• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1996년도 봄 학술발표회 논문집
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• pp.103-110
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• 1996

In this paper, behaviour of underground structural systems due to excavation and change of groundwater level is analyzed using finite elements. Equilibrium equations based on the effective pressure theory and transient flow equations considering the groundwater level are derived. Integration equations are derived using Galerkin's approximation and time dependent analysis is employed to compute groundwater level change and pore pressures. This computed pore pressures are employed in equilibrium equations and then finally displacements and stresses are computed. The developed program is applied to analyze the behaviour of ground excavation below the groundwater level. The program is also applied to multi-step excavation at the same model. The results show that the displacements of the ground surface are much influenced by the change of the groundwater level. Therefore, it is concluded that the change of the groundwater level should be considered in order to analyze the behaviour of the underground structural systems accurately

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.395-402
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• 2000

Recently, the deep excavations have been peformed to utilize the under ground space. As the ground excavation is deeper, the damage of the adjacent structure and the ground occurs frequently. The analysis of the retaining structures is necessary to the safety of the excavation works. There are many methods such as elasto-plastic, FEM, and FDM to analyze the displacement of the retaining structure. The elasto-plastic method is generally used in practice. In this thesis, GEBA-1 program by the Nakamura-Nakajawa elasto-plastic method was developed. The program for Windows was used the Visual Basic 6.0, and the Main of the program consists of three subroutines, SUB1, SUB2, and SUB3. The lateral displacement of the wall was analyzed by the developed program GEBA-1, SUNEX, and EXCAD, and compared with the measured displacement by the Inclinometer(at three excavation work sites). The excavation method of each site is braced retaining wall using H-pile. Each excavation depth is 14m, 14m, or 8.2m. The results of the analyses are the followings ① In the multi-layer soil, the lateral displacement by the GEBA-1 and EXCAD which is considering the distribution of the strut load is equal to the measured displacement. Elasto-plasto programs can't consider the change of the ground water in clay. Therefore, the analysis displacement was expected only 20% of the measured wall displacement. ③ At the final excavation step, the maximum lateral displacement of analysis and field occurred 7∼18m at the 85∼92% of the excavation depth. ④ The maximum lateral displacement in clay, as 50mm, occurred on the ground surface.

• 터널과지하공간
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• 제7권3호
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• pp.191-201
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• 1997

Geological and geotechnical surveys, in general, should precede the excavation to ensure the safety of the tunnel and should be followed up according to the various geological condition during the excavation. However actually the standard support patterns which were decided during the design step used be insisted for the whole excavation steps in spite of the various geological conditions. OO tunnel was excavated with NATM and a support pattern type-V in weak rocks. When the tunnel was excavated up to 25m long, the severe displacement was generated in the portal area and the shotcrete was damaged to make the cracks and the tunnel face was totally collapsed. It might happen owing to the one-day heavy rain, but the exact reason for that accident should be found out and the new optimal support patternt needed. Consequently three dimensional numerical analysis was applied for the evaluation of the cause of the tunnel collapse instead of two dimensional analysis, because three dimensional analysis can show better the real field phenomenon than two dimensional analysis in which the load distribution methods are adopted for the tunnel excavation. We could simulate the actual situations with three dimensional finite difference code and propose the new optimal support patterns.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1224-1239
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• 2008

The earth retaining walls using stabilizing piles can be applied to shallow excavation works without any stiffener. But, It demends a variety of installed composite stiffener on the earth retaining walls when it is installed as deep excavation works. Because, it causes an excessive displacement of walls. This research tried to overcome the problems created by the above issues and intended to apply the composite stiffener. The model test, focused on the effect of installed composite stiffener, measured the bending stress with stabilizing piles and walls, the settlement of earth surface, the displacement of walls for a step excavation and an increase in strip load. With the test results and soil deformation analysis, the reinforcement effect(relating to control displacement and earth presure) was analyzed in a qualitative and quantitative manner. It is expected to overcome a deep excavation works.

• Geomechanics and Engineering
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• 제37권1호
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• pp.31-48
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• 2024

To stabilize the excavations in urban area, soil anchorage is among the very common methods in geotechnical engineering. A more efficient deformation analysis can potentially lead to cost-effective and safer designs. To this end, a total of 116 three-dimensional (3D) finite element (FE) models of a deep excavation supported by tie-back wall system were analyzed in this study. An initial validation was conducted through examination of the results against the Texas A&M excavation cases. After the validation step, an extensive parametric study was carried out to cover significant design parameters of tie-back wall system in deep excavations. The numerical results indicated that the maximum horizontal displacement values of the wall (δ_hm) and maximum surface settlement (δ_vm) increase by an increase in the value of ground anchors inclination relative to the horizon. Additionally, a change in the wall embedment depth was found to be contributing more to δ_vm than to δ_hm. Based on the 3D FE analysis results, two simple equations are proposed to estimate excavation deformations for different scenarios in which the geometric configuration parameters are taken into account. The model proposed in this study can help the engineers to have a better understanding of the behavior of such systems.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.998-1007
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• 2006

In former times, It is obvious that the earth retaining cantilever wall using stabilizing piles is definitely superior to the other methods due to economical efficiency and the efficiency of construction through model tests using a soil tank and practical application(Kim, 2006). However, this method was not proved in theoretical basis from the viewpoint of geotechnical engineering. Accordingly, a variety of model experiments in order to analyze the behavior of the earth retaining cantilever wall and stabilizing piles according to excavation step and earth pressure and stress acting on stabilizing piles according to excavation step were performed. On the basis of analyzing the result of model tests using a soil tank, this study suggests failure mechanism of clods and a method calculating virtual supported point. In addition, this study contributes to developing the analyzing method of retaining piles, stabilizing piles and beams connecting two piles and, this study helps this method to be established as a new design method through analyzing the results of model tests using a soil tank.

