Compared to silica sand. carbonate sand has considerably higher angularity, lower grain hardness and higher intraparticle porosity. which result in high friction angles and compressibility, The corresponding dilatancy is affected strongly by the confining stress. Thus, even for low relative densities, dilation occurs at low confining stresses, reflecting the greater particle interlocking compared to silica sand, However. with the increase of confining stress. the dilatancy is suppressed quickly, and finally diminishes completely at a relatively low stress level, due to particle degradation. This distinctive characteristic significantly influences the behaviour of continuously penetrating spudcan foundations in calcareous sediments. Centrifuge tests were carried out on spudcan foundations penetrating multi-layer soils with an interbedded strong layer composed with either carbonate or silica sand. All measures of spudcan punch-through severity were significantly lower for interbedded carbonate sand despite its higher friction angle (phi(crif) = 40 degrees) compared to silica sand (phi(crif) =34 degrees). For the spudcan penetration through the sand layer to the lower clay layer, the soil failure mechanisms quantified by particle image velocimetry (1'IV) analysis allowed for identifying the differences in the evolution of sand frustum beneath the advancing spudcan. The spreading angle of the frustum, which determines the size of the projected bearing area. was found to be proportional to the mobilised dilatancy.
