Rock and Soil Mechanics ›› 2023, Vol. 44 ›› Issue (10): 2809-2820.doi: 10.16285/j.rsm.2023.5392

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Evolution model of unsaturated shear strength indices over a wide range of saturation

ZHAO Yu-xin1, LI Xu1, ZHAO Hong-fen2, 3, LIU Yan1   

  1. 1. Key Laboratory of Urban Underground Engineering of Ministry of Education, Beijing Jiaotong University, Beijing 100044, China 2. School of Civil Engineering, Sun Yat-sen University, Zhuhai, Guangdong 519082, China 3. Southern Marine Science and Engineering Guangdong Laboratory, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
  • Online:2023-10-21 Published:2023-12-30
  • Supported by:
    the National Natural Science Foundation of China (51979002, 52279121, 52278325).

Abstract: The variation of shear strength indices of unsaturated soil with the degree of saturation Sr is complicated. In order to describe the experimental phenomena, the existing literature on the variations of cohesion, internal friction angle and dilation angle with Sr is analyzed. The results show that: (1) When Sr decreases and the pore water gradually transits from capillary water to adsorbed water, the friction angle increases. The turning point can be defined as critical degree of saturation Src. When Sr is greater than Src, the value of the friction angle is constant; when Sr is less than Src, the friction angle increases linearly with the decreasing Sr, and the extended Mohr-Coulomb criterion is no longer applicable. (2) The “peak effect” exists in the process of cohesion changing with Sr, i.e. the cohesion first increases exponentially with the decrease of Sr and reaches its maximum when Sr reaches Srv corresponding to the peak unsaturated strength, and then decreases, which is the main reason for the “peak effect”. (3) A linear model can describe how the dilation angle increases with the decrease of Sr and vertical load. In addition, an unsaturated shear strength model over a wide Sr range is proposed. The proposed model is verified by the comparisons between the published experimental data and the predicted results of the proposed and existing equations, which illustrate the superiority of the proposed model.

Key words: unsaturated soil, degree of saturation, shear strength indices, unsaturated shear strength model