Abstract: Many experiments are carried out to study strength of expansive soil reinforced by polypropylene fiber with different lengths and weight ratios of fiber to dry soil (0.0%, 0.1%, 0.2%, 0.3% and 0.4%), respectively. The results show that the shear strength of expansive soil is enhanced significantly by adding fiber, and the unconfined compressive strength increases dramatically with the increase of fiber contents. While the fiber content exceeds the optimal content 0.3%, the unconfined compressive strength and the shear strength all decrease. Under the condition of the same fiber content, the strength of expansive soil also increases significantly with the increase of fiber length. Polypropylene fiber can also improve the peak strength and fracture toughness of expansive soil, delay the destruction of expansive soil. The study results provide a useful method for improvement of expansive soil.

Key words: optimal water content, expansive soils, polypropylene fiber, shear strength, unconfined compressive strength