Lytton This project is to determine how empirical strength and plastic deformation properties of unsaturated soils are related to more fundamental physical, chemical, and thermodynamic properties of the soil particles, water, and salts dissolved in the water. The more fundamental properties referred to are the Helmholtz surface energies, wetting and dewetting angles, solute concentrations, particle size gradations of the soil particles, and the volumetric concentrations of soil, water, and air. These are expected to underlie the fracture and healing properties of the unsaturated soil and explain the logarithmic work hardening, yield, and plastic potential characteristics of the soil under repeated loading. To the knowledge of the research team, there has been little done in the past to make use of the connection, which has been recently established in polymers, between the viscoelastic characteristics of a soil, the Helmholtz surface energies, and the rate of change of dissipated "pseudo-strain" energy in the fracture of that soil. In addition, it has recently been discovered that under repeated loading, the rate of change of dissipated pseudo-strain energy explains the plastic work hardening of a composite material like an unsaturated soil. It is the purpose of this proposed project to explore these connections in fine-grained unsaturated soil to see if the same connections can be made. It is also proposed here to determine the effect of the osmotic water potential on the fracture and plasticity properties of a soil. The osmotic potential is related to the concentration of organic or inorganic salts dissolved in the pore water. A major effect of the concentration of solute in pore water is to alter the wetting or dewetting angle. It is known that some salts will increase and other salts will decrease the wetting angle and thus will have a distinctive effect upon the strength of the soil.
What makes the measurement of these properties possible is the recent acquisition at Texas A&M of a German-built Universal sorption apparatus and the recent construction of a triaxial unsaturated soil stress path cell with unusually broad capabilities. The first equipment makes it possible to measure all of the components of the Helmholtz surface energies: the Lifshitzvan der Waals apolar components and the Lewis acid and base polar components. The second item of equipment makes it possible to make carefully controlled tests on unsaturated soils while measuring all components of mechanical stress and strain and all components of the water potential over larger ranges than have been achieved with similar equipment in the past. The final unique capability that fits these two test apparati together is the ability recently developed at Texas A&M to analyze the test data to determine the dissipated pseudo-strain energy with each load cycle. ***
