ABSTRACT
In Japan, the New Austrian Tunneling Method (NATM) is commonly used for shallow overburden tunnels. Full-face excavation is typically preferred for its efficiency, but it can lead to tunnel collapse when the ground lacks stability. In such cases, the heading and benching method is used, where the top heading is excavated first, followed by the bench. A wide ramp needed to access the heading can destabilize the ground at the tunnel’s base, increasing the risk of collapse. This study analyzed the collapse of the Kakibara Tunnel using PLAXIS 3D software, focusing on the impact of ramp width on stability. The results showed that excavation causes stress redistribution and concentration at the heading base, leading to instability. A wider ramp further amplifies these stress changes, increasing the risk of large tunnel displacements after benching, compromising overall tunnel stability.
