Behavior of tunnel adjacent to weak zone by using scaled model test

Recently, the construction of tunnel frequently involves neighboring weak ground conditions. In this case, the stabilized ground could be relaxed by the excavation of tunnel. This will create issues in terms of stability of tunnel. Major factors determining the stability of tunnel can be the direction (angle) of weak zone, the distance between tunnel and boundary of weak zone and so on. In this study, by quantifying the displacement and crack propagation during the excavation of tunnel constructed neighboring weak zone, the influence of the direction of weak zone and the distance between tunnel and boundary of weak zone on the mechanical behavior of tunnel is investigated. A series of experimental scaled model tests by changing the direction of weak zone and the distance between tunnel and boundary of weak zone, are performed and analyzed under the condition of homogeneous material. The results show that as the angle between ground surface and boundary of weak zone moves from horizontal to perpendicular plane, displacement near tunnel increases. An increased distance between tunnel and boundary of weak zone induces displacements near tunnel to decrease and stabilizes beyond a certain level of distance. These findings verify and extend the earlier studies quantitatively. Finally, an appropriate distance between tunnel and boundary of weak zone according to the angle of weak zone is justified. This fundamental insight provides the basis for a more rational design of tunnel neighboring weak ground conditions.