Stiffness degradation of coarse and fine sand mixtures due to cyclic loading

Abstract

Abstract A large earthquake may lead to the generation of excess pore water pressure in soils. With the increasement of excess pore water pressure, the stiffness degradation may lead to noticeable levels of deformation even without liquefaction. More than 20 cyclic triaxial tests were conducted in this study to investigate the stiffness degradation of soils during loading under an undrained condition. These tests involved four variables: cyclic stress ratio, void ratio, loading frequency, and fine particle concentration. The test results indicated that the average axial strain in the first cycle determined the degradation path of soils. The average axial strain in the first cycle changed in response to the variation in void ratio and cyclic stress ratio. By adding fine particles, we found that the equivalent granular void ratio was more effective in modeling the collected data on the average axial strain in the first cycle than the void ratio was. The relationships among average axial strain in the first cycle, cyclic stress ratio, and equivalent granular void ratio were investigated. Excess pore water pressure is a factor that is usually considered to weaken soils. A simple stiffness degradation model was proposed as a function of the excess pore water pressure ratio. This model was further transformed as a function of the factor of safety against liquefaction. The average axial strain in the first cycle and the stiffness degradation ratio were used to evaluate the developing axial strain in the degradation process.