Unsaturated soil mechanics & near-ground-surface phenomena

经典土力学的课本中有两个主要的主题历来被忽略；即非饱和土的行为和地表水分通量条件的量化。在过去的40年里，我们对非饱和土力学的理解取得了长足的进步，因为它适用于相对均匀的连续体。有;然而，非饱和土力学的两个方面还有待进一步研究。第一个方面涉及近地表土壤条件的结构特征。这些土通常含有广泛的裂缝、断裂和裂缝，这对非饱和土的性质有很大的影响。提出用双峰数学函数来表征这些土壤的二级宏观结构。提出了一个与土壤宏观结构特征相关的空气进入值和另一个与土壤完整基质相关的空气进入值。靠近地表的非饱和土因此变得双峰、非线性和迟滞。许多这些土壤在干湿过程中也表现出显著的体积变化。非饱和土力学需要研究的第二个方面是地表水分流动条件的量化。水的渗透和蒸发过程中的渗漏（以及蒸发蒸腾）都是实践岩土工程师非常感兴趣的主题领域。这些情况与我们对气候变化影响的理解密切相关。通过对地表水平衡状况进行数学量化的能力，可以通过数值模拟研究来考虑气候变化的影响。笔者认为，近地表裂隙、断裂、开裂土体的表征和地表水分通量条件的定量化是非饱和土力学有待进一步研究的两个主要课题。

There were two primary subjects that have been historically been by-passed in textbooks on classical soil mechanics; namely, the behavior of unsaturated soils and the quantification of moisture flux conditions at ground surface. The last 40 years have witnessed rapid strides in our understanding of unsaturated soil mechanics as it applies to relatively homogeneous continua. There are; however, two aspects of unsaturated soil mechanics that stand in great need of further research. The first aspect involves the structural characterization of the soil conditions near ground surface. Often these soils contain extensive fissures, fractures and cracks that significantly affect the unsaturated soil properties. It is proposed that the secondary macrostructure of these soils be characterized through use of bimodal mathematical functions. It is proposed that there be one air entry value associated with the macrostructures features and another air entry value associated with the intact matrix of the soil. The unsaturated soils near to the ground surface thus become bimodal, nonlinear and hysteretic. Many of these soils also exhibit significant volume change during wetting and drying. The second aspect of unsaturated soil mechanics in need of research is the quantification of moisture flow conditions at the ground surface. Both the infiltration of water and the exfiltration during evaporation (as well as evapotranspiration) are subject areas of great interest to practicing geotechnical engineers. These conditions are closely related to our understanding of the impact of climate change. It is through the ability to mathematically quantify water balance conditions at the ground surface that the effects of climate change can be taken into consideration through numerical modeling studies. In my estimation, the characterization of fissured, fractured and cracked soil masses near the ground surface, and the quantification of ground surface moisture flux conditions are two of the main topics requiring further research in unsaturated soil mechanics.