Failure mode and genesis of bare dispersive soil slope in the cold dry region: insights from Southwest Songnen Plain, China

Dispersive soil features rapid disintegration characteristic while interacting with liquid water, which is attributed to the chief culprit for the failure of many earthen infrastructures worldwide. How to quickly identify such a problematic soil in the field relies on the prior knowledge of its failure mode. Take the seasonally frozen semiarid southwest Songnen Plain as investigation background, in this study, five typical failure modes on bare dispersive soil slope are sorted out, including soluble salt crystallization, rill erosion, relaxation tension fissure-associated collapse, subsurface suffosion, and gully erosion, and their formation and evolution features are analyzed. We figured that the silt-dominant soil composition governs the dispersity to a great extent, and the existence of high percentage of sodium ion contributes to reduce the cementation strength of clay particles to silt and sand particles in the presence of water. In addition, analyses indicate that rainfall is the direct trigger factor for failure, and fissures induced by freeze-thaw and dry-wet cycles speed up the water infiltration, enlarge the soil-water interaction surface, and aggravate the bare slope soil destruction in the final. Practices suggest that the adoption of water isolation measures or enhancing cementation strength between soil particles via mixing additives are core failure prevention principles of bare dispersive soil slope.