Analysis of mudstone deterioration and its effect on tunnel performance

Tunnelling through Tertiary mudstone bedrocks often encounters long-term instability in terms of high rock pressure or excessive displacement of tunnel walls. These deposits tend to soften due to water absorption upon unloading, moisture/humidity changes and weathering, and deteriorate with time. In this paper, strength deterioration due to softening of mudstone and its interaction to tunnel performance are briefly discussed; then, a finite element analysis is presented as an example for illustrating the influence of strength deterioration upon tunnel behaviour. Also described is stress transfer around tunnel associated with progressive yielding due to softening.