Relationship of Forest Road Aggregate Test Properties to Sediment Production

This study investigated the sediment production from various aggregates. The objectives of this study were 1) to evaluate the erodibility of a range of aggregate surfacing materials and relate it to standard and non-standard specification tests, 2) provide a means of specifying aggregate materials and understand the sedimentation implications, and 3) to provide a relative ranking of the erosive potential of aggregates. To accomplish this, eighteen aggregates from the Pacific Northwest were selected based on quality and geologic parent material. A suite of aggregate specification tests were performed to characterize each aggregate. The sedimentation from a simulated rain storm on a plot representing a freshly constructed road section was measured. Traffic was applied and the sediment production from a simulated storm again measured. The two best indicators of aggregate quality were Sand Equivalent and Oregon Air P20 test results. Knowledge of whether an aggregate was classified as good or marginal was not sufficient to estimate sediment production. The best indicator of sediment production was the percent passing the number 30 sieve.