Simulation of Subsurface Drainage of Highway Pavements

An analysis of the drainage of a pavement system from initial saturation incorporates a realistic assessment of the drainable porosity of the base. This analysis indicates that if a granular base is to drain under the force of gravity, the drainage material must be very coarse. The capillary suction that can be developed by gravity drainage is limited by the geometry of the pavement section. This suction may be too small to desaturate the pores of the drainage material. If a pavement drains at all, it drains fairly quickly. The FHWA's subdrainage design procedure greatly overestimates the drainability of base courses with hydraulic conductivities in the normal range.