Rainfall plays an important role in affecting the slope stability in a tropical country such as Singapore. The soil in Singapore is mainly residual soil with a deep groundwater table that is commonly found in the unsaturated condition in the presence of matric suction. This paper presents the unsaturated properties of soil with roots of Caesalpinia crista and their effects on slope stability during rainfall. Laboratory tests were carried out to obtain the index properties, saturated properties (i.e. permeability and shear strength) and unsaturated properties (i.e. unsaturated shear strength and soil–water characteristic curve) of soil with and without roots of C. crista. Seepage analyses were performed to obtain the variations in pore-water pressures during and after rainfall. Slope stability analyses were conducted to obtain variations in the factor of safety during and after rainfall. The results indicated that soil with roots of C. crista had a higher saturated volumetric water content, a higher air entry value, a lower saturated permeability and a higher shear strength compared with soil without roots. In addition, the soil with roots of C. crista was effective in reducing the water infiltration into the slope during rainfall. Hence, slope stability can be maintained during rainfall.

中文翻译：

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非饱和特性对新加坡Caesalpinia crista覆盖的斜坡稳定性的影响

降雨在影响新加坡等热带国家的边坡稳定性中起着重要作用。新加坡的土壤主要是残留的土壤，地下水位很深，通常在存在基质吸力的情况下处于非饱和条件下。本文介绍了Caesalpinia crista根系土壤的非饱和特性及其对降雨过程中边坡稳定性的影响。进行了实验室测试，以获取有或没有C. crista根的土壤的指数特性，饱和特性（即渗透性和抗剪强度）和不饱和特性（即不饱和抗剪强度和土水特征曲线）。。进行渗流分析以获得降雨期间和降雨后孔隙水压力的变化。进行了边坡稳定性分析，以获得降雨期间和降雨后安全系数的变化。结果表明，与无根土壤相比，具有C. crista根的土壤具有较高的饱和体积含水量，较高的空气进入值，较低的饱和渗透率和较高的剪切强度。此外，具有C. crista根的土壤可有效减少降雨过程中水分渗入斜坡。因此，在降雨期间可以保持斜坡稳定性。