Modulus Anisotropy and Shear Stability of Geofiber-Stabilized Sands

A systematic laboratory approach is established to evaluate shear stability or bearing capacity improvement of sand-geofiber stabilization for rapid road and airfield construction. The approach deals with the investigation of directional dependency, anisotropy, and modulus properties and links stability to shear stress levels typically applied on specimens during testing in relation to their strength. An advanced triaxial testing machine referred to as the University of Illinois FastCell is used together with direct shear tests for determining the anisotropic resilient moduli and the strength properties of two geofiber-reinforced sands (poorly and uniformly graded sands) prepared with three 51-mm geofibers: fibrillated, monofilament, and tape. The use of different geofiber types and the various amounts of clay and silt fines present in the sand mixtures significantly affected the recorded horizontal and vertical moduli and the shear stresses at applied stress states. Monofilament-type geofiber stabilization was found to be the most effective, with the recorded highest vertical moduli and the highest shear strength and stability improvement indicated by the lowest shear stress ratios, especially when mixed with 10% to 20% clay. The tape-type geofiber reinforcement generally was not very effective. For the geofiber stabilization of sands to be a viable construction alternative, the sand-geofiber mixtures should contain an optimal amount of fines needed for geofibers to mobilize the shear strength of the mix effectively and thereby improve the shear stability and resistance to permanent deformation.