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

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