Cyclic settlement behaviour of spudcan foundations

Abstract

This paper examines the cyclic settlement behaviour of spudcan foundations in sand, using centrifuge model data. By means of a servo-electrohydraulic system, loading episodes comprising several thousand cycles of sinusoidal loading were applied to model spudcan foundations. The findings showed that, in dry sand, non-preloaded spudcans settle by penetration into the soil, resulting in a large increase in cyclic stiffness. In contrast, preloaded spudcans appear to settle by densification of the sand, leading to a smaller increase in cyclic stiffness. In saturated sand, where excess pore pressure can accumulate, the effects of preloading are less evident. A non-preloaded spudcan tends to generate a bulb of negative pore pressure around itself, conferring some apparent preloading on the near-field soil, and thereby resisting further penetration. In a preloaded model, the negative pore pressure bulb is smaller and surrounded by a zone of positive pore pressure. As the positive pore pressure propagates into the negative pore pressure bulb, the effective stress of the sand around the spudcan decreases, allowing further penetration. This is manifested as an apparent loss of preload. Thus non-preloaded and preloaded spudcans may settle by densification and penetration.