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Abstract In order to discuss the relationship between the unsaturated shear strength and the soil-water characteristic curve(SWCC) of Jingmen intact，compacted and lime-treated expansive soils，nonlinear curve fittings are carried out to fit the experimental data of SWCC based on Fredlund-Xing model，and the correlation analysis is presented for the shear strength results of the suction-controlled consolidated-drained triaxial compression tests based on the Fredlund equation(1996) for predicting shear strength with respect to SWCC. The results show that the experimental data of SWCC for the three types of expansive soils can be well fitted by the Fredlund-Xing model. The air entry value of Jingmen intact，compacted and lime-treated expansive soils is 210，68 and 18 kPa respectively. For the water stability，the lime-treated expansive soil is the best，followed by the compacted one，and the intact one is the worst；each of the residual suction of the three types of expansive soils can be taken as 3 000 kPa. For the three types of expansive soils，neither the effective angle of shearing resistance(j¢) nor the angle of shearing resistance with respect to matric suction(jb) is constant，where j¢ is influenced by the matric suction，and jb is influenced by matric suction and stress state，which means the Mohr-Coulomb failure surface is bidirectional bending. The unsaturated shear strength of the three types of expansive soils can be well predicted by the Fredlund equation over a wide matric suction；and the soil parameter κ of Jingmen intact，compacted and lime-treated expansive soils is 2.4，2.7，3.4，respectively. The main causation of the difference between the predicted shear strength；and the test results show that the Fredlund equation does not consider that jb is influenced by stress state.
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Received: 27 November 2009
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