Experimental simulation and quantification of migration of subgrade soil into subbase under rigid pavement using model mobile load simulator

Rigid pavement structure typically consists of a surface layer (concrete), underlying granular layers (subbase and/or base), and a compacted subgrade soil layer. Because the subgrade is saturated during wet seasons, cyclic loading caused by heavy traffic may lead to pumping of fine particles from the subgrade into the granular layers, redistribution of materials underneath the slabs, and gradual ejection of materials through pavement joints. This phenomenon results in faulting and can be a major contributor to pavement failure in wet regions. The objective of this study was to simulate and quantify the migration of subgrade soil into the subbase at rigid pavement joints. The cyclic traffic loading was simulated on a geometrically scaled model of rigid interstate highway pavement using a one-third-scale model mobile load simulator (MMLS3), an accelerated pavement testing device. Nonplastic saturated silt and partially saturated aggregate subbase were used as subgrade and subbase layers, respectively. The results indicated a significant amount of fines migration into the subbase under repeated traffic loading. The subgrade soil migration in mass percentage increased with the simulated traffic loading cycles. More fines accumulated in the subbase beneath the approach slab than beneath the leave slab. Faulting was observed and is another indication of fine particles migration. The migration of subgrade soil into the subbase also varied with the depth in the subbase; more fines accumulated in the lower section (closer to the subgrade) than in the upper section of the subbase.