Littérature scientifique sur le sujet « Georadar Borehole survey »

We have used a combination of surface ground‐penetrating radar (GPR) profiling, crosshole radar tomography, and natural gamma‐ray logging to characterize a gravelly braided stream deposit. In a gravel pit, we conducted a survey using 300‐MHz surface GPR, 250‐MHz crosshole radar, and densely sampled gamma‐ray logging at single‐borehole locations. After excavation, we validated the geophysical results by comparison with the sedimentological and hydrogeological information obtained from the corresponding outcrop wall. We found the visual lithofacies boundaries agreed very well with the images provided by applied geophysical techniques. Our results illustrate how GPR reflector images are improved using tomographic velocity information. In addition, the structural interpretation of tomographic velocity fields is guided by the GPR reflector images in combination with natural gamma‐ray logging results. Groundwater flow and transport modeling was also performed on different subsurface models. The hydrogeological response of parameter distributions derived from a digitized outcrop image are compared with the response of a parameter field derived from the combined geophysical data and with the response of a simple block interpolation between the boreholes. Comparison of cumulative particle arrival times (breakthrough curves) indicates that the characterization of an appropriate real aquifer would benefit from incorporating high‐resolution geophysical data into the analysis.

A complex geomorphological research was car-ried out on an aeolian sand dune in Inner Somogy, Hungary. Sedimentological analysis showed three layers of sediment composed of sand with differing characteristics (Györgyövics et al., 2014) which suggested at least 3 aeolian phases in the region. OSL dating of samples from the same boreholes con-firmed these periods and determined that sand was deposited during the Late Glacial, the Dryases and Boreal phase (Kiss et al. 2012). However, carrying out a GPR survey revealed much more detailed structure of the particular dune. Compar-ing research results and applying GPR profiling in the early stages of geomorphological investigation could help choos-ing the OSL sampling points and depths resulting in a more precise study.

In the area of the Šlapanice school buildings a large frontal landslide in Lower Badenian clay covered by loesses and anthropogenic sediments was documented. Length of the landslide is ca 200 m, width at the base up to 720 m, thickness of the body of the landslide based on geophysical research reaches to 10 m. The landslide is a complex body consisting of older and active parts. The school buildings were founded in old landslide originally. Georadar (two profiles) and geoelektric (one profile) measurements were used for geotechnical evaluation of the landslide. Multi electrode cable tomography (ERT) and dipole electromagnetic conductivity survey (DEMP) were used from geoelectric method. Closely the northern part of the building was measured and interpreted geological-geophysical profile PF0 which was constructed based on georadar measurement and hydrogeological borehole VS-1, the sharp boundary between sediments of the Lower Carboniferous and the Lower Badenian of the Carpathian Foredeep was found. There were intepreted two fault systems of SW–NE direction taking place parallel to the margin of the basin. In the profile PF1 the structure of the landslide in detail was documented. Due to geophysical measurements and study of the borehole database a new fault system within the school buildings area was intepreted.

