Influence of front slope gradient and the angle between tunnel and slope on stability of tunnel portal

Shallow buried and unsymmetrically loaded tunnel is the most common type of mountain portal. Currently, studies mainly focus on stability side slope, while investigation deformation front slope after excavation relatively less. In this paper, influence gradient angle between portal was analyzed by FLAC3D. The results show that: When greater than 40°, caused larger with increase angle. order to ensure safety construction, we should not only pay attention treatment before excavation, but also monitoring during section. And suitable entry axis 0°, which can control vertical displacement large deformation. research conclusions provide some reference for support design