• Geomechanics and Engineering
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• 제11권6호
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• pp.879-896
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• 2016

A new earth pressure equation considering the arching effect in $c-{\phi}$ soils was proposed for the accurate calculation of earth pressure on circular vertical shafts. The arching effect and the subsequent load recovery phenomenon occurring due to multi-step excavation were quantitatively investigated through laboratory tests. The new earth pressure equation was verified by comparing the test results with the earth pressures predicted by new equation in various soil conditions. Resulting from testing by using multi-step excavation, the arching effect and load recovery were clearly observed. The test results in $c-{\phi}$ soil showed that even a small amount of cohesion can cause the earth pressure to decrease significantly. Therefore, predicting earth pressure without considering such cohesion can lead to overestimation of earth pressure. The test results in various ground conditions demonstrated that the newly proposed equation, which enables consideration of cohesion as appropriate, is the most reliable equation for predicting earth pressure in both ${\phi}$ soil and $c-{\phi}$ soil. The comparison of the theoretical equations with the field data measured on a real construction site also highlighted the best-fitness of the theoretical equation in predicting earth pressure.

• 대한토목학회논문집
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• 제32권5D호
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• pp.499-505
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• 2012

도심지의 굴착공사 시 굴착심도가 깊어지고 있어 굴착공정에 따른 문제점들을 개선할 수 있는 방안에 대한 연구가 시급한 실정이다. 본 논문은 도심지 굴착공사 시 공사기간을 단축시키면서, 주변 구조물에 미치는 영향을 최소화 할 수 있는 굴착공법에 대한 연구이다. 본 연구의 방법으로 국내 및 국외에서 다수 시공된 벽식 지하연속벽의 공법인 Slurry Wall 공법의 문헌자료를 통해 지하연속벽 시공의 이론적 고찰을 실시하고, 기존 지하연속벽 공법의 트렌치 굴착 시 발생되는 비효율적인 시공단계의 주요한 문제점들을 분석하여 기술요소를 도출하였다. 도출된 기술요소를 반영하여 개선 가능한 새로운 공법을 제시하였고, 제시된 굴착공법을 현장에 적용한 사례를 바탕으로 기존 굴착공법과의 공사기간을 비교 분석하였다. 본 논문에서 제안된 공법을 현장에 적용한 결과, 기존예정공정표에 표시된 48일에서 15일 단축된 33일에 굴착공정을 마칠 수 있었다. 또한, 제안된 공법은 기존 지하연속벽 공법들에 비해 공기단축의 효과는 물론 경제성, 환경성 및 안정성 또한 뛰어난 것으로 기대되며, 향후 지하연속벽 시공의 공기단축에 기여하리라 사료된다.

• 대한토목학회논문집
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• 제13권5호
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• pp.109-122
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• 1993

유체포화 다공매체에서의 단계적 굴착시 형상변화로 인한 구조거동을 시간종속적 배수이론으로 예측하기 위한 유한요소해석방법을 제시하였다 시간종속적 배수거동을 고려한 유한요소방정식을 유도하기 위하여 Biot의 방정식을 사용하였다. 이론해가 존재하는 재하 하중에 의한 시간종속적 배수거동 문제의 해석과 완전배수거동시 1단계 굴착과 다단계 굴착시의 변형이 동일한가를 확인하므로써 유도된 방법의 타당성을 검증하였다. 1차원 및 2치원 문제에 대하여 시간종속적 배수모형과 완전배수모형에 의한 결과를 비교하여 그 차이를 예시하였다. 또한 단계적 굴착시 굴착속도 및 투수계수의 변화에 따른 영향도 분석하였다. 수치해석 시뮬레이션을 통해, 다공매체지반의 굴착해석시에는 시간종속적 배수거동에 근거한 해석이 보다 신뢰할 수 있음을 고찰하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1007-1013
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• 2004

A three-arch NATM tunnel with a total length of 53.5m has been constructed for a metropolitan subway station in Daejon, Korea. The tunnel, whose crown is located 22m below the ground, crosses the old Daejon station underneath. Since the tunnel comprises a very large section (10${\times}$28 m; largest in Korea), it shows complicated mechanical behaviors, especially near portal, due to its short length relative to width. As far as its construction step is concerned, the center tunnel is excavated with pre-excavated pilot tunnel, which is a unique feature of this tunnel (first in Korea) to secure safety during construction and prevent excessive settlements. The both side tunnels are then excavated along with the center tunnel. Since significant amount of settlement was predictable from the design stage, extensive monitoring was performed during construction. During excavation of the side tunnels, unexpected large settlements up to ${\~}$140mm (estimated 41.8 mm at design stage) was measured at the center tunnel. In this paper, we study the causes of this unusually large ground settlement. We believe that the extra-wide tunnel excavation increases the stress influence zone of portal in longitudinal direction and consequently add more settlements to the existing due to excavation and consolidation.