• Title/Summary/Keyword: tunnel excavation

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Ground Behavior and Reinforcing Methods of NATM Tunnel through Deep Weathered Zone (대심도 풍화대층에서 NATM 터널의 지반거동 및 보강방법)

  • Chun, Byung-Sik;Song, Seung-Hoon;An, Jung-Whan
    • Journal of the Korean Geotechnical Society
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    • v.23 no.8
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    • pp.87-95
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    • 2007
  • This study analyzed ground settlement and ground stress depending on tunnel excavation and the ground reinforcing grouting methods for double line road tunnel through deep weathered zone. Diameter of double line road tunnel was approximately 12m and umbrella arch method and side wall reinforcing grouting were applied. The ring-cut split excavation method and CD-cut excavation method for excavation method were applied. Analyses of failure rate and vertical stress ratio show that the tunnel for which the height of the cover (H) was higher than four times the diameter, can be considered a deep tunnel. Comparisons of various excavation and ground reinforcement methods showed that CD-cut method results in lower surface and crown settlement, and lower failure rate than that obtained by Ring-cut split method. In addition, the side wall reinforcing grouting resulted in reduction of tunnel displacement and settlement.

Application of Seismic Reflection Method in the tunnel of Youngdong Railroad(Mt. Dongbaek~Dokye) (영동선 동백산-도계간 터널내 반사법 탄성파탐사 적용사례)

  • 김용일;윤영훈;조상국;양종화;김장수;이내용
    • Proceedings of the KSR Conference
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    • 2002.10a
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    • pp.696-708
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    • 2002
  • Seismic Reflection Methods(TSP, HSP) have been applied in the junction between 2nd Adit and Main Tunnel (Solan Tunnel) of Youngdiong Railroad(Mt. Dongbaek∼Dokye). In this paper, methods and case study will be introduced to predict discontinuties in the tunnel before excavation by the Seismic Reflection Methods(TSP, HSP)and secure construction stability of the tunnel in blasting and excavation.

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Effect of widening excavation in divergence section of a double-deck tunnel on its stability (복층터널 분기구 확폭구간 굴착에 따른 안정성 영향)

  • La, You-Sung;Kim, Yunhee;Lee, Kangil;Kim, Yongseong;Kim, Bumjoo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.22 no.4
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    • pp.435-450
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    • 2020
  • The divergence section of a double-deck tunnel can be divided into a 'widening pre-divergence section', a large cross-section with a cap shape and a 'post-divergence section' where the separation between the main and the branch tunnel is made. Since the cross-section of the widening pre-divergence section is considerably larger than that of the post-divergence section, the influence of excavation due to the different sizes and shapes in the cross-section should be considered in the examination of the tunnel stability. In this study, the effect of the preceding excavation, that is the excavation of the widening pre-divergence section, on excavation stability of the post-divergence section was examined by varying the excavation methods and bench lengths through 3D finite element analysis. The results showed that although the effects of the excavation methods and the bench lengths are not significant on the variation of principal stresses, the preceding excavation causes a relatively large variation on the stresses which may have an impact on the stability of the post-divergence section from the comparison of Stress-Strength Ratio (SSR) between the cases with and without the consideration of the preceding excavation effect by 2D finite element analysis.

Behavior of the Ground in Rectangularly Crossed Area due to Tunnel Excavation under the Existing Tunnel (II) (기존터널에 근접한 직각교차 하부터널의 굴착에 따른 교차부지반의 거동 (II))

  • Kim, Dong-Gab;Lee, Sang-Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.2
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    • pp.133-141
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    • 2005
  • The behavior of the ground in crossed zone due to the excavation of new lower tunnel rectangularly crossed to that was studied by model tests and numerical analysis in shallow cover. Results of the model tests show that earth pressure of the ground in crossed zone were redistributed due to the longitudinal arching effect by the excavation of lower tunnel. By the numerical analysis, minimum principal stress in crown of single tunnel has more decrease than parallel tunnel or crossed tunnel. Vertical stress at rectangularly crossed tunnel decrease more than single tunnel by stress shadow.

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Study on Ground Surface settlement of a 3-Arch-shaped Tunnel (3아치터널의 지표면 침하에 관한 연구)

  • Shin Kang Ho;Park Tu Sung;Park O Sung;Kim Jae Kwon
    • Proceedings of the KSR Conference
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    • 2004.06a
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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.

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The behavior of tunnel and ground according to the loading of building construction on the ground (터널 상부 지반에 시공되는 건물 하중에 따른 터널 및 주변지반의 거동)

  • Cha, Seok-Kyu;Lee, Sang Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.4
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    • pp.731-742
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    • 2018
  • Recently, the construction of the urban area has been rapidly increasing, and the excavation work of the ground has been frequently performed at the upper part of the existing underground structure. Especially, when the structure is constructed after the excavation of the ground, the loading and unloading process is repeated in the lower ground of the excavation so that it can affect existing underground structures. Therefore, in order to maintain the stability of the existing underground structure due to the excavation of the ground, it is necessary to accurately grasp the influence of the excavation and the structure load in the adjoining part. In this study, the effects of the ground excavation and the new structure load on the existing tunnel were investigated by large - scale experiment and numerical analysis. For this purpose, a large model tester with a size reduced to 1/5 of the actual size was constructed, and model tests and numerical analyzes were carried out to investigate the effects of the excavation of the body ground by maintaining the distance between the excavation floor and the tunnel ceiling constant, The impacts were identified. As a result of the study, it was confirmed that the deeper the excavation depth, the larger the influence on the existing tunnel. At the same distance, it was confirmed that the tunnel displacement increased with the increase of the building load, and the ground stress increased up to 2.4 times. From this result, it was confirmed that the effect of the increase of the underground stress on the existing tunnel is affected by the increase of the building load, and the influence of the underground stress is decreased from the new load width above 3.0D.

