Interpretation of Piezocone Test in Overconsolidated Clays Using SHANSEP-Paper

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The paper evaluates using the SHANSEP framework to interpret piezocone (CPTU) tests in overconsolidated clays. Conventional interpretation applies a constant cone factor, \(N_{kt}\), to estimate undrained shear strength. This can be unreliable where overconsolidation ratio (OCR) varies with depth and clay behaves dilatively, because laboratory strength is defined at a specified strain that may differ substantially from strains mobilized around the cone.<br /><br />The proposed SHANSEP–\(N_{kt}\) approach relates normalized undrained strength to OCR and uses CPTU data to estimate OCR. It therefore allows \(N_{kt}\) to vary with depth, while its parameters can be calibrated to reflect laboratory test results and dilative behavior.<br /><br />A case study from heavily overconsolidated North Sea clay compared the method with constant-\(N_{kt}\) interpretations and anisotropically consolidated undrained triaxial compression tests. A constant factor did not capture the laboratory strength trend and could overestimate strength at shallow depths, potentially leading to unsafe designs for shallow foundations under static and cyclic loads. The SHANSEP-based interpretation better matched the laboratory trend. The inferred \(N_{kt}\) values ranged from 20 to 32 and generally decreased with depth, following the OCR profile. Very high values in some shallow, sandy or fissured layers highlight limitations in applying the method uniformly.<br /><br />The authors recommend selecting SHANSEP parameters using site-specific laboratory data where possible, or relevant databases and engineering judgment otherwise. Parameter uncertainty becomes increasingly important at high OCR. Further case studies are needed to test the approach across different soils and stress histories.

Keywords

SHANSEP

piezocone

CPTU

overconsolidated clays

cone factor

undrained shear strength

OCR

North Sea clay

dilative behavior

laboratory calibration