Mechanical Behavior of a Guabirotuba Formation Soil Stabilized with Lime, Silica Fume, and Polypropylene Fibers

Abstract

Problematic expansive soils from the Guabirotuba Formation present engineering challenges, some of them are low shear strength and high compressibility. This research addresses these problems by evaluating the mechanical behavior of this soil when stabilized with lime-activated silica fume (SF) and reinforced with polypropylene fibers (PPF). The experimental program evaluated mixtures containing 6–12% SF, 9% lime, and 0.5% PPF through unconfined compressive strength (UCS), splitting tensile strength (STS), and consolidated undrained (CU) triaxial tests, alongside scanning electron microscopy (SEM). The main findings reveal that lime is essential to activate the pozzolanic reaction of SF. The lime-SF blends form a Calcium Silicate Hydrate (C–S–H) matrix, significantly increasing UCS and STS. While the inclusion of PPF slightly reduced peak STS and had a negligible effect on peak UCS, its primary contribution was transforming the failure mode from brittle to ductile by bridging micro-cracks and preventing abrupt failure. Furthermore, triaxial testing demonstrated that fiber reinforcement consistently increases effective cohesion (c') but decreases the effective friction angle (ϕ'). SEM analysis corroborated these macroscopic findings, illustrating a densified matrix and strong fiber-matrix adhesion. This study demonstrates that the synergistic use of lime, SF, and PPF enhances the mechanical stability and ductility of Guabirotuba soil, which is relevant in geotechnical engineering applications such as pavement layers, embankments, and earth structures where enhanced post-peak behavior and structural integrity are desirable.