In order to clarify an effect of the cutoff grouting, a series of field experiments were performed during construction of the waterway tunnel from the River Gilancheon(Andong) to the Youngcheon dam. The experiments were conducted in three different ways based on the grouting time in the construction sequence, i.e., the pre-grouting, after-grouting and consolidation grouting tests. And those were also planned to compare the efficiency of grouting in relation to the material types of grout, base rock types and other geologic factors such as discontinuities, depth and direction of grouting holes, and number of grouting stages. Among the materials of grout employed in the experiments, such as a common Portland cement, a micro-cement, a micro-cement with sodium silicate, and a urethane, the urethane was the most effective as the cutoff grouting. And for the same grout material, the pre-grouting was more effective to cutoff the water inflow comparing to the after-grouting and the consolidation grouting. For the rock types, the grouting efficiency in the sedimentary rocks as a base rock was less than the other rocks such as granite and volcanic rocks, which is believed due to the smaller separation of joints and the abundance of infilling materials in the joints developed in the sedimentary rocks. There was no direct relationship between the total RMR value of the rock mass and the grouting efficiency, however, the joint separation which is one of the RMR criteria is believed to have positive relation to the grouting efficiency. And the direction of the grouting holes might not so much affect on the grouting efficiency while increasing the number of grouting stage showed the better results.
터널의 차수그라우팅 효과를 확인하기 위하여 영천댐 도수터널 건설공사 중에 현장 그라우팅 시험을 수행하였다. 시험은 그라우팅 시기에 따라 굴착전, 굴착후 및 콘크리트 라이닝일 설치된 이후의 압밀 그라우팅 등으로 구분하였고, 주입재료, 암종 및 지질인자, 그라우팅공의 천공방향 및 주입단계에 따른 효과를 비교하도록 계획하였다. 재료의 특성에 따른 차수효과는 포틀랜드시멘트, 마이크로시멘트, 마이크로시멘트 마이크로시멘트+규산에 비해 우레탄이 가장 뛰어났으며, 시공시기에 따라서는 라이닝후 및 굴착후에 비해 굴착전 그라우팅시 차수효과가 뛰어났다. 암종에 따라서는 화산암 및 화강암지반에 비해 퇴적암지반에서 차수효과가 낮게 나타났는데 이는 퇴적암에 발달하는 절리틈새가 적고 절리 충전물이 많아서 주입재의 침투성 저조에 기인한 것으로 사료된다. RMR값과는 직접적인 상관성이 없으나 RMR 요소 중 절리틈의 간극이 클수록 차수효과가 높게 나타났다. 천공방향은 차수효과에 영향을 미치지 않았으나 주입방법은 천공 및 주입의 단계를 세분할 수록 높은 차수 효과를 기대할 수 있다.
