Estimating relative density from shallow depth CPTs in normally consolidated and overconsolidated siliceous sand

Current interpretation of relative density ( D r ) based on cone penetration test (CPT) end resistance ( q c ) data in sand relies on empirical expressions established from calibration chamber studies for which a deep failure penetration mechanism is attained. These expressions are mainly based on stress normalised q c data. Previous studies have highlighted the importance of performing the normalisation procedure with respect to the mean effective stress ( p′) in overconsolidated (OC) sand deposits instead of the vertical effective stress ( σ′ v ) that has been used in normally consolidated deposits. Due to a large variation in the coefficient of earth pressure at rest ( K 0 ), on which p′ depends, in the uppermost 3–5 m of OC sand, a recent study has demonstrated a rigorous unified approach for estimating a varying K 0 with depth. However, the surficial shallow failure penetration effects are not accounted for, and consequently, interpretation of the upper 0.5–1.5 m of sand is still erroneous. This depth range is very important for low-stress geotechnical applications such as offshore flowlines and mudmats. With a reinterpretation of previously published data, a new global model is presented that potentially enables estimation of D r from shallow CPTs in siliceous sand by taking into account both the shallow failure penetration effects (important in the uppermost 0.5–1.5 m) as well as the varying K 0 with depth for OC sand (important in the uppermost 3–5 m). However, the new model needs future calibration with controlled laboratory testing.