Hydraulic Response of Sandy Soil to Fungi-Biopolymer Treatment

¹ Department of Engineering, Durham University, Durham, DH1 3LE; E-mail: smitha.sivadasan@durham.ac.uk
² Department of Engineering, Durham University, Durham, DH1 3LE; E-mail: sravan.muguda-viswanath@durham.ac.uk
³ Center for Bio-mediated and Bio-inspired Geotechnics, Arizona State University, Tempe, 85287-3005; E-mail: emmanuel.salifu@asu.edu
⁴ Center for Bio-mediated and Bio-inspired Geotechnics, Arizona State University, Tempe, 85287-3005; E-mail: hkhodada@asu.edu
⁵ Department of Civil, Chemical and Environmental Engineering, Università di Genova, Genova, 16145; E-mail: agostinowalter.bruno@unige.it
⁶ Department of Civil, Chemical and Environmental Engineering, Università di Genova, Genova, 16145; E-mail: domenico.gallipoli@unige.it

^* Corresponding author: smitha.sivadasan@durham.ac.uk

Abstract

This study explores a novel technique combining biopolymers with fungi to modify the hydraulic behaviour of a sandy soil. Fungi are known for inducing water repellence in soil by producing hydrophobic compounds, while biopolymer hydrogels, such as xanthan, exhibit hydrophilic properties. The combined action of these two agents is hypothesised to create a dynamic system influencing soil-water interactions. Liquid cultures of two saprotrophic fungal strains, Pleurotus eryngii and Pleurotus ostreatus, were separately applied in conjunction with xanthan biopolymer to treat a sandy soil. Fungal mycelia interact with soil particles to form a network that modifies pore structure and water movement pathways. Simultaneously, biopolymers retain water through their hydrogel properties, enhancing the soil’s water- holding capacity. Soil water retention curves (SWRC) were obtained by measuring suction at different drying stages using a WP4c dew point potentiometer for untreated, biopolymer-treated, and fungi- biopolymer-treated soils. Results showed a significant increase in saturated gravimetric water content (θs) and air-entry suction (lower α) for treated soils, allowing increased water retention. A notable reduction in the desaturation rate (n), particularly in fungi-biopolymer-treated soils, indicated reduced moisture loss, which might be critical for limiting shrinkage cracks and maintaining soil strength during dry conditions. Additionally, the suction at residual water content (θr) was found to increase, suggesting prolonged moisture availability in treated soils. These findings suggest potential application of fungi-biopolymer soil treatment for slope stabilisation, pavement subgrade improvement, and erosion control, where retaining moisture and reducing desaturation is crucial and to enhance long-term soil stability under unsaturated conditions.