Rapid Stabilization of Highly Expansive Clays: Synergistic Approach with Polyurethane and Waste Tire Textile Fiber for Enhanced Mechanical Properties

Highly expansive clays pose significant threats to the stability of structures built on them due to their specific physicochemical characteristics. Addressing these challenges within a limited time frame can be one of the primary geotechnical considerations in some projects. This study explores the utilization of a sustainable and eco-friendly approach, integrating polyurethane (PU) and waste tire textile fiber (WTTF), for the rapid treatment process of highly expansive clays. Various contents of PU (up to 10%) were initially mixed with the parent clayey soil at the corresponding optimum moisture content (OMC). All mixtures were cured for 3 h, 1 day, and 3 days, and then subjected to a comprehensive series of unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), and swelling tests as well as various microstructural analyses. Subsequently, the clay soil samples treated with the optimum PU dosage were reinforced by WTTFs in a wide range of contents (0%, 0.5%, 1%, 1.5%, 2%, and 4%) and lengths (1, 2, and 3 cm) and then subjected to similar mechanical tests. The results show that the strength and stiffness properties of highly expansive clays significantly increased with the addition of PU up to an optimum content of 8%. Moreover, the incorporation of WTTF into the PU-stabilized samples led to remarkable improvements in both the strength and ductility characteristics, surpassing those achieved solely with the PU additive. In particular, the inclusion of 2% WTTF with a length of 2 cm provided optimal performance and provided PU-treated soil with superb strength and ductility. The findings also indicate that the synergistic application of PU and WTTF at a targeted depth of 0.5–1 m can effectively control the swelling potential.