• Title/Summary/Keyword: tunnel behavior

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Behavior of Grouted Bolts in Consideration of Seepage Forces (침투수력을 고려한 전면접착형 록볼트의 거동연구)

  • Lee, In-Mo;Kim, Kyung-Hwa;Shin, Jong-Ho;Park, Jong-Kwan
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.1259-1266
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    • 2005
  • In a NATM tunnel, fully grouted bolts are widely used as part of supporting system. Grouted bolts play an important role not as to take some parts of load acting on a tunnel lining but as to reinforce the ground adjacent the tunnel. In conjunction with tunnel construction, the presence of groundwater may pose a number of difficulties. With respect to tunnel design, influences of groundwater on tunnel behavior have been considered in many aspects. However, the effect on grouted bolts has been rarely investigated. In this study, the behavior of grouted bolts, which are affected by the seepage forces, was examined. To investigate the effects of seepage forces, the theoretical solutions for a drained condition were also found. Based on the theoretical solutions, ground reaction curves considering seepage forces were obtained. By comparing the ground reaction curves supported by grouted bolts with those for the unsupported cases, the effect of reinforcement was evaluated. Finally, through comparison between supported ground reaction curves in the drained condition and those in the case of groundwater flow, it was found that the grouted bolts are more structurely beneficial when the seepage occurs towards the tunnel than when there is no groundwater flow.

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Investigation on the Behavior of Tunnel Face Reinforced with Longitudinal Reinforcements using Reduced-Scale Model Tests (모형실험에 의한 수평보강재로 보강된 터널 막장의 거동 분석)

  • Yoo, Chung-sik;Shin, Hyun-Kang
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.2 no.2
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    • pp.32-40
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    • 2000
  • This paper presents the results of a parametric study on the behavior of tunnel face reinforced with horizontal pipes. A series of reduced-scale model tests was carried out to in an attempt to verify previously performed three-dimensional numerical modeling and to investigate effects of reinforcement layout on the tunnel face deformation behavior. The results of model tests indicate that the tunnel face deformation can significantly reduced by pre-reinforcing the tunnel face with longitudinal members and thus enhancing the tunnel stability. In addition, the model tests results compare fairly well with those from the previously performed three-dimensional finite element analysis. Therefore, a properly calibrated three dimensional model may effectively be used in the study of tunnel face reinforcing technique.

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Deformation characteristics of tunnel bottom after construction under geological conditions of long-term deformation

  • Kim, Nag-Young;Park, Du-Hee;Jung, Hyuk-Sang;Kim, Myoung-Il
    • Geomechanics and Engineering
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    • v.21 no.2
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    • pp.171-178
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    • 2020
  • Mountainous areas cover more than 70% of Korea. With the rapid increase in tunnel construction, tunnel-collapse incidents and excessive deformation are occurring more frequently. In addition, longer tunnel structures are being constructed, and geologically weaker ground conditions are increasingly being encountered during the construction process. Tunnels constructed under weak ground conditions exhibit long-term deformation behavior that leads to tunnel instability. This study analyzes the behavior of the bottom region of tunnels under geological conditions of long-term deformation. Long-term deformation causes various types of damage, such as cracks and ridges in the packing part of tunnels, as well as cracks and upheavals in the pavement of tunnels. We observed rapid tunnel over-displacement due to the squeezing of a fault rupture zone after the inflow of a large amount of groundwater. Excessive increments in the support member strength resulted in damage to the support and tunnel bottom. In addition, upward infiltration pressure on the tunnel road was found to cause severe pavement damage. Furthermore, smectite (a highly expandable mineral), chlorite, illite, and hematite, were also observed. Soil samples and rock samples containing clay minerals were found to have greater expansibility than general soil samples. Considering these findings, countermeasures against the deformation of tunnel bottoms are required.

Field Measurements with the Construction of Cut and Cover Tunnel (복개 터널구조물의 현장 시공에 따른 계측 분석 사례)

  • 박시현;이석원;이규필;배규진;전오성;이종성
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.03a
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    • pp.149-156
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    • 2002
  • Field measurements were carried out in this study to investigate the behavior of cut and cover tunnel such as the distribution and the magnitude of the earth pressure during back fill process of the ground material. Three kinds of measuring instruments, such as the earth pressure load cell, the concrete strain gauge and the reinforcing bar meter of embedded type in concrete structure were installed and measured. Earth pressure load cells, installed after construction of the tunnel lining, measure the outside forces acting on the tunnel lining with radial directions. Three load cells were installed at the crown, the right and the left shoulder of the tunnel, respectively. Three sets of reinforcing bar meter were installed in the double reinforcements of the tunnel lining and their locations were the same with the position of the earth pressure load cells. Concrete strain gauge was installed only one site of the upper compressive part at the tunnel crown. Based on the measuring results in the field, the deformation and the earth pressure acting on the tunnel lining were investigated with the back fill process of the ground material. Considerations on the validity of the measuring results were paid. For the analysis of measurements, after dividing back fill process into three steps, various factors which affect on the behavior of tunnel lining were investigated at each step.

