Influence of fines content on the compression characteristics of calcareous sand and the related meso-mechanism

The engineering properties of calcareous sand are closely related to the construction of island reef projects. It is inevitable that some fine particles will be interspersed in the process of island reef filling, thus affecting the overall stability of the island reef. Current research on the physical and mechanical properties of calcareous sand with varying fines content primarily focuses on the macroscopic perspective, while analyses of the deformation mechanisms and particle breakage patterns from the point of meso view remain deficient. Therefore, in this paper, the effect of fines content on the compression behavior of calcareous sand with different water contents is investigated through compression tests. Furthermore, combined with the mesoscopic observation, internal structural changes of calcareous sand with different fines contents during compression are revealed, and particle breakage features of calcareous sand are also obtained. It is found that low fines content can improve the deformation resistance of calcareous sand to a certain extent and reduce the compression of calcareous sand, while high fines content will exacerbate the deformation of the calcareous sand; the deformation of saturated specimens is more significant, which indicates that water has an obvious lubricating effect during the compression process and promotes compression deformation. The detailed analysis shows that, with the increase of fines content, the external and internal pores between the calcareous sand particles are filled, and the fines form a “protective layer” wrapping the calcareous sand particles, thus weakening the particle breakage; when water and fines coexist, the lubrication effect of water further aggravates the deformation of the calcareous sand and reduces the particle breakage.