Most soils strain-soften to some extent during deformation. Many models already exist that facilitate strain-softening in finite element simulations; however, the standard finite element method suffers from mesh-dependency due to element size dependent localisation of strains (de Borst et al. 1993). Regularisation methods can be used to average the strains from which the degree of softening is determined, so as to avoid such mesh dependent localisation issues (Summersgill et al. 2017); however, an appropriate characteristic length for the regularisation must be specified and is difficult to determine. In essence, current state-of-the-art in numerical modelling has eliminated a mesh-dependency by replacing it with a characteristic length dependency. The rate of softening is also difficult to determine since element tests often cannot impart sufficient strain on the soil specimens for them to achieve a residual (fully-softened) state.
In order to address this deficiency, this ARC funded project (Project ID: DE170100119) proposes to use image-based deformation measurement techniques to measure the size and distribution of strains occurring within and surrounding experimentally observed strain localisation features, in a well-defined boundary value problem. Such measurements will allow appropriate regularisation functions and characteristic lengths to be determined. In addition, the image analysis will be populated with finite elements allowing constitutive relations with strain-softening capabilities to be incorporated into the analysis using aspects of the finite element method, allowing appropriate values for the constitutive parameters that control strain-softening to be inferred via optimisation. This research could potentially unlock the ability to reliably model the strain-softening behaviour of soils in finite element simulations, allowing many classical yet poorly understood problems to be revisited numerically (e.g. slope stability in quick clays; cyclic T-bar and ball penetrometer testing).
If you are interested in working on this project as a post-graduate student based at UWA in Western Australia, first please check your eligibility to apply for a UWA Research Training Program Scholarship (for either domestic or international applicants), then feel free to contact Dr Sam Stanier for further information.
de Borst, R., Sluys, L.J., Mühlhaus, H.-B. & Pamin, J. (1993). Fundamental issues in finite element analyses of localization of deformation. Engineering Computations, 10: 99-121.
Summersgill, F., Kontoe, S. & Potts, D. (2017). Critical assessment of nonlocal strain-softening methods in biaxial compression. International Journal of Geomechanics, doi: 10.1061/(ASCE)GM.1943-5622.0000852.