United States Department of Transportation
i
Backcalculation of unbound granular layer moduli.
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2011-03-01
[PDF-2.85 MB]
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Abstract:The state of Michigan is geographically located within the wet-freeze zone identified by the
American Association of States and Highway Transportation Officials (AASHTO). The frost
depth in the State ranges from 2.5 feet near the Ohio and Indiana borders to about 5.0 feet in
parts of the Upper Peninsula. To minimize the impact of freeze-thaw cycles on pavement
performance, granular subbase (typically sand) and base (typically gravel) layers are
conventionally used to provide protection to the roadbed soils from the detrimental effects of
freezing and to minimize the stresses delivered to the roadbed soils. In general, the strengths of
the granular layers are lower than that of the asphalt or concrete surface layer and, in most cases,
higher than the strength of the roadbed soils. The most common and available aggregate types
used by the Michigan Department of Transportation (MDOT) in pavement construction include
natural gravel, limestone/dolomite, slag, and crushed concrete. In this study, the value of the
resilient modulus of commonly used granular materials were backcalculated using two- and
three-layer systems and Nondestructive Deflection Test (NDT) data obtained by MDOT. The
backcalculated resilient modulus values of the unbound granular layers were subjected to various
to determine the most appropriate values to be used in the pavement design process. This final
report provides details of the analyses and the resulting outcomes.
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