Swelling and shrinkage of expansive subgrade soils in North Texas causes deep cracks and surficial distresses in pavements. Since this behavior is affected by changes in water content of the soil, evaluating moisture variation in the subgrade soil could provide an estimation of pavements deformation. The objective of the current research is to investigate the moisture variation of a pavement site due to real time environmental factors. For this study, a 2-lane rural road in Kaufman County, Texas was selected for data acquisition and monitoring purposes. Soil test borings were conducted to determine subgrade condition and moisture sensors were installed at 1m and 4.5m depth to monitor in-situ moisture content every hour. In addition, a rain gauge was used to record the precipitation at the site. The main wetting branch of the soil water characteristics curve (SWCC) was estimated from soil's physical properties and incorporated into Finite Element (FE) software PLAXFlow for transient analysis of moisture variation. The FE results were compared with direct field measurements. Model outputs and sensor readings indicated significant variation of moisture content due to rainfall. Lower moisture content accompanied with considerable variations was recorded at shallow depths, while moisture variation at greater depths was mainly controlled by groundwater. The FE results were in line with direct field measurements, confirming the validity of the estimated parameters. The FE analysis could be utilized for determination of the hydraulic balance of the subgrade and has the potential to be considered as part of the future design procedures.