Thin-layer effects on the CPT qc measurement

A numerical analysis is presented to model the cone penetration test (CPT) tip resistance in layered soil. Analyses are performed for two-layer soils composed of either sands with different relative densities or different materials (sand and clay). Parametric numerical modeling is used to determine the distance that a cone senses a new upcoming soil layer interface or a layer interface behind. Analyses are also carried out for a thin sand layer embedded in soft clay. It is seen that the full tip resistance may not be reached in thin stiff layers. This is especially true for penetration in thin dense sand layers interbedded in softer clay. A correction factor is suggested to correct the cone tip resistance in thin sand layers. The higher the stiffness and the thinner the layer, the larger the correction factor. The numerical results obtained in this paper are in good agreement with experimental observations. Some limitations of a previously proposed correction factor are discussed.