The effect of an anisotropic in-situ stress on the bending moment in a yielding lining

When deep tunnels are excavated in poor ground, squeezing conditions occur and the design of supports must follow the yielding principle. To this aim, special yielding ele ments embedded in the preliminary support can be employed. The presence of the yielding ele ments radically modifies the ground-lining interaction mechanisms making necessary the use of numerical analyses. Particularly relevant is the case of the anisotropic geostatic in-situ stress. The paper reports and discusses some results obtained by 2D numerical ground-lining interaction anal yses of yielding preliminary support with initial non-isotropic stress field. Results of classic rigid support and isotropic in-situ stress are also reported and compared. Specific attention will be given to the effect that the stress anisotropy has on the lining bending moment.