Mechanical Performance and Water Stability of Gobi Soil Reinforced with Polypropylene Fibers for Photovoltaic Power Station Foundations

The poor engineering properties of Gobi soil, such as low strength and poor water stability, pose challenges for foundations in arid regions, especially large photovoltaic plants. This study examines the effect of polypropylene (PP) fiber reinforcement on Gobi soil from Dabancheng, Xinjiang. Laboratory tests including unconfined compressive strength, direct shear (orthogonal experimental design), slake durability, and scanning electron microscopy were performed to investigate the influences of fiber length (6, 9, 12 mm), fiber content (0.3–1.1% by dry soil mass), and water content (4–12.5%). Results indicate that PP fibers change the failure mode from brittle to ductile. The optimal combination (9 mm fiber length, 0.7% content, and Proctor optimum water content of 10.5% corresponding to maximum dry density) improves cohesion by 122% (reinforcement coefficient K = 2.22). Moreover, fibers alter the disintegration behavior from complete to stable partial disintegration; the 12 h disintegration ratio decreases from 100% to 13% under optimal conditions. Microstructural analysis shows that an appropriate fiber content creates a uniform three-dimensional reinforcing network, enhancing mechanical interlocking and fiber bridging, whereas excessive fiber leads to agglomeration and increased pore connectivity, degrading overall performance. This study provides a low-carbon, sustainable soil stabilization method and practical design parameters for Gobi desert infrastructure.