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A study on the longitudinal optimum separated distance of tunnel face in 2-arch tunnel (2-Arch 터널의 막장면 종방향 적정 이격거리에 관한 연구)

  • Lee, Min-Kyu;Jeong, Ji-Su;Lee, Sung-Ki;Lee, Seung-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.4
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    • pp.323-330
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    • 2007
  • Recently, due to the effective land utilization and environmental protection, the construction of 2-arch tunnel has been gradually increased. In spite of this tendency, the mechanical information for the 2-arch tunnel, especially such as its behavior characteristics and mechanism are not enough. Therefore in this study, the theoretical and numerical studies on the behavior characteristics of 2-arch tunnel are carried out and longitudinal optimum separated distance of tunnel face is proposed by considering the analysis results from the behavior of advanced excavation of tunnel and stress of central pillar. As a result, longitudinal optimum separated distance of tunnel face is in 0.5D for the better safety of 2-arch tunnel by rapidly decreasing the stress concentration of central pillar.

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Mechanical evolution law and deformation characteristics of preliminary lining about newly-built subway tunnel closely undercrossing the existing station: A case study

  • Huijian Zhang;Gongning Liu;Weixiong Liu;Shuai Zhang;Zekun Chen
    • Geomechanics and Engineering
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    • v.35 no.5
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    • pp.525-538
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    • 2023
  • The development of a city is closely linked to the construction and operation of its subway system. However, constructing a new subway tunnel under an existing station is an extremely complex task, and the deformation characteristics and mechanical behavior of the new subway tunnel during the excavation process can greatly impact the normal operation of the existing station. Although the previous studies about the case of underpass engineering have been carried out, there is limited research on the condition of a newly-built subway tunnel that closely undercrossing an existing station with zero distance between them. Therefore, this study analyzes the deformation law and mechanical behavior characteristics of the preliminary lining of the underpass tunnel during the excavation process based on the real engineering case of Chengdu Metro Line 8. This study also makes an in-depth comparison of the influence of different excavation methods on this issue. Finally, the accuracy of numerical simulation is verified by comparing it with on-site result. The results indicate that the maximum bending moment mainly occurs at the floor slab of the preliminary lining, while that of the ceiling is small. The stress state at the ceiling position is less affected by the construction process of the pilot tunnel. Compared to the all-in-one excavation method, although the process of partial excavation method is more complicated, the deformation of preliminary lining caused by it is basically less than the upper limit value of the standard, while that of the all-in-one excavation method is beyond standard requirements.

Stability Analysis of Rock Pillar in the Diverging Area of Road Tunnel (도로터널 분기부 암반 필라의 안정성 평가)

  • Kang, Jae-Gi;Yang, Hyung-Sik;Jang, Sun-Jong
    • Tunnel and Underground Space
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    • v.24 no.5
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    • pp.344-353
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    • 2014
  • In this study, the behavior of rock pillar in the diverging area of road tunnel was assessed by using a three dimensional numerical analysis. Based on parameters affecting the behavior of rock pillar, different safety factors according to pillar width, depth and rock conditions were evaluated. It turned out that as the pillar width increases, the change curve of safety factors in accordance with depth and rock conditions shows more of the nonlinear behavior. By the assessment of the minimum safety factor, a safety factor chart on the behavior of rock pillar in the diverging area of road tunnel was suggested.

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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A Study on the Analysis Method of Safety Cost of Tunnel Accident (터널사고 재난 안전비용 분석 방법에 관한 연구)

  • Baek, Chung-Hyun
    • Journal of the Korea Safety Management & Science
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    • v.23 no.1
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    • pp.23-30
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    • 2021
  • This paper analyzed a survey of 388 general target samples to analyze the correlation between disaster safety costs and human risk factor analysis and evacuation behavior due to tunnel accidents. Considering the impact of the tunnel accident on disaster safety costs and the correlation between human evacuation and risk factors in the tunnel environment, the system should be reorganized to reflect the tunnel's basic plan, tunnel cross-section, tunnel installation.

Deformation Analysis of a Shallow NATM Tunnel using Strain Softening Model and Field Measurement (변형률 연화모델과 현장계측을 이용한 저토피 NATM터널의 변형해석)

  • Lee, Jaeho;Kim, Youngsu;Moon, Hongduk;Kim, Daeman;Jin, Guangri
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.6
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    • pp.29-36
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    • 2007
  • The control and prediction of surface settlement, gradient and ground displacement are the main factors in urban tunnel construction. This paper carried out the estimation and prediction of ground behavior around tunnel due to excavation using computational method and case study in detail for the analysis of deformation behavior in urban NATM tunnel. Computational method was performed by FLAC-2D with strain softening model and elastic plastic model. Field measurements of surface subsidence and ground displacement were adopted to monitor the ground behavior resulting from the tunneling and these values were applied to modify tunnel design parameters on construction.

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