ABSTRACT
The usual techniques for the simulation of a shallow tunnel excavation in two-dimensional numerical analyses often produce relatively wide and flat surface settlement profiles, even when highly nonlinear and sophisticated elasto-plastic soil models are used. In this paper, the first results of a new approximate procedure for the simulation of the effects of the excavation is proposed. The technique is based on a differential reduction of the vertical and horizontal components of the geostatic stresses initially acting on the tunnel boundary. A conventional and simple elasto-plastic Mohr-Coulomb soil model was adopted because of its wide application in engineering practice. The results obtained from the numerical study showed that the proposed procedure is able to furnish surface settlement profiles in agreement with the experimental-based inverted normal (Gaussian) distribution form, right from the very small strain levels. The differential stress reduction relationships were found to be dependent from the geometry of the problem and from the soil parameters: thus, a trial and error procedure must be followed in order to obtain the appropriate ‘differential reduction rules’.
