ABSTRACT
In constructing long mountain tunnels over 10 km, tunnel work occurs where a working drift intersects the main tunnel midway. There are risks, such as loosened zones and degraded support stability due to stress release in poor rock conditions. This paper explores the use of 3D-FEM for predicting the stability of the natural ground and support structures where a 63.5 m² drift intersects an 82.6 m² main tunnel at a 66-degree angle in the Hokkaido Shinkansen project. The study emphasized underground beam gate-type supports to reinforce openings and minimize section widening. Pre-construction analysis demonstrated that these supports effectively managed stress concentrations in the intersection area. During construction, measurements indicated that stress levels remained below predicted thresholds. Overall, stability in the surrounding rock and supports was maintained, allowing for safe and economical project completion. These findings underscore the importance of advanced modeling techniques and appropriate support structures in complex tunneling operations.
