Abstract:
This thesis presented the study of engineering properties of Decomposed Granite reinforced with Vetiver grass root focusing on the shear strength of soil and root tensile strength affecting shear strength of soil. The study of shear strength comprised of direct shear test of both reinforced soil and non-reinforced soil in laboratory concerning effects of growing periods. The study of root tensile strength was carried out by considering effects of root diameter and growing periods in laboratory. In laboratory, the grass were planted in PVC cylinder with the diameter of 15 cm. Tensile test of vetiver root and direct shear test of soil were undergone in laboratory for growing periods of 2, 4, 6, 8, and 10 months, respectively. From test results, the growing rate of Srilanka Vetiveria Zizanioided Nash Roots and Loei Vertiveria Nemoralis A.Camus Roots have direst proportion to the growing period which range between 154 %to 1356% and 156% to 1480% respectively. The tensile resistance is directly proportional to root diameter. The ultimate tensile strength is indirectly proportional to root diameter as well which tensile strength and modulus of elasticity is indirectly proportional to root diameter. In comparing between same root diameter of Srilanka Vetiveria Zizanioided Nash Roots and Loei Vertiveria Nemoralis A.Camus Roots, it was found that tensile force and tensile strength of Loei Vertiveria Nemoralis A.Camus Roots are more than Srilanka Vetiveria Zizanioided Nash Roots , but modulus of elasticity of Srilanka Vetiveria Zizanioided Nash Roots are more than Loei Vertiveria Nemoralis A.Camus Roots. Shear strength of soil reinforcement in laboratory is depended on the ratio or root cross sectional area to soil cross section and growing period ,have tendency to increase after 4 mounts.