Studies have been undertaken to compare the relative advantages of the acoustic televiewer and the optical televiewer in a number of practical situations. High-resolution borehole imaging using the optical televiewer provides comparable geological information to that which we would obtain from a surface geological survey. This is very useful for interpreting geological structure. The acoustic televiewer provides both topography and acoustic impedance information about the borehole wall. The acoustic image often correlates with other geophysical measurements such as the sonic log, suggesting that the acoustic image reflects physical properties better than the optical image. In geotechnical site investigations, the existence of weak layer, such as a fracture zone or unconsolidated thin layer, is one of the most crucial topics. We can utilise the acoustic televiewer images for the analysis of weak layers in this application. Each type of televiewer provides a different image, which reflects different physical properties. While the OPTV works as the eyes of a geological or geotechnical engineer, the BHTV works as his hands, his hammer and his micrometer. The limitations of use for each televiewer are also different. For example, while the optical televiewer requires a borehole with clear fluid or a dry hole, the acoustic televiewer can only work in a water-filled hole. Understanding such features, we can select the most suitable televiewer to obtain the best data for the purpose of each geotechnical site Investigation.
展开▼
