Abstract: The weathered granite soil varies significantly from Lüliang mountains to south of the Yangtze river. To comprehensively understand the mechanical properties of weathered granite and evaluate of the engineering properties of subgrade filling in mountains, a series of laboratory tests was performed in this study, including routine soil test, X-ray diffraction test and large-scale triaxial test. The experimental results show that the increase in peak deviatoric stress qf due to an increase in mean stress p is observed as nonlinear under lower confining pressure because of the existence of particle breakage. The relationship between peak stress ratio Mf and state stress ratio Mc is modified on the basis of previous research results. the elastic-plastic constitutive model of compacted granite soil in Lüliang mountains is proposed. Based on the continuity assumption of the isotropic compression-unloading test and the initial shear, combined with the Duncan-Chang model, all the parameters of the proposed constitutive model of weathered soil under the modified strength condition were obtained. After comparing the results of numerical calculation of proposed model with the experimental stress-strain data, it is found that the product of the state stress ratio and peak stress ratio was not constant but the power function of average main stress.

Key words: subgrade engineering, compacted weathered granite soil, large-scale triaxial test, strength characteristics, constitutive model