• Geomechanics and Engineering
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• 제31권3호
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• pp.237-248
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• 2022

Nowadays, more and more subway tunnels were planed and constructed underneath the ground of urban cities to relieve the congested traffic. Potential damage may occur in existing tunnel if the new tunnel is constructed too close. So far, previous studies mainly focused on the tunnel-tunnel interactions with circular shape. The difference between circular and horseshoe shaped tunnel in terms of deformation mechanism is not fully investigated. In this study, three-dimensional numerical parametric studies were carried out to explore the effect of different tunnel shapes on the complicated tunnel-tunnel interaction problem. Parameters considered include volume loss, tunnel stiffness and relative density. It is found that the value of volume loss play the most important role in the multi-tunnel interactions. For a typical condition in this study, the maximum invert settlement and gradient along longitudinal direction of horseshoe shaped tunnel was 50% and 96% larger than those in circular case, respectively. This is because of the larger vertical soil displacement underneath existing tunnel. Due to the discontinuous hoop axial stress in horseshoe shaped tunnel, significant shear stress was mobilized around the axillary angles. This resulted in substantial bending moment at the bottom plate and side walls of horseshoe shaped tunnel. Consequently, vertical elongation and horizontal compression in circular existing tunnel were 45% and 33% smaller than those in horseshoe case (at monitored section X/D = 0), which in latter case was mainly attributed to the bending induced deflection. The radial deformation stiffness of circular tunnel is more sensitive to the Young's modulus compared with horseshoe shaped tunnel. This is because of that circular tunnel resisted the radial deformation mainly by its hoop axial stress while horseshoe shaped tunnel do so mainly by its flexural rigidity. In addition, the reduction of soil stiffness beneath the circular tunnel was larger than that in horseshoe shaped tunnel at each level of relative density, indicating that large portion of tunneling effect were undertaken by the ground itself in circular tunnel case.

• Geomechanics and Engineering
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• 제24권4호
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• pp.323-335
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• 2021

This paper aims to estimate the range of the excavation damaged zone (EDZ) formation caused by the tunnel boring machine (TBM) advancement through dynamic three-dimensional large deformation finite element analysis. Large deformation analysis based on Coupled Eulerian-Lagrangian (CEL) analysis is used to accurately simulate the behavior during TBM excavation. The analysis model is verified based on numerous test results reported in the literature. The range of the formed EDZ will be suggested as a boundary under various conditions - different tunnel diameter, tunnel depth, and rock type. Moreover, evaluation of the integrity of the tunnel structure during excavation has been carried out. Based on the numerical results, the apparent boundary of the EDZ is shown to within the range of 0.7D (D: tunnel diameter) around the excavation surface. Through series of numerical computation, it is clear that for the rock of with higher rock mass rating (RMR) grade (close to 1st grade), the EDZ around the tunnel tends to increase. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional to the magnitude of the EDZ. However, the relationship between the formation of the EDZ and the stability of the tunnel was not found to be consistent. In case where the TBM excavation is carried out in hard rock or rock under high confinement (excavation under greater depth), large range of the EDZ may be formed, but less strain occurs along the excavation surface during excavation and is found to be more stable.

• Geomechanics and Engineering
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• 제33권5호
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• pp.477-486
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• 2023

In the studies on fault dislocation of tunnel, existing literatures are mainly focused on the problems caused by normal and reverse faults, but few on strike-slip faults. The paper aims to research the deformation and failure mechanism of a tunnel under strike-slip faulting based on a model test and test-calibrated numerical simulation. A potential faulting hazard condition is considered for a real water tunnel in central Yunnan, China. Based on the faulting hazard to tunnel, laboratory model tests were conducted with a test apparatus that specially designed for strike-slip faults. Then, to verify the results obtained from the model test, a finite element model was built. By comparison, the numerical results agree with tested ones well. The results indicated that most of the shear deformation and damage would appear within fault fracture zone. The tunnel exhibited a horizontal S-shaped deformation profile under strike-slip faulting. The side walls of the tunnel mainly experience tension and compression strain state, while the roof and floor of the tunnel would be in a shear state. Circular cracks on tunnel near fault fracture zone were more significant owing to shear effects of strike-slip faulting, while the longitudinal cracks occurred at the hanging wall.

