Unsaturated Hydraulic Characterization of Expansive Clays

本研究的总体目标是通过实验确定膨胀粘土的非饱和水力特性，同时，深入了解这些水力特性和膨胀幅度之间的关系。 占土壤体积应变作为一个额外的变量在框架内的非饱和水力特性增加了复杂性已经错综复杂的，非线性关系，代表响应的体积含水量和水力传导率作为土壤基质吸力的函数。 这项调查将使用离心技术，允许测量的非饱和水力特性和相关的体积变化膨胀粘土。 具体而言，离心试验将用于连续和快速测量非饱和流期间发生的土壤含水量、吸力、水力传导率和孔隙比的变化。 这项研究将允许：（i）深入了解高塑性粘土的非饱和水力性质和体积变化之间的关系，（ii）迅速确定高塑性粘土的水力性质，（iii）理解进行开放流离心的粘土试样的边界条件和应力，（iv）量化法向应力、初始含水量、初始孔隙比的影响，土壤结构和施加的入流速率对膨胀量和膨胀率的影响，以及（v）开发适合于描述土壤水分保持曲线、水力传导函数和膨胀土膨胀-应力关系的模型。由于概念和实验的复杂性，膨胀性粘土的非饱和水力特性的表征在很大程度上仍未被探索。 然而，显着的好处将导致深入了解的变量，在膨胀性粘土中的非饱和流动，在美国每年的损失引起的水分波动膨胀土已被报道超过洪水，飓风，地震和龙卷风的总和。 拟议活动产生的更广泛影响包括：（i）不仅将离心试验用于岩土建模，而且用于膨胀性粘土的水力特性，（ii）提高社区对与膨胀性粘土存在相关的问题的认识，（iii）将本研究的基本发现转化为实际建议，和（iv）开发教育模块，有助于将研究纳入岩土工程教学，并将地质灾害概念引入外展少数民族方案。

The overall objective of this research is to experimentally determine the unsaturated hydraulic properties of expansive clays while, at the same time, gain insight into the relationships between these hydraulic characteristics and the magnitude of swelling. Accounting for the soil volumetric strains as an additional variable within the framework of unsaturated hydraulic characteristics adds complexity to the already intricate, non-linear relationships representing the response of volumetric water content and hydraulic conductivity as a function of the soil matric suction. This investigation will use centrifuge technology to allow measurement of the unsaturated hydraulic characteristics and associated volumetric changes in expansive clays. Specifically, centrifuge testing will be used for the continuous and expeditious measurement of the changing soil moisture content, suction, hydraulic conductivity and void ratio that occur during unsaturated flow. This study will allow: (i) gaining insight into the relationships between unsaturated hydraulic properties and volume changes in highly plastic clays, (ii) expeditiously determining the hydraulic properties of highly plastic clays, (iii) understanding the boundary conditions and stresses in clay specimens subjected to open flow centrifugation, (iv) quantifying the effect of normal stress, initial moisture content, initial void ratio, soil fabric and imposed inflow rate on the magnitude and rate of swelling, and (v) developing models that are suitable to represent the soil water retention curve, the hydraulic conductivity function, and the swell-stress relationship of expansive clays.Because of conceptual and experimental complexities, the characterization of unsaturated hydraulic properties of expansive clays has remained largely unexplored. Yet, significant benefits will result from gaining insight into the variables governing the unsaturated flow in expansive clays, as the annual cost of damages in the US induced by moisture fluctuations in expansive soils has been reported to exceed that caused by floods, hurricanes, earthquakes and tornadoes combined. The broader impacts resulting from the proposed activity include: (i) using centrifuge testing not only for geotechnical modeling but also for hydraulic characterization of expansive clays, (ii) increasing community awareness of the problems associated with the presence of expansive clays, (iii) transferring of fundamental findings from this research into practical recommendations, and (iv) developing educational modules that are useful to integrate research into geotechnical instruction as well as to introduce geo-hazards concepts into outreach minority programs.