Roadway Failure Study No. III. Source of Water Infiltrating Expansive Clay Subgrades

摘要

The study is the third in a series concerned with pavement failure over expansive clay foundation soil. The first two studies indicated that increasing water content and softening of the upper few feet of the clay was the main cause of pavement failure at the sites studied. The objectives of the third study were to further define the source of moisture and the depth of moisture increase, and to determine possible preventive measures. Moisture content, changes in pavement elevation and pavement performance were observed. Moisture contents were measured with nuclear depth probes and undisturbed sampling. At one point of failure, the moisture content of the subgrade approached saturation. The source of water appears to be condensation, within the granular base, of moisture in the air voids. Apparently fresh air and moisture are drawn into the base during each daily cycle of temperature change. Recommended treatment includes waterproofing the entire subgrade surface including ditches and the lower portions of backslopes and the upper portions of fill slopes. (BPR abstract)