• The Journal of Engineering Geology
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• v.12 no.2
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• pp.127-135
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• 2002

The relationship between the seismic velocity and RQD was estimated using the RQD data obtained from the optical borehole image processing and drill core logs and the seismic velocity measured from the PS logging. The seismic velocity and crack aperture show a high correlation in the granite in Yuseong area and banded gneiss in Paldang area. However, such a relationship cannot be found in the sedimentary rock in Sabuk area. In the sedimentary rock of Sabbuk area, the seismic velocity shows widespread distribution especially in the 0∼20mm range of accumulated crack aperture probably because the wide distribution of fracture zone in coaly shale results in the inaccurate measurements of the crack aperture.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.17-30
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• 2020

An optical televiewer is a geophysical logging device that produces continuous high-resolution full-azimuth images of a borehole wall using a light-emitting-diode and a complementary metal-oxide semiconductor image sensor to provide valuable information on subsurface discontinuities. Recently, borehole imaging logging has been applied in many fields, including ground subsidence monitoring, rock mass integrity evaluation, stress-induced fracture detection, and glacial annual-layer measurements in polar regions. Widely used commercial borehole imaging logging systems typically have limitations depending on equipment specifications, meaning that it is necessary to clearly verify the scope of applications while maintaining appropriate quality control for various borehole conditions. However, it is difficult to directly check the accuracy, implementation, and reliability for outcomes, as images derived from an optical televiewer constitute in situ data. In this study, we designed and constructed a modular fractured borehole model having similar conditions to a borehole environment to report unprecedented results regarding reliable data acquisition and processing. We investigate sonde magnetometer accuracy, color realization, and fracture resolution, and suggest data processing methods to obtain accurate aperture measurements. The experiment involving the fractured borehole model should enhance not only measurement quality but also interpretations of high-resolution and reliable optical imaging logs.