Abstract

The monograph deals with selected problems of the constitutive modelling of natural fine grained soils commonly known as clays. The main idea is not to propose a unified model which is capable of describing all known features of mechanical behaviour of fine grained soils. Instead, separate models are proposed describing the mechanical behaviour of heavily overconsolidated, lightly overconsolidated and normally consolidated clays. This categorisation also follows characteristic strain regions of the model application in practice, i.e. small strains, intermediate strains and large strains. For small strains application of hyperelasticity is recommended as the sound theory. Hyperelastic models are reviewed and two new models are proposed and verified: the hyperelastic model with linear stress dependency of stiffness and the cross-anisotropic model based on the hyperelastic Vermeer’s model. The latter model is employed in the core of the models proposed for the range of intermediate strains occurring in the prefailure regime of heavily overconsolidated clays. The strain degradation of the reference shear stiffness modulus is introduced and additionally shear strength is controlled by the conventional isotropic criterion in stress space. Two optional methods of strain degradation are examined: simple hyperbolic degradation function of shear strain invariant for monotonic loading cases and refined hyperbolic degradation based on the so-called Simpson’s Brick framework. Lightly overconsolidated and normally consolidated fine grained soils are represented by soft clays and typically large strain yielding of these soils is important to simulate in geotechnical analyses. Modelling of the compressional strength and yielding is in the main focus of interest. A model based on the multi-laminate framework is proposed. A new feature applied in the model is microstructure based directional distribution of overconsolidation resulting in the inherent anisotropy of compression strength. Additionally, the model allows to model the destructuration which occurs in the naturally bonded soft soil deposits.

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