MOISTURE VARIATION BENEATH HIGHWAY PAVEMENTS AND THE ASSOCIATED CHANGE IN SUBGRADE SUPPORT

Preliminary investigations of seasonal variation of subgrade moisture and other influencing parameters on the change in subgrade bearing support as monitored by pavement deflection, are presented. This report summarizes one year's data for the period 1971-1972. With respect to the moisture measurement methods, the sensing devices used performed satisfactorily as far as moisture detection was concerned. Pavement profile moisture experienced its wettest condition in the spring. Moisture change occurred at a depth of 5 feet or more. This change can be associated with infiltration from surface cracks, lateral movement from the shoulders, and a general use in the groundwater table. The effect of moisture on change in subgrade report revealed a definite lag in increased moisture with increases in precipitation. A definite relationship between change in subgrade moisture and deflection was also noted. The following conclusions were noted: Moisture content beneath highway pavements varied with seasons; the lowest moisture content of the year usually occurred in September or October and the highest generally occurred in April; long periods of precipitation increased the moisture content beneath highway pavements; a lag period was also observed between precipitation and corresponding increase in moisture content; changes in subgrade support for flexible pavements placed on plastic subgrades could be predicted statistically with reasonable accuracy.