Physical Modeling of Cone Penetration in Layered Sand

This paper presents the results of cone penetration tests performed in layered, uniformly graded silica sand samples prepared inside a calibration chamber specifically designed for digital image correlation (DIC) analysis. The tests aimed to investigate the effect of a layer interface on the cone penetration resistance as well as on the soil displacement and deformation fields resulting from cone penetration. The results, which are also of interest in connection with the calculation of the base resistance of piles embedded in bearing layers, are interpreted based on the sensing distance and development distance concepts. The results show that the sensing and development distances are affected by the density of the soil on either side of the layer interface. Based on the results obtained in this paper, the sensing and development distances are of the order of 2.2–5.4 cone diameters. The vertical displacement profile next to the shaft of the penetrating cone changes significantly near the layer interface, which implies that the vertical displacement profile can be used to identify the presence of a layer interface in a DIC test. The incremental displacement and deformation analyses within the sensing distance show that, when the cone starts sensing the underlying sand layer, the average direction of the soil displacement rotates toward the underlying layer for strong-over-weak layers and away from it for weak-over-strong layers. It is also observed that the size of the shear strain bulb next to the cone surface increases when reaching a strong layer and decreases when reaching a weak layer.