Compression Behaviour Of Clays Research Articles

A conceptual constitutive model unifying slurried (saturated), compacted (unsaturated) and dry states

Reconstituted and compacted soils are commonly assumed to exhibit a fundamentally different behaviour due to different microstructure. However, inspection of pore size distribution of the same soil in compacted and reconstituted states suggests that the boundary between these two states is more blurred. This paper explores the continuity between the microstructure of reconstituted and compacted states of kaolin clay and formulates a conceptual constitutive model unifying these states. Clay samples were prepared by saturating the pore space with different fluids (water, acetone and air) and the effect of pore-fluid fraction on the micro- and macroscale response of the clay was investigated experimentally. A conceptual constitutive model for unsaturated clays for quasi-isotropic stress states was therefore formulated, which allows the modelling of various unsaturated hydro-mechanical paths based on constitutive parameters only derived from the compression behaviour of clay under dry and saturated conditions (testing on samples formed from dry powder and slurry, respectively).

Estimation of the compression behaviour of reconstituted clays

The void index is a relative quantity measuring the position of the current void ratio of a clay against the void ratios of the clay at two specific vertical effective stresses (i.e., σv′=100kPa and σv′=1000kPa). Based on this concept, a simple systematic tool is proposed for estimating the compression behaviour of reconstituted clays over a wide range of stresses and water contents. Following the practice of geotechnical engineering computation, the compression behaviour of clays is idealised as linear segments in the Iv~lnp′ (or the void index and the mean effective stress) space. Considering the variation in the available data, there are three related but independent models for describing the compression behaviour of reconstituted clays. The accuracy of estimation increases with the level of available data. The proposed estimation is used to simulate the behaviour of a variety of reconstituted clays over a wide range of stresses and water contents. With different levels of available data, the estimation is evaluated on the basis of these simulations. The proposed estimation can take maximum use of available data and provide a simple yet practical tool for calculating the compression behaviour of reconstituted clays and a basic parameter for geotechnical engineering computations, the compression index. An empirical equation for the initial compression index is also suggested and verified.

Quantification of the effects of structure on the compression of a stiff clay

A detailed analysis was made of the compression behaviour of London Clay from oedometer tests, investigating the effects of the clay structure through comparisons between the behaviour of the intact soil and that of the same soil in a reconstituted state. The normalizing parameters commonly used in the literature to analyze the effects of structure on the compression behaviour of clays were found not to represent accurately the real behaviour of those clays that have a gradual yield in compression and require very high stresses to reach and cross the intrinsic compression line. For these soils, it is often difficult to identify a clear yield stress and the effects arising from the structure of the intact material may be concealed by the effects arising from the sample depth and the curvature of the intrinsic compression line at high stresses. A new normalizing parameter is introduced that refers the compression of the natural soil to the intrinsic swelling behaviour and the intrinsic compression line of the material. This was found to better represent the enhanced resistance of the intact material in compression while not requiring numerous loading and unloading stages in the oedometer tests as required by other methods.