• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.231-234
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• 2001

When constructing subsurface structures and/or wells, the precise estimates of hydraulic parameters must be obtained for operating safety and/or for developing necessary quantity of groundwater. Hydraulic conductivity is mainly subjected to the characteristics of fracture network in the fractured media such as fracture orientation and angle, fracture aperture and frequency, fracture length, interconnectivity of fractures, and filling material, feature of fracture plane. In this study we conducted water injection test at afferent depths on six boreholes drilled in granite of Mt. Geumjeong. hydraulic conductivity was calculated using Moye and Hvorslev methods. The relation between hydraulic conductivity and fracture frequency data obtained from acoustic televiewer and core log were analyzed. The result shows that the correlation between the hydraulic conductivity and the fracture frequency data obtained from acoustic televiewer is better than that with the core log.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.237-244
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• 2002

Televiewer is a logging tool capable of scanning the borehole wall. The tool uses a rotating acoustic beam generator that acts as both a transmitter and receiver. The beams are sent toward the wall. The amplitude of a returning signal from the wall has nearly a linear relationship with the reflection coefficient R of the borehole wall, when the wall is smooth. As R depends only on rock impedance for fixed water impedance, the amplitude is directly associated with mass density and seismic velocity of rock. Meanwhile, the amplitude can be further reduced by wall roughness that may be caused by drilling procedures, differences in rock hardness, because the rough surface can easily scatter the acoustic energy and sometimes the hole becomes elongated in all directions according to the degree of weathering. In this sense, the amplitude is related to the hardness of rocks. For convenience of analysis, the measured amplitude image(2-D data(azimuth ${\times}$ depth)) is converted, with an appropriate algorithm, to the 1-D data(depth), where the amplitude image values along a predetermined fracture signature(sinusoid) are summed up and averaged. The resulting values are subsequently scaled simply by a scalar factor that is possibly consistent with a known strength. This scaled Televiewer reflectivity is named, as a matter of convenience,“Televiewer rock strength”. This paper shows, based on abundant representative case studies from about 8 years of Televiewer surveys, that Televiewer rock strength might be regarded, on a continuous basis with depth, as a quitely robust indicator of rock classification and in most cases as an approximate uniaxial strength that is comparable to the rebound value from Schmidt hammer test.

• The Journal of Engineering Geology
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• v.11 no.3
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• pp.279-294
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• 2001

When constructing subsurface structures and drilling wells, the precise hydraulic parameters must be obtained for operating safety and for developing enough quantity of groundwater, respectively. In this study we conducted water injection test at different depths on six boreholes drilled in the granite of Mt. Geumjeong. Hydraulic conductivity was calculated using Moye and Hvorslev methods. The relation between hydraulic conductivity and fracture frequency data obtained from acoustic televiewer and core log was analyzed. From the result, though the correlation coefficient between the hydraulic conductivity and the fracture frequency from acoustic televiewer data is higher than that between the hydraulic conductivity and the fracture frequency from core log data on most of the test holes, the correlation coefficient between the hydraulic conductivity and the fracture frequency from the televiewer data is lower than 0.5. This suggests that the hydraulic conductivity of granite in the study area is influenced not only by the fracture frequency but also by various factors of fracture network such as fracture aperture and length, interconnectivity of fractures, fracture orientation and angle, filling material and so on.

• 한국지구물리탐사학회:학술대회논문집
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• 1999.08a
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• pp.137-155
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• 1999

Recently, Televiewer(Borehole Acoustic Scanner(Televiewer)) has come to be widely used specially for the general engineering construction design. The Televiewer tool using a focussed acoustic beam is to detect the amplitude and traveltime of each reflected acoustic signal at the wall, resulting in the amplitude- and traveltime image respectively. Fractures can be well detected, because they easily scatter the acoustic energy due to the highly narrow beam. In addition, the drilling work will rough the borehole wall so that the acoustic energy can be scattered simply due to the roughness of the wall. Thus, the amplitude level can be directed associated with the elastic properties(impedance) and the hardness of the rock as well. Meanwhile, the traveltime image provides an information about the borehole shape and can be converted to a high precision 3D caliper log(max. 288 arms). In this paper, based on the high resolution of Televiewer images, general evaluation methods are illustrated to derive very reliable rock parameters.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.261-273
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• 1998

Multiple well log analysis technique consisting of geophysical well log and geological core log has been made to analysis the discontinuities of a test borehole-PABH1 located in Pungam sedimentary basin, Sosok, Hongchon-gun, Kangwon Province. Well log methods consist of normal resistivity log, focussed log, single point resistance log, SP log, gamma log, natural gamma log as well as acoustic televiewer log and borehole television log. Core scanning technique was used as an aid for geological core log. The analysis was made by comparing firstly the televiewer and core discontinuities, and then the results from conventional geophysical log analysis were compared to those from core log and acoustic televiewer log. Fractures deduced from the acoustic televiewer log coincide well with discontinuities shown on the core and conventional geophysical logs. Particularly close coincidence could be observed between fractures derived from acoustic televiewer and conventional geophysical log analysis. It has been noted that the geophysical logs such as, caliper, resistivity, density and high resolution gamma gamma curves are effective in delineating the fractures. For example the ratio between density and resistivity (BRD/SHN) provides also an alternative indicator for discerning the fracture condition in the study area.

