STABILITY CHARTS FOR A TALL TUNNEL IN UNDRAINED CLAY

Abstract

The stability of a plane strain tall rectangular tunnel in undrained clay is investigated in this paper using shear
strength reduction technique. The finite difference program FLAC is used to determine the factor of safety for
unsupported tall rectangular tunnels. Numerical results are compared with upper and lower bound limit solutions,
and the comparison finds a very good agreement with solutions to be within 5% difference. Design charts for tall
rectangular tunnels are then presented for a wide range of practical scenarios using dimensionless ratios ~ a similar
approach to Taylor’s slope stability chart. A number of typical examples are presented to illustrate the potential
usefulness for practicing engineers.