Volume 31, Issue 6 (November 2008)
Profiling of Heterogeneous Soil Using the Nuclear-Density Cone Penetrometer
This paper describes a series of experimental investigations conducted to investigate and interpret the density profiles obtained by a nuclear-density cone penetrometer (ND-CP) used in the characterization of a highly heterogeneous lumpy fill. The key features involved in the interpretation of these wet density profiles, termed “signatures” in this paper, were discussed. First, it was established that the maximum radius of the influence zone for the ND-CP used in the present study is about 23.6 cm radius, and this parameter decreases with increasing density of the material. It was also established that the ND-CP measurement provides the average wet density of the composite soil within the measuring volume. The signatures of wet density profiles for layered soil and lumpy fills were also investigated so as to improve the interpretation of the actual soil profile. Backscatter and linear mixture theoretical models were adapted and applied to the ND-CP to provide a framework for this interpretation of the signatures of wet density profiles. A back analysis of a set of lumpy fill results obtained from the actual field tests was also conducted and the results demonstrated that the signature of wet density profiles obtained from the ND-CP is useful for identifying the zones of the soil occupying the big clay lumps and initial inter-lump voids, something that is very difficult to establish without the use of ND-CP and the technique to carry out the interpretation.