The long-term performance of geo-structures and energy-related geosystems depends on the soil response to all kinds of repetitive loads. These include stress cycles associated with wind, waves, and traffic, cyclic changes in pore fluid chemistry, thermal cycles, drying and wetting sequences, freeze-thaw cycles, and repetitive changes in pore water pressure. This thesis explores the mechanical response of soils (sands-to-fines) subjected to repetitive loading under various boundary conditions. Experimental studies involve various repetitive loading frames. In most cases, the vertical deformation and the shear wave velocity are continuously monitored during ten thousand repetitive loading cycles. The plastic strain accumulation is a function of the initial void ratio, the maximum stress obliquity, and the cyclic stress amplitude; data gathered in this experimental program suggest simple procedures to estimate the potential deformation geostructures may experience when subjected to repetitive mechanical loads. Experimental results show that the void ratio evolves towards the terminal void ratio as the number of load cycles increases. Furthermore, data analyses reveal that the fines in soil mixtures have a marked effect on repetitive loading-induced asymptotic contraction and small strain sediment stiffness even when the fines fraction is significantly lower than the 50% used in the Unified Soil Classification System USCS. Therefore, a Revised Soil Classification System RSCS is proposed herein for engineering purposes by providing a physics-inspired, data-driven approach that benefits from the experience gained in our discipline since the inception of current soil classification systems.
Dr. J. Carlos Santamarina
Dr. J. David Frost, Dr. Susan E. Burns, Dr. Sheng Dai, Dr. Guillermo Goldsztein (MATH)