• Steel and Composite Structures
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• 제22권1호
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• pp.63-77
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• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• 한국터널지하공간학회 논문집
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• 제7권4호
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• pp.285-294
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• 2005

본 연구에서는 저토피 구간에서 기존터널 하부에 새로운 터널이 경사로 교차하여 신설할 때 하부 터널굴착으로 인하여 발생하는 교차부 주변지반과 상부터널의 거동을 분석하였다. 4.0m (폭), 3.8m (높이), 4.1m (길이) 크기의 콘크리트로 제작된 대형토조에서 모래를 이용하여 상대밀도기 일정한 모형지반을 3.4m높이로 조성하였고, 상하터널의 교차 각도가 $56^{\circ}$인 경우에 대하여 대형모형실험을 실시하였다. 또한, 모형실험과 동일한 조건으로 수치해석을 실시하여 실험결과와 연관하여 분석하였다. 연구결과 교차부 주변지반은 하부터널 종방향의 응력 전이로 인하여 교차 전과 교차 후에 응력과 지반변위의 차이가 발생하였다. 모형실험 결과로부터 교차 전 후의 하부터널굴착에 따른 종방향 응력전이가 상부터널에 의하여 차단됨을 알 수 있었다.

• 한국터널지하공간학회 논문집
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• 제11권4호
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• pp.419-425
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• 2009

최근에 저토피 및 터널 갱구부에 반개착식 공법을 적용하여 구조적인 안전성과 자연친화성을 높인 사례가 증가하고 있다. 반개착식 공법은 저토피구판에시 원지반을 터널 천단아치에 해당하는 기초까지만 굴착하고 아치형 구조달을 설치하여 복토한 후에 터널하반을 굴착하여 기존 개착공법에서 발생되는 지반 과다절취에 따른 대절토 비탈면 발생과 굴착면 보강에 따른 고비용과 불안정성 증대 문제를 해결할 수 있는 공법이다. 본 논문에서는 저토피 구간에서 반개착식으로 굴착한 Braced Rib Arch의 거동에 대하여 연구하였다. 아치형구조물의 Rib Arch는 지간이 1.8 m인 아치형 강재를 간격재는 목재를 사용하였으며 1:10의 축척으로 4.0 m(폭)$\times$3.3 m(높이)$\times$4.0 m(연장)의 크기를 가진 대형토조에서 실험을 수행하였다. 모형실험결과 아치형 구조물에 작용하는 성토하중은 기존 개착터널에서 사용하는 하부구조물의 폭에 해당하는 상부토체의 크기보다 작은 것으로 나타났다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.214-220
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• 2003

Pipe jacking is a name for a method to excavate a tunnel by pushing pipe into the ground from an especial pit. Size of tunnels in this method is different from under 900mm (microtunneling) to more than 3,000mm. Method of excavation is also different from hand digging to use of any kind of tunnel boring machines such as slurry and earth pressure balance (EPB) machines. Slurry pipe jacking was firmly established as a special method for the nondisruptive construction of the underground tunnels in urban area. During the pipe jacking and microtunneling process, the jacking load is an important parameter, controlling the pipe wall thickness, need to and location of intermediate jacking station, selection of jacking frame and lubrication requirements. The main component of the jacking load is due to frictional resistance. In this paper the skin friction between pipe surface and surrounding condition also lubricant quality based on a few fundamental tests, were considered. During this study unconfined compressive strength test, dynamic friction measurement test and direct shear box test were raised for one of the largest diameter slurry pipe jacking project in Fujisawa city in Japan. It could be concluded that in slurry pipe jacking, prediction of frictional forces are mainly dependent on successful lubrication, its quality and lubricant strength parameters. Conclusions from this study can be used for the same experiences.

• Steel and Composite Structures
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• 제26권1호
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• pp.55-66
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• 2018

In this paper, the response of an underground fibreglass reinforced plastic (FRP) composite pipe system subjected to realistic loading scenarios that may be experienced by an actual buried pipeline is investigated. The model replicates an arbitrary site with a length of buried pipeline, passing through a $90^{\circ}$ bend and into a valve pit. Various loading conditions, which include effects of pipe pressurization, differences in response between stainless steel and fibreglass composite pipes and severe loss of bed-soil support are studied. In addition to pipe response, the resulting soil stresses and ground settlement are also analysed. Furthermore, the locations of potential leakage and burst have also been identified by evaluating the contact pressures at the joints and by comparing stresses to the pipe hoop and axial failure strengths.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1637-1641
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• 2003

Korea Gas Corporation(KOGAS) is a Liquified Natural Gas(LNG) supplier through out the Korea. LNG, which is imported wholly from foreign countries, is compressed 1/600 for easy transportation and is stored in a liquid state in the storage tanks at Incheon, Pyeongtaek and Tongyeong. At LNG receiving terminals, LNG is vaporized to natural gas before supplying to City Gas Consumer of Power Plant. The secondary pump is a equipment which compress LNG from 1- kgf/cm2 to 70 kgf/cm2. The secondary pump at Tongyeong LNG receiving terminal is consisted of two pumps in one underground PIT, and is connected to supporting structures. It is therefore expected that there is a vibration problem whit the pump and was found that high level vibration was occurred in a low frequency band($5^{\sim}10Hz$). In this paper, the vibration of secondary pump was analyzed, and the main cause of vibration was found out.

