Dynamic Response of Sand Reinforced with Randomly Distributed Fibers

Laboratory resonant-column and torsional shear tests are performed to determine the dynamic response (i.e., shear modulus and damping) of sands reinforced with discrete, randomly distributed fibers. The effect of fiber inclusion is evaluated as a function of shearing-strain amplitude, confining stress, prestrain, number of cycles, fiber content, aspect ratio, and modulus. The dynamic modulus increases with increasing fiber aspect ratio, modulus, and with increasing fiber content to a limiting weight fraction. The presence of fibers reduces prestrain effects often observed in unreinforced sands. The increase in dynamic modulus of fiber-reinforced sand is decidedly more pronounced at high shearing-strain amplitudes. The maximum percentage increase in modulus as a result of fiber inclusions occurred over a narrow range of confining stresses from 3 to 10 psi (21 to 48 kPa). Damping was less affected by the inclusion of fibers tan shear modulus. The dynamic response of sands reinforced with vertically oriented fibers is very similar to that of randomly distributed fibers.