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Considerations on the Difficulties in Velocity Logging in the Near Surface Environments  

Jo, Churl-Hyun (Subsurface Information Technologies, Inc.)
Byun, Joong-Moo (Dep. Geoenvironmental system eng., Hangyang University)
Hwang, Se-Ho (Geological & Environmental Hazard Div., Korea Institute of Geoscience and Mineral Resources)
Publication Information
Geophysics and Geophysical Exploration / v.9, no.3, 2006 , pp. 185-192 More about this Journal
Abstract
Cares should be taken when performing the P and S wave velocity loggings in engineering and environmental fields. Some of them are the effect of casing, which is installed to prevent the borehole collapsing when the drilling is done on the loose ground such as soil and/or soft rock, and the discrepancy of the velocities of the same media according to the difference of the source wave frequency spectrum. The elastic moduli obtained from the P and S wave velocity logging have the dynamic characteristics. To overcome these difficulties, the following suggestions are recommended; (1) develop and apply a careful drilling technique that can keep the borehole wall without a casing, and (2) apply the logging methods with the suitable frequency bandwidth for the object of the velocity logging. It is important to make the aseismological engineers understand the difference between the dynamic elastic moduli and the static ones obtained from mechanical test, and to advise them to use the information properly.
Keywords
velocity logging; casing effect; frequency dependency of velocity; dynamic elastic modulus;
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