Abstract: Based on structure nature, firstly, the granularity constituent, micro-structure and physico-mechanical parameters of granite residual soil (GRS) are studied; secondly, the shortages of the existing classification methods are analyzed; thirdly, the granularity quantitatively affecting on classification is studied; so that, main conclusions are drawn as follows: GRS is a mixed-particle soil or a mixture of coarse and fine soil particles, so both coarse and fine faction should be comprehensively considered for the classification; the physico-mechanical parameters are affected in varying degrees by disturbance, in which, the cohesive force and compression coefficient (or compression modulus) are much more serious than the porosity ratio, internal friction angle and plastic index, so the latter is suitable for the classification study, but the former isn’t; Soil Engineering Classification Criterion (GBJ145－90) is suitable for GRS on classifying coarse and fine soils; the content 35 % of granule over 0.5 mm is the dividing line for granularity effects. Finally, a new classification method or comprehensive classification method is advanced. The new method will contribute to study in depth on engineering natures of GRS.

Key words: granite residual soil, mixed-particle soil, structural nature, comprehensive classification method