MODELLING OF CYCLIC BEHAVIOR OF SATURATED MONTEREY NUMBER 0/30 SAND (LIQUEFACTION, CYCLIC TRIAXIAL TESTS, STRESS-STRAIN, PORE WATER PRESSURE).

摘要

Cyclic liquefaction on saturated loose sand is associated with reduced cyclic shear strength and decreased stiffness of the sand by excess pore water pressure generated by shocks such as earthquakes. The resulting ground failure generally takes the form of excess settlement, bearing capacity failure, sand blow, flow slide, or similar phenomena. Any sandy soil can develop cyclic mobility, if cyclic stresses are large enough. However, liquefaction is most likely in saturated fine, clean, loose, uniform sand.; To analyze the response of earth structures or soil deposits to shocks like earthquakes requires a mathematical model representation of soil behavior. The model should be capable of simulating the gradual reduction of shear strength, loss of stiffness, accumulation of pore water pressure and deformation of saturated soil during cyclic loading. This thesis presents the results of a static and cyclic triaxial test program on saturated sand and the mathematical model proposed to simulate the static and cyclic triaxial response of the sand.; First, critically examined are the results of static and cyclic triaxial tests involving compression loading, extension loading, and stress reversal loading for the characteristics of strength reduction, stiffness degradation, excess pore water pressure accumulation, and hardening and softening behaviors. The particle rearrangement and the tendency of densification of saturated sand are believed to be responsible for the above-mentioned phenomena. In this test program, saturated Monterey No. 0/30 sand was used.; Based on the response characteristics observed in the static and cyclic triaxial tests, a mathematical model is developed to simulate the response. The model involves the concepts of equi-strain lines in stress space, shear-induced pore water pressure, and dilatant elasticity. The model is simple; all equations involved are reversible in stress and strain; the simulation process is nonincremental, and, thus, no iteration procedure is needed. The model successfully simulates the undrained stress-controlled and strain-controlled cyclic triaxial behavior of saturated Monterey No. 0/30 sand as well as the static triaxial behavior of the sand.