• Journal of the Mineralogical Society of Korea
• /
• v.18 no.3 s.45
• /
• pp.165-181
• /
• 2005

The granitic rocks distributed in the southern part of the Yangsan Fault are classified into five distinct rock facies based on the field relation, petrography and geochemical characteristics. These five different rock facies can be grouped into two considering their origins. Group I, which reveals various evidences of magma mixing, includes three rock facies of granodiorite, enclave-rich porphyritic granite, and enclave-poor porphyritic granite. Group H intruding Croup I includes equigranular granite and micrographic granite with no evidence of magma mixing. It is suggested that the distinctively different trace element and isotopic chemistries between group I and II, support evolution from the different parental magma. It is suggested that the three rock facies in group I were generated by different degrees of magma mixing in addition to fractionation of plagioclase. MMEs experienced fractionation of biotite. The two facies in group H seem to have been generated from different parent magma from group I and evolved by fractionation of K-feldspar. The Rb-Sr whole-rock ages of the group I rocks yield $59.2\~58.9Ma$, and those of the group II rocks give 53. $3\~51.7Ma$, regardless of their distribution whether they occur in the eastern or western parts of the Yangsan Fault. Based on Sm-Nd isotope compositions, depleted mantle model ages $(T_2DM)$ of the group I range $0.8\~0.9Ga$, while those of the group II$0.6\~0.7Ga$.

• Tunnel and Underground Space
• /
• v.31 no.4
• /
• pp.211-220
• /
• 2021

Tunnel collapse often occurs during deep underground tunneling (> 40 m depth) in South Korea. Natural cavities as well as water supply pipes, sewer pipes, electric power cables, artificial cavities created by subway construction are complexly distributed in the artificial ground in the shallow depths of the urban area. For deep tunnel excavation, it is necessary to understand the properties of the ground which is characterized by porous elements and various geological structures, and their influence on the stability of the ground. This study analyzed geological factors for risk assessment in deep excavation in South Korea based on domestic and overseas case study. As a result, a total of 7 categories and 38 factors were derived. Factors with high weights were fault and fault clay, differential stress, rock type, groundwater and mud inrush, uniaxial compressive strength, cross-sectional area of tunnel, overburden thickness, karst and valley terrain, fold, limestone alternation, fluctuation of groundwater table, tunnel depth, dyke, RQD, joint characteristics, anisotropy, rockburst and so forth.

• Economic and Environmental Geology
• /
• v.7 no.3
• /
• pp.101-122
• /
• 1974

The study area is located in between Susanri and Hwanggangri where the formations of Okcheon group and Chosun group supposedly come in contact so that the area is structurally very import. Present study reveals that the meta-volcanic rocks distribute from south to north along contact zone of Okcheon and Chosun groups in the center of the area. Meta-volcanic rocks seem to be originated from the andesite or andesitic basalt rocks which was known to be Surchangri formation consist of phyllite and black slate by previous workers. The meta-volcanic rocks intruded along the fault zone one existed between Okcheon and Chosun groups but obliterated at present by the intrusion of volcanic rocks. The fault seems to be overthrust, and one of the positive evidences of thrust fault is the Yamisan nappe structure in Yamisan near Susanri. This interpretation coincides with O.J. Kim's work which states that the Precambrian Okcheon group is largely overturned and thrusted over the Chosun group. The relation between the Surchangri and the Majeonri formation marks facies change. This fact together with northpluging anticlinal structure made it possible that both formation came into contact along direction without fault. Yongam formation is not overlain unconformably used to be believed by previous workers, but interbed in the Great Limestone series of Chosun goup. It is also clarified that the rock formerly designated as limesilicate rock was meta-liparite. The origin of amphibole pebbles in the Kunjasan formation is of primary and secondary ones; the secondary pebbles were formed by metamorphism of the fragments of limestone or dolomite.

• Tunnel and Underground Space
• /
• v.26 no.2
• /
• pp.59-67
• /
• 2016

In this paper, we perform a numerical analysis to evaluate the potential of fault reactivation during gas production from hydrate bearing sediments and the moment magnitude of induced seismicity. For the numerical analysis, sequential coupling of TOUGH+Hydrate and FLAC3D was used and the change in effective stress and consequent geomechanical deformation including fault reactivation was simulated by assuming that Mohr-Coulomb shear resistance criterion is valid. From the test production simulation of 30 days, we showed that pore pressure reduction as well as effective stress change hardly induces the fault reactivation in the vicinity of a production well. We also investigated the influence of stress state conditions to a fault reactivation, and showed that normal fault stress regime, where vertical stress is relatively greater than horizontal, may have the largest potential for the reactivation. We tested one simulation that earthquake can be induced during gas production and calculated the moment magnitude of the seismicity. Our calculation presented that all the magnitudes from the calculation were negative values, which indicates that induced earthquakes can be grouped into micro-seismic and as small as hardly perceived by human beings. However, it should be noted that the current simulation was carried out using the highly simplified geometric model and assumptions such that the further simulations for a scheduled test production and commercial scale production considering complex geometric conditions may produce different results.

• Journal of the Mineralogical Society of Korea
• /
• v.28 no.2
• /
• pp.109-126
• /
• 2015

Because fault gouge developed at the center of fault is recognized as one of the most important weak sites, it is evident that clay mineralogy and physical properties greatly affect the rock stability. The purpose of this study is to establish the relationship of mineralogy and physical factors that control rock stability in fault zones. We analyzed a total of 51 samples from 16 main faults which were selected from a Korea fracture map, using XRD, SEM, and physical analyses like unit weight, friction and cohesion properties. Though it is considered that the most common clay minerals comprising fault gouge are kaolinite, illite and smectite, clay mineralogy slightly varies depending on lithology: illite > smectite > kaolinite and chlorite in volcanic rocks, kaolinite and chlorite > illite > smectite in sedimentary rocks, and illite > smectite > kaolinite and chlorite in abundance, respectively. Friction angle decreases with increasing clay content. Cohesion increases with increasing clay content below the 45 % region while it decreases with increasing clay content at the region higher than 45%, with some scatters in the data. It is likely that these results are ascribed to the physical heterogeneity of fault gouges with varying content of different clay minerals.

