Effect of suction on the instability of silty sand under constant shear drained testing

The stability of the slopes is critical for ensuring the safety and longevity of soil structures including, embankments, stockpiles, and retaining walls. Many of these soil structures remain in partially saturated conditions throughout their design life. In such cases, the matric suction ( Ψ m ) becomes a key parameter influencing the stability of the soil. However, Ψ m in soil varies during the water infiltration, leading to potential instability and collapse. To better understand this behaviour, constant shear drained (CSD) tests, which replicate the stress path experienced by the soil during water infiltration were conducted. A series of CSD experiments on silty sand in the partially saturated state was performed to examine the effects of Ψ m on the onset of instability. The results show that the onset of instability in silty sand increases with Ψ m . The volume change behaviour for partially saturated silty sand exhibits dilative behaviour compared to the fully saturated condition for the density considered in this study. Moreover, the methodology for the onset of instability for fully saturated soils was extended to analyse the onset of instability in partially saturated soil. A unique onset of instability was obtained for partially saturated soil using various methods considered for this study.