Abstract: The natural repose angle of sand has important guidance for mound construction, foundation design and slope stability analysis. The natural repose angle is mainly affected by friction, particle shape, grain size and water content of sand. In this paper, the natural repose angle of calcareous sand under various conditions is tested. In the three common particle shapes of calcareous sand, the flake particles present the largest repose angle; the rod stick particle shapes present less, and the block shape ones show the smallest value of angle. The natural repose angle of calcareous sand increases with the increase of grain size. When the mean particle size is the same, the natural repose angle increases as the inhomogeneous coefficient increases, and decreases as the curvature coefficient increases. The natural angle of repose of quartz sand is smaller than that of calcareous sand. It is mainly determined by the mineral composition and particle shape. The underwater repose angle of calcareous sand is smaller than that of natural repose angle in general. The maximum angle of foundation ditch slope is larger than the tested natural angle of repose. The results are instructive for coral reef mound constructions and design.

Key words: calcareous sand, natural angle of repose, particle shape, non-uniform coefficient