Evolving fabric and its impact on the shearing behaviour of a compacted clayey silt exposed to drying-wetting cycles

The fabric and the hydro-mechanical behaviour of compacted clayey silt samples were investigated before and after drying-wetting cycles. Drying-wetting cycles changed the soil fabric by increasing the macro-porosity, while the total void ratio remained almost constant. The cycled samples were more compressible than the original ones and experienced a smaller decrease of suction during shearing at constant water content. The higher compressibility is associated to a more evident reduction of macro-porosity. The smaller suction decrease is reproduced with a double structure water retention model accounting for changes in macro-porosity during shearing. Cycled samples mobilised higher strength and showed a higher dilatancy than original samples sheared at the same initial total stress and suction; furthermore, dilatancy increased with suction for both fabrics. The Li and Dafalias stress-dilatancy relationship, formulated in terms of a macrostructural Bishop stress and accounting for a suction dependency, allowed reproducing the experimental results accurately.