Dynamic Properties of Reinforced Sand

A series of dynamic shear tests was performed on large hollow cylindrical reinforced and unreinforced sand samples. Steel rods were used to reinforce the specimens uniaxially and biaxially. A newly developed test apparatus was used to perform cyclic torsional shear strain control tests with strain amplitudes ranging from $1\times {10}^{-2}\%$ to 7% and frequencies varying between 0.5 Hz and 10 Hz at different levels of confining pressure. Test results indicate that confining pressure and strain level affect the dynamic shear modulus and damping of unreinforced and reinforced sands. Dynamic shear modulus and internal damping were independent of frequency (up to 10 Hz) for both reinforced and unreinforced samples. Reinforcements have no effect on the complex shear modulus of the material up to a strain amplitude of 5%. At large strains (>7%) uniaxial reinforcements inhibited the formation of helical shear bands, which had been observed on the unreinforced specimen. However, vertical shear bands parallel to and equidistant from the reinforcements were observed. Biaxial reinforcements prevented the formation of all rupture surfaces, thus greatly increasing the ductility of the material. The results indicate that the effect of the reinforcements on the dynamic properties of the reinforced soil composite can be ignored when analyzing the dynamic response at small strains, but should be considered when evaluating the dynamic response at larger strains.