Desiccation cracking in unsaturated soils

Abstract

A comprehensive study of desiccation shrinkage and cracking in unsaturated soils is performed, including macroscopic and microscopic desiccation tests on two commercially available soils. In addition, a new fully coupled drainage-deformation numerical model is developed for analysing desiccation in variably saturated soils. The contributions made in this thesis include: i) a new set of experimental data for unconstrained and linear constrained desiccation testing of clayey soils as well as drying induced crack pattern test data, ii) new experimental data on the effect of micro-structure on desiccation induced cracking, investigated using scanning emission microscopic and image analysis techniques, iii) a 2-dimensional pore-network model prediction of soil water characteristic curve (SWCC) in unsaturated soils, iv) a model for a realistic reconstruction of pore size distribution in soils based on the particle size distribution curve of the soil constrained by the void ratio, and v) a fully coupled two-phase distinct lattice spring model (DLSM) to simulate desiccation shrinkage and cracking in soil, taking into account explicitly the interaction of pore fluid with the deformation of the soil matrix through a new water bond constitutive model. All the input model parameters are physically identified, and procedures are discussed for their determination in the laboratory. All constitutive and numerical models proposed are verified against experimental data generated during the course of this investigation as well as data from the literature. Remarkable agreement between numerical results and experimental data are obtained in all the cases considered. Through the study of the desiccation test results, it is revealed that three important parameters control cracking of soil during desiccation: air entry value of the largest pores, heterogeneity of pore size distribution, and constraints (e.g., traction or friction boundary condition, residual stresses in the soil, and soil structure with the help of traction or friction boundary condition).