Failure of fiber-reinforced granular soils

Short fibers have been tried in the past few years as a soil-improvement admixture (reinforcement), yet no failure criteria for fiber-reinforced soils, consistent with numerical methods for solving boundary-value problems, are available. An attempt at deriving the limit condition for a fiber-reinforced granular soil is presented. An energy-based homogenization scheme is used to arrive at the macroscopic failure stress of the fibrous granular composite. A piecewise closed-form failure criterion is derived. The internal friction angle is used to quantify the strength of the granular matrix, and the fibers are characterized by volumetric concentration, aspect ratio, yield point, and the fiber-soil interface friction angle. Laboratory tests on specimens with low fiber content indicate a good agreement of the model predictions with the actual test results.