Case Study: Evaluating Road Performance and Sediment Generation during Simulated Wet Weather Hauling
Abstract
Aggregate
roads are the primary means of access to managed forestlands in western Oregon,
but may facilitate sediment transport during rainfall, especially with traffic
from heavy trucks. This transported sediment, typically in the means of
suspended sediment or turbid effluent, may have detrimental effects on aquatic
ecosystems, especially when roads are in proximity to creeks, streams and
rivers. However, due to past construction practices and difficult terrain, many
existing roads are stream-adjacent, and may require retrofitting to address
potential delivery of fine sediment from its surface during rainfall. To
evaluate a potential treatment to this problem, a heavily-instrumented field
test was performed on a reconstructed aggregate forest road in Western Oregon
which sought to test the potential of geosynthetic materials to sequester road
sediment and improve road performance during wet-weather hauling. A sand filter
berm wrapped with a non-woven geotextile provided 70% and more reduction in
turbidity when tested under idealized laboratory conditions. Additionally, a
geogrid reinforcement placed on the native road subgrade material prior to
placing the aggregate layer reduced subgrade pressures experienced during loading,
improving mechanical performance. When applied to well-graded aggregate, the
geogrid reinforcement reduced rutting, a potential channel for flow of turbid
runoff. When applied to a poorly-graded aggregate the geogrid reinforcement
reduced relative breakage. Aggregate degradation and road performance may be
improved with use of the geogrid reinforcement and road sediment may be
effectively sequestered with use of a geotextile-wrapped filter sand berm when
applied correctly. Targeted applications of these approaches are recommended
where desired levels of road performance and water quality improvement may
justify the additional labor and materials required. However, more replicates
and larger scale application may address some levels of variability that are
difficult to address under the constraints of an intensive field test.
Keywords
References
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