Displacements, Strains, and Shear Bands in Deep and Shallow Penetration Processes

When penetrometers or probes are pushed into sand, complex displacement fields, strain fields, and shear band patterns develop. Deep and shallow penetration processes in sands generate substantially different patterns. This paper reports the results of penetration experiments performed in dense air-pluviated sand samples prepared in a half-cylindrical calibration chamber equipped with observation windows that allow the collection of images of the sand during penetration. Both a cone penetrometer (diameter $d=38\mathrm{mm}$) and a model footing (width $B=90\mathrm{mm}$) are used in the penetration experiments. Incremental displacement and strain fields in the soil domain are obtained by analysis of the collected images using digital image correlation (DIC) and continuum mechanics. The zero-extension line concept is used to study shear strain localization, and a method is proposed to automatically obtain the orientation of shear band patterns from the incremental strain fields. For the model footing, the strain fields are found to localize not only near the footing but also away from it, depending on the level of penetration. The shear bands develop in a traditional wedge shape below the model footing and in a fan shape on either side of it. In contrast, for the cone penetrometer, the strain fields localize more intensely near the penetrometer tip. The shear bands develop along the inclined face and near the shoulder of the penetrometer.