Medium-strain dynamic behavior of fiber-reinforced sand subjected to stress anisotropy

A comprehensive database is established to investigate the behavior of polypropylene fiber reinforced sands under anisotropic stress state in a wide range of strain amplitudes from about 4 × 10⁻⁴% to 1.4 × 10⁻¹%. A fixed-partly fixed Hardin-type resonant column which has a system that allows the specimen to be tested in resonance while maintaining an anisotropic loading path, is utilized. The results show important influence of the fiber content as well as the anisotropic stress state on the normalized modulus reduction and damping increase curves of the reinforced soils. Specifically, the increase of fiber content and stress ratio tend to increase the linearity in the normalized modulus reduction curves. On the other hand, the inclusion of fiber leads to the damping increase curves to shift to greater values, while the stress ratio has an opposite effect. An expression is proposed to predict the normalized shear modulus, as a function of mean effective confining pressure, stress ratio, coefficient of uniformity of the host sand and fiber content. The damping ratio, in a normalized form, is correlated with the normalized shear modulus reduction.