Postcyclic Degradation of Strength and Stiffness for Low Plasticity Silt

Stress-controlled undrained cyclic triaxial tests followed by strain-controlled monotonic compressive shear tests were carried out on normally consolidated and overconsolidated reconstituted Keuper Marl silt to investigate the strength and stiffness degradation characteristics of a low plasticity silt. Special attention was paid to the changes in undrained strength and deformation modulus after undrained cyclic loading. It was observed that cyclic degradation in stiffness for low plasticity silt is more marked than that of strength, and this tendency increases with increasing overconsolidation ratio. It was found that a previously proposed model for predicting postcyclic degradation in strength and stiffness of normally consolidated fine-grained soils could be applied to that of overconsolidated silt but not however to the postcyclic degradation in Youngʹs modulus. Thus, an attempt was made to correlate postcyclic degradation of overconsolidated silt to the equivalent cyclic shear strain instead of the normalized excess pore pressure. It was concluded that cyclic shear strain was a better parameter than cyclic-induced excess pore pressure for correlating the postcyclic stiffness degradation not only for normally consolidated but also for overconsolidated silt.