United States Department of Transportation
i
Determining an Acceptable California Bearing Ratio (CBR) Value for Kansas Subgrades Based on Pavement Distress Data
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2024-11-01
[PDF-2.00 MB]
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Edition:Final Report April 2018 – December 2021
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Abstract:The major objective of this study was to develop scientifically based recommendations for acceptable California Bearing Ratio (CBR) values for Kansas subgrades. To this end, multiple statistical analyses including: 1) Principal Component Regression Analysis (PCRA), 2) Regression Analysis (RA), 3) Multivariate Principal Component Regression Analysis (MPCRA), and 4) Multivariate Regression Analysis (MRA) were performed on in service flexible pavements in the state of Kansas. Statistically significant correlations were found between results of Dynamic Cone Penetrometer (DCP) tests conducted on subgrade soils and total rutting, fatigue cracking code one (FC1), percent of good pavement core, and percent of poor pavement core. Additional statistically significant correlations include the correlations between traffic volume and transverse cracking code one (TC1), and two (TC2), correlations between the thickness of unbound layer and pavement roughness, and percent of good core and percent of poor core. Corresponding equations are provided in the report. Furthermore, x-y graphs depicting time in years needed for the unit increase in rutting severity code versus DCP or CBR value are provided. An additional set of graphs depicting percent of good core, poor core and fair core versus DCP or CBR value is also provided for different thicknesses of unbound layer. These graphs along with additional equations can be used to determine scientifically based acceptable values of CBR.
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