Abstract: The mechanical properties(tensile and shear properties) of roots are pivotal factors affecting the soil and water conservation. The roots of Indigofera amblyantha Craib and Cassia bicapsularis Linn were selected to research the mechanics of slope protection in Karst area. The relationship between the roots’ tensile strength and the shear characteristics of soil-root composite was investigated through indoor tensile test on single root and direct shear test on soil-root composite. The applicability of model WU in Karst area was also analyzed. Results indicated that tensile strength declined overall with the increasing of root diameter; however, such trend differs corresponding to different plant types. The shear characteristic of soil-root composite was jointly affected by tensile strength and friction between soil and roots, of which the former had larger influence; the shear characteristic with thin root and thick root together was better. Modified model WU is applicable to Karst area; but the modification coefficient varies corresponding to different plants. The research findings would lay a good foundation for the ecological restoration and selection and allocation of tree species in Karst area.

Key words: root-soil composite, tensile strength, shear characteristics, model WU, Karst area