Abstract: To develop offshore facilities in South China Sea, it is vital to understand the characteristics of particle shape and breakage properties of the calcareous sand. As a result, micro- and macro-mechanical behaviors of crushable calcareous sand sampled from South China Sea are addressed in this study. Firstly, calcareous sand particles are scanned by electron microscope and analyzed by an image processing software (i.e., ImageJ). Based on the processed image, two shape parameters, namely circularity and solidity, are defined and quantified. Secondly, drained triaxial tests on calcareous sand at various confining stresses are carried out, so as to investigate the effects of particle breakage on deformation, shear strength and energy dissipation of the calcareous sand. Results show that the shape of the calcareous sand with relatively large particle size (diameter greater than 2 mm) and relatively small particle size (diameter less than 0.5 mm) tend to be circular and the particle surface is relatively smooth. Comparatively, shape of calcareous sand with moderate-size diameter (grain diameter ranged between 0.5 and 2 mm) is more irregular, and sand particles have more surface edges. Particle breakage is identified to occur in triaxial tests, leading to a better graded sand packing. With the increasing initial confining pressure, the degree of particle breakage and the energy dissipation due to the breakage both increase. In the meantime, dilation of the sand is partially suppressed by the breakage. Under two conditions only considering friction dissipation and considering both friction and volume dissipation, the dissipated energy resulting from breakage in the triaxial tests with relatively high (600 kPa) initial confining stresses could account for 25% and 18% of the total plastic energy input, respectively.

Key words: calcareous sand, triaxial tests, particle crushing, dilatancy, energy dissipation