Moisture and strength variability in some Arizona subgrades

A series of cone penetrometer tests was performed on subgrade materials at 18 sites along Arizona highways. At each site, water content and cone penetration data were obtained at two locations, 10 m apart, along the right-wheel path of the right lane and at a third location along the adjacent shoulder. The cone penetration and water-content data indicate pronounced variations in subgrade properties over distances of only a few meters horizontally. Variations in subgrade properties were also significant over small vertical distances. Soil profiles at the 18 test sites contained a wide range of soil types; however, most upper subgrade materials were classified as silts or sands with silty fines. Relationships among soil water content, soil suction, and shear strength are explored, and the effect of highly variable subgrade properties on pavement design is discussed.