有荷干湿循环条件下不同膨胀土抗剪强度基本特性

针对膨胀土分布区公路边坡常浅层坍滑现状，选取南、北方3种典型膨胀土样，模拟干湿循环并计及边坡破坏时滑面的上覆压力，改变常规试样吸湿及施剪条件开展试验研究，以获得较符合实际的膨胀土抗剪强度及其衰减规律。结果表明：不同上覆压力对膨胀土抗剪强度的影响为荷载越大其强度绝对衰减率越小；用双直线能较好表征其抗剪强度线特征，强度指标c、? 宜按高、低应力段分别获取；随干湿循环次数增加，c值呈指数函数衰减，是造成边坡浅层坍滑的主要原因；? 值随作用次数增加虽有减小趋势，但降幅不大；通过控制基本相同的试验条件，实测得3种膨胀土的最终抗剪强度均降至某一幅值范围。研究结论为解读膨胀土坡为何多浅层坍滑提供了有价值的信息。

Shear strength of expansive soils under wet-dry cycles with loading

The shallow landslide of highway slopes in areas with expansive soil often occurs. Three representative types of expansive soil from the south and north of China are tested under wet-dry cycle in the laboratory. The collapse of slope surface in low pressure conditions, and the conventional process of saturation and shear test are considered in the experimental study. The purpose is to obtain the actual shear strength of expansive soil and its reduction. The results show that the shear strength of the expansive soil affected by different vertical load is not identical. The larger vertical load results in the smaller reduction ratio of shear strength. The sectional double line method is adopted to approximately reflect the nonlinear characteristics of strength of expansive soil. It can also be used to calculate the index of shear strength c and ?. The c reduces exponentially as the number of wet-dry cycles increases, and it is considered as the main reason for the shallow landslide. ? decreases as the number of wet-dry cycles increases. The amplitude of reduction decreases. Under the same wet-dry conditions, the ultimate shear strengths of different expansive soils drop to a certain range. Research conclusion can provide reference for analysis of shallow landslide of expansive soil slope effectively.