Abstract: To investigate the failure behavior of different graded coral sand cementations under static and dynamic loads, a series of impact tests is carried out on the coral sand cementations with different gradations through the drop hammer impact test facility. Combined with static compression tests, the mechanical behavior and failure modes of coral sand cementations are analyzed. The experimental results show that the wider the grading of the coral sand is, the greater the compressive strength of the cement test block is, the stronger the impact resistance is, the smaller the damage angle is, and the crushing angle decreases gradually. The coral sand cement blocks show different failure modes under different kinds of loads, which are obviously different from concrete blocks. Additionally, a 3D discrete element model is established and the paremeters are calibrated according to the the stress-strain curves of the experimental results, then the numerical impact tests are conducted. The numerical results show that, from the perspective of fracture distribution, as the gradation interval and the average particle size increase, the impact-induced micro-fractures that are uniform and dispersed will be more concertraded in a certain direction, leading to the reduction of the number of cracks and the damage degree. From the perspective of system adhesion, the cohesive force inside the block with narrow gradation range is small and distributed uniformly, while the cohesive force in the block with wide gradation size range is large and unevenly distributed.

Key words: coral sand, gradation, impact load, crack, discrete element method