A critical assessment of nonlocal strain softening methods in biaxial compression

Abstract

When modelling the development of slip surfaces in strain softening soils, the finite element method can suffer from mesh dependency and a lack of convergence of the analysis. The calculation of strains using a nonlocal method avoids the independent softening of a solitary point that can cause these symptoms. Nonlocal methods calculate the strain at a point with reference to the strains at calculation points surrounding it. In this study, a biaxial compression analysis is used to compare the original and two modified nonlocal methods to local strain softening analysis. Three nonlocal parameters are introduced and their influence on the nonlocal strain calculation is investigated. Meshes with different discretisations permit a comparison of the mesh dependency of these methods and a sensitivity analysis of nonlocal parameters. All the nonlocal methods are found to have significantly less mesh dependency than the local method. Both modified nonlocal methods exhibit less mesh dependency than the original approach, but one of the two modified methods, the Over-nonlocal method, is shown to be unstable as the mesh is refined for certain values of the nonlocal parameters.