Seepage Analysis in Construction of Ciuyah Tunnel, Lebak, Banten, Indonesia

The Ciuyah Tunnel is 1,329 meters long, with excavation progress reaching 720 meters from the inlet and 120 meters from the outlet. However, the excavation process from the inlet had to be stopped because of groundwater leakage. Groundwater management has become essential in reducing this tunnel project’s environmental disasters. Seepage analysis is needed to determine the potential leaks in the following excavation process. So the determination of handling methods for leaks and the impact of leaks can be anticipated. The objective of this study is to identify how groundwater leakage occurs during excavation based on the characteristics of the rock masses on the tunnel excavation faces and surface outcrops. This study also predicts the potential seepage point in unexcavated sections. The results show that the tunnel construction area consists of slightly to moderately weathered intercalated tuffaceous sandstone and claystone with many discontinuities. The groundwater leakage on the inlet side occurred due to excavation cutting the discontinuities on the roof. While at the outlet side, it is influenced by syncline geometry and joint planes. The potential for seepage points can occur at excavation points that affect the geometry of the fold where the water goes to a lower place.