In this Award project, a series of suction-controlled ring shear tests will be conducted on several identically prepared specimens of compacted sandy silt and silty clay to investigate several key features of unsaturated soil behavior over a whole range of deformations, including pre-failure and post-failure mobility, peak strength, residual strength, threshold deformation levels triggering loss of matric suction (i.e., menisci failure) and time for post-failure menisci regeneration.
Ring shear testing will be accomplished at UT-Arlington, under the direct supervision of PI Hoyos, using a novel ring shear testing apparatus that will be made suitable for testing unsaturated soils under controlled-suction states, over a large range of deformations, via axis-translation technique.
Results from this research Award will provide the following: (1) A more reliable assessment of shear strength parameters for the analysis/design of foundations, embankments, subgrades, slopes and earth retaining walls resting on or made of unsaturated soils; (2) A better understanding of the mechanisms governing long-runout landslides triggered by rainfalls, such as the recent slope failures in La Conchita, California; (3) A more accurate identification of threshold strain levels causing considerable decrease in unsaturated soil strength during small-to-large strain shearing; (4) A better assessment of the loss of suction effects (menisci failure) during large-strain shearing, and; (5) A better understanding of the influence of cyclic wetting-drying on stress-strain-strength response of unsaturated soils.
The suction-controlled ring shear testing apparatus to be developed herein will be the first of its kind to ever be implemented at any geotechnical research institution in the US, and will constitute a major advancement in the state-of-the-art of unsaturated soil testing. The apparatus will facilitate the early exposure of civil engineering graduates to basic and advanced concepts of soil mechanics for unsaturated soils and its applicability in the analysis and design of geotechnical infrastructure resting on unsaturated ground.
This Award will also promote partnerships between UTA and other researchers, practitioners, and private instrument developers, worldwide, who are interested in the advancement of the unsaturated soil mechanics discipline. Potential collaborative efforts have already been devised by PI Hoyos with several colleagues at different universities in the U.S., the E.U., and South America.
