## ABSTRACT

Themost commonly used apparatuses for evaluating the shear behavior of soil are small direct shear box and triaxial apparatus because of the simplicity of their construction and operation (Skempton, 1985). However, these apparatuses are not suitable to determine residual shear strength of slip zone soils containing abundant coarse particles and to simulate the actual landslide conditions due to their limited capacities in respect of shear displacement and large particle size of the specimen. Although the ring shear apparatus is not easy to construct and operate (Bishop et al., 1971), it does have the obvious advantages that the shear displacement can be unlimited without having to stop (Bishop, 1971; Bromhead, 1979; Sassa, 1996). Alternatively, reversal direct shear with intermediate and large shear boxes can also be employed to measure the residual strength of the soils.