Analytical study on quantifying the magnitude and rate of subgrade fines migration into subbase under flexible pavement

Particle transport and subsequent deposition in porous media play a significant role in the performance of civil infrastructure. For example, in pavement systems, the migration (also known as pumping) of fine-grained soil from saturated subgrades into subbase layers can compromise the pavement serviceability and performance. In this paper, an analytical framework is formulated to understand the mechanisms of particle transport in pavements and to provide a reasonable prediction of the amount of fines migration from a saturated pavement subgrade to subbase. The model is verified using results from a set of experimental investigations previously conducted to quantify the magnitude and rate of subgrade fines migration. The tests were performed on two classes of flexible pavement roadways, using one-third scale model mobile load simulator (MMSL3), an accelerated pavement testing (APT) device. Non-plastic saturated silt and partially saturated aggregate were used as subgrade and subbase, respectively. The study suggests that the migration of the subgrade soil into subbase is governed by hydraulic condition, grain size of subgrade, grain size and pore size of subbase, permeability of subbase, and viscosity of pore fluid in the subbase. Moreover, magnitude and duration of applied loads play key roles in the amount of pumping in pavement.