| Popis: |
We investigate the face failure mechanism for shallow circular tunnels that are excavated in a dry, cohesionless soil by means of a physical model and analyse the experimental results by means of limit equilibrium calculations. The physical model consists of a sand box with a tunnel, which was modelled by a clear acrylic half pipe. The tunnel face support was modelled in two ways: as a rigid movable face with a PVC plate; and as a flexible face with a pressurised air bag. A series of tests were performed with an overburden of one, two and three times the tunnel diameter. The kinematics of the failure body were determined, as well as the required support pressure. The test results agree well with the predictions of the analytical model. |