The relevance of the work is determined by the fact that no radiowave methods have ever been used to study the water areas of rivers and lakes and their geoelectric sections within the Baikal natural territory (BNT) in winter time. The purpose of the research is to determine the electrical and geometric characteristics of the layered medium "ice – water – bottom soil" and the ice cover of the Selenga River on the BNT in the VLF-LF and VHF radio wave bands according to the data of instrumental radiophysical measurements by GPR and radio impedance methods, including the determination of the structure of the ice crossings over the Selenga River. Using the Selenga River as an example, consideration has been given to the results of combining VLF-LF and VHF methods of electromagnetic diagnostics of a layered medium in a wide range of radio waves (from tens of kilohertz to units of gigahertz). Radio impedance profiling and sounding in the VLF-LF bands with the IPI-300 equipment made it possible to determine the sub-bottom structure of the soil from the change in impedance and geoelectric section. GPR in the VHF band made it possible to differentiate the fine structure of the Selenga River in winter by thickness of snow, ice and water. The sounding involved the use of georadar "Oko-2" with antenna units "Triton" (central frequency 50 MHz), AB-400 (central frequency 400 MHz), AB-700 (central frequency 700 MHz), and AB-1700 (central frequency 1700 MHz). The thickness of ice of the road crossing in the Mostovoy microdistrict of Ulan-Ude city was 0.5–1.2 m – 0.1–0.2 m thicker than that beyond the road crossing. It was found that the presence of snow cover beyond the road crossing prevents the ice mass from freezing. Calibration sounding of ice with borehole drilling yielded ice dielectric constant ε=3.17. The specific electrical resistance (SER) of water from boreholes is 71–74 Ohm·m at a temperature of 1 °C. The methods used complement each other and provide a quantitative description of the object of research. The integration of various methods of radio wave diagnostics provides more detailed information on the structure of the layered medium "ice – water – bottom soil". The obtained results and the developed methods of radio impedance and GPR sounding and profiling of an inhomogeneously layered underlying environment in winter time can be used in engineering and geological surveys in the eastern and northern regions of Russia.

The research subject of this PhD thesis consists in the development and application of techniques for analyzing well‐log, well‐test, and tracer data to infer the distribution of hydrologic properties in heterogeneous geologic settings, including fractured rock and complex aquifer systems. This thesis is organized in an introductory section presenting the state of the art about heterogeneous geologic media characterization and a focus on flowmeter log analysis. The second chapter regards applications of an integrated surveying approach where an hydrogeophysical characterization was used for a complex aquifer in calcareous and gypsiferous formation. The most important topic is the joint use of the Electromagnetic Borehole Flowmeter (EBF) in single hole mode and the Ground Penetrating Radar in single and cross borehole configuration. The third chapter is a completion of the studies performed and described in chapter two, with an extensive study involving a conventional hydrogeological characterization (pumping test, core analysis) with flowmeter log in cross hole mode and its application to design and interpretation two tracer tests. The aim is to provide an approach to optimize a set of hydrogeological and geophysical survey techniques. In chapter four another application of the flowmeter log is presented. This application has been designed to monitor infiltration in the vadose zone of a sandy‐gravelly soil and use results as calibration data for the geophysical investigation (ERT and Georadar Borehole survey). This thesis involved coordination of laboratory and field work; collaboration with geophysicists, geochemists and geologists in interdisciplinary studies. Main applications of this work include advanced hydrogeological characterization, groundwater and vadose‐zone contaminant remediation as well as optimal utilization of water resources.

Identification of water-saturated zones in the tailings dams is an actual scientific and practical task in terms of providing, first of all, their mechanical strength and filtration stability. The prevention of accidents in tailings is complicated by the circumstance that the processes of increased filtration, appearing and developing in the dam body, are not fixed on the initial stages by visual and traditional methods. Insufficiency, from the point of view of data completeness, of networks of piezometric boreholes on tailings dams does not allow solving the tasks of necessary information hydrological support. At the same time, the use of active- sounding geophysical study methods allows obtaining sufficiently detailed information about the peculiarities of the internal structure of the tailings dam and the degree of water saturation of the composing soils. A reasoned choice of geophysical methods, as well as their combination, allows increasing the level and reliability of obtained data at subsurface studies. The paper presents the results of in-situ experiments on the study of the tailings dam of the mining enterprise by different in nature wave GPR (georadar) and seismic methods. A comparative analysis of the conducted studies has allowed clarifying the internal structure and assessing the dam’s condition, paying special attention to the identification of local zones of increased water saturation and filtration. Based on the calculated correlation coefficient of electromagnetic and seismic wave velocity values, it was revealed that synchronization of geophysical surveys allows significantly increasing the reliability of in-situ determinations, as well as obtaining more reliable data. The results of the studies are the basis for predicting the most vulnerable places (zones) of a bulk ground hydraulic facility, as well as the localization of water-saturated areas in the body of the ground structures with greater reliability and performance.