Abstract
This paper investigates the stability of plane strain tunnel headings in undrained soils. Using the factor of safety approach via the strength reduction technique, the idealised tunnel heading models are studied using the finite difference program FLAC. This problem is also similar to underground long wall excavations in plane strain condition. The finite difference results are presented alongside upper and lower bound limit solutions for validation. A thorough comparison between these two methods finds a very good agreement. Design charts are presented for a wide range of practical scenarios using dimensionless ratios, similar to Taylor's design charts used for slope stability. Typical examples are presented to illustrate the usefulness for practising engineers.