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.
