• Geomechanics and Engineering
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• 제33권1호
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• pp.53-63
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• 2023

Rock disturbance caused by blasting and stress relaxation is commonly observed during excavation. As the distance from the source of disturbance increases, the degree of disturbance decreases, and rock at a large depth does not experience disturbance. However, in stability analyses, a single value of disturbance is often applied to the entire rock mass, which leads to underestimated results. In this study, this modeling mistake is addressed by considering realistically varying rock disturbance. The safety of infinite slopes in a disturbed rock mass with a strength governed by the Hoek-Brown failure criterion is investigated based on the kinematic approach of limit analysis. The maximum disturbance is assigned to the outermost slope face because it is directly exposed to blasting damage and dilation, and the disturbance progressively decays with distance in the rock mass. The safety analysis results indicate that the assumption of uniform disturbance in the entire rock mass leads to underestimation of the rock strength and safety on infinite rock slopes. A critical slip surface appears to be within the disturbed rock layer as well as the interface between the disturbed upper rock and undisturbed lower rock.

• 터널과지하공간
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• 제20권3호
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• pp.225-232
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• 2010

본 연구에서는 절리에 작용하는 수직변형과 전단 팽창을 고려할 수 있는 수정된 3차원 변형률 의존성 수리전도도 변화 방정식을 제안하였다. 현지 암반을 직교절리가 발달한 매질로 가정하기 때문에 제시된 방정식을 사용하여 수리전도도의 이방성을 평가할 수 있다. 현지암반의 변형계수를 필요로 하는 탄성계수감소비를 손쉽게 결정하기 위하여 GSI와 교란계수를 기초로 하는 경험식을 사용하였다. 현지 암반 내에 존재하는 절리는 일반적으로 전체좌표계와 평행하지 않고 기울어져 있는 경우가 많기 때문에 기울어진 방향에서의 수리전도도를 구하기 위하여 변형률 회전식을 사용하였다. 해석 결과 GSI가 증가함에 따라 수리전도도는 감소하는 것으로 나타났다. 교란계수는 수리전도도의 변화 거동에 영향을 미치는 것으로 나타났는데 특히 GSI가 50 이상인 암반의 수리전도도 변화에 큰 영향을 미치는 것으로 해석되었다. 절리의 경사도 수리전도도 변화에 영향을 미치는 것으로 나타났다.

• 한국해양생명과학회지
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• 제6권2호
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• pp.117-123
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• 2021

Post-disturbance recovery pattern of subtidal soft corals-macroalgae mixed community and the role of water depth were investigated. The experiment was conducted in a subtidal rock wall of Munseom, Jeju Island, Korea for 2.5 years. Artificial disturbance was done at established treatment plots at depths of 10, 15 and 20 m and were then compared with undisturbed control plots. After disturbance, recovery of soft corals was very slow, whereas macroalgae quickly occupied the plots and reached a similar level as the control in 6 months, and this pattern was consistent at all water depths. This unbalanced speed of recovery caused higher macroalgae establishment than soft corals in treatment compared to control plots, indicating a possible phase shift in the community structure. This study provides an important implication for the necessity of monitoring the influence of disturbance at a larger scale, from a conservation perspective of soft corals in Jeju coast.

• 자원환경지질
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• 제24권3호
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• pp.261-276
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• 1991

The main aspect of this study are to clarify igneous activity of igneous rocks, which is a member of various intrusives and volcanics exposed in Naju-Namchang area of southern central zone of Ogcheon Geosynclinal Belt, southern part of Youngdong-Kwangju depression zone of tectonic provinces in Korea. Naju-Namchang area are subdivided into three rock belts based on occuring of Cretaceous granites. Three rock belts consist of foliated granites, Jurassic granites and Cretaceous granites in central granitic rock belt (C-C), and acidic tuff and lavas in northwest volcanic rock belt(C-NW) and southeast volcanic rock belt(C-SE). Chemical composition of these igneous rocks show mostly similar trend to the Daly's values on Harker diagram and correspond to VAG + Syn-COLG region on Pearce's discrimination diagram. These igneous rocks vary wide range in total REE amount(37.4-221.3ppm) characterized by enriched LREE content and steep negative slope in Eu(-) anomaly. It is concluded each synchronous granites which composed of serveral rock facies is considered to formed by differentiation of co-magma at continental margin, and igneous activity of study area are two more Pre-Cambrian Orogenies, Songrim Disturbance, Daebo Orogeny and Bulkuksa Disturbance.

• 한국지반공학회논문집
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• 제18권5호
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• pp.99-108
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• 2002

본 연구에서는 탄성, 탄소성 및 실험을 통해 유도된 비선형-취성-소성 모델을 지하 심부 원형터널의 경우에 적용하여 각 모델에 따른 특성과 추정되는 응력재분배 및 응력교란 범위를 비교하였다. 현지 초기응력의 크기와 주응력차가 커질수록 파괴영 역이 파괴되지 않은 영역에 미치는 응력재분배와 교란의 영향이 증가되기 때문에, 탄소성 또는 탄성 해석의 경우보다 비선형-취성-소성 해석결과에서 응력재분배 및 교란영역, 주응력차와 변위가 더 크게 발생하였다. 따라서 현지 응력 수준과 현지 주응력차가 클 경우, 비선형-취성-소성 해석에 의해 손상영 역의 범위가 더 크게 발생할 것으로 예측되므로 손상해석의 필요성이 증대될 것으로 판단되었다.

