A theoretical internal stability classification chart with considerations of soil density and stress

Recent research found that stress state and relative density could influence internal instability significantly, however, current internal stability criteria were material-specific, and the effect of stress and density were not accounted for. Furthermore, current criteria were drawn from the dense soils, which could lead to unconservative assessments of loose soils. Because of this, this paper proposes a theoretical internal stability classification chart with considerations of soil density and applied stress. Based on soil fabric and force transmission, a texture triangle chart for three-component mixtures made up of coarse grains, fine grains, and voids was proposed through theoretical analysis of the void filling mechanism in coarse grains. The proposed chart demarcated the boundary between internally stable and unstable granular soils and the boundary between suffusion and suffosion phenomena for internally unstable granular soils. The classification chart relied on identifications of maximum and minimum porosities that coarse grains, fine grains, and coarse–fine mixtures may attain. The internal stability of coarse–fine mixtures with various densification levels could be evaluated by plotting their position in the proposed texture triangle chart. The influence of applied stress on internal stability could also be evaluated in this proposed chart by assessing the changes in volumetric strain.