Relative density estimation from shallow depth CPTs in siliceous sand: an updated approach

Revised version submitted to Geotechnical Research (status: Accepted)

Abstract

Cone penetration tests (CPTs) in sands are governed by two distinct mechanisms: a shallow failure mode, which dominates in the upper ~0.2–1.0 m of field CPTs, and a deep failure mode, which develops once sufficient embedment is achieved. Industry-standard correlations between CPT cone resistance (q_c) and relative density (D_r) are calibrated under deep failure conditions, and their application in the shallow zone produces erroneous results. This paper reviews shallow depth interpretation methods and introduces an updated global model integrating shallow and deep penetration mechanisms. Building on Jensen (2024), the formulation addresses prior limitations through recalibration using controlled laboratory tests and a database of 132 onshore and offshore CPTs, enabling improved differentiation of near-surface densities and closer agreement with measured q_c profiles. The model shows reduction in shallow-zone D_r bias relative to earlier approaches and is most reliable for clean, young, uncemented, uniformly graded siliceous sands under saturated or dry conditions. Deviations occur in sands of higher compressibility, increased fines content, or pronounced angularity, and within the top 2–4 cone diameters where mudline definition and minor cone disturbance become influential. Site-specific validation of the model against direct D_r measurements is required for reliable application, even within the calibrated range.