Particle-scale insights into sand deformation during open-ended pile installation using DIC and X-ray CT

This paper presents the results from two model open-ended pipe pile installations in sand and subsequent particle-scale analysis using X-ray computed tomography. The experiments were performed in a large half-cylindrical calibration chamber with imaging capabilities. During testing, digital images were captured and later analysed using digital image correlation (DIC) to obtain displacement and strain fields in the sand domain. After installation, sand around, below and inside the pile was impregnated using an epoxy resin. The epoxy-impregnated samples collected from the calibration chamber were scanned using X-ray computed tomography and, from the reconstructed three-dimensional (3D) volumes, the sand fabric was determined. Kinematics obtained from two-dimensional (2D) DIC analyses of the experiment provide insights on the underlying mechanisms leading to changes in sand fabric due to pile installation. Results show that interparticle contact normal unit vectors tend to have vertical orientations below the pile base, but sub-horizontal orientations after entering the sand plug. This rotation of contact normal directions occurs in a region immediately below the pile base where the sand is being partially forced into the pile. Overall, sand particles tend to rearrange so that contact normal orientations match the direction of compressive principal strains near the model pile.