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49CBR from DCPThe California Bearing Ratio (CBR) test was another way of evaluating stiffness of thesubgrade and uniformity of the in-situ soil. CBR is defined as the ratio of penetrationresistance developed by a subgrade soil to penetration developed by a specimen of a standardbase material (Burnham, 1993). CBR test is less cost efficient and more technically involvedthan DCP test, therefore, an empirical correlation between the DCP and CBR parameters wasused. While, there are many correlations that have been established between PI, mm/blowand CBR, % in the past, the one that found the most application is US is shown in Equation17 (Webster et al., 1992). ASTM D 6951-03 also provided means for converting DCP valuesto CBR, however this approach was not taken due to a more widespread practice of usingWebster’s equation.Equation 17: CBR and DCPI correlationCBR=292 / (DCPI) 1.12 (Equation 17)Table 5: DCPI and CBR average values for matrix soil of single piers compacted viadifferent beveled headsAggregateAggregate Pier Aggregate AggregatePier Cone Truncated Pier Flat Pier WedgeAVERAGE ST. DEV. COVCone305 610 305 610 305 610 305 610 305 610 305 610 305 610Pier type mm mm mm mm mm mm mm mm mm mm mm mm mm mmDCP TOP610mm(mm/blow)CBR TOP610mm(%)34 26 34 65 34 61 97 97 49.8 62.3 31.5 29.0 63 4727 27 27 - 27 - - - 27.0 27.0 - - - -7.8 7.0 7.8 2.8 7.8 4.2 1.8 1.9 6.3 4.0 3.0 2.2 48 569.8 6.6 9.8 2.9 9.8 2.2 2.2 1.9 7.9 3.4 3.8 2.2 48 64