To investigate unsaturated soil-water interaction at micro-scale, this study extends the numerical manifold method (NMM) by incorporating a soil-water coupling model considering specific capillary water distribution and capillary force calculation. The soil skeleton is constructed by a soil skeleton generation algorithm with random polygons. To more realistically capture the interaction between soil grains and capillary water, a capillary mechanics-based geometric algorithm is proposed to iteratively calculate the capillary water distribution. The capillary forces corresponding to the capillary water distribution are calculated based on the Young-Laplace equation. The proposed capillary water solving framework is first verified by reproducing the soil-water characteristic curve and the capillary water distribution of an ideal contact-disk model against analytical solutions. To further validate the ability of the capillary water solving framework to predict hydraulic behavior of the real soil, a laboratory test on the Toyoura sand is reproduced numerically. Then an ideal direct shear test is performed to further validate the two-way soil-water coupling procedure, in which a comparison between the numerical and analytical results regarding the shear strength and matric suction is presented. Finally, microscopic hydraulic and compression tests are conducted on two soil specimens with the same porosity and mean grain diameter but different uniformity coefficients. The results elucidate that the extended method is a potential tool to explore unsaturated soil behaviors at micro-scale.

中文翻译：

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微尺度非饱和土-水相互作用分析的一种扩展数值流形方法

为了在微观尺度上研究非饱和土 - 水相互作用，本研究通过结合考虑特定毛细管水分布和毛细管力计算的土 - 水耦合模型扩展了数值流形方法 (NMM)。土壤骨架是由土壤骨架生成算法构建的，具有随机多边形。为了更真实地捕捉土壤颗粒和毛细管水之间的相互作用，提出了一种基于毛细管力学的几何算法来迭代计算毛细管水分布。对应于毛细管水分布的毛细管力是根据 Young-Laplace 方程计算的。所提出的毛细管水求解框架首先通过针对解析解再现理想接触盘模型的土壤-水特征曲线和毛细管水分布来验证。为了进一步验证毛细管水求解框架预测真实土壤水力行为的能力，对 Toyoura 沙子的实验室测试进行了数值再现。然后进行理想的直剪试验以进一步验证双向土水耦合程序，其中比较了关于剪切强度和基质吸力的数值和解析结果。最后，对孔隙率和平均粒径相同但均匀系数不同的两个土样进行了微观水力和压缩试验。