• Journal of the Korean earth science society
• /
• v.25 no.1
• /
• pp.22-31
• /
• 2004

Laboratory experiments were conducted in order to find effects of the intermediate principal stress of ${\sigma}_{2}$ on rock fractures and faults. Polyaxial tests were carried out under the most generalized compressive stress conditions, in which different magnitudes of the least and intermediate principal stresses ${\sigma}_{3}$ and ${\sigma}_{2}$ were maintained constant, and the maximum stress ${\sigma}_{1}$, was increased to failure. Two crystalline rocks (Westerly granite and KTB amphibolite) exhibited similar mechanical behavior, much of which is neglected in conventional triaxial compression tests in which ${\sigma}_{2}$ = ${\sigma}_{3}$. Compressive rock failure took the form of a main shear fracture, or fault, steeply dipping in ${\sigma}_{3}$ direction with its strike aligned with ${\sigma}_{2}$ direction. Rock strength rose significantly with the magnitude of ${\sigma}_{2}$, suggesting that the commonly used Mohr-type failure criteria, which ignore the ${\sigma}_{2}$ effect, predict only the lower limit of rock strength for a given ${\sigma}_{3}$ level. The true triaxial failure criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. It is found that the onset of dilatancy increases considerably for higher ${\sigma}_{2}$. Thus, ${\sigma}_{2}$ extends the elastic range for a given ${\sigma}_{3}$ and, hence, retards the onset of the failure process. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Microcracks gradually align themselves with the ${\sigma}_{1}$-${\sigma}_{2}$ plane as the magnitude of ${\sigma}_{2}$ is raised.

• Korean Journal of Mineralogy and Petrology
• /
• v.35 no.3
• /
• pp.377-386
• /
• 2022

In addition to anthropogenic origins, fluorine (F) is naturally enriched in rocks due to geological events, such as magma dissemination, hydrothermal alteration, mineralization, and fault activities. Generally, it has been well known that F is chiefly enriched in the region of igneous and metamorphic rocks, and biotite granite was mostly distributed in the study area. The F enrichment mechanism was not sufficiently elucidated in the previous studies, and the study on a fault zone was conducted to reveal it more precisely. The mineral composition of the fault zone was identical to that of the Eulwangsan biotite granite (EBG), but they were quantitatively different between the two areas. Compared with the EBG, the fault zone showed relatively higher contents of quartz and F-bearing minerals (fluorite, sericite) but lower contents of plagioclase and alkali feldspar. This difference was likely due to hydrothermal mineral alterations. The results of microscopic observations supported this, and the generation of F-bearing minerals by hydrothermal alterations was recognized in most samples. Accordingly, it might be interpreted that the mineralogical and petrological differences observed in the same-age biotite granite widely distributed in the Yongyudo was caused by the hydrothermal alterations due to small-scale geological events.

• Geomechanics and Engineering
• /
• v.12 no.1
• /
• pp.35-52
• /
• 2017

In order to evaluate the grouting effects of water-rich fault in tunnels systematically, a feasible and scientific method is introduced based on the extension theory. First, eight main influencing factors are chosen as evaluation indexes by analyzing the changes of permeability, mechanical properties and deformation of surrounding rocks. The model of evaluating grouting effects based on the extension theory is established following this. According to four quality grades of grouting effects, normalization of evaluation indexes is carried out, aiming to meet the requirement of extension theory on data format. The index weight is allocated by adopting the entropy method. Finally, the model is applied to the grouting effects evaluation in water-rich fault F4-4 of Qingdao Jiaozhou Bay Subsea Tunnel, China. The evaluation results are in good agreement with the test results on the site, which shows that the evaluation model is feasible in this field, providing a powerful tool for systematically evaluating the grouting effects of water-rich fault in tunnels.

