Physical modelling of deformations around piling augers in clay

Small-scale model tests are reported in which miniature augers were installed in beds of transparent synthetic soil simulating clay. As the auger advanced, the movement of reflective particles seeded into the soil and illuminated by laser light was recorded photographically. The displacement field in a vertical plane aligned with the auger axis was then determined using particle image velocimetry. The pattern of deformation of the soil around an auger of the type used to form a cast-in-situ screw pile was similar to that around a cylindrical straight-sided pushed pile. Deformations around an auger of the type used to form a rotary displacement pile depended on the rotation speed of the auger and the extent to which the flights carried soil upwards away from the tip. Lateral displacements in the model tests exhibited roughly similar trends to those observed in the field.