Fungal-induced water repellency in sand

Water infiltration into granular soils and the associated pore water pressure increase and reduction in shear strength can trigger landslides, instability of vertical cuts and failure of retaining walls. Water-repellent soils can reduce infiltration to maintain soil suction. Recent research has demonstrated the creation of synthetic water-repellent soils using chemical methods. This paper investigates a biological treatment for creating water-repellent sand by way of the growth of the fungus Pleurotus ostreatus. Water repellency was assessed using: (a) the water drop penetration test; (b) the molarity of ethanol drop test; and (c) the modified sessile drop method with contact angle (theta) determination by way of image analysis. Fungal-induced water repellency was found to be 'extreme' (theta > 110 degrees) up to 4 weeks and 'severe' (theta > 105 degrees) up to 12 weeks, even with no further supply of moisture or nutrients. A water-repellent layer was formed and maintained in saturated conditions, which is difficult to achieve using chemical methods.