Creep characteristics of calcareous coral sand in the South China Sea

In recent years, a series of lands have been built or enlarged on the top of some natural coral reefs by the means of reclamation in the South China Sea (SCS). The reclamation material used is the calcareous coral sand extracted from nearby lagoons. As a kind of special geotechnical material, its mechanical characteristics are different from that of conventional terrestrial soil. It is of great significance to study the time-dependent creep characteristics of the calcareous coral sand for evaluating the post-construction settlement of some important structures built on these reclaimed lands. In this study, a series of drained triaxial tests are conducted to study the long-term creep characteristics of calcareous coral sand under different loading types (single-level and multi-level tests). Based on the experimental results, it is found that calcareous coral sand indeed shows considerable time-dependent creep deformation under a constant stress state. There are two development modes for the volumetric strain versus axial strain curves during creeping under single-level loading; while there is only one development mode under multi-level loading. It is shown that the unfavorable effect of the air entrapped in the micro inner cavities of coral sand particles leads to a spurious volumetric strain measured in the middle and late stages of creep. The determination of the particle size distribution after the tests shows that the relative slippage and rearrangements of sand particles play the leading role in the creep deformation process for calcareous coral sand. The effect of sand particle breakage on creeping is not obvious. Based on these test data, a novel four-parameter mathematical model is proposed to model the creep characteristics of the calcareous coral sand in the South China Sea.