• The Journal of Engineering Geology
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• v.5 no.2
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• pp.167-179
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• 1995

The only three elements such as RQD, N -value and Es were used as a quantitative standard for the design of supporr pattern determidetion on subway line 8th in Seoul. Because the support pattern that was obtained by these elements could not he determined on the basis of the quantitative of geology and the orientations and properties of discontinuity planes, there have been some problems in determining the economic support pattern and tunnel stability. Therefore, in an attempt to determine the stable and economic support pattern with more quantitative elements, more flerrible rock mass classification with geologic conditions was performed by using RMR at 1745 sections and Q-system at 374 sections within Seongnam block on subway line 8th. Then, rusults by these two methods were compared with standard support pattern of the subway line 8th. Moreover, relationships between geology, geologic structures and topography to rock mass grades were studied. According to the rusult of this study, it is judged that the standard support pattern designed with PD-4 or PS - 4 should have been subdivided into 4~6 support patterns. Some sections where geologic structures such as faults and joints are developed tend to have rock mass grades. And they also have low rock mass grades near valley. On thr other hand, they show intermediate grades at piedmont area and the greatest ones at high mountains.

• The Journal of Engineering Geology
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• v.12 no.2
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• pp.137-150
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• 2002

Recently, plane failure mode occurred frequently along the bedding plane having low angle dip about 20 degree when cutting slopes were constructed in sedimentary rock region of the Gyeongsang Basin. Landslide of the Whangryeong Mountain which was occurred at Busan Metropolitan City in 1999 belongs to the category mentioned above. Reconstruction for cutting slope of the Whangryeong Mountain has finished in 2000 and final grade of reconstructed cutting slope is 1:2.0. To analyze slope failure mode for landslide of the Whangryeong Mountain, various analyses were performed such as in-situ investigation and test, drilling, laboratory test, aerial photograph interpretation, X-ray diffraction analysis, and slope stability analysis using Stereographic Projection and Limit Equilibrium methods. As the result, it is identified that tension cracks had been developed one year before the landslide took place. The tension crack semis to be formed by merging several joint sets. It appears that failure blocks broke down along the sliding planes of different layers. Risk of plane failure is conformed as a result of stability analysis using Stereographic Projection and Limit Equilibrium methods in case that greenish gray tuffaceous shales, regared as sliding planes, are weathered. From now on, a detailed investigation is needed for the thin layers which is sensitive to weathering, and stability analysis for this layer is performed at cut slope construction site having similar geological condition.

• Journal of the Korean Society for Railway
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• v.12 no.4
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• pp.548-556
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• 2009

In order to evaluate applicability of rock cut-slope investigation system, typical clinometer and photogrammetry investigation system were used for rock slopes; first for 7 discontinuities, and secondly, 10 discontinuities, and the results were compared. The first verification was performed depending on discontinuity joint shapes and slope angles, and the second verification was performed depending on shot time and shot locations. The results showed that differences of dip direction $1^{\circ}{\sim}4^{\circ}$, dip $0^{\circ}{\sim}4^{\circ}$. In the second verification test, the differences of dip direction was $0^{\circ}{\sim}6^{\circ}$, and dip $0^{\circ}{\sim}6^{\circ}$. The photogrammetry method for rock slope survey system is quite reliable when clinometer generally shows ${\pm}10^{\circ}$ errors due to surface roughness and investigator.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.25-33
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• 2010

Most of contaminated groundwater in the study area was contaminated by $NO_3-N$ due to inflow of contaminated shallow surface groundwater inflow into groundwater well. Poor grouting and teared screen have increased contaminated shallow surface groundwater inflow into groundwater well. Contaminated shallow surface groundwater was inflowed into groundwater well throughout faults, joints and fracture zone of ESE-WNW, NNW, NW-SE and NS direction. The objective of this paper is to evaluate an improvement of water quality for contaminated groundwater by $NO_3-N$ using compression packer. For this study groundwater samples collected from 46 groundwater wells were analyzed to clarify $NO_3-N$ contents. Groundwater wells over 10 mg/L in $NO_3-N$ content is 9 wells showing 20% among total samples. $NO_3-N$ contents after compression packer installation showed 26~81% low value compared with before compression packer.

• The Journal of Engineering Geology
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• v.1 no.1
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• pp.19-37
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• 1991

The geology of the northwestern Cheju Island consist of Pleistocene to Holocene volcanic rocks which could be devided into basalt layers, the Sungsan Formation composed mainly of volcaniclastic debris exposed along the shoreline, and more than 30 cinder cones. Columnar joints and vesicles are dominant in the basalts of the Pyeosunri and the Sihungri basalt Formations. Volcaniclast and clay layers are intercalated in basaltic layers. When volcaniclast of the interlayers would be swept away by ground water and some caves of channel shape would be formaed. Overlying lavas cracked by columnar joints could be easily destroyed, collapsed and/or sunk. Geomechananical nature of the rocks such as strength may be controlled by the vesicularity(size, shape, and orientation of the vesicles) of the rocks. On the basis of vesicularity as a factor of strength, the effective strength ratio(Ke) could be calculated as Ke=0.3-0.72, in which the smaller Ke value reflects the lower in internal stress. In the studied area, the strength of the rocks tends to decrease as increasing in altitude of provenance of the rocks. The rocks in the area show relatively low values in angle of failure strength($\phi$) ranging from 10$^{\circ}$ to 30$^{\circ}$. In conclnsion, the rocks in question, majority of which the critical value exceeds 0.33, belong to the unstable rocks in the aspect of engineering geology.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.530-548
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• 2022

