Methods and results of monitoring subgrade moisture under seven aggregate-surfaced roads in northern idaho are presented data were collected over a 5-year period from 1978 to 1982. The data were collected to predict subgrade moisture for consideration of seasonal variations in subgrade strength in aggregate thickness design. One hundred forty-six specially calibrated electrical resistance moisture-temperature cells and 100 nuclear depth probe tubes were installed in the roads' subgrades. About 9, 100 electrical cell observations were analyzed. Electrical cell measurements were within about 1 to 2% saturation of gravimetric (oven-dry) tests. Coparison between nuclear depth-probe measurements and gravimetric-volumetric tests was poor, and the method was abandoned about midway through the project. Saturation decreased from a maximum of about 95% in early spring to a minimum of about 65% in early fall, and then increased until freeze-up. Two regression equations for percent saturation that are based on electrical cell readings are given: one as a cosine function of time (r-squared equals 0.76) And the other as a function of antecedent precipitation index (r-squared equals 0.78). This paper appears in transportation research record no. 1291, Fifth international conference on low-volume roads, may 19-23, 1991, raleigh, north carolina, volume 2.
Samenvatting