Abstract: In this paper, the influence of coarse grains (d_s>0.5 mm) on the engineering properties of weathered granite soils and the calculation method of liquid index of weathered granite soil are discussed. The correlation between the liquid index I_L and the standard penetration test blow count number N is studied. The liquid index value of the boundary point of the state of weathered granite soil is also developed. Two comprehensive classification methods of weathered granite soils are proposed: namely, simple synthesis method and comprehensive index method. These methods are also compared with the single N value classification method. The application of these two methods is demonstrated by an engineering case history.

Key words: coarse grains, weathered granite soil, liquidity index, standard penetration test blow counts, state boundary