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Abstract Lots of geotechnical engineering problems are closely related to the anisotropic behavior of unsaturated soils. In this paper, suction-controlled, consolidated, drained triaxial shear tests were conducted on clay under unsaturated conditions. For unsaturated clay, the effects of matrix suction (suctions of 30 kPa, 100 kPa, and 200 kPa), initial stress ratio (R1 = 0. 5 and 1) and subsequent stress ratio (R2 = 1, 2 and 3) on the hydro-mechanical behavior were studied, and the evolution of water retention, stress-induced anisotropy characteristics and critical state parameters under different stress paths were obtained. The stress path exerted a substantial influence on the water retention capacity of the clay, and the initial stress ratio was found to be the determining factor for the air entry value of the clay. Under identical initial stress ratio conditions, the water retention capacity of the clay was observed to diminish commensurately with an increase in the subsequent stress ratio. As suction increases and subsequent stress ratios escalate, the specimen transitions from a state of shear shrinkage to dilatancy, the peak shear strength (qf) and initial stress ratio change from negatively to positively correlated, while the critical state volumetric strain (\ (ₕ^{c}\) ) and initial stress ratio are positively to negatively correlated, and the anisotropy of unsaturated clay undergoes a transformation from negative correlation to positive correlation with the subsequent stress ratio. The critical state saturation (\ (Sₑ^{c}\) ) exhibits a negative correlation with the initial stress ratio and subsequent stress ratio. Under the same stress path and different matrix suctions, there exists a unique critical state line in the p'-q plane passing through the origin, with its slope is critical state effective stress ratio (M'). The initial stress ratio determines the range of variation for the M' value, which is positively correlated with the subsequent stress ratio.
Su et al. (Wed,) studied this question.