Strength, Stiffness and Radial Anisotropy of Compacted Silty Sand Under Suction-Controlled Axisymmetric Shearing

Abstract

A thorough analysis of strength, stiffness, and stress-induced anisotropy of statically compacted silty sand is presented based on results from a comprehensive suction-controlled (drained) triaxial test program. Induced soil suction values, via either axis-translation or relative humidity techniques, ranged between 0.05 to 300 MPa, with net confining pressures varying from 100 to 300 kPa. A relatively simple model/equation for peak friction angle (ϕpeak), over the entire test suction and net confinement range, is presented. As expected, peak strength response to suction-controlled monotonic shearing is influenced by the level of suction and net confining pressure, as well as the amount of dilatancy experienced by the silty sand. The nonlinear nature of the variation of deviator stress at peak and critical state conditions, with degree of saturation, was fitted reasonably well via fourth order and second order polynomial equations, respectively. A thorough analysis and modeling of stress-dilatancy behavior is presented in a companion paper. Finally, the inherent-anisotropy observed in the original soil fabric, as well as the stress induced-anisotropy observed in the sheared samples, are discussed based on results from suction-controlled isotropic consolidation and axisymmetric shearing, respectively; including the effect of suction on the rate of degradation of stiffness (moduli) of compacted silty sand under monotonic shearing.