• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.37-56
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• 2001

As a preliminary study to establish fracture network model in crystalline rocks, detail investigation on fracture characteristics were performed. Five fracture sets were determined on the basis of regional survey of geological structures and fractures on outcrops. Among the fracture sets, S1 set has the highest density and longest trace length of fractures which was identified on surface in the study area. S4 and S5 sets are composed of foliations and foliation parallel shear joints of gneisses, which are very important sets at the aspect of weighting of fracture length. For characterization of subsurface fractures, detail core logging was performed to identify fractures and fracture zones from five boreholes. Acoustic televiewer logging and borehole geophysical loggings produced images, orientations and geophysical properties of fractures which intersect with boreholes. According to the result of the investigations, subsurface fractures can be grouped as three preferred orientations(B1, B2 and B3), which correspond to S1, S2 and S4/S5 of surface fracture sets, respectively. Actually, B1 set is expected to be intensely developed at subsurface. However, it has low frequency of intersection with boreholes due to its parallel or sub-parallel direction to boreholes. According to the inference of conductive fractures, B1 and B3 sets have possibilities of water flow and their intersection lines are also thought to consist of important conduits of groundwater flow. In particular, faults which are parallel to foliations control major groundwater flow in the study area.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.88-100
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• 1998

Since fractures may serve as major conduits of groundwater flow in crystalline rocks, characterization of conductive fractures is especially important for interpretation of flow system. In this study, characterization of fractures to investigate hydraulically conductive fractures in gneisses at an abandoned mine area was performed. The orientation, width, length, movement sense, infilling materials, spacing, aperture, roughness of both joints and faults and intersection and connectivity to other joints were measured on outcrops. In addition, characteristics of subsurface fractures were examined by core logging in five boreholes, of which the orientations were acquired by acoustic televiewer logging from three boreholes. The dominant fracture sets were grouped from outcrops; GSet 1: N50-82$^{\circ}$E/55-90$^{\circ}$SE, GSet 2: N2-8$^{\circ}$E/56-86$^{\circ}$SE, GSet 3: N46-72$^{\circ}$W/60-85$^{\circ}$NE, GSet 4:Nl2-38$^{\circ}$W/15-40$^{\circ}$SW and from subsurface; HSet 1: N50-90$^{\circ}$E/55-90$^{\circ}$SE, HSet 2: N10-30$^{\circ}$E/50-70$^{\circ}$SE, HSet 3: N20-60$^{\circ}$W/50-80$^{\circ}$NE, HSet 4: N10-50$^{\circ}$E/$\leq$40$^{\circ}$NW. Among them, GSet 1, GSet 3 and HSet 1, HSet 3 are the most intensely developed fracture sets in the study area. The mean fracture spacings of HSet 1 are 30-47cm and code 1 fractures, such as faults and open fractures, comprise 21.0-42.9 percent of the whole fractures in each borehole. HSet 3 shows the mean fracture spacings of 55-57cm and the ratio of code 1 fractures is 15.4-26.9 percent. In spite of the mean fracture spacing of 239cm, code 1 fractures of HSet 4 have the highest ratio of 54.5 percent. From the fact that faults or open fractures have high hydraulic conductivity, it can be inferred that the three fracture sets of N55-85$^{\circ}$E/50-80$^{\circ}$SE, N20-60$^{\circ}$W/50-75$^{\circ}$NE and N10-30$^{\circ}$E/$\leq$30$^{\circ}$NW from a fracture system of relatively high conductivity. It is indirectly verified with geophysical loggings and constant injection tests performed in the boreholes.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.107-127
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• 2003