• Economic and Environmental Geology
• /
• v.24 no.3
• /
• pp.287-299
• /
• 1991

The study area is mainly composed of metasedimentary rocks which are included in Ogchon, Choson and Pyongan Groups. Because of thrust faults which are developed in this area, a coal bearing formation is repeatedly distributed two times, and Choson Group is thrusted over Pyongan Group. Deformation in this area was taken place in a series of three phases ($D_1$, $D_2$ and $D_3$) ; $D_1$ was most intense whereas $D_3$ was weakest. Thrust faults developed in the upper curst duringD2 produced cataclastic rocks and fault breccia,truncating regional slaty cleavage and earlier folds which were formed during $D_1$ stage. The quartz microstructures of metapsammitic rocks in Choson and Pyongan Groups suggest that dislocation creep mechanism predominated early in fabric development, afterwards deformation mechanism was transfered to pressure solution which intensified the earlier fabrics. According to strain analysis using quartz grains and quartz aggregate grains, the strain magnitude(Es) of Pyongan Group represents larger values than that of Choson Group due to the contrast of constituent minerals, the size of original quartz grains and matrix content. Apparent flattening type in strain pattern appears in the whole area. It is suggested that the relationship between Ogchon Group and Choson Group may be thrust contact.

• Economic and Environmental Geology
• /
• v.28 no.6
• /
• pp.571-577
• /
• 1995

Several acid-sulfate clay deposits associated with silicic magmas occur in the Haenam area of the southwestern part of Korea. Geology of the studied area consists of tuffs, granitic rocks, quartz porphyry, rhyolite, andesite and sedimentary rocks. The granitic rocks and quartz porphyry intruded tuffs and sedimentary rocks. The rhyolite and tuffs around the mines have undergone hydrothermally weak or strong alteration. Gold contents with major and trace elements have been determined for a total of sixty-seven specimens of fresh igneous rocks, wall rocks and minerals such as dickite and alunite by graphite furnace atomic absorption spectrometer and inductively coupled plasma. Gold is enriched in the alunite vein and the silicified zone, but is depleted in dickites and hydrothermally altered rocks with dickite of the Seongsan deposit. Gold is especially concentrated near the faults or conjunction area of two faults. High content of gold is shown in the mineral assemblages of alunitequartz- pyrite in the alunite vein and silicic zone of the Seongsan deposit compared with that of minerals and rocks from another deposits distributed in the studied area. Gold content in tuffs and dickites with pyrite is generally low. Gold content in silicified tuff tends to show positive correlations with content of As, Hg and Sb. Variation trends of Cd, Hg and Sb are similar to those of gold content. From the result of gold content variations, gold may be transported and concentrated by mineralizing solutions ascending along the cracks like fault. Therefore, it is important to survey alunite vein and silicified zone at the conjunction of faults, and to analyze pathfinder elements such as As, Hg and Sb for geological and geochemical exploration of gold in the studied deposits.

• Economic and Environmental Geology
• /
• v.31 no.6
• /
• pp.519-526
• /
• 1998

A high-resolution seismic survey was conducted at the northeastern boundary of Pungam basin, one of the Cretaceous sedimentary basins in Korea. A 100 kg weight was used as an energy source and was found to be better than a sledge hammer in mapping deeper geologic structures. Several processing techniques such as f-k filtering, predictive deconvolution, and time-variant filtering are useful to enhance the signal-to-noise ratio by suppressing unwanted seismic energy. Four seismic units are recognized where many vertical faults are developed. The boundary fault between sedimentary rocks and Precambrian gneiss is identified along with a fracture zone of approximately 30 m wide. Bedding planes of the sedimentary rocks dipping westward are interpreted to be limbs of a syncline or volcanic flow. There faults and tilted bedding planes indicate that the basin had undergone significant tectonic deformation.