• Journal of Preventive Medicine and Public Health
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• 제30권3호
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• pp.555-566
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• 1997

This study was carried out to evaluate the cytotoxicity of rock wool fibers(RWFs) such as cell division disturbance, chromosomal and DNA damage, and mutagenicity using cultured cells. RWFs were the man made mineral fibers. In order to find the correlation between the cytotoxicity of RWFs and the phagocytic capacity of cells, the phagocytic processes were observed using scanning electron microscope. Cell division disturbance by RWFs was evaluated by the formation of multinucleated giant cells. The chromosomal damage was evaluated by the micronucleus formation. For the evaluation of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (8-OH-dG) formation was measured utilizing calf thymus DNA. Mutagenicity was determined by the point mutation of HGPRT and the effect of RWFs on cell transformation was also observed. 1. Compared with the results of chrysotile, RWFs were no or little effect on the cell growth according to the results done by the tests of cell proliferation inhibition and relative plating efficiency. 2. The frequency of multinucleated giant cell formation was increased by the treatment of RWFs and it was dose-dependent. However, the effect of RWFs was weaker than that of chrysotile. 3. The number of micronuclei formed in the RWFs treated cells was between those of cells treated with chrysotile and those of untreated cells. 4. The 2 fold increase in the formation of 8-OH-dG in calf thymus DNA was observed in the cells treated with RWFs in the presence of $H_2O_2$. On the other hand, chrysotile had no effect on the 8-OH-dG formation. 5. RWFs had no effect on the HGPRT point mutation and cell transformation. These results showed that RWFs could induce chromosomal damage, cell division disturbance and oxidative DNA damage in the RWFs treated cells.

• Geomechanics and Engineering
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• 제30권2호
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• pp.123-138
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• 2022

Present study computes the ultimate bearing capacity of an embedded strip footing situated on the rock slope subjected to seismic loading. Influences of embedment depth of strip footing, horizontal seismic acceleration coefficient, rock slope angle, Geological Strength Index, normalized uniaxial compressive strength of rock mass, disturbance factor, and Hoek-Brown material constant are studied in detail. To perform the analysis, the lower bound finite element limit analysis method in combination with the semidefinite programming is utilized. From the results of the present study, it can be found that the magnitude of the bearing capacity factor reduces quite substantially with an increment in the seismic loading. In addition, with the increment in slope angle, further reduction in the value of the bearing capacity factor is observed. On the other hand, with an increment in the embedment depth, an increment in the value of the bearing capacity factor is found. Stress contours are presented to describe the combined failure mechanism of the footing-rock slope system in the presence of static as well as seismic loadings for the different embedment depths.

• Geomechanics and Engineering
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• 제29권2호
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• pp.99-111
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• 2022

Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.

• ALGAE
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• 제32권4호
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• pp.325-336
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• 2017

Intertidal community recovery and resilience were investigated with quantitative and qualitative perspectives as a function of disturbance timing. The study was conducted in a lower intertidal rock bed of the southern coast of South Korea. Six replicates of artificial disturbance of a $50cm{\times}50cm$ area were made by clearing all visible organisms on the rocky substrate in four seasons. Each of the seasonally cleared plots was monitored until the percent cover data reached the control plot level. There was a significant difference among disturbance timing during the recovery process in terms of speed and community components. After disturbances occurred, Ulva pertusa selectively preoccupied empty spaces quickly (in 2-4 months) and strongly (50-90%) in all plots except for the summer plots where non-Ulva species dominated throughout the recovery period. U. pertusa acted as a very important biological variable that determined the quantitative and qualitative recovery capability of a community. The qualitative recovery of communities was rapid in summer plots where U. pertusa did not recruit and the community recovery rate was the lowest in winter plots where U. pertusa was highly recruited with a long duration of distribution. In this study, U. pertusa was a pioneer species while being a dominant species and acted as a clearly negative element in the process of qualitative recovery after disturbance. However, the negative effect of U. pertusa did not occur in summer plots, indicating that disturbance timing should be considered as a parameter in understanding intertidal community resilience in temperate regions with four distinct seasons.

• 지구물리와물리탐사
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• 제7권1호
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• pp.62-69
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• 2004

The objective of this study is to estimate the distribution of a zone disturbed by excavation (EDZ) around tunnels that have been excavated at about 500 m depth in pre-Tertiary hard sedimentary rock. One of the most important tasks is to evaluate changes in the dynamic stability and permeability of the rock around the tunnels, by investigating the properties of the rock after the excavation. We performed resistivity and acoustic tomography using two boreholes, 5 m in length, drilled horizontally from the wall of a tunnel in pre-Tertiary hard conglomerate. By these methods, we detected a low-resistivity and low-velocity zone 1 m in thickness around the wall of the tunnel. The resulting profiles were verified by permeability and evaporation tests performed at the same boreholes. This anomalous zone matched a high-permeability zone caused by open fractures. Next, we performed resistivity monitoring along annular survey lines in a tunnel excavated in pre-Tertiary hard shale by a tunnel-boring machine (TBM). We detected anomalous zones in 2D resistivity profiles surrounding the tunnel. A low-resistivity zone 1 m in thickness was detected around the tunnel when one year had passed after the excavation. However, two years later, the resistivity around the tunnel had increased in a portion, about 30 cm in thickness, of this zone. To investigate this change, we studied the relationship between groundwater flow from the surroundings and evaporation from the wall around the tunnel. These features were verified by the relationship between the resistivity and porosity of rocks obtained by laboratory tests on core samples. Furthermore, the profiles matched well with highly permeable zones detected by permeability and evaporation tests at a horizontal borehole drilled near the survey line. We conclude that the anomalous zones in these profiles indicate the EDZ around the tunnel.