After detailed geological mapping, structural and fracture-density data were collected and analyzed in the vicinity of Cheonseong and Jeongjok Mts., Gyeongsangnam-do. A extensive dextral strike-slip fault (Beopgi Fault) Parallel to Yangsan and Dongrae Faults, a dextral-transtensional-NW fault, and a few intermittent faults have been found in the study area. Based on strike and frequency, fracture system has been divided into three sets such as NNE-trending J1 ($NS-40^{\circ}E$), WNW-trending J2 ($N50^{\circ}-80^{\circ}W$), and ENE-trending J3 ($N60^{\circ}-90^{\circ}E$). According to analysis of fracture density, it is revealed as follows: (a) Jl is the combination of Y-, P-, and R-shear fractures due to the dextral strike-slip of the Beopgi Fault. (b) J2 is the preexisted fracture zone conducting the intrusion of granite. Two tensional fractures dipping to NNE and SSW respectively have been induced by intrusion of granite and followed crustal uplift. (c) J3 is the tensional fracture developed between Yangsan and Dongrae Faults having NNE trend and dextral strike-slip sense. This study aims to reduce environmental impact and insure stability of underground facilities and tunnels.

• The Journal of Engineering Geology
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• v.12 no.3
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• pp.305-317
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• 2002

Geological, structural, and fracture density maps were drawn up to clarify the groundwater flow system around the Geumjeong Mountain, Busan. The results show that the topographical basin formed in the Sanseong Town is considered as a major recharge area of groundwater around the Geumjeong Mt. Because NS-trending fault and ENE-trending fault are intersecting and NS-trending and EW-trending fracture sets are highly developed in the basin, it is believed that the geological structure was developed in the basin which facilitates ground recharge. Based on the density distributions and characteristics of fractures, it is possible that the recharged groundwater in the basin would circulate to the depth of about 3~4 km and finally would reach the Dongnae Hot-spring region.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.4
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• pp.257-263
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• 2008

We analyzed the statistical properties for the conductive background fractures in the Low and Intermediate Level Waste(LILW) disposal site to conceptualize of its groundwater flow system. The background fractures were classified to fracture sets based on their trends and plunges that were obtained from the borehole logging data, and then the fracture transmissivity distribution was inferred from the fixed interval hydraulic test results. The fracture size distribution of each fracture set was estimated using the fracture density and fracture mapping data. To verify the analyzed results, we compared observed field data to simulated one from the DFN model that was constructed with the analyzed statistical properties of the background fractures, and they showed a good agreement.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.615-627
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• 2021

The Baekildo fault, a dextral strike-slip fault developed in Baekil Island, Goheung-gun, controls the distribution of tuffaceous sandstone and lapilli tuff and shows a complex fracture system around it. In this study, we examined the spatial variation in the geometry and connectivity of the fracture system by using circular sampling and topological analysis based on a detailed fracture trace map. As a result, both intensity and connectivity of the fracture system are higher in tuffaceous sandstone than in lapilli tuff. Furthermore, the degree of the orientation dispersion, intensity, and average length of fracture sets vary depending on the along-strike variation in structural position in the tuffaceous sandstone. Notably, curved fractures abutting the fault at a high angle occur at a fault bend. Based on the detailed observation and analyses of the fracture system, we conclude as follows: (1) the high intensity of the fracture system in the tuffaceous sandstone is caused by the higher content of brittle minerals such as quartz and feldspar. (2) the connectivity of the fracture system gets higher with the increase in the diversity and average length of the fracture sets. Finally, (3) the fault bend with geometric irregularity is interpreted to concentrate and disturb the local stress leading to the curved fractures abutting the fault at a high angle. This contribution will provide important insight into various geologic and structural factors that control the development of fracture systems around faults.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.483-492
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• 2008

