Tunnels in bedded rock with high horizontal stresses: Discussion

Abstract

The authors have presented a very interesting account on the behavior of relatively shallow tunnels in bedded rock under a very high horizontal ground stress. The horizontal stress is actually so high (1000 psi or 6895 kPa) that the stress field is nearlv uniaxial in horizontal direction, with a much smaller vertical stress due to the overburden. Due to this peculiar situation, conventional tunnel design methods did not apply and the authors had to develop a new method appropriate to the situation at hand. For designing the tunnel lining, one needs a reasonable prediction method for stresses and displacements around the tunnel. The authors show that elastic analysis comes close to predicting at least the correct magnitude and the sign of the displacements around the tunnel. While accepting in general the design principles stated by the authors, which are based partly on the elastic analysis and partly on the observation of time-dependent displacements and failure of the tunnel walls, it may, nevertheless, be useful to make some comments that may be of some help in clarifying certain points and in further developing the design method for tunnel linings in such a case. (1 ) The first comment concerns the rock properties which the authors have used in their analysis. Their calculation is based essentially on the elastic properties and anisotropy of thk rock substance. It seems, however, quite probable that large scale deformation moduli of the