Formation of shear zones in reinforced sand

A series of tests was conducted in a plane-strain hollow cylindrical testing device. The reinforced sand samples developed wider shear zones than the unreinforced samples and had wider shear zones than similarly reinforced samples tested in direct-shear devices. Shear-zone width increased with increasing reinforcement concentration, reinforcement stiffness, and soil-reinforcement bond strength. Reduction of displacement data to a strain basis reveals that shear, elongational, compressional, and volumetric strains differ in unreinforced and reinforced samples. Dense, dilatant unreinforced sand samples formed narrow shear zones with large strains, whereas the reinforced samples had smaller but more uniform strains distributed throughout the samples. Reorientation of zero-extension shear planes in the reinforced samples limited the range of orientations over which the reinforcements contributed to strength. Overall, the results indicate that reinforced soils deforming in uniform stress fields do not develop narrow shear zones, and, therefore, reinforcement contribution to strength through reorientation and mobilization of bending moments is unlikely under field conditions. To insure that reinforcements are loaded in tension, they should be oriented well within 45 degrees of the minor principal stress.