The characteristics of joint system (joint orientation and density) were studied for Cretaceous sedimentary rocks in the Nakdong River mid-basin (Haman-Gun, Changnyeong-Gun, and Uiryeong-Gun areas), and were related with faults, river system, and groundwater usage in the study area. The joint system was classified into JI ($N90^{\circ}-110^{\circ}E$), J2 ($N0^{\circ}-35^{\circ}E$), and J3 ($(N0^{\circ}-35^{\circ}W$), and was dominant along N-S and E-W directions. The N-S trending joint system is dominant in Haman Formation in the eastern and western parts of the study area, while the E-W trending joint system is prevalent in Chilgok Formation in the central part. The joint system may be associated with the faults located in the eastern and western parts in the study area which are elongated to NNE-SSW direction. Additionally, the joint density is higher along the Nakdong River, indicating close relationship between E-W trending joints and the river. Daily groundwater discharge versus joint density shows weak positive relationship, and specific capacity versus joint density appears negatively related. This indicates that groundwater occurrence does not greatly rely on joint density.

• The Journal of Engineering Geology
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• v.9 no.3
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• pp.227-241
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• 1999

Groundwater flow in a fractured rock mass is related to the geometric characteristics of the fracture system. The objective of this study aims to analyze the probabilistic density function of fracture properties md their relations to the hydraulic conductivity in volcanic rocks of the northern Yosu area. Fracture characteristics were investigated by core logging and acoustic televiewer logging in four boreholes and the hydraulic conductivity was obtained from the constant pressure injection and fall-off tests. The 303 fractures were grouped into three sets by their orientation and three fracture types by the degree of opening in aperture. As a result of the study, the hydraulic conductivity in the test section intersected by open and semi-open fractures, conductive fractures, and set 1 fractures was very high, while closed fractures did rarely affect the hydraulic conductivity. It was recognized that the hydraulic conductivity in a fractured rock mass was preferentially affected by the aperture size of conductive fractures and fracture intersection frequency and size, secondly.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.173-189
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• 2011

Basic to acidic dykes and systematic joints are observed pervasively in the Jukbyeon-Bugu area, Uljin, east Korea. In order to classify the dykes and joints and to determine the relative chronology, their geometries, kinematics, and cross-cutting relationships, and the petrography and geochemistry of dykes are synthetically analyzed. Based on the orientations and cross-cutting relationships of 144 dykes (137 basic and 7 acidic dykes) and 370 systematic joints, three basic dike swarms (M-10, M-80, and M-100), one acidic dyke group (AD), and four joint sets (J-10, J-40, J-80, and J-150) are classified. Some of the J-150 joints reactivated as dextral strike-slip fault are recognized in the field and named as F-340R. According to petrographic, geochemical, and occurrence features in the field, M-80 and M-100 dykes have originated from a co-magma and intruded under the same stress field, even though they have intruded through different passages, preexisting fractures and new fractures created by magmatic pressure, respectively. And the relative chronology of dyke swarms and joint sets in the study area is determined as follows : ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ . And the M-80 (M-100) and M-10 dyke swarms intruded under NNE-SSW and NW-SE trending horizontal minimum stress fields, respectively. According to a synthesis of the results of the previous and this studies, the M-80, M-10, and F-340R are interpreted to have been formed about 64-52 Ma, Eocene~Oligocene, and Miocene, respectively.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.455-469
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• 2007

The study area, Bonggil-ri, Gyeongju, SE Korea, is composed of Cretaceous sedimentary rocks, and Tertiary igneous rocks and dykes. A research on fracture developing history and density distribution was carried out on well exposed Tertiary granites. The fractures developed in this area have the following sequence; NW-SE trending duo-tile shear bands (set a), NNW-SSE trending extensional fractures (set d), WNW-ESE trending extensional or normal fractures (set b), NE-SW trending right-lateral fractures (set c), WNW-ESE trending reverse fault reactivated from normal faults (set e) and NW-SE trending left-lateral faults reactivated from shear bands (set a) under brittle condition. According to the result of fracture density analysis, the fracture density in this area depends on rock property rather than rock age, and also higher fracture density is observed around fault damage zones. However, this high fracture density may also be related to the cooling process associated with dyke intrusion as well as rock types and fault movement. Regardless of the reason of the high fracture density, high fracture density itself contributes to fluid flow and migration of chemical elements.