Microfracture and Repeated Plastic Deformation in Unsaturated Soils as Influenced by Surficial Properties

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***9978672LyttonThis project is to determine how empirical strength and plastic deformationproperties of unsaturated soils are related to more fundamental physical,chemical, and thermodynamic properties of the soil particles, water, and saltsdissolved in the water. The more fundamental properties referred to are theHelmholtz surface energies, wetting and dewetting angles, soluteconcentrations, particle size gradations of the soil particles, and thevolumetric concentrations of soil, water, and air. These are expected tounderlie the fracture and healing properties of the unsaturated soil andexplain the logarithmic work hardening, yield, and plastic potentialcharacteristics of the soil under repeated loading. To the knowledge of theresearch team, there has been little done in the past to make use of theconnection, which has been recently established in polymers, between theviscoelastic characteristics of a soil, the Helmholtz surface energies, and therate of change of dissipated "pseudo-strain" energy in the fracture of thatsoil. In addition, it has recently been discovered that under repeatedloading, the rate of change of dissipated pseudo-strain energy explains theplastic work hardening of a composite material like an unsaturated soil. It isthe purpose of this proposed project to explore these connections infine-grained unsaturated soil to see if the same connections can be made. Itis also proposed here to determine the effect of the osmotic water potential onthe fracture and plasticity properties of a soil. The osmotic potential isrelated to the concentration of organic or inorganic salts dissolved in thepore water. A major effect of the concentration of solute in pore water is toalter the wetting or dewetting angle. It is known that some salts willincrease and other salts will decrease the wetting angle and thus will have adistinctive effect upon the strength of the soil.What makes the measurement of these properties possible is the recentacquisition at Texas A&M of a German-built Universal sorption apparatus and therecent construction of a triaxial unsaturated soil stress path cell withunusually broad capabilities. The first equipment makes it possible to measureall of the components of the Helmholtz surface energies: the Lifshitzvan derWaals apolar components and the Lewis acid and base polar components. Thesecond item of equipment makes it possible to make carefully controlled testson unsaturated soils while measuring all components of mechanical stress andstrain and all components of the water potential over larger ranges than havebeen achieved with similar equipment in the past. The final unique capabilitythat fits these two test apparati together is the ability recently developed atTexas A&M to analyze the test data to determine the dissipated pseudo-strainenergy with each load cycle.***