Magnitude and Rate of Migration of Fine Subgrade Soil into Granular Subbase under Scaled Flexible Interstate Pavement

Typically pavement structure is comprised of a surface layer (i.e., asphalt or concrete), underlying granular layers known as subbase and/or base, and a compacted subgrade soil layer. During wet seasons when the subgrade becomes saturated, cyclic loading caused by the moving traffic may result in pumping of fine particles from the subgrade up into the subbase. This presents a serious challenge to the pavement structure and may lead to failure of the pavement. The objective of this research is to investigate occurrence of migration of fine particles and to quantify the magnitude and rate of such migration. One-third scale model mobile load simulator (MMLS3), a type of accelerated pavement testing (APT) device, is utilized to simulate the cyclic traffic loading on scaled flexible pavement that simulates interstate highways. Kenlayer linear elastic program is used to determine the equivalent scaled pavement in the laboratory. The pavement section is constructed on a bed of non-plastic saturated silt as subgrade soil and partially saturated aggregate subbase. The lab testing reveals that under cyclic loading condition considerable amount of fine particles migrated into the subbase. The migrated soil in mass percentage increases with the simulated traffic loading cycles. The migration of subgrade soil into the subbase also varies with the depth in the subbase: more migration occurred in the lower section (closer to the subgrade) than in the upper section of the subbase.