采用常规直剪仪对干湿循环作用下的非饱和膨胀土进行了不排水剪切试验，获得了不同含水率试样的总应力抗剪强度指标，可采用总黏聚力和总内摩擦角来反映土体的不排水抗剪性能；采用滤纸法测定了剪切完成后试样固定剪切面的基质吸力，结合直剪试验结果建立了全吸力范围内非饱和膨胀土的抗剪强度模型，通过试验对比验证了模型的合理性。干湿循环会显著降低膨胀土的不排水抗剪强度，其中对土体总黏聚力的削弱程度远大于对总内摩擦角的削弱程度。总应力抗剪强度指标与基质吸力的对数值近似为线性关系，土体抗剪强度随着基质吸力的增加而非线性增大，增大速率逐渐减小。试验结果表明，采用常规直剪仪和滤纸法开展干湿循环条件下非饱和膨胀土的抗剪强度研究是可行的。

This study measures the total stress shear strength indices of unsaturated expansive soils at different water contents under drying-wetting cycles by undrained shear tests using the conventional direct shear apparatus. Specifically, the total cohesion and the total internal friction angle are obtained to reflect the undrained shear strength of expansive soils. The matric suctions of soil samples in a fixed shear plane are measured using filter papers after shearing. A model of shear strength for the entire suction range of expansive soils is established based on the results of shear tests. The model is verified by experiment. The drying-wetting cycles significantly reduce the undrained shear strength of expansive soil. The total cohesion weakening is more significant than total internal friction angle reduction. The shear strength index of total stress shows a linear positive correlation with the logarithmic values of matric suction. The shear strength of soil increases nonlinearly with the increase of matric suction, and the increasing rate decreases gradually. The findings confirm that it is feasible to investigate the shear strength of unsaturated expansive soil using the conventional direct shear apparatus and filter paper method.