Effect of deviator stress on the initiation of suffusion

Stress state has significant influence on the initiation of suffusion, whereas the effect of deviator stress has not been investigated thoroughly. This paper presented a series of hydro-mechanical coupling suffusion tests on four internally unstable cohesionless soils to investigate the effect of deviator stress on the initiation of suffusion. A dimensionless parameter, shear stress ratio, which is the ratio of deviator stress to mean effective stress, was introduced to denote the variation of deviator stress under the same confining pressure. The results indicate that the deviator stress or shear stress ratio has significant influence on the initiation of suffusion. The relationship between shear stress ratio and critical hydraulic gradient initiating suffusion is piecewise linear, and there is a critical shear stress ratio for different internally unstable soils. The critical hydraulic gradient first linearly increases with the increase in shear stress ratio, and it reaches the maximum value at the critical shear stress ratio, then it decreases suddenly and significantly, finally it increases linearly again with the increase in shear stress ratio. The critical shear stress ratio is not the division between volumetric contraction and dilation, but it can be determined by a consolidated drained triaxial compression test. Based on the characteristic of the relationship between shear stress ratio and critical hydraulic gradient, an empirical method determining the critical hydraulic gradients under complex stress states was developed.