Internal erosion in hydrophobic and hydrophilic soils

The water repellency of soil occurs when organic matter coats the soil particle surface; this can either happen naturally due to wildfire and fungal growth or be induced by chemical treatments. The internal stability of water-repellent soils subjected to seepage has not been explored in the literature. In this study, the mechanical responses to internal erosion in three synthetic water-repellent soils, treated by different organic matters, were first investigated using a modified stress-controlled triaxial apparatus. The degree of hydrophobicity of the test soils was assessed through the measurement of apparent water contact angle. In each internal erosion test, the cumulative particle loss, deformation and hydraulic conductivity were evaluated. The water-repellent coatings efficiently suppressed the progression of internal erosion at practical hydraulic gradients because of their smaller fluid-solid adhesion. Continuously increasing the hydraulic gradient would finally result in a breakthrough of internal erosion due to the saturation of the hydrophobic soils under high pore-water pressures. Post-erosion contact angle measurements and scanning electron microscopy images confirmed the durability of the three water-repellent coatings against seepage erosion. The findings of this study confirm the potential of applying hydrophobic soils to mitigate internal erosion under normal hydraulic loading conditions.