• Economic and Environmental Geology
• /
• v.24 no.2
• /
• pp.167-176
• /
• 1991

The Yeongweol - Yemi area, in the area between the Kagdong thrust fault and Samcheog Coalfield, comprises Paleozoic and Mesozoic sedimentary and igneous rocks. Geologic structures related with thrust movements are dominant in the area. These are thrust faults, imbricate structures and hanging-wall anticline. Thrust sheets were transported from NW to SE and these differ from the Cretaceous Bulkuksa Orogeny of which thrust sheets were transported from N to S. NE - trending folds are dominant, but NW - trending folds and refolded folds are also found. NW - trending folds are only found in the Cambro-Ordovician sedimentary rocks. It might be an indication of the presence of late Paleozoic tectonism in the Korean Peninsula.

• The Journal of Engineering Geology
• /
• v.15 no.3
• /
• pp.349-363
• /
• 2005

Many Quaternary faults are recognized as thin gouge and narrow cataclastic zone juxtaposing the Bulguksa granite and Quaternary deposit bed in the eastern block of the Using Fault, Korea: Gaegok 1, Caegok 2, Singye, Madong Wonwonsa and Jinhyeon faults. This study was performed to calculate chemical change, volume change, silica loss and fluid-rock ratio taken place in gouge zones of these Quaternary faults using XRF, XRD, EPMA. The chemical compositions of fault rocks reveal that the fault gouges are depleted in $SiO_2,\;Na_2\;O,and\;K_2O$ and enriched in $Al_2O_3,\;Fe_2O_3,\;P_2O_5,\;MgO,\;MnO,\;CaO,\;and\;LOI(H_2O+CO_2)$ relative to protoliths. The fact that there is enrichment of relatively immobile elements and depletion of the more soluble elements in the fault gouges relative to protoliths can be explained by fluid-assisted volume loss of $56\%$ for Caegok 1 fault, $22\%$ for Caegok 2 fault,$34\%$, for Singye fault, $8\%$ for Madong fault, $2\%$ for the Wonwonsa fault and $53\%$ for the linhyeon fault. Madong fault and Wonwonsa fault where ratios of the volume change, silica loss and fluid-rock are low might have acted as a closed system for fluid activity, whereas Caegok 1 fault and Jinhyeon fault with high ratios in those factors be an open system. The volumetric fluid-rock ratios range $10^2\sim10^4$ for all faults, being highest in Caegok 1 fault and Jinhyeon fault whose fluid activity was most significant.

• Tunnel and Underground Space
• /
• v.19 no.2
• /
• pp.132-145
• /
• 2009

Faults in rock mass have strong influences on the behaviors of rock structure such as rock slope, tunnel and underground space. Thus, it is very important to analyse for the characteristics of fault rocks in design for tunnel. But, due to the limitation of geotechnical investigation in design stages, tunnel engineers have to carry out the face mapping and additional geological survey during tunnel excavation to find the distribution of faults and the engineering properties of faults for support and reinforcement design of tunnel. In this study, various geological survey and field tests were carried out to analyse the characteristics of the large thrust fault zone through the large sectional tunnel is constructed in mica-schist region. Also, the distribution of structural geology, the shape of thrust faults and the mechanical properties of fault rock were studied for the reasonable design of the reinforcement and support method for the highly fractured fault zone in the large-span tunnel.

• Geomechanics and Engineering
• /
• v.24 no.5
• /
• pp.471-478
• /
• 2021

Water damage is one of the five disasters that affect the safety of coal mine production. The erosion of rocks by water is a very important link in the process of water inrush induced by fault activation. Through the observation and experiment of fault filling samples, according to the existing rock classification standards, fault sediments are divided into breccia, dynamic metamorphic schist and mudstone. Similar materials are developed with the characteristics of particle size distribution, cementation strength and water rationality, and then relevant tests and analyses are carried out. The experimental results show that the water-rock interaction mainly reduces the compressive strength, mechanical strength, cohesion and friction Angle of similar materials, and cracks or deformations are easy to occur under uniaxial load, which may be an important process of water inrush induced by fault activation. Mechanical experiment of similar material specimen can not only save time and cost of large scale experiment, but also master the direction and method of the experiment. The research provides a new idea for the failure process of rock structure in fault activation water inrush.