Abstract: Particles of calcareous sand, labeled as porous, irregular shaped, easily crushable, etc., have great influence on its engineering properties. To investigate the effect of particle size and shape on its compressibility, we group the samples from an island in the South China Sea into different particle sizes and shapes, and conduct mineral composition analysis and statistical analysis of the particle shapes, and oedometer tests. Statistical analysis shows that the sand particles can be classified into massive granules, arborescent granules, and bioclastic granules in terms of particle shape. The mineral composition is mainly aragonite-based calcium carbonate, and similar mineral composition is also found in calcareous sand with different particle sizes and shapes. The oedometer tests illustrate compressive deformation of the sand is mainly an irreversible plastic deformation that occurs through two stages ? initial compaction and particle crushing. In initial compaction (vertical pressure p = 0 - 100 kPa), the deformation of the sample mainly depends on movement and rearrangement of particles, as a consequence, a sample with small particle size has larger compression in this stage; As p increases further, particles begin to crush (p > 200 kPa in this stage) and the deformation is controlled by particle crushing. Larger particles are broken more easily, and thus more compressive deformation occurs to a sample of larger particle size. In addition, compressibility of arborescent granules is also much greater than that of massive and bioclastic granules.

Key words: soil mechanics, calcareous sand, particle shape, compression characteristics, particle crushing