagation distance and travel-time of radar wave are deduced by simplifying the models, and the borehole radar RCS of different geologic objects is researched.4. Based on the high-resolution digital borehole images, the extensibility and correlation of discontinuities between adjacent boreholes and their uncertainty are discussed, and then the necessary conditions of connected discontinuities between two adjacent boreholes are studied with the calculated results, such as azimuth, dip angle, depth position and geologic characteristics etc.5. Combined the detected data of borehole radar and borehole imaging, a new estimate method of dielectric constant is proposed to meet the special requirement of borehole radar detection that sometimes drills through several stratum with possibly different dielectric constant in each stratum. Moreover, the estimate methods of the azimuth, dip angle and extensibility of discontinuities and the size and position of cavities are studied with these two combined data.6. A dynamic exploration survey technique is put forward to solve the actual problems that meet in the real detection engineering with borehole radar and borehole imaging system, and the operating flow, implementation procedure and basic analysis methods are preliminarily given as a regulation in dynamic exploration survey work.