Geotextile Drains in Road Sections Subjected to Unsaturated Conditions

In many cases, the intrusion of water (either through rainfall or capillary rise) into the subgrade or aggregate base course in road sections can result in the swelling of the subgrade, decreasing the effective stress and, consequently, the shear strength. To mitigate these adverse conditions, a geotextile drain (GD) can be introduced to intercept upward and downward water flow and divert it towards edge drains, with flow induced under unsaturated conditions. Design of this type of system for the general case of partial saturation, however, is significantly complicated by the significant scale differences in the spatial extent and hydraulic properties of the soil and geotextile layers. In this paper, a road section consisting of aggregate base course (ABC) and subgrade is modeled using the finite element program SIGMA/W. Results show that the suction head in the subgrade and the air entry value of the GD have important effects on downward water flow into the subgrade. Low air entry value geotextiles cause a decrease in suction above the GD leading to a decrease in shear strength and increase in deformation. Guidelines are presented for the efficient design of GD as capillary barriers in roadways to minimize intrusion of water into the subgrade and ABC.