Cone penetration testing in unsaturated silt with matric suction measurements

Jonathan M.H. Wong, David Elwood

Dans les comptes rendus d’articles de la conférence: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: In-Situ Testing

ABSTRACT: While most empirical correlations used to interpret Cone Penetration Test (CPT) results have been developed from and for saturated soils, there is a lack of understanding as to their applicability for unsaturated soils. This paper presents the experimental results of Cone Penetration tests in an instrumented chamber filled with an unsaturated silt. The experiments were conducted by advancing a 10 cm2 piezocone into a 1.6 m tall 0.9 m diameter pipe, which was instrumented with four rapid-response tensiometers. The silt was placed at two different water contents with depth. Two pore pressure dissipation tests (PPD) were conducted after 400mm to 500mm penetration in each layer. Negative pore-water pressures (matric suction) were monitored during advancement of the cone and the PPD tests. The cone resistance, sleeve friction and pore-water pressure were also recorded. The experiment was repeated for seven different water contents. All the results of these Cone Penetration tests indicate that the built-in pore-water pressure transducer was incapable of providing useful information regarding pore pressure and hydraulic properties of the unsaturated soil. Hence, tensiometers ought to be used to obtain pore pressure measurements during and after penetration. Tensiometer readings can also be used to characterize the unsaturated soil, namely the in-situ SWCC, unsaturated hydraulic conductivity, in-situ pore-water pressure profile and the in-situ effective stress. Existing empirical correlations used to interpret the results of Pore Pressure Dissipation test (PPD) and Soil Behaviour Type (SBT) are reviewed.

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