• Geomechanics and Engineering
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• 제34권2호
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• pp.115-124
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• 2023

By conducting three-dimensional simulation with consideration of small-strain characteristics of soil stiffness, the effects of excavation geometry and tunnel cover to diameter ratio on deformation mechanisms of an existing tunnel located either at a side of basement or directly underneath the basement were systematically studied. Field measurements were used to verify the numerical model and model parameters. For basement excavated at a side of an existing tunnel, the maximum settlement and horizontal displacement of the tunnel are always observed at the tunnel springline closer to basement and tunnel crown, respectively, regardless of basement geometry. By increasing basement length and width by five times, the maximum movements of tunnel located at the side of basement and directly underneath the basement increase by 450% and 186%, respectively. Obviously, tunnel movements are more sensitive to basement length rather than basement width. For basement excavated at a side of an existing tunnel, tunnel movements at basement centerline become stable when basement length reaches 10 H_e (i.e., final excavation depth). Moreover, tunnel heaves due to overlying basement excavation become stable when the normalized basement length (L/H_e) is larger than 8.0. As tunnel cover to diameter ratio varies from 2.5 to 3.0, the maximum heave and tensile strain of tunnel due to overlying basement excavation decrease by up to 41.0% and 44.5%, respectively. If basement length is less than 8 H_e, the assumption of plane strain condition of basement-tunnel interaction grossly overestimates tunnel movements, and ignores tensile strain of tunnel along its longitudinal direction. Thus, three-dimensional numerical analyses are required to obtain a reasonable estimation of tunnel responses due to adjacent and overlying basement excavations in clay.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 가을 학술발표회 논문집
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• pp.185-192
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• 1999

This paper presents the results of a parametric study on the behavior of tunnel face reinforced with horizontal pipes. A three-dimensional finite element model was adopted in this study to capture the three-dimensional nature of tunnel face behavior under various boundary conditions. A parametric study was peformed on a wide range of boundary conditions with emphasis on the effect of reinforcing layouts on the deformation behavior of tunnel face. The results of analysis such as tunnel face deformation behavior under various conditions were thoroughly analyzed, and a database for the behavior of tunnel face under different reinforcing conditions was established for future development of a semi-empirical design/analysis method for the tunnel face reinforcing technique. The results indicated that there exits an optimum reinforcing layout for a given tunnel condition, which must be selected with due consideration of tunnel geometry and ground condition.

• 터널과지하공간
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• 제17권5호
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• pp.428-434
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• 2007

터널의 굴착에 따라 발생하는 변형은 터널의 안정성 판단에 중요한 요인으로, 계측을 통해서 측정할 수 있으나 현장에서 재래식 방법에 의한 계측치는 시 공간적인 요인으로 계측결과에 차이를 나타내게 된다. 그러나 시공 중 터널에 발생하는 변위에 대한 연구는 수치해석적 연구가 대부분이며 실제 현장 계측연구는 그 사례가 많지 않다. 본 논문에서는 대상 터널에 대한 재래식 방법에 의한 내공변위 계측치와 선행변위를 계측할 수 있는 방법인 수평경사계를 설치하여 얻은 천단변위를 분석하여 상호 비교하였다. 또한 이를 통하여 시공 중 터널의 변위 발생 양상을 확인하고 굴착 중 터널의 변위 특성을 파악하고자 하였다. 수평경사계 계측의 결과는 선행변위에 대한 일반적인 거동과 잘 일치하였으며, 이 계측 자료로 전체 변위 양상을 예측할 수 있을 것으로 판단된다.

