Sustainable silty sand reinforcement using stipa tenacissima Fibers: insights from triaxial testing

As a sustainable alternative, natural plant fibre reinforcements offer an economical and environmentally friendly solution for enhancing the mechanical performance of earthen construction materials. This study investigates the use of Stipa Tenacissima (Alfa) plant as inclusions to improve silty sand’s mechanical properties. Initially, unsaturated triaxial tests at a constant water content were conducted on, compacted silty sand soil reinforced with 2% Alfa fibres, enabling the evaluation of the complete stress-strain behaviour while controlling confinement and suction. Alfa fibres, which were either cut into 10 mm stems or milled, were blended with natural silty sand, and specimens were compacted under optimum proctor conditions prior to triaxial shear testing. The results indicate an increase in shear strength of 8-15% and an improvement in stiffness modulus exceeding 50%, together with a notable increase in friction angle. Microstructural interactions analysed using scanning electron microscopy reveal smooth fibre surface morphologies that facilitate physical adhesion and interlocking at the fibre-soil interface. While cut fibres primarily enhance the apparent cohesion, milled fibres are shown to modify the mechanical interlocking with the soil particles and to increase the frictional interaction. These findings present novel perspectives and analysis using Alfa fibres-reinforced soil as a sustainable natural reinforcement material.