A Case Study of Minimizing Construction Time in Long and Large Twin Tube Tunnel (대단면 장대터널 공기단축 사례연구)

  • No Sang-Lim;Noh Seung-Hwan;Lee Sang-Pil;Kim Moon-Ho;Seo Jung-Woo
    • Tunnel and Underground Space
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    • v.15 no.3 s.56
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    • pp.177-184
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    • 2005
  • The Sapaesan tunnel, the longest twin tube tunnel (4km) in Korea with 4 lanes each, is under construction with two years of delayed schedule because of the strong opposition from environmental bodies. Therefore, maximizing the construction efficiency was needed in tunnel project to compensate for time delay. This study includes improvements in the construction of the Sapaesan tunnel such as increasing excavation length and changing excavation sequence. In this paper the system for predicting tunnel face ahead is also introduced. Bulk-Emulsion explosive and Cylinder-Cut method were adopted in tunnel blasting to increase the excavation length. Optimum tunnel excavation step was designed to make up delayed time. Tunnel foe mapping, TSP survey and geological prediction system using computerized jumbo-drill were performed fnr safe construction of long and large twin tube tunnel.

A Numerical Analysis on Ground Deformation due to Tunnel Excavation : Case Study of Seoul Subway NATM Tunnel (터널 굴착에 따른 지반 변형 수치해석 : 서울 지하철 NATM 터널 해석 사례 연구)

  • 손준익;이원제
    • Proceedings of the Korean Geotechical Society Conference
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    • 1991.10a
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    • pp.133-151
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    • 1991
  • In this paper an analytic discussion was made for a finite element analysis performed for the case study of Seoul subway NATM tunnel. The effects mainly discussed on the ground deformation analysis were the staged tunnel excavation and the excavated distance from a tunnel facing. The concept of ground characteristic line has been applied to properly consider the loading condition given by staged tunnel excavation so that the imaginary supporting pressure is applied on the excavated tunnel face. Discussions on the results of the performed finite element analysis were mainly made with respect to the ground settlement, tunnel displacement, earth pressure, stress mobilized in supporting members. And the three dimensional supporting effect due to the tunnel facing was evaluated based on an elastic closed-form solution and a result of two dimensional axisymmetric finite element analysis.

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Optimum Construction Duration for Road Tunnel Excavation Works (도로터널 굴착공사의 적정공기 판단기준)

  • Kim, Ha-Na;Kim, Dae Young;Kim, Dae-Young;Jeong, Seong-Chun;Huh, Young-Ki
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.4
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    • pp.59-64
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    • 2018
  • Construction schedule acceleration due to unreasonable construction planning frequently leads to construction accidents. In order to avoid such inevitable acceleration and to ensure safety in construction sites, there is a need for objective standards to determine appropriate construction duration for each construction process earlier in the process. In order to achieve the goal, intensive experts interviews were firstly conducted to identify candidate drivers affecting construction schedule of road tunnel excavation works. Then, a total of 34 field data was collected from on-going sites to analyze. It was found that actual excavation length per one day on site is varied mostly by Rock Mass Rating(RMR) types from various statistical analyses. Therefore an one-way table of excavation length per a day by RMR types were presented in a form of percentile. The results will help industry experts determine the most appropriate construction schedule for the works, which eventually lead to a zero accident site in many ways.

Behavior of tunnel under the influence of pre-loading on braced wall during the adjacent ground excavation (근접굴착 시 벽체에 선행하중 재하에 따른 터널의 거동)

  • Kim, Il;Lee, Sang-Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.4
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    • pp.331-341
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    • 2007
  • Pre-loads could be imposed on the braced wall to prevent the horizontal displacements during the ground excavation adjacent to the existing tunnel. For this purpose, new pre-loading system through which large pre-loads could be applied to the braced wall was used in the model tests. Large scale model tests were performed in the real scale test pit which was 2.0 m in width and 6.0 m in hight and 4.0 m in length. Test ground was constructed by sand. Model tunnel in 1.2 m diameter was constructed before test ground excavation. Test ground was excavated adjacent to existing tunnel and was braced. To investigate the effect of pre-loading, tests without pre-load were also performed. During the ground excavation were the behavior of braced wall, test tunnel, and ground measured. Model tests were also numerically analysed and their results were compared to that of the real scale tests. As a result, it was found that the stability of the existing tunnel was greatly enhanced when the horizontal displacements of braced wall was reduced by applying pre-load larger than the design load.

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