Measuring the migration of subgrade fine particles into subbase using scaled accelerated flexible pavement testing – a laboratory study

Pavement structure typically consists of an asphalt concrete or concrete surface layer, underlying granular layers (subbase and/or base) and compacted subgrade soil layer. During wet seasons when the subgrade becomes saturated, cyclic traffic loading may result in pumping of fine particles from the subgrade up into the granular layer, which may lead to failure of the pavement. The objective of this research is to investigate occurrence of migration of fines and to determine the magnitude and rate of such migration. A one-third scale accelerated pavement testing device is utilised to simulate the cyclic traffic loading on two geometrically scaled flexible pavements representing typical collector roadways and interstate highways. The pavement sections are constructed on partially saturated aggregate subbase overlying non-plastic saturated silt as subgrade. The lab testing reveals that, under cyclic loading conditions, a considerable amount of fines migrated into the subbase. The subgrade fines migration in mass percentage increases with the simulated traffic loading cycles. The resulting gradation from the migration of subgrade fines into the subbase also varies with the depth in the subbase: more fines are deposited in the lower section (closer to the subgrade) than in the upper section of the subbase.