Strength and deformation behavior of the Yellow River silt under triaxial drained condition considering characteristic states

Currently, the application of the Yellow River silt in subgrade, especially in expressway subgrade, has not been widely promoted. The main reason is that the research on the mechanical characteristics of the Yellow River silt used for subgrade filling is extremely limited. In this study, the static shear test of the Yellow River silt under drained condition was carried out using Global Digital Systems (GDS) triaxial apparatus, and the effects of confining pressure, relative density and shear rate on the strength and deformation behavior of the Yellow River silt were investigated. The cohesive force of the Yellow River silt is low, and the friction angle is the main factor determining the shear strength. Friction angle at phase transformation state φ_pt, friction angle at peak state φ_ps, friction angle at critical state φ_cs, were obtained via the observation on the evolution law of mobilized friction angle during the whole shearing process. The friction angles corresponding to three different characteristic states have the following magnitude relationship, namely φ_ps > φ_cs > φ_pt. The strength parameters for low-grade subgrade and highgrade subgrade were chosen to be 29.33° and 33.75°. The critical state line (CSL), envelop of phase transformation (EOP), and envelop of dilatancy (EOD) for three different characteristic states were determined. The critical stress ratio M, the phase transformation stress ratio M_pt and the dilatancy stress ratio M_d of the Yellow River silt are 1.199, 1.235, 1.152, respectively. These results provide a basis for the mechanical analysis of the Yellow River silt subgrades and the subsequent establishment of dynamic constitutive model of the Yellow River silt.