Characterization of the strength and plastic deformation properties of unsaturated soils

As the advances of triaxial testing equipment have evolved, more and more has been learned about the behavior of unsaturated soils. There has been a limitation in the level of matric and total suction that could be achieved in a triaxial cell due to limitations on the materials that could be used in its construction. Advances in our understanding of unsaturated soil mechanics can be achieved by using newly available materials and technology in new testing systems. The use of 15 bar porous disks, an internal load cell, an on-specimen axial deformation device, and a closed-loop feedback control system makes this unsaturated soil triaxial cell unique in its ability to measure and characterize unsaturated soil behavior. Behavioral data from this triaxial testing system will form the basis of a more comprehensive and robust soil constitutive model for unsaturated soils.; The unsaturated soil testing system consists of four axis actuators: axial load, pore-water, pore-air, and confining pressure. Each actuator works independently. The development of the system and the layout of the actuators are contained within this document. After completion of the testing system, the system was proof tested using a stainless steel “dummy” specimen at different test conditions. The proof testing allowed for the investigation of the repeatability of the system in measuring a Young's modulus at different testing conditions.; After proof testing of the system, soil samples were tested to evaluate the repeatability of the sample preparation and strength testing. This allowed for an analysis to be made on the ability of the testing system to make repeatable measurements on a soil sample under constant shear rate conditions. In addition to constant shear rate tests, a repeated load test was conducted. The data from this test were analyzed by investigating the effects of the cyclic loading on the pseudo-stiffness, pseudo-strain energy hysteresis, and damage, which includes plastic deformation and may or may not include micro-cracking.