Navegando por Autor "McCartney, John S."

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Formation of secondary containment systems using permeation of colloidal silica.
(2011) McCartney, John S.; Nogueira, Christianne de Lyra; Homes, Daniel; Zornberg, Jorge Gabriel
U.S. Environmental Protection Agency (USEPA) regulations require the capture of spills from liquid tanks containing hazardous chemicals by using a secondary containment system. Compacted clay or geomembrane liners are commonly used in secondary containment systems, but they are cumbersome when used in conjunction with existing liquid tanks because of pipeline networks surrounding the tanks. This study evaluates the formation of hydraulic barriers for secondary containment through the permeation of colloidal silica grout. A simplified infiltration model is presented to predict the downward movement of the colloidal silica grout into a soil layer, considering the timedependent increase in dynamic viscosity of the colloidal silica for different concentrations of an electrolyte accelerator. Because the simplified infiltration model cannot predict the soil-grout interaction or the permeation of the colloidal silica by fingering, its results were calibrated by using the observations from a large-scale column test involving the permeation of colloidal silica into sand. The predicted position of the wetting front was found to match that of the experiment when the parameter governing the change in viscosity of the colloidal silica was increased by a factor of 30. The infiltration model calibrated with observations from column infiltration experiments provides a simple approach to the design of the secondary containment systems using permeation of colloidal silica.
Moisture migration in geogrid reinforced expansive subgrades.
(2008) Gupta, R.; McCartney, John S.; Nogueira, Christianne de Lyra; Zornberg, Jorge Gabriel
Highways in Texas, Arkansas, Colorado, Wyoming and other parts of the United States are often constructed atop expansive clay subgrades. Considerable damage to flexible pavements has been observed in these areas in the form of longitudinal cracking. A geogrid placed between the subgrade and base layers has been used successfully in Texas as a stabilization alternative to prevent longitudinal cracking, although the mechanism of geogrid reinforcement is not well understood. This study involves measurement of the time variation in water content of an expansive clay subgrade beneath a flexible pavement to investigate if differential volume changes in the subgrade are a cause of longitudinal cracking. Two years of moisture monitoring and visual observations indicate that significant moisture fluctuations occur in the clay subgrade under the unpaved shoulder of the road, while negligible moisture fluctuations occur in the clay subgrade under the pavement. This contrast in water content changes between the shoulder and pavement indicates that both bending and stretching of the subgrade are probable causes of longitudinal cracks.