Nano-level constitutive model for expansive clays.

Expansive clayey soils, which are prevalent across the surface sediments of the earth, are considered problematic for the structures and infrastructure founded in them. These soils are also challenging for environmental engineers involved in the design and construction of municipal and nuclear waste liners, petroleum engineers dealing with shale oil and gas, and agricultural scientists. Because their overall behaviour is controlled by molecular-level processes and interactions, a behaviour model encompassing the contributions from these interactions is required to predict the behaviour of these soils. This interaction becomes increasingly complex for natural expansive clays where a complex composition of clay and non-clay minerals exists. Unfortunately, none of the existing constitutive models pertaining to expansive clays comprehensively incorporates all the factors contributing to volume change behaviour of naturally occurring expansive soils. This study led to the development of a nano-level constitutive model for natural expansive clays through a three-phase study consisting of macro-level swell potential testing on laboratory control and natural field samples, micro-investigation of the pre- and post-swell specimens, and molecular level modelling through molecular mechanics, molecular dynamics and Monte Carlo techniques. This swell potential behaviour model incorporates all the major contributing factors such as moisture content, density, cation exchange capacity, exchangeable cations and interaction of clay minerals with non-clay minerals. The developed models have been successfully validated through close prediction of the swell potential behaviour of the laboratory control samples and natural field samples. [ABSTRACT FROM AUTHOR]