Moisture migration in geogrid reinforced expansive subgrades.

Abstract

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.