The role of geotextile reinforcement in the control of pumping at the subgrade-subbase interface of highway pavements

Based on observations of laboratory tests, this paper considers the role of geotextile reinforcement at the subgrade-subbase interface in controlling subgrade pumping of highway pavements. The four stages that develop during a pumping test are identified: (i) the development of tension under the subbase particles; (ii) the development of a gap under the subbase particles; (iii) the plastic flow of subgrade soil into the gap; and (iv) global separation in which a gap develops between the underside of the geotextile and the top of the subgrade. Two mechanisms of geotextile reinforcement are identified and their role in the development of pumping is considered. Global reinforcement concerns the whole area subjected to traffic loading, while local reinforcement considers the area of contact between a subbase particle, the subgrade surface, and the unloaded zone surrounding the subbase particle. Global separation occurs when the load carried by the geotextile becomes equal to the minimum total applied load, during the unloading stage of a load cycle. Calculation methods to assess the permanent deformation of the subgrade soil at which separation occurs both in small-scale laboratory tests and field tests are presented.