How Stiffness of Reinforcement Affects the Type of Major Reinforcement Force Developed at Various Orientations in Reinforced Sand?

Reinforced soil is any soil system in which some reinforcing elements called inclusions are placed to improve its mechanical properties. The reinforcement acts by restraining the deformation of the soil mass achieved by soil-reinforcement interface bonding. It results in increased stiffness and consequently the strength by increasing confinement and reducing dilation tendency of the soil mass. Large scale experimental study on soil-reinforcement interaction in the literature supported the conclusion that the improvement in soil strength attained from the bending stiffness of the reinforcement is always small as compared to the improvement obtained from the axial capacity of reinforcement. The objective of the current investigation is to evaluate the effect of relative stiffness of the reinforcement on the type of major reinforcement force developed in the reinforcement at various orientations of reinforcement with respect to shear plane using small-scale direct shear tests. In this study, a series of small size direct shear tests were conducted on clean, poorly graded medium grained sand under undrained condition. Two types of reinforcements of annealed rigid reinforcement binding wire and flexible Geogrid (SGi-100) strips were used of relatively varying stiffnesses. The reinforcements were only embedded in the sand and were not anchored to the shear box at any point. The sand was tested in loose and medium dense states with reinforcement oriented at various angles with the vertical plane. Based on the test results, it was concluded that the attainment of maximum increase in shear strength was observed for specific (optimum) orientations with the vertical for both inward and outward orientations and that the stiffness of reinforcement influenced the optimum orientation of reinforcement corresponding to the attainment of maximum shear strength in terms of both, the composite friction angle as well as the apparent cohesion developed due to reinforcement in the reinforced soil mass.