The soil response under cyclic loading conditions is of interest for a number of geotechnical structure such as road pavements, tank foundations and offshore structures. When a geotechnical structure is subjected to cyclic loading, permanent settlements and rotations are accumulated affecting the serviceability of the structure. In the last years, a number of modelling strategies have been proposed to quantify the strain accumulation of soils under cyclic loading; however, most of the models are valid only for limited loading and drainage conditions, and they generally employ complex constitutive formulations. In this thesis, a new constitutive model, the Memory Surface Hardening model, which accounts for the effects of cyclic loading on the soil response, is proposed. The primary aim of this research is to develop a simple set of equations which can accurately predict the cyclic mechanical response of granular soils under generalised loading and density conditions. The modelling strategy is developed in an existing critical state - bounding surface - state parameter - elasto-plastic framework. A new surface, the memory surface, is introduced to track the experienced stress history. In the experiments available in the literature, it is observed that the soil response is highly affected by the experienced loading states. The memory surface evolution responds to two rules: the yield surface is always enclosed by the memory surface; the memory surface expands or contracts following the experienced plastic strains. The last rule is the key to reproduce the typical features observed experimentally for granular soils subjected to cyclic loading. Whenever the soil experiences contractive volumetric strains, the memory surface expands; on the contrary, when the soil experiences dilative plastic volumetric strains, the memory surface contracts. The plastic soil stiffness is affected by the size of the memory surface. The evolution of the memory surface can be interpreted as a representation of the evolution of the soil fabric when the soil is subjected to cyclic loading conditions. The model is developed by maintaining the same hardening rules for any loading conditions, minimising the number of implemented rules and employing a limited number of constitutive parameters. The model is proposed for both the triaxial and the multiaxial stress space. The model has been validated for different types of granular soils under different loading conditions, drained and undrained conditions. The evolution of model surfaces for different loading conditions is presented in the simulations and the occurring mechanisms are widely described.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:702493 |
| Date | January 2016 |
| Creators | Corti, Riccardo |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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