• Title/Summary/Keyword: relaxed rock mass height

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The estimation of the relaxed rock mass height of a subsea tunnel under the overstressed ground conditions in coupled analysis (과지압 조건에서 해저터널의 연계해석 시 이완하중고 평가 연구)

  • Yoo, Kwang-Ho;Lee, Dong-Hoon
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.03a
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    • pp.716-724
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    • 2008
  • In the case of subsea tunnels, hydro-mechanical coupled analysis is necessary for an exact design and construction. The consideration of the overstretched ground condition is also required because they are usually located at the great depth unlike the usual tunnels. Many researches have been performed on the estimation of relaxed rock mass height. However, there have been no researches on the estimation of relaxed rock mass height under overstretched ground conditions. In this study, therefore, hydro-mechanical coupled analyses were performed under the overstressed ground conditions and the relaxed rock mass heights were estimated based on the contour of the local safety factor around a tunnel.

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A numerical comparison study on the estimation of relaxed rock mass height around subsea tunnels with the existing suggested methods (해저터널의 이완하중고 산정을 위한 제안식들과의 수치해석적 비교 연구)

  • You, Kwang-Ho;Lee, Dong-Hoon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.10 no.1
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    • pp.25-36
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    • 2008
  • When constructing subsea underground structures, the influence of high water and seepage pressure acting on the structures can not be neglected. Thus hydro-mechanical coupled analysis should be performed to estimate the behavior of the structures precisely In practice, relaxed rock load is generally used for the design of tunnel concrete lining. A method based on the distribution of local safety factor around a tunnel was proposed for the estimation of a height of relaxed rock mass ($H_{relaxed}$). In this study, the validation of the suggested method is investigated in the framework of hydro-mechanical coupled analyses. It was suggested that inducing inflow by pumping through a drainage well gave more reliable results than inducing inflow with shotcrete hydraulic characteristics in case of rock condition of Class III. In this study, therefore, inducing inflow by pumping through a drainage well are adopted in estimating $H_{relaxed}$ due to a tunnel excavation with the rock condition of Class I, III, and V. Also the estimated $H_{relaxed}$ results are compared with those of the existing suggested methods. As the result of this study, it is confirmed that estimating $H_{relaxed}$ based on the distribution of local safety factor around a tunnel can be effectively used even for the case of hydro-mechanical coupled analysis. It is also found that inducing inflow pumping through a drainage well gives more precise and consistent Hrelaxed of a subsea structure.

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A Study on Concrete Lining Stress Changes Considering Load Supporting Capacity of Primary Supports of NATM Tunnel (NATM 터널에서 1차지보재의 지보압을 고려한 콘크리트라이닝 응력변화에 관한 연구)

  • Jeon, Sang Hyun;Shin, Young Wan;Yoo, Han Kyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.4C
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    • pp.147-154
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    • 2011
  • Currently NATM tunnels are designed by applying the initial ground loads caused during construction to the primary supports, conisting of shotcrete, steel ribs and rock bolts. For long term considerations, it is assumed that the primary supports lose its functionality and therefore the secondary support, i.e. concrete lining, is design to resist against the entire ground loads. But the steel ribs, usually applied to bad ground conditions, are embedded in shotcrete causing very little corrosion and therefore the assumption that the primary support will lose all of its functionality is too conservative. Also even though shotcrete carbonates in long term, excluding it from design is also too conservative. In this study, we have, through analytical and numerical analysis, set a rational level of support pressure and allowable relaxed rock mass height sustainable by the primary support for long term design. Changes in sectional forces of the concrete lining considering the calculated support pressure of the primary supports was also carried out. Shallow subway tunnels were considered in the analysis with weathered rock and soft rock ground conditions. The analysis results showed that, by considering the support pressure of steel ribs, an economical design of the concrete lining is possible.