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Dynamic mechanical characteristics of coral sand is of vital importance for foundation compaction. In the present study, a series of tests were conducted to estimate the dynamic behaviors of coral sand under drop weight impact. The coral sands with original and uniform gradations were impacted with different energies and different repeating times. The test results show that the dynamic force–displacement or the stress–strain response roughly undergoes the initial intense fluctuation, quasi-free fall, subsequent descending fluctuation and the inverse rebound periods. The reduction in the void ratio of coral sand increases with single impact energy increasing, while it decreases with the repetition of impact. The breakage of coral sand under impacting is progressive along the height of the sample, revealing by the multiple yield points in the e-logp curve. It is found that the predominant size fraction of fragmented particles corresponds well to the inflection interval of its initial PSD curve. The ratio of the dissipated energy to the absorbed energy generally reduces as the repetition of impact loading. The breakage index can be closely correlated to the dissipated energy. As compared to the original coral sand, the uniform coral sand exhibits more sensitive behaviors in terms of compressibility, particle crushing and energy dissipation. Furthermore, the scenario of few impacts at high energy level is proved to be more efficient than that of multiple impacts at low energy level in the reinforcement of coral sand. [ABSTRACT FROM AUTHOR]

This paper reports a simulation-based dynamic confined compression analysis of coral sand under an impact load using the discrete element method (DEM). The evolution of particle breakage on the mesoscale was studied by investigating force chain distributions, crack development, and breakage modes. Crushable sand particles were simulated by replacing rigid particles with flexible basic unit aggregates. The Weibull parameters were incorporated within the mesoscopic parameters of particles, and random numbers were introduced. The obtained results for particle strengths were consistent with the experimental data. The numerical results demonstrated that the force chain was significantly strengthened along the loading axis during loading and weakened during unloading. The cracks were primarily generated along the strong force chain, and particle breakage caused the strong force chain to move towards relatively more complete fragments nearby. The crack was primarily oriented along the loading axis, and its anisotropy was observed to decrease with an increase in the load. Before yielding, particle breakage in the specimen was dominated by attrition at the edges and corners. After yielding, the crack extended into the particle perpendicular to the intergranular contact surface and was deflected by the simultaneous influence of pores. The fracture and shattering of particles occurred successively, and the consequent fall-off and slip filling of the fragments promoted the deformation development. [ABSTRACT FROM AUTHOR]

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Coral sand is characterized by high porosity, high compressibility and high crushability mainly due to its irregular particle shape and internal pore structure. Single coral particles in a size fraction tend to have a variety of shapes from bulky to flaky, which emerges as one of the most pivotal factors affecting the macro-scale performances of coral sand. A series of confined one-dimensional dynamic compression tests were conducted on coral sand with four classified shapes (e.g., blocky, dendritic and rodlike, flaky particles, and coral debris) via a modified 37-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. The effects of particle shape on the dynamic mechanical behaviours of coral sand at high strain rates were assessed in terms of the stress-strain response, compressibility, particle breakage and the change in particle shape measures. It is revealed that coral sand exhibits high small-strain stiffness, a low crushing strength, a notable strain hardening and a high compressibility behaviour as subjected to dynamic compression at high strain rates. In the low-stress level, it is the high interparticle friction and interlocking induced by the irregular shape form and rough surface texture that lead to a gentle descending tendency in the void ratio. While in the high-stress level, it is the particle crushing along with its rearrangement that results in the high compressibility of the coral sand assemblage. In general, the particle crushing strength tends to decrease as the particle shape shifts from bulky to elongated and to flaky. The large-strain stiffness decreases and the compressibility increases with an increase in the overall particle irregularity. Coral particles are prone to be more spherical and smoother as the average degrees of sphericity, convexity and aspect ratio approach to unity, due mainly to the intense asperity damage and primary fracture under dynamic tests. Furthermore, the percentage in the degrees of sphericity, convexity, aspect ratio and flatness increases with respect to the initial degrees of themselves. It can be further postulated that the extent of breakage could be quantified by the statistical change in the particle measures such as sphericity and convexity aside from particle dimensions for granular materials with irregular shapes. • A series of confined one-dimensional dynamic compression tests are performed on coral sand with four classified shapes. • Effects of particle shape on mechanical properties of coral sand are assessed quantitatively. • The compressibility, particle breakage and the change in particle shape measures are quantified. • The force chain evolution along with the rearrangement and breakage of particle are revealed. • Correlations between particle shape measures and particle breakage are estimated. [ABSTRACT FROM AUTHOR]