Modeling microstructural mechanical behavior of expansive soil at various water contents and dry densities by molecular dynamics simulation

Microstructural behaviour plays an important role in building up the constitutive model of expansive soil. However, the responses of microstructural mechanical behaviour of expansive soil subjected to different water contents under varying dry densities are still poorly understood. In this study, we computed the bulk modulus and shear modulus of montmorillonite under various water contents and dry densities through molecular dynamics (MD) simulations. The mechanism that controls the changing of elastic properties subjected to water content and dry density changes was revealed by energy variation and water density field evolution. Results show that the microscopic bulk modulus is strongly influenced by dry density and water content while the dependence of shear modulus with water content and dry density is not as significant as bulk modulus. The comprehensive micromechanical studies demonstrate the critical water contents identified from either energies (bond, angle, and interfacial energies) or bulk/shear modulus are all highly related to the water content with full microscopic water filling ratio. The microscopic water filling ratio of the interlayer space thus can be considered as the key fundamental factor to control the variation of bulk/shear modulus through changing the energies in clay-water system.