Effects of Aggregate Masking on Soil Infiltration under an Aggregate Bed

Abstract

This research seeks to address questions about the reduction in soil infiltration rates due to masking or embedding when a layer of open-graded aggregate is placed on top of soil. This is pertinent to the design and modeling of many low impact development (LID) technologies that incorporate infiltration such as porous pavements, infiltration trenches, and dry wells. A large permeameter was used to first measure the infiltration rate of five different soils and a No. 67 aggregate separately, and then measure the effective infiltration rate of the soils with an aggregate layer on top and with aggregate embedded in the top of the soil. The actual effective infiltration was then compared to the theoretical effective infiltration, assuming no masking or embedding effect. It was found that the measured infiltration rate was consistently lower than predicted, indicating a reduction in infiltration due to the presence of the aggregate layer. The average reductions were 29 and 43% for masking and embedding, respectively, which are consistent with computer modeling results from a previous study, but are significantly less than the reduction factors used in other porous pavement modeling applications. As such, existing modeling approaches for LID infiltration technologies may underpredict actual performance.