Following the investigation of the shear behavior of the artificial soilmixtures presented in Chapter 4, one further step was taken in this chapter to present the shearing behavior of the natural slip zone soils in the TGP area. A total of 33 samples obtained from three landslide slip zones with different mineralogical composition and particle size distribution were tested using the large ring shear apparatus, reaching shear displacements of up to 160 cm at three different shearing rates (i.e. 0.1mm/sec, 1.0mm/sec and 10mm/sec). Both residual and peak strength of these soils were examined in relation to soil properties and testing conditions. Soil properties, such as mineralogy, plastic limit, liquid limit and plasticity index, grain size distribution, which were routinely used for studying cohesive soils, and those widely used for cohesionless soils, such as particle shape, particle size and particle roughness, were all taken into account. The aim was to examine the effects of these factors on the shear behavior and to establish the shear mode of the slip zone soils in the TGP area.