Influence of Footing Shape on the Bearing Capacity of Soft Clay

Most marine structures tend to use deep foundations. However, using shallow foundations would be a more cost-effective alternative for some situations, especially for subsea infrastructure. An important factor in the general bearing capacity equation is the shape factors. In this study, the effect of different footing shapes on the bearing capacity of marine soft clay was investigated, with the aid of a transparent soil that permits visualizing deformations within it. Five shapes having the same cross-sectional area and the same material properties were used. The marine soft clay was simulated by a synthetic transparent soil made of magnesium lithium phyllosilicate (MLPS). The undrained shear strength was measured using a miniature ball penetrometer. An embedded seeded plane was employed to track soil movements. Those movements were captured by a high-speed camera, and the resulting images were analyzed using digital image correlation (DIC) methods (aka. PIV). The internal shear strain was determined during different stages of loading. The failure stage was observed through the image analysis and the failure mechanism could be observed. The shape factor for each footing was determined based on the general bearing capacity equation and the ultimate load measured. A comparison between the results and traditional shape factors in common use supports the validity of shape factors proposed by Terzaghi or Meyerhof for marine foundations supported by very soft clay soils.