• 터널과지하공간
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• 제18권5호
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• pp.338-342
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• 2008

기존의 연구에서 터널 종단변형도는 대부분 수치해석적 방법으로 구해졌으나, 본 논문에서는 실제 계측치를 이용하여 종단변형도를 구성하고 굴착에 따른 터널의 종단변위 발생 경향을 검토하였다. 막장전방의 변위는 수평경사계 계측치의 최대변위에 대한 지점 변위를 비교 분석하여 가장 적합한 결과를 나타내는 지점의 변위를 채택하였고, 막장 후방은 천단변위계에 의한 계측치를 회귀분석하여 구하였다. 연구 대상 터널의 계측치로 천단변위를 분석한 결과, 막장 3D 이전부터 변위가 발생하였고, 막장에서는 수치해석적으로 구한 내공 변위에 비해 10%, 정도 높은 약 40%의 변위가 발생하였으며, 막장 후방 4D 이후 최종변위에 수렴하는 것으로 나타났다.

• 한국지반환경공학회 논문집
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• 제23권8호
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• pp.23-28
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• 2022

우리나라 지형조건은 산악이 70%를 차지하고 있어 철도 및 도로공사 시 구조물이 차지하는 비중이 높다. 특히, 최근 들어 고속주행을 위한 고속철도와 고속도로 건설이 급증하고 있고 이와 더불어 터널 건설도 증가하고 있고 터널 굴착 완료 후 장기변형이 발생하는 터널 시공사례가 증가하는 추세이다. 이러한 터널 구조물의 안정성은 터널 굴착 주변 암반특성에 전적으로 좌우된다. 본 연구에서 대상인 화산쇄설암의 경우, 전반적으로 풍화에 취약하고 장기간에 걸쳐 강도가 저하되는 특성이 있어서 이를 고려한 터널 설계 및 시공계획 수립이 반드시 필요하다. 본 연구는 화산쇄설암 구간에 터널 현장에서 발생 된 과다변형 사례를 분석하여 향후 화산쇄설암 구간에서는 인버트 설치 및 하부보강을 고려한 방안을 제시하였다.

• 한국터널지하공간학회 논문집
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• 제9권1호
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• pp.91-97
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• 2007

절리가 존재하는 암반에서 2-Arch 터널을 굴착할 때 절리방향과 굴착단계에 따른 필라하중의 변화를 실험적으로 연구하였다. 이를 위해, 대형 모형 실험기(폭 3.3m, 높이 3.0m, 길이 0.45m)에 1/10 크기의 2-Arch 모형터널을 갖는 다양한 각도의 절리를 포함한 지반을 조성하고, 실제 시공과정을 따라 굴착하면서 터널굴착으로 인한 터널 주변지반의 변형을 측정하고, 굴착단계에 따라 필라에 작용하는 하중을 측정하였다. 계측된 데이터로부터 2-Arch 터널의 굴착에 따른 거동을 분석한 결과 절리의 각도에 따라 굴착단계별로 터널 주변지반의 변형 및 필라에 작용하는 하중이 크게 영향을 받는 것을 확인하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.64-71
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• 2009

The stresses acting on shotcrete lining of tunnel have been measured virtually by monitoring instruments installed during construction. However, the malfunction of instrument and the lack of consistency of signal have always been controversial, but re-installation of instrument after construction of tunnel lining is practically impossible. Therefore, authors have carried out the study to develop a new technique for estimating the stress acting on shotcrete lining during and after construction. In the technique, stresses of shotcrete lining can be estimate by the measurement of deformation of free face. Therefore, the relationships between the stresses of shotcrete lining and deformation of free surface are indispensable factor. In this paper, the parametric study using 2D FEM analysis was carried out to estimate the relationships between the stress level acting on the tunnel shotcrete lining and the deformation near the free face (e.g. artificial crack in this study). The distribution of stresses of shotcrete lining is also investigated in this study as the preliminary investigation for the large-scale tunnel lining test and detailed 3D FEM analysis.