3D Numerical Investigation of Face Stability in Tunnels With Unsupported Face

The paper studies the stability of unsupported tunnel faces by analyzing results a large number 3D numerical analyses, in various ground conditions and overburden depths. analyses calculate average face extrusion (Uh) averaging axial displacement over face. Limiting occurs when becomes very convergence problematic. Using dimensionless “face parameter” is defined, which depends on suitable combination strength, depth size. parameter correlates well with critical parameters, like safety factor against instability, extrusion, radial wall at excavation face, volume loss deconfinement ratio Thus, semi-empirical formulae are proposed for calculation these parameters terms obtained from basic parameters. useful conclusions can be drawn