It is imperative to study the engineering characteristics of residual soils which is weathered violently under large deformation. Making use of the test features of ring shear apparatus

the change law of shear strength of soils under large shear displacement can be studied. The experimental determination of residual strength and peak strength indexes of residual soil is conducted by ring shear tests. Test data are analyzed through arrangement and comparison. The relationship between water content and residual strength proved the existence of property of watering softening under large deformation. The character of strain softening of residual soil is analyzed by strain threshold

that is

various shear strengths should be different with various shear displacements. Specifically

the peak strength corresponding to the range of strain is between 0.02 and 0.06 while the residual strength corresponding to the range of strain is between 0.06 and 0.20. Besides

the results also indicate that the residual strength of residual soil is directly affected by the difference of mineral composition

which is the internal cause of inhomogeneity of residual soils