Hydro-mechanical behaviour of bio-cemented sediments reinforced with posidonia oceanica fibres

The reuse of dredged or waste sediments in geotechnical engineering aligns with sustainability goals. However, these sediments often exhibit high compressibility upon loading, significant shrinkage upon drying, and low shear strength, necessitating effective stabilisation and reinforcement strategies. At the same time, natural lignocellulosic fibres, such as Posidonia Oceanica (PO), are well known for their mechanical benefits, yet their influence on key hydraulic properties, including water retention properties and pore structure, remains insufficiently explored. This study investigates the hydro-mechanical performance of dredged sediments (DS) treated with marine-derived biomaterials: mussel shell (MS) powder as a partial cement (T) substitute, and PO fibres for hydro-mechanical reinforcement. Three mixtures were tested on DS treated with: (i) 12% w/w cement and 4% w/w MS powder (DS12T4MS), (ii) 12% w/w cement, 4% w/w MS powder, and 1% w/w PO fibres (DS12T4MS1PO), and (iii) 16% w/w cement alone (DS16T). The water retention curve was determined with a chilled-mirror dewpoint psychrometer, while microstructural changes were assessed using scanning electron microscopy (SEM). Results show that MS powder improves structural densification of the mixture by filling macropores, increasing shear strength and the airentry value (AEV), and consequently enhancing, the water retention capacity at low suctions. In contrast, PO fibres, due to their lumen-rich morphology, induce an increase in macropores that facilitates their desaturation, and decreases the AEV. The combined use of MS and PO offers complementary benefits, enabling performance-based design of sediment composites tailored to specific hydro-mechanical requirements. This contributes to advancing sustainable ground improvement solutions using marine waste materials.