• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.35-43
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• 2012

Following the companion paper (I. Comparisons with Well-known Seismic Code and Site Response Characteristics), several acceleration data recorded during recent earthquake events in Korea were analyzed to verify the suitability of the proposed two-parameters site classification system and the corresponding site coefficients. For all of rock-soil site pairs less than 30 km distant, response spectrums and corresponding site coefficients, $F_a$ and $F_v$, were determined. Unfortunately, some of data have an eccentric error, where the spectral acceleration of rock site is more amplified than that of soil site. The $F_a$ and $F_v$ for all of pairs except the pairs of error were compared with those in the current code and the proposed system. The $F_a$ and $F_v$ from the recorded motions show definitely different trend from that of the current code. In addition, the site coefficients from recorded motions at four 765 kV substation sites, which are several hundred meters distant, have a remarkably similar trend and absolute values to those in proposed two-parameters site classification system. Based on earthquake motions recorded in domestic areas including data from the four 765 kV substation sites, the two-parameters site classification and site coefficients are superior to the results obtained from the current Korean seismic code.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.304-315
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• 2016

In this study, the current horizontal stress characteristics of the Tertiary rock formations in the Pohang Basin are investigated on the basis of the in-situ rock stress measurements at depths from 75 m to 716 m of the 3 test boreholes in the Doumsan area, Pohang. The deep hydraulic fracturing stress measurement results indicated that the horizontal stress components in the test site appear far lower than the average ones by the linear fit for the data set measured from the other domestic sites. But, borehole scanning revealed clearly that lots of small and large scale borehole failures occurred due to the low strength characteristics of the existing rocks. To obtain more accurate and overall information on the horizontal stress direction, the integrated analysis combining the hydraulic fracturing stress measurement and borehole scanning data set were additionally carried out. The analysis results showed that in the upper sedimentary and the lower volcanic rock formation, the dominant orientations of the current maximum horizontal stress components were appeared in the range of $80^{\circ}{\sim}100^{\circ}$ (N80E~N80W) and $120^{\circ}{\sim}140^{\circ}$ (N60W~N40W), respectively. From this study result it was found that the maximum horizontal stress directions have a tendency to rotate in a clockwise direction as the rock formation changes with depth in the test site.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.271-285
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• 2020

In this study, a numerical experiment related to the stress-strain analysis was performed on 3-D discrete fracture network(DFN) systems based on the distinct element method to evaluate the effect of joint geometry on deformability of jointed rock masses. Using one or two joint sets with deterministic orientation, a total of 12 3-D DFN blocks having 10m cube domain were generated with different joint density and size distribution. Directional deformation modulus of the DFN cube blocks were estimated along the axis directions of 3-D cartesian coordinate. In addition, deviatoric stress directions were chosen at every 30° of trend and plunge in 3-D for some DFN blocks to examine the variability of directional deformation modulus with respect to joint geometry. The directional deformation modulus of the DFN block were found to reduce with the increase of joint size distribution. The increase in joint density was less likely to have a significant effect on directional deformation modulus of the DFN block in case of the effect of rock bridges was relatively large because of short joint size distribution. It, however, was evaluated that the longer the joint size, the increase in the joint density had a more significant effect on the anisotropic deformation modulus of the DFN block. The variation of the anisotropic deformation modulus according to the variations in joint density and size distribution was highly dependent on the number of joint sets and their orientation in the DFN block. Finally, this study addressed a numerical procedure for stress-strain analysis of jointed rock masses considering joint geometry and discussed a methodology for practical application at the field scale.

• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.109-118
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• 2007

The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition. displacement. groundwater flow conditions have been altered due to the excavation. Various studies have been carried out on EDZ, but most studies have been focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the' hydraulic EDZ' was defined as the rock Lone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation. And hydraulic EDZ (hydraulic aperture changed zone) estimated by two-dimensional DEM program was considered in three-dimensional DFN model. From this approach the groundwater flow characteristics corresponding to hydraulic aperture change were examined. Together. a parametric study was performed to examine the boundary conditions that frequently used in DFN analysis such as constant head or constant flux condition. According to the numerical analysis, hydraulic aperture change induced by the hydraulic-mechanical interaction becomes one of the most important factors Influencing the hydraulic behavior of jointed rock masses. And also from this study, we suggest the proper boundary condition in three-dimensional DFN model.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.587-591
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• 2003

방사성폐기물 처분연구의 일환으로 결정질 암반에서의 지하수의 함양특성을 알아보기 위하여 연구지역의 강수량, 지표유출량 및 지하수위 변동량을 시간별로 일정기간동안 모니터링하였고 채취된 강수, 지표수 및 지하수의 수소동위원소 분석을 수행하였다. 강수사건 (Rainfall event)에 따른 지표유출량과 지하수위는 급격히 증가되며, 지하수위는 약 1일경과 후 최대값을 갖는다. 연구지역 5개 시추공으로부터 모니터링된 지하수위결과는 강수사건에 따라 지하수위의 증감특성을 보여주나, 변화되는 양상은 시추공의 수리특성에 따라 다르게 나타난다. 지표수 및 지하수의 수소동위원소조성은 강수사건에 따라 상응하여 변화되고 있어, 강수, 지표수 및 지하수의 양적변화와 함께 동위원소결과의 해석은 지하수의 함양특성을 정량적으로 추정할 수 있을 것이다.