• Journal of the Mineralogical Society of Korea
• /
• v.15 no.2
• /
• pp.85-94
• /
• 2002

XRF, XRD, EPMA have been used to investigate microstructures and mineralogical changes caused by the faulting and fluids associated with faulting in the Quaternary fault gouge zones at the Sangchon, Ipsil and Wangsan faults located at the southeastern part of the Korean Peninsula. The chemical compositions of faulted rocks and protoliths analyzed by XRF show that the fault gouges are relatively enriched in TiO$_2$, P$_2$O$_{5}$, MgO, and Fe$_2$O$_3$) compared with protoliths, indicating that the fluids associated with faulting were highly activated. XRD results show that the fault gouges predominantly consist of quartz, feldspar, calcite and clay minerals. Clay minerals formed in the gouge zones are mainly composed of smectite characterized by a dioctahedral sheet. Based on EPMA analyses various kinds of sulfide, carbonate, phosphate minerals were identified in the gouge zones and protoliths. Xenotime of grey fault gouge of the Sangchon fault and sulfide minerals of contact andesitic rock of Ipsil fault and contact grey andesitic rock of Wangsan fault were probably formed by inflow of hydrothermal solution associated with faulting prior to the Quaternary. Carbonate minerals of contact andesitic rock and gouge zone of the Ipsil fault were formed by inflow of fluid associated with faulting prior to the Quaternary. They are heavily fractured and have reaction rim on their edge, indicating that faultings and inflow of fluids were highly activated after carbonate minerals were formed. Calcites of Wangsan fault seemed to be formed in syntectonic or posttectonic Quaternary faulting.g.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.3 no.3
• /
• pp.45-56
• /
• 2001

It is very important to survey in construction for acquiring informations about geological structure which influence the tunnel construction. Usually, TSP(Tunnel Seismic Prediction) one of the seismic survey method in tunnels in Korea has been used for prediction of geological condition ahead of tunnel face, but in this study HSP(Horizontal Seismic Profiling) was used. As a result of field application, we predicted that there exist rock discontinuity such as fault, joints and bedding planes. In addition, RMR value from rock mass evaluation coincided with that from seismic survey for rock condition. We compared with rock classifications and evaluation results for proving.

• The Journal of Engineering Geology
• /
• v.23 no.2
• /
• pp.149-160
• /
• 2013

Volcanic activity commonly creates a highly complicated volcanic complex due to the admixture of lava flow and sedimentation of volcanic ash. The Song-Gok site is composed of volcanic rocks that collapsed at the lower part of the slope, in combination with several discontinuities in and around a fault. The results of projection analysis indicated the possibility of plane, wedge, and toppling failure in the failure section. The results of discontinuity modeling using the Distinct Element Method (DEM) revealed a total displacement of 207 mm and a joint shear displacement of 114 mm. The yield surface zone was verified at the fault plane of the failure section. In geotechnical terms, volcanic rock slopes are characteristically vulnerable to failure because of differential weathering among the various rock types, the effect of groundwater based on the permeability of the rocks, and the presence of systematic joints generated by the cooling and contraction of lava. When considering the stability of a volcanic rock slope, it is necessary to consider data such as the geological features of the rock, as obtained through detailed geological survey, and variations in discontinuities and rock blocks.

• The Journal of the Petrological Society of Korea
• /
• v.26 no.3
• /
• pp.167-181
• /
• 2017

Cheongryangsan area ($49.51km^2$) has been designated as the Provincial Park in 1982, because it has magnificent aspect and seasonally spectacular landscapes. Especially, Cheongryangsa sitey ($4.09km^2$) has been designated as Noted Scenery No. 23 in 2007, because it has the same topographical landscape as rock cliffs, rock peaks and caves. The most spectacular landscapes are exhibited in the Cheongryangsan Conglomerate and Osipbong Basalt. There are twelve rock peaks on the ridges of the two strata, and many rock cliffs in the several valleys of strata, in which a few caves are formed by differential weathering and erosion. The valleys, in which flow Cheongryang, Bukgok and Cheonae streams, are classified as fault valleys along WNW-ESE faults. The rock cliffs were generated from vertical joints parallel to WNW-ESE faults in the two strata, and the caves were formed by differential weathering and erosion along bedding of sandstones and shales intercalated in the conglomerates. The rock peaks are landscapes formed by differential erosion along crossed vertical joints in the ridges. The vertical joints are developed subparallel to two WNW-ESE faults and a NNE-WWS fault. Therefore the topographical features are caused by existence of the faults and Lithologic difference in the Cheongryangsan Conglomerate and Osipbong Basalt, and by differential weathering and erosion along them.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2005.03a
• /
• pp.74-81
• /
• 2005

The purpose of this study is to suggest a proper analysis model that can evaluate seismic stability for local rock foundation of nuclear power plant. Sliding Analysis, Pseudo-static Analysis and Danamic Analysis methods are used for analysing NPP rock foundation with the conditions like acting directions of input earthquake, boundary conditions, width and depth of analysing model, and modeling methods of weakness fault zones. As the results of study, Pseudo-static Analysis for lateral roller and dynamic analysis for transfer boundary condition showed good results, and analysing ranges of width and depth were 5 times of structure width and over 2 times of structure depth.