中文摘要：

干密度和饱和度是影响非饱和膨胀土强度和变形特性的重要因素。为研究干密度和饱和度对非饱和膨胀土抗剪强度的影响,以南阳膨胀土为试验材料,对不同饱和度和干密度的南阳膨胀土的压实样进行直剪试验,得到了不同干密度及饱和度下的抗剪强度;利用滤纸法试验测得了南阳膨胀土在不同初始干密度下的土水特征曲线,并利用Fredlund-Xing方程进行全吸力范围内的拟合。通过土-水特征曲线将饱和度换算成吸力,得到了不同密度和吸力下南阳膨胀土的抗剪强度。结果表明：低吸力范围内非饱和膨胀土的强度随吸力的增大而增大;而高吸力时随着吸力的增大,土的强度变化趋势与干密度和应力大小有关,竖向压力较大和干密度较小时,强度随吸力增大而增大。

英文摘要：

Dry density and degree of saturation are important factors that affect the strength and deformation of unsaturated expansive soil. In order to study the effects of dry density and degree of saturation on the shear strength of expansive soil,Nanyang expansive soil was taken as a testing material,and direct shear tests on the soil with different degrees of saturation and dry densities were carried out. Filter paper method was used to obtain the soil-water characteristic curves of the soil with different initial dry densities,and Fredlund-Xing＇s equation was used to simulate the soil-water characteristic curves in full suction range. According to the conversion of degree of saturation and suction by the fitting soil-water characteristic curves,the shear strength of the soil with different densities and suction were obtained. The results showed that the strength of Nanyang expansive soil increased with increasing suction in low suction range. In high suction range,the change in strength was related with dry density and stress,and the strength increased with increasing the suction for higher vertical pressure and lower dry density.