• The Journal of Engineering Geology
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• v.5 no.3
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• pp.277-288
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• 1995

Fracture detection has always been very attractive to the log, because it is important in many of our prospecting activities, e.g. in understanding the underground rock formation and also the fluid flow as a high permeability path. This paper demonstrates the use of high resolution borehole acoustic scanner for the detection of fractures. The tool, known as Televiewer, is the first acoustic borehole imaging system to use a focussed beam. The acoustic beams generated by a single transducer are sent toward the borehole wall, scanning the wall in a tight helix as the tool moves along the borehole. The amplitudes and travel times of the reflected signals are then measured, which produces the corresponding images. The highly resolved amplitude image allows to recognize various size of fractures and in addition to derive the rock strength from the image. Meanwhile, the travel time image itself can be directly converted to a precise caliper image, providing detailed information of deviations of the borehole shape. It also allows correction of and explanations for amplitude variations. Field measurements were carried Out at the Cheongyang study sites in Korea to illustrate the efficiency of the televiewer log.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.41-46
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• 2008

After choosing twenty sluice culverts located at national rivers by detailed appearance evaluation, hydraulic response test and acoustic televiewer in addition to surface geophysical explorations were carried out to investigate the cavities which exist at the boundary of sluice culvert and ground. Tapping, GPR, 3-D resistivity surveys and acoustic televiewer imagery obtained successful results in limited conditions according to characteristics of the sites. On the other hand, hydraulic response test successfully detected cavity existing at the lower part of sluice culvert and its continuity. However, hydraulic response test can not supply the quantitative informations on the scale and the shape of cavity. Thus it is very important for accurate investigation to make comprehensive interpretation after supplying various surveys proper to site characteristics.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.751-758
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• 2002

Boreholes that are drilled in soft or unconsolidated materials such as gravels and coals are prone to collapse. To maintain the hole, some kinds of casing pipes are needed. If thereby a plastic pipe e.g. PVC is used for the casing, Televiewer tool is still capable of detecting structural features such as fractures in the borehole wall behind the pipe, whereas other borehole-imaging logging devices such as BIPS (Borehole Image Processing System) and FMS(Formation Micro Scanner) won't provide any information about that. Televiewer's primary component is a piezoelectric transducer centered in the hole. It acts as both a transmitter and receiver, and sends an ultrasonic beam. That is reflected, in the same manner as the seismic wave propagation, from the both sides(inner and outer surfaces) of the casing pipe, transmits through the pipe and then reflected from the borehole wall. With an appropriate choice of time-windowing, it is possible to capture the returning signals from both the borehole wall and the outer side of casing pipe as well. A suite of laboratory tests were performed on various physical models composed of plastic pipes with different diameters. Although the amplitudes of returning signals were reduced to about half the usual value due to the transmission loss, the dynamic range of Televiewer tool was sufficient to observe the structural features behind the casing pipe. Besides, several representative case studies at various research areas in our country are presented. The results demonstrate the usefulness of the transmissivity of Televiewer acoustic km, which will assist in further structural interpretation.

• The Journal of Engineering Geology
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• v.6 no.1
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• pp.1-13
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• 1996

The fracture transmissivity($T_f$) is the most important parameter of fracture in assessing groundwater flow in fractured rock masses by using the DFN(Discrete Fracture Network) modeling. $T_f$, the most sensitive parameter m DFN modeling, is dependent upon aperture, size and filling characteristics of each fracture set. In the field test, the accuracy of $T_f$ can be increased with Borehole Acoustic Scanning (Televiewer) and Fixed Interval Length(FIL) test in constant head. $T_f$ values measured from FIL test was modified and estimated by each fracture set on the basis of the Cubic Law and the information of aperture and filling characteristics obtained from Televiewer. The modified $T_f$ results in the increase of confidence and reliability of modeling results including the amount of tunnel inflow.And, this approach would reduce the uncertaintity of the assessment for groundwater flow in fractured rock masses using the DFN modeling.

• The Journal of Engineering Geology
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• v.29 no.1
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• pp.1-12
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• 2019

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.