TUNNEL STABILITY ANALYSIS AFFECTED BY WATER SATURATION IN THE CASE OF "AG" TUNNEL CONSTRUCTION

• Main Author: Agatha Putra Gultom, Albert
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/40223
• Institution: Institut Teknologi Bandung

With the underground infrastructures development in Indonesia, especially tunnels, regional geological structure, strength of the surrounding ground, groundwater level and water saturation are some of the important factors in determining tunnel stability for the construction idea. Reviewing the tunnel located in West Java, with a depth of 80 m above ground level, the "AG" Tunnel is the object of this research. The purpose of this study is analyzing the stress distribution caused by tunnel construction, such as the geometry of the face of the tunnel and the effect of excavation on the surrounding rocks. This study also analyzed the tunnel stability affected by variations of groundwater levels and variations of water saturation Mohr-Coulomb failure criteria. To accommodate the unstable tunnel walls, this study provides tunnel support preferences that need to be installed to accommodate the stress. The "AG" Tunnel is horseshoe shaped with 4.8 m high and 5.6 m wide; compared with 5.6 m diameter of circular tunnel. The rainy season makes the water level rise to the tuff-sandstone layer boundary or 20 m above the tunnel; gradually falls to 12 m and 4 m during the seasonal change period, and 1 m below the tunnel floor in the dry season. Data is processed with numerical calculation, by using finite element method, using Phase2 program. The difference in tunnel geometry (angular or circular) greatly affects the stress distribution on the wall, especially at the abutment point of the tunnel. Excavations from the "AG" Tunnel increase the compressive stress around the wall until 2 m from the wall. While for each variation in groundwater level and saturation value, the wall of the "AG" Tunnel has not been able to accommodate the stress that works, other than on the tunnel’s floor. Therefore, tunnel support is needed, which consists of supporting concrete lining with a minimum thickness of 2.2 mm on the tunnel wall to accommodate stress for the initial period of tunnel construction.