The influence of localisation in strain-softening soils has been investigated using classical continuum theory, and both fixed mesh and adaptive mesh refinement (AMR) finite element approaches. For this purpose, a non-associated cohesion-softening Mohr-Coulomb soil model has been developed and, for the adaptive mesh study. an existing AMR algorithm has been upgraded by implementing the superconvergent patch recovery smoothing technique. Both fixed mesh and adaptive mesh approaches have been used to analyse the problem of passive earth pressure failure, with the computed results for limit load and failure plane orientation being compared with analytical solutions available in the literature. Parametric studies have been included to consider the influence of degree of softening and material dilation angle. The fixed mesh results highlight the findings of previous investigators who showed that, in the presence of strain-softening, the solution is non-unique: in particular. as the mesh density increases, so the post-peak load-displacement response becomes steeper, without there being any sign of convergence. However, this mesh dependency is shown to be less significant for a rough retaining wall (i.e. as compared to a smooth wall), due to the increased influence of progressive failure. The adaptive mesh results show that, in the absence of an internal length scale facility, shear band width reduces without limit as the minimum element size gets smaller. However- for both smooth and rough walls, load-displacement response converges to a unique solution, suggesting that adaptivity may be an alternative solution to non-standard continuum theories in countering mesh dependency in strain-softening computations. A major advantage of the adaptive mesh algorithm is its ability to update meshes during an analysis, to account for new and changing regions of strain concentration. Stress and strain contours show that this gives a better definition of developing failure mechanisms, compared to the fixed mesh approach. Using AMR, the solutions are relatively free from mesh alignment effects, with mesh configurations following strain concentrations, rather than vice versa. Furthermore, the efficient use of elements means that mesh adaptivity has an important role to play in the solution of much larger geotechnical problems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:521355 |
| Date | January 1999 |
| Creators | Bakar, Abu |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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