The site selection process for deep geological disposal of high-level radioactive waste will be conducted in stages, and 103 evaluation parameters related to site selection have been proposed. In the field of rock mechanics and rock engineering, there are 33 evaluation parameters for intact rock, joint and rock mass, and they are applied in the basic and detailed investigation stages. In this report, uniaxial compressive strength, in-situ stress, joint distribution, and rock mass classification were selected as the main evaluation parameters, and among them, uniaxial compressive strength and in situ stress were selected as key evaluation parameters. Statistical techniques or regression analysis were performed for granite in Wonju and Chuncheon to evaluate the distribution range for the selected key evaluation parameters. The average of the uniaxial compressive strength in the Wonju area estimated through the posterior distribution is about 171 MPa, and about 123 MPa in the Chuncheon area. The maximum in situ stress acting in the Wonju area was less than 30 MPa and less than 40 MPa in the Chuncheon area. The direction of the maximum horizontal stress calculated by regression analysis was 101° in Wonju, and in the case of Chuncheon, it was 95°, respectiviely.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.315-336
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• 2009

We have studied the orientational characteristics of microcrack frequency, it's length and density in Tertiary crystalline tuff from the northeastern part of the Gyeongsang Basin. 134 sets of microcracks on horizontal surfaces of 3 rock samples from Heunghae-eup were distinguished by enlarged photomicrographs of the thin sections. The variability in patterns among microcrack length-frequency histograms for three rock samples from different altitudes were derived. The pattern of histograms changes progressively from negative exponential form to log-normal form in proportion to altitude. The distribution pattern for rock sample no.1 from lower altitude shows the broad length distribution characterized by higher mean and median, and higher standard deviation. Meanwhile, this distribution pattern corresponds with characteristics of joint length distribution in sedimentary rocks of the lower part of the Gyeongsang Supergroup. The occurrence frequency of shorter microcracks increases toward both NW and NE directions from the $N0{\sim}10^{\circ}W$, with the dominant direction of $N80{\sim}90^{\circ}W$ and $N80{\sim}90^{\circ}E$, respectively. This distribution pattern represents the relative differences in formation timing among microcrack sets and the result of the new initiation of shorter microcracks. Meanwhile, the longest microcracks within $N60{\sim}70^{\circ}W$($L_{max}$:1.18 mm) and $N0{\sim}10^{\circ}W$($L_{max}$:0.80 mm) directions are seen, but this kind of microcracks are very limited in number. Whole domain of the directional angle($\theta$)-frequency(N), length(L) and density($\rho$) chart can be divided into five sections in terms of phases of the distribution of related curves. From the distribution chart, density curve shows five distinct peaks in the WNW-ESE($N70{\sim}80^{\circ}W$), NS~NNE-SSW($N0{\sim}10^{\circ}W$, $N10{\sim}20^{\circ}E$), ENE-WSW($N50{\sim}60^{\circ}E$), and nearly EW($N80{\sim}90^{\circ}E$) directions, respectively. Especially, main directions of faults correspond with the directional angle showing high density. Consequently, these distribution patterns of density curve reflect the representative maximum principal stress orientations suggested in previous studies.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.86-96
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• 2015

In this study, the performance-based evaluation factors for rock slopes have been deducted using Delphi-method. Validity of the result was verified through factor analysis. Performance of rock slope is classified as soundness, stability and durability. Through the Delphi survey, 17 factors including discontinuity orientation are deducted for soundness, 4 factors and 3 factors are selected for stability and durability, respectively. Validation is conducted using Exploratory Factor Analysis (EFA) for 24 factors, and all factors are found to be valid. As a result of Exploratory Factor Analysis (EFA), 3-types of performance were subdivided into internal soundness, external soundness, risk, damage and durability of slopes and protection (reinforcement) facilities.

• The Journal of Engineering Geology
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• v.5 no.3
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• pp.249-258
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• 1995

The landslide occurred in the Nongong area of Dalseong - gun, Kyeongbuk, is described and analysed in terms of structural geology and clay mineralogy to understand the causes of the landslide. The result of the analyses shows that the slip direction and the scale of the landslide of the study area were controlled by the attitude of the major discontinuity planes m the area such as joints, faults and dikes. In addition, the surface of the slip planes of the landslide is composed of clay minerals, which are mostly tri - octahedral vermiculite and smectite. From this study it can be concluded that the presence of expandable clay minerals within the bedding joints and fracture zones in bed rock played an important role in causing the landslide of the study area.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.440-449
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• 2004

Rock mass includes natural discontinuities such as joints and faults during its formation. Discontinuities are also referred as planes of weakness because of their weak mechanical characteristics. In the design of underground structures, it is necessary to consider the properties of discontinuities to insure the stability. During the excavation of a tunnel, these discontinuities have to be identified as early as possible so that proper change in excavation method or support design can be made accordingly. The excavation of the tunnel in a stable rock mass causes a 3-dimensional arching effect around the excavation face. It was revealed by previous studies that the existence of a weak zone or a fault zone ahead of tunnel foe induces a typical displacement tendency of convergence. For better understanding of the meaning of influence/trend lines of various displacement components, three-dimensional numerical analyses were conducted while varying deformation moduli, thicknesses and orientations of discontinuities. Numerical results showed that the changes in influence/trend lines of various displacement components were very similar to those by measurements. The discrepancies from the expected values were dependent on the physical properties, thicknesses and orientations of discontinuities.