Cyclic and post-cyclic instability of unsaturated non-plastic silt

Cyclic and post-cyclic behavior of an unsaturated silt was investigated to elucidate the degradation mechanism during the process approaching from unsaturated condition to saturated one. The following was obtained from the test results. i) The apparent cohesion force was observed during undrained compression tests on unsaturated silt. However, the magnitude of the apparent cohesion decreases with increasing the degree of saturation. ii) Cyclic strength of unsaturated silt decreases with increasing the degree of saturation. However, this tendency is more marked in sand than that in silt. This is attributable to the fact that silt pose a higher suction than that in sand and this higher suction in unsaturated silt disappears more markedly than in unsaturated sand. iii) Post-cyclic degradation in undrained compressive strength and stiffness decreases with increasing excess pore water pressures generated during undrained cyclic loading. The severity of strength and stiffness degradation depends on the degree of saturation.