Effect of undrained creep on instability behaviour of loose sand

Prefailure instability in the form of a runway deformation can occur for loose sand under undrained conditions. The effect of creep on the instability behaviour of loose sand is studied experimentally in this note. Previous studies have established that instability can only occur when the stress state is above the instability line. However, if creep is allowed to develop under undrained conditions, instability can still possibly occur even when the stress state at which creep develops is below the instability line. A boundary that specifies the condition in which instability may be induced by undrained creep is determined based on the experimental data.