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Evaluation of Guidelines for Subgrade Treatments
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2005-02-01
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[PDF-1.22 MB]
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Edition:Final report.
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Abstract:ODOT has recently developed guidelines for subgrade treatments to be used during plan
development and construction. This study evaluates these guidelines by comparing them with
existing guidelines developed elsewhere and validating them through comparison of the actual
treatment methods and quantities used with those suggested by the guidelines. Soil boring data
and construction record from 7 reconstruction and 2 new construction projects were obtained.
Actual treatment methods and quantities were obtained from the project field offices. Dynaflect
deflection data, when available, were analyzed to determine their usefulness in subsurface
assessments. GB1 criteria for excess moisture content predicted the undercut quantity reasonable
well, but the criteria for acceptable moisture content tend to under predict the undercut quantity in
many cases, likely due to increased soil moisture content after removal of existing pavement. For
reconstruction projects, the average undercut depths (i.e., the overall undercut quantities) versus
the corresponding SPT NL values seem to fall reasonably well within the upper bound provided in
the Section 204 guidelines. However, the actual undercut depths vary significantly even for soils
with similar or same NL values. Actual undercut depth and quantity are somewhat correlated with
the average SPT NL value, Dynaflect W5 deflection, and soil moisture content. The regression
equation developed has a coefficient of determination (or R-square value) as high as 0.71.
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