• Environmental Engineering Research
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• 제18권1호
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• pp.37-43
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• 2013

Water distribution pipes installed underground have potential risks of pipe failure and burst. After years of use, pipe walls tend to be corroded due to aggressive soil environments where they are located. The present study aims to assess the degree of external corrosion of a distribution pipe network. In situ data obtained through test pit excavation and direct sampling are carefully collated and assessed. A statistical approach is useful to predict severity of pipe corrosion at present and in future. First, criteria functions defined by discriminant function analysis are formulated to judge whether the pipes are seriously corroded. Data utilized in the analyses are those related to soil property, i.e., soil resistivity, pH, water content, and chloride ion. Secondly, corrosion factors that significantly affect pipe wall pitting (vertical) and spread (horizontal) on the pipe surface are identified with a view to quantifying a degree of the pipe corrosion. Finally, a most reliable model represented in the form of a multiple regression equation is developed for this purpose. From these analyses, it can be concluded that our proposed model is effective to predict the severity and rate of pipe corrosion utilizing selected factors that reflect the fuzzy soil environment.

• Geomechanics and Engineering
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• 제9권6호
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• pp.689-707
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• 2015

Progressive increase in population causing land scarcity, which is forcing construction industry to build multistory buildings having underground basements. Normally, basements are constructed for parking facility. This research work evaluates important factors which have caused the collapse of pile-anchor system at under construction five star hotel. 21 m deep excavation is carried out, to have five basements, after installation of 600 mm diameter cast in-situ contiguous concrete piles at plot periphery. To retain piles and backfill, soil anchors are installed as pit excavation is proceeded. Before collapse, anchors are designed by federal highway administration procedure and four anchor rows are installed with three strands per anchor in first row and four in remaining. However, after collapse, system is modeled and analyzed in plaxis using mohr-coulomb method. It is investigated that in-appropriate evaluation of soil properties, additional surcharge loads, lesser number of strands per anchor, shorter grouted body length and shorter pile embedment depth caused large deformations to occur which governed the collapse of east side pile wall. To resume work, old anchors are assumed to be standing at one factor of safety and then system is analyzed using finite element approach. Finally, it is concluded to use four strands per anchor in first new row and five strands in remaining three with increase in grouted and un-grouted body lengths.

• Geomechanics and Engineering
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• 제31권5호
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• pp.529-543
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• 2022

The lattice-spring-based synthetic rock mass model (LS-SRM) technique has been extensively employed in large open-pit mining and underground projects in the last decade. Since the LS-SRM requires a complex and time-consuming calibration process, a robust approach was developed using the Response Surface Methodology (RSM) to optimize the calibration procedure. For this purpose, numerical models were designed using the Box-Behnken Design technique, and numerical simulations were performed under uniaxial and triaxial stress states. The model input parameters represented the models' micro-mechanical (lattice) properties and the macro-scale properties, including uniaxial compressive strength (UCS), elastic modulus, cohesion, and friction angle constitute the output parameters of the model. The results from RSM models indicate that the lattice UCS and lattice friction angle are the most influential parameters on the macro-scale UCS of the specimen. Moreover, lattice UCS and elastic modulus mainly control macro-scale cohesion. Lattice friction angle (flat joint fiction angle) and lattice elastic modulus affect the macro-scale friction angle. Model validation was performed using physical laboratory experiment results, ranging from weak to hard rock. The results indicated that the RSM model could be employed to calibrate LS-SRM numerical models without a trial-and-error process.

• 한국광물학회지
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• 제19권4호
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• pp.239-246
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• 2006

대전광역시 유성구 덕진동 한국원자력연구소에 위치한 지하처분연구시설은 2003년 부지조사를 시작으로 최근에 완공하였다. 이 곳의 지질은 약한 변성작용을 받은 지역으로 소규모 단열이 잘 발달되어 있는 곳이다. 단열을 따라서 많은 종류의 이차충전광물들이 존재하지만, 그 중에서 광범위하게 분포하고 지하 핵종 이동에 상당한 영향을 끼치는 방해석의 광물학적 특징을 살펴보았다. 지하처분연구시설 암석 단열에 분포하는 방해석은 다른 이차광물들과 유사하게 단열대를 따라 분포하며, 부분적으로 두꺼운 층을 형성하기도 한다. 방해석으로 충전되어 있는 대부분의 단열대에는 석영, 철 산화물 및 돌로마이트 등이 소량 부성분 광물로 존재하고 있다. 방해석 결정은 일정한 방향성을 가지고 성장한 모습을 보여주고 있으며, 피복 물질로 산화철 광물인 침철석이 방해석 표면으로부터 성장하는데, 주로 방해석 결정의 가장자리 부근과 상부 표면의 용식된 부분에서 과밀하게 성장하고 있다. 터널 벽체의 숏크리트에서 녹아 나온 성분들이 침전되어 새로운 방해석 결정들이 형성되었는데, 지하수의 성분 및 흐름에 의해 형태 변화가 있었다. 단열충전광물 중 방해석은 지하수 화학특성을 변화시키고 핵종의 흡착 거동에 큰 영향을 끼치는 광물로, 본 연구에서 관찰된 방해석의 결정학적 구조 및 표면 특성은 추후 핵종 이동 실험시 중요한 기초 자료로 활용될 것이다.