Silty sand characterization in the geotechnical centrifuge

The geotechnical characterization of soil deposits from piezocone data can be quite challenging when it comes to intermediate soils, like silty sand. There are well established and widely used empirical correlations for the characterization of cohesionless and cohesive soils, however there are still open questions when it comes to the interpretation of piezocone measurements for silty sand deposits.

This study aims at improving the understanding of the mechanical behavior of silty sand. In order to do so cone penetration tests with pore pressure measurement at the shoulder of the penetrometer were performed on silty sand samples in the geotechnical centrifuge. After a literature review on the current sample preparation methods, the moist tamping method with under compaction has been employed to ensure a homogeneous silty sand sample.

Three samples have been prepared at 23%, 33% and 55% fine content (non plastic). The stress level effect has been studied by performing CPTUs at different g levels. In addition, the CPTU results were interpreted to evaluate strength parameters of the soil. Element triaxial tests were carried out and the results were compared with the interpretations of the CPTU data.

Sieve analysis indicate that the reconstituted samples were homogeneous and uniform, except from the low fine content sample which was over compacted at larger depths. The interpretation methods are capturing the classification of soil type but underestimate the fine content for the silty sand with non plastic fines.

The results indicate higher peak angle of friction at higher fine content, which is consistent in both empirical correlations and triaxial test results.