Limit Analysis for Tunnelling

The proposed research aims at improvements in numerical predictions in geomechanics with particular emphasis on tunnelling by approaching the problem from two aspects, the first one being finite element modelling employing advanced constitutive models, the second one being limit analyses, also based on numerical procedures. The advantage of the limit analysis approach is that, once the complex numerical algorithms required for the optimization procedure are sorted out, run times on the computer are very low, i.e. solutions for the problem at hand are obtained typically in the order of minutes. The disadvantages of the method are that only limit loads can be obtained yielding no information on the stress and displacement field before failure. The contrary holds for finite element techniques employing highly advanced constitutive models. Here stresses and displacements are obtained for working load conditions as well as for near failure conditions. If appropriate models are implemented accounting for strain softening behaviour the post failure regime can also be investigated. The disadvantage of this approach is twofold. Generally speaking run times are very high due to the complex solution strategies required and secondly material parameters are not always easy to determine for such complex models. In addition only limited experience is available from the field because failures are often not very well documented.