Thin-layer effects on the CPT q_c measurement

Abstract

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.Key words: cone tip resistance, modeling, sand, clay, interface influence distance, layering.

Cone penetration test (CPT)-based stratigraphic profiling using the wavelet transform modulus maxima method

“…Using numerical analyses, Ahmadi and Robertson (2005) demonstrated that depending on the strength of the soil and the in situ stress, the cone in a CPT can sense a layer boundary at a distance of up to 15 cone diameters ahead and behind. The distance is longer for stiff soils and under low effective stress and is shorter for soft soils and under high effective stress.…”

End Bearing Capacity of Drilled Shafts in Sand: A Numerical Approach

“…Hence, the bulk and shear modulus are considered to be stress dependent. and Ahmadi and Robertson (2005) have also used stress dependent Mohr-Coulomb model parameters to numerically predict the cone tip resistance in sand. They suggested the following relations for bulk and shear modulus:…”

Centrifuge modelling of cone penetration tests in layered soils

“…There have also been some numerical simulations conducted for the analysis of layered effects and the definition of the influence zones around soil interfaces (e.g. van den Berg et al, 1996;Ahmadi & Robertson, 2005;Xu & Lehane, 2008;Walker & Yu, 2010). The first analytical solution for penetration in layered soils was proposed by Vreugdenhil et al (1994), which is an approximate solution for simple linear-elastic media.…”