This project involves the study of strain localization on the stability and deformation behavior of open and supported excavations. Previous studies have demonstrated the usefulness of the standard finite element (FE) method in modeling the process of sequential excavation and construction particularly when the soil mass is deforming homogeneously. However, when a narrow band of intense shearing forms within the soil, the standard FE interpolation becomes inadequate because it is incapable of representing the effect of shear bands which could form across the finite elements. Therefore, in the regime of intense shearing, the standard FE method would predict a stiffer structural behavior even though a bifurcated response is already in order. In braced and tied-back excavations, this implies that the predicted movements and support loads will be smaller, and so the standard FE solution will err on the unsafe side. This research will address this problem by modeling strain localization as a problem of strong discontinuity, which involves jumps in the displacement field. The idea of slip lines in soil mechanics is consistent with this analysis. Within the context of FE analysis, problems involving strong discontinuities result in solutions that are completely independent of the FE mesh, in particular showing a sharp resolution of the discontinuities even in unstructured meshes. Furthermore, this approach admits the use of traditional rate-independent models of continuum mechanics, even those which do not offer a characteristic length scale, since the discontinuities are now assumed to correspond to sets of measure zero in the mathematical sense. The investigation will cover drained and undrained behavior using a finite deformation theory based on multiplicative plasticity, and will involve the use of J2 plasticity and modified Cam-Clay plasticity models. There are numerous field cases where strain localizations are known to have formed during the process of sequential excavation, and these will be used to test the accuracy of the proposed analytical methodology.
