In Situ Determination of Density Profiles in Complex Strata Using the Nuclear Density Cone Penetrometer

Abstract

The nuclear density cone penetrometer (ND-CP) is an in situ testing device that can provide continuous data on soil density, but it measures the composite density (ρc) of the soil within a spheroid centered at the midpoint between the gamma ray source and the detector. A theoretical model for predicting ρc of the ND-CP is proposed, and equations for calculating ρc are derived when the ND-CP penetrates into strata with different functions of density distributions. The calculated ρc profiles provide a good fit to the laboratory-measured ρc profiles by the ND-CP, indicating that the proposed theoretical model can be used to calculate the ρc within the spheroid. The comparisons of the density (ρ) and ρc values show that the ρc profiles are considerably different from the actual ρ profiles at the boundaries of each stratum where density changes suddenly. Therefore, a method for deducing the actual ρ profiles from the measured ρc profiles in complex strata is proposed, and this method is used to determine the actual ρ profiles from the ND-CP measured ρc profiles in the field. The research results would be beneficial for the in situ determination of the density profile in complex strata using the ND-CP.