Pavement Structural Analysis of the Design Recommendations for ...

Pavement Structural Analysis August 2004
Report No. 15953-2/1 ARA-ERES Consultants
96, they should be adjusted using the correction factors recommended by Von Quintus, et
al. (6)
Based on the boring logs provided, the subgrade soils encountered along the section of I-
96 are believed to have a frost susceptibility classification of moderate or medium using
the Corps of Engineers classification system (refer to figure 6). (7) It is suggested that a
non-frost susceptible material be placed above the subgrade to minimize the potential for
frost heave over time. Thus, a minimum of 36 inches (914 mm) of non-frost susceptible
materials were included in the pavement cross-sections analyzed in this study.
Results from the subsurface investigations did not indicate ground water at the time of
drilling. Seasonal variation in ground water is expected for this area. Thus, subsurface
drains were assumed in the design computations for determining the required layer
thickness. It is understood that subsurface drains and a geotextile fabric-separator are
included in the planned reconstruction.
3.3 Non-Frost Susceptible Material
For this climatic area, the Michigan DOT requires that 36 inches (914 mm) of non-frost
susceptible material be placed above any frost-susceptible soil based on historical data
and experience. The thickness of non-frost susceptible material requirement was
assumed for this design study and not re-evaluated, as noted above.
Two unbound aggregate materials are available for use in the reconstruction of this
segment along I-96: a class IIA sand subbase and a 21AA-MOD crushed stone aggregate
base. Resilient modulus tests were completed and are available for similar materials from
the FHWA-LTPP database for test sections in Michigan. This laboratory data was used to
estimate the resilient modulus for each of these materials, similar to the method used to
develop Pavement Structural Design Study – A Simplified Catalog of Solutions. (2) A
geotextile fabric should be used as a separator layer between the crushed aggregate base
and sand subbase.
Sand Subbase Material
It is understood that the existing sand material encountered in the borings along I-96 will
be replaced with Class IIA material for the flexible pavement design option. Resilient
modulus tests on the sand proposed for use were unavailable. However, repeated load
resilient modulus tests performed on materials classified as sand subbases were
previously extracted from the LTPP database.
Figures 17 to 20 in Appendix B graphically present the distribution of the resilient
modulus measured at specific stress states. It is important to note that the distributions
appear to be normal for those groups with a sufficient number of tests. This normal
distribution of resilient modulus values at specific stress states is also applicable to other
unbound materials that have a sufficient number of resilient modulus tests.
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