Relationship between DCP, Stiffness, Shear Strength, and R-value

A brief review of some studies undertaken reveal that direct relationships between DCP penetration and R-value are not reliable for general use in California. Limited studies appear to have been carried out and any relationships developed are based on very small samples that have significant variation. Good correlations between DCP penetration and shear strength and DCP penetration and stiffness have been developed, although these are material property dependent and need to be used with caution. Very little work on the development of relationships between these properties and R-value appears to have been carried out. Thus attempting to predict R-value from DCP penetration indirectly through the shear strength or stiffness will be very unreliable. A statistically valid relationship between DCP penetration and R-value is probably feasible in that some soil properties influencing the result are common to both. However, a very large experiment will need to be carried out in order to develop a reliable relationship. The need for such an experiment is questioned given that wider use of mechanistic empirical analysis and design methods will render the R-value obsolete in favor of modulus tests. It is therefore recommended that: * Any relationships already developed between DCP penetration and R-value should be used with extreme caution, especially if those relationships were developed outside of the area and/or on different soils in which the DCP penetrations have been carried out * Indirect prediction of R-value from DCP penetration using the elastic or resilient modulus is not recommended * If the development of a relationship between DCP penetration and R-value is pursued, a comprehensive factorial experimental design should be followed, which considers a wide variety of soil properties, soil moistures, densities and confining pressures. The reproducibility and repeatability of the R-value test should also be quantified.