• Tunnel and Underground Space
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• v.19 no.5
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• pp.450-462
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• 2009

To analyze the behavioral characteristics of rocks on indirect tests and uniaxial compressive strength, researchers have investigated 1417 pieces of rock block, which include igneous, metamorphic and sedimentary rocks in Korea. The same behavioral characteristics have been shown in every type of sedimentary rock and in the same species of rock in the case of Brazilian strength application. This suggests that correlations of rocks for geological considerations can lead to high reliability of the experimental results in case of an indirect method.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2007.03a
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• pp.64-80
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• 2007

This paper presents a case study on the excavation of a long tunnel(16.2km) named as "Sol-An tunnel", which connects between Mt. Dongbaek station and Dokye station in the Young-dong Railroad. This site is located in a complex geological region with faults, cavities and coal measures as sedimentary rocks area. It occurred geotechnical problems unexpectedly by running water when tunnelling in limestone area within those geological structures. This tunnel caused surface settlements through the decrease of ground water level and soil washed-out affecting by cavities and faults within limestone formation. This paper presents a analysis of source through a close investigation and measures. And also, does preventive measures about returns of settlements reflected by properties of limestones.

• Tunnel and Underground Space
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• v.13 no.3
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• pp.215-224
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• 2003

Weathering in nature was simulated by freeze-thaw cyclic test which represents mechanical weathering. Measured physical properties were elastic wave velocities, absorption rate, volume change and weight change. Uniaxial compression tests were also conducted before and after the weathering tests. The change in weight and volume of the specimens were not clearly related to the weathering process, but P, S wave velocities, uniaxial compression strength and Young's modulus were clearly decreased as weathering progresses. Test result can be used for the assessment of long-term stability of rock slopes.

• Tunnel and Underground Space
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• v.7 no.1
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• pp.39-50
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• 1997

Reference concepts for the disposal of spent nuclear fuel and the current status of underground rock laboratory were studied. An analysis to simulate the deep disposal of spent nuclear fuel in saturated rock mass was conducted. Main input parameters for numerical study were determined based on the KBS-3 concept. A series of results showed that the temperature distribution around a cavern reached the maximum value at about 10 years after the emplacement of spent fuel. The maximum temperature at the surface of canister was more than about 12$0^{\circ}C$ at about 4 years. This temperature was not much higher than the temperature criteria to meet the performance criteria of an artificial barrier in the KBS-3 concept. The maximum upward displacement due to the heat generation of spent fuel was about 0.9cm at about 10 years after the emplacement of spent fuel. It turned out that the vertical displacement became smaller with the decrease in heat generation of a canister. The quantity of groundwater inflow into a disposal tunnel increased by about 1.6 times at 20 years after the emplacement of spent fuel with the increase of pore pressure around a cavern.

• Explosives and Blasting
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• v.22 no.1
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• pp.23-32
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• 2004

터널 발파를 원활히 수행하기 위해서는 암반조건에 적합한 합리적인 설계와 정밀한 천공, 정확한 기폭초시가 기본요소로서 이는 현재 국내 터널 설계.시공 기술 및 기자재의 발달로 만족할 만한 성과를 얻을 수 있다. 특히. 터널발파에서 정확한 기폭초시 부여는 굴진율 및 버럭 파쇄율, 굴착예정선 미려도, 잔여 암반 손상도 등의 시공성에서 뿐만 아니라 소음 및 진동 발생율을 좌우하는 환경적인 측면에서 매우 중요한 요소이다. 기폭요소는 최초 도화선을 활용한 공업뇌관에서 전기뇌관, 비전기식뇌관의 순으로 기폭안전성과 정밀성 면에서 눈부신 성장을 이룩하여 왔으며 특히, 90년대 초에 개발되어 전 세계적으로 최근까지 지속적으로 사용량이 급증하고 있는 전자뇌관은 기폭방식에 일대혁신을 이루었다. 전자기폭 시스템은 기존뇌관의 초시를 결정하는 화약성분의 지연요소 대신에 IC board(전자회로)에 의한 Digital timer로 신호를 발생하여 초시를 결정하는 방식이다. 본 논문에서는 국내 최초로 전자기폭시스템을 활용하여 2003년 9원 23일에서 동년 11월 2일까지 강원도 양구 지역의 $\bigcirc\bigcirc$터널에 전자뇌관을 이용한 시험발파를 실시하였고, 발파에 의한 진동 등을 조사하여 그 효율성을 검토하였다. 이를 위해 전자뇌관의 특성과 장점을 최대한 샅리기 위하여 각공을 발파하는 방식, 즉 1지발에 1공을 발파하는 방식을 채택하고 일반 뇌관과 전자뇌관으로 설계를 하여 각각의 발파효율을 비교하여 보았다. 그 결과 발파진동의 경우 기존뇌관을 이용하여 1공씩을 1지발로 발파를 한 경우에는 18~56%의 진동저감 효과가 있었고. 본선 설계에 의해 진행된 발파에 비하여는 최대 70% 이상의 진동저감 효과가 있는 것으로 나타났다.