Laboratory triaxial compression, resonant column, and torsional shear tests were performed to determine both the static and dynamic stress-strain response of sands reinforced with discrete randomly distributed fibers, and to observe the influence of various fiber properties, soil properties, and test variables on soil response. In addition to the experimental program a theoretical model was developed, based on statistical theories of composites, to predict the fiber contribution to strength under static loads.; Randomly distributed fiber inclusions significantly increased the ultimate strength and stiffness of sands under the action of static loads (triaxial compression tests). The increase in strength and stiffness was a function of sand granulometry (i.e., gradation, particle size and shape) and fiber properties (i.e., weight fraction, aspect ratio, and modulus). An increase in gradation and particle angularity of sands, and aspect ratio and modulus of fibers resulted in a higher contribution of fibers to strength. At low confining stresses strength increase was also proportional to the weight fraction or amount of fiber inclusions, up to some limiting content. Thereafter, the strength increase approached an asymptotic upper limit.; The sand-fiber composites had either a curved linear or a bilinear failure envelope with the break or transition to a linear envelope occurring at a threshold confining stress called the "critical confining stress". At confining stresses below critical the fibers slipped during deformation, and at confining stresses above critical the failure envelope of the composite parallels that of sand alone. The magnitude of the critical confining stress decreased with an increase in sand gradation, particle angularity, and fiber aspect ratio; and increased with an increase in fiber modulus. The critical confining stress was insensitive to changes in sand particle size and fiber content.; Randomly distributed fiber inclusions influenced the dynamic behavior of sand with respect to shear modulus and damping. The effect of fiber inclusion was evaluated as a function of shearing strain amplitude, confining stress, prestrain, number of cycles, fiber content, aspect ratio, and modulus. The presence of fibers reduced prestrain effects often observed in unreinforced sands. The increase in dynamic modulus of fiber reinforced sand was decidedly more pronounced at high shearing strain amplitudes. (Abstract shortened with permission of author.)
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