Design of Effective Subsurface Drainage for Flexible Pavement

In this paper, numerical simulations of subsurface drainage in a flexible pavement system were conducted using DRIP program and 2-D SEEP/W program. A baseline pavement section profile was selected to represent typical flexible pavement design incorporating drainable base course. Using the baseline pavement cross section, a series of parametric numerical simulation studies were conducted to evaluate the influencing factors on the subsurface drainage efficiency. The predicted time to drain 50% of free water, computed by DRIP program and 2-D SEEP/W program, was compared for all cases investigated. The assumptions made in DRIP program, namely, seepage in fully saturated base course, seemed to make the predicted time to drain 50% of free water in base course shorter than that predicted by SEEP/W program, which takes into account of unsaturated seepage condition in the base materials. At the end of the paper, insights gained from numerical simulations using SEEP/W were given to enable design of effective subsurface drainage system in a flexible pavement.