Abstract: A series of tensile tests was conducted on gravelly soil based on a new self-developed soil tensile device. The different gravel contents and fiber contents were considered in the test. It is found that the tensile strength of gravelly soil decreases with the increase of gravel content, and the tensile strength and ultimate tensile strain of gravelly soil increases significantly after polypropylene fiber is added. The tensile strength and ultimate tensile strain of fiber-reinforced gravelly soil are positively correlated with the fiber content. However, as the gravel content in the gravelly soil increases, the effect of fiber incorporation on its tensile strength is significantly reduced. Scanning electron microscope analysis shows that the friction of interface between the fiber and the soil particle is the main reason for the increase of the tensile strength of the fiber-reinforced gravelly soil. For the pure clay specimen with a gravel content of 0%, the tensile strength of the soil is dramatically improved because there are only type-I fibers at the fiber/soil particle interface. As the gravel content increases, the proportion of type-II fibers at the fiber/soil particle/gravel interface increases, and the effect of fiber incorporation on the improvement of its tensile strength is markedly reduced. Finally, based on the test results of 60 specimens, a multivariate regression model for the tensile strength of fiber-reinforced gravelly soil is proposed, which can quickly predict the tensile strength of gravelly soil with different gravel contents and fiber contents. The test results can provide references for the anti-cracking design of core wall of high earth core wall dams.

Key words: gravelly soil, polypropylene fiber, tensile strength, ultimate tensile strain, microscopic mechanism