| Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world. When liquefaction happens, liquefied soil loses the ability to support foundations for buildings and bridges, exerts higher pressure on retaining walls and cause them to tilt or slide. Hence, it is of great importance to understand the cyclic stress-strain behavior of soil.; Cyclic behavior of pavement materials under traffic loading is another challenging task for geotechnical engineers. A typical example is railroad ballast. The ballast is used to fill in irregular surface topology, distribute and transfer loads from a surface structure or system to the subgrades or subsoils as uniformly and widely as possible in order to provide stable and stiff long-term embankment support for railways. The performance of modern high-speed trains relies heavily on the dynamics interaction behavior of the vehicle-support system. Thus, it is of special interest to determine the over characteristics and constitutive properties of the ballast and to ensure stable and long-lasting properties for such a material that is not homogeneous.; The research focuses on the development of a cyclic constitutive model based on fuzzy set concepts, its numerical integration, and finite element implementation as well. The concept of elasto-plastic constitutive modeling in terms of fuzzy set terminology was first introduced by Klisinski (1988). Unlike conventional elasto-plastic hardening models, the fuzzy set model is physically intuitive and easy to visualize. It provides analytical and simple geometrical interpretation to formulate hardening, hysteresis features, material memory, and kinematic mechanisms without invoking a complex analytical formulations in terms of kinematic hardening rules.; The cyclic constitutive model developed in this study accounts for: realistic stress-strain behavior under repeated load cycles, nonlinear dilatancy behavior, material memory, accurate reverse loading features, critical state soil mechanics concepts, density and mean effective stress dependence, features concerning long-term cyclic effects (fatigue, damage, and shakedown), and non-proportional loading. Finally, the implicit integration scheme for the fuzzy set plasticity model is also described and implemented in a finite element analysis computer code. The long-term effect of granular materials under repeated loading condition is examined, and a model is developed to capture the permanent strains at corresponding number of cycles. |
