针对膨胀土堑坡防护工程中不同的施工工序和降水入渗诱发灾害频发现象，基于原位孔内剪切试验，通过施加不同法向应力水平，以及成孔后注水浸泡等工况下的现场剪切试验，获得南阳某堑坡膨胀土强度特性随荷载施加方式与浸水条件的变化规律。结果表明：膨胀土孔内剪切试验所得的剪应力-剪切位移曲线总体上呈现弱硬化变形特征；浸水对抗剪强度影响很大，最大降幅达56.9%，主要表现为黏聚力的降低，最大值达18.1 kPa。预加载荷对浸水软化效应具有一定抑制作用，但当预加载荷超过某一应力水平时，难以发挥更大的抑制效果。黏聚力与预加载荷呈线性正相关；内摩擦角与预加载荷呈线性负相关，但降幅甚微。在实际工程中，膨胀土边坡稳定性分析应考虑降雨入渗对强度参数的影响，同时充分利用抗剪强度参数和预加载荷的线性关系，可根据工程要求达到的安全系数反推出所需的预加载荷大小，从而指导实际工程施工。该研究可为膨胀土工程场地评价、参数选取与灾害评价提供技术依据和参考。

To study the impact of different construction procedures for cut slope protection of expansive soils and to prevent disasters triggered by rainfall infiltration, in-situ borehole shear tests (BST) were conducted under different normal stress levels and soaking conditions. Strength characteristics of expansive soils cut slope in Nanyang were obtained with various loading paths and soaking conditions. Results show that the relationship between shear stress and displacement from BST presents weak hardening as the shear strain increases. A max drop of 56.9% in shear strength, and a decrease of 18.1 kPa in cohesion are observed. Preloading inhibits softening but fails when it increases to some threshold. The cohesion has a positive linear relationship with the preloading stress, while the internal friction angle has a negative linear relationship with the preloading stress, but internal friction angle rarely varies. In engineering practices, effect of rainfall infiltration on strength parameters should be considered. Meanwhile, the linear relationship between parameters of shear strength and preloading stress should be used to back-calculate the preloading needed according to the safety factor that the project should satisfy. The study results provide technical reference for site evaluation, parameters selection and disaster assessment of the similar sites of expansive soils.