A Review of Laboratory Cone Penetration Test (CPT) in Unsaturated Soil

Abstract

Cone penetration testing (CPT) is a common site investigation method used to determine soil profiles and characterize in-situ soil properties. However, most of the existing interpretations of CPT data are established for dry or saturated soil. In recent years, studies have shown that ignoring the matric suction effect in unsaturated conditions during data interpretation could lead to biased soil characterization and soil property estimates. Still, due to the lack of fundamental understanding of the mechanics during cone penetration in unsaturated soils, accounting for the matric suction effect on the CPT data-soil properties/characterization is not clearly defined, and more laboratory testing in controlled environments is required to fill this gap in knowledge. Existing studies are different in terms of penetrometer diameters (dcpt), chamber dimensions, penetration rate, sample preparation, and suction control techniques. This paper first presents a review of the existing literature on CPTs performed in unsaturated soils in a controlled laboratory environment and discusses the effects of the aforementioned factors on the measured tip resistance. In addition, new results from centrifuge CPTs performed with controlled water levels in a rigid chamber are presented. For the purpose of such experiments, a 12.7 mm diameter miniature cone penetrometer was designed and fabricated to measure tip resistance values. Unsaturated CPT data show that the presence of matric suction in the soil tends to increase the tip resistance measurement during the cone penetration process. More tests are planned in the future to quantify this increase in CPT response with respect to other soil properties.

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