Infiltration behavior and face stability of carbonate-added slurry shield tunnel

Abstract

최근 연약지반 터널 현장에 활용되는 슬러리 쉴드 TBM은 굴진면으로 슬러리가 주입됨으로 그 안정성을 확보하는 공법이다. 하지만 간극이 과다하여 슬러리에 의한 폐색이 발생하지 않는 조립질 지반에서는 적용이 어렵기 때문에 첨가제를 혼입하여 사용하기도 한다. 본 연구에서는 첨가제의 역할로서 탄산가스를 주입함으로 슬러리가 주입되었을 때에 간극 내에 탄산가스가 흡착하여 폐색현상을 촉진시키는 효과를 규명하였다. 실내실험 결과 탄산 혼입에 따라 슬러리 쉴드 터널이 적용 가능한 유효입경이 1.0 mm에서 2.6 mm가량으로 증가하였고, 필터계수 <TEX>${\lambda}$</TEX>가 <TEX>$0.007sec^{-1}$</TEX>이상인 경우에 탄산에 의한 효과가 발생함을 알 수 있었다. Slurry shield tunnelling ensures stability by pressurizing the tunnel face with the slurry contained in the chamber. It resists water and earth pressure in order to prevent the failure in the tunnel face during tunnel excavation. If the ground is relatively coarse, slurry can not clog the tunnel face and excessive slurry infiltration will occur. In this case chemical compounds or additives should be added to the slurry in order to improve the clogging phenomena at the tunnel face. In this study, the effect of the carbon dioxide gas as an additive to the slurry instead of chemical compounds on the capability of enhancing the clogging in the tunnel face is investigated. Bubbles arising from the carbonate-added slurry are trapped in the soil voids enhancing the clogging capability. This effect is studied in this paper by performing laboratory model tests simulating in-situ conditions, and by adopting the fine particle clogging theory. Tunnel face stability analysis was also performed and it was found that the effective size (<TEX>$D_{10}$</TEX>) of soils which can guarantee tunnel stability utilizing the carbonate-added slurry increased from 1.0 mm up to 2.6 mm. Moreover, Stability analysis showed that the tunnel face is stable if the <TEX>${\lambda}$</TEX>(deposition coefficient) value is greater than <TEX>$0.007sec^{-1}$</TEX>.