Effects Of Particle Size On The Particle Breakage Of Calcareous Sands Under Impact Loadings

Particle breakage of calcareous sands under impact loadings,closely related to marine and geotechnical engineering,has attracted a great deal of attention.A series of impact tests were carried out on calcareous and quartz sands with four different particle sizes(5.00-2.00 mm,2.00-1.00 mm,1.00-0.50 mm and 0.50-0.25 mm).Currently,while there is extensive research on the effects of the particle size for calcareous sands,limited research has been conducted on these quantitative comparisons and the relationship between the particle size and the particle breakage.Furthermore,there is still no clear understanding of the size-dependent behavior and the particle breakage mechanism of calcareous sands under impact loadings.Therefore,it is significance to research the size-dependent behavior and the impact characteristics of calcareous sands for further applications in coral reef projects.(1)In this paper,calcareous and quartz sands under different impact energies were screened.The grading evolutions of the two geotechnical materials were explored.The particle size distribution(PSD)curve of calcareous sand moves upward with the increase of impact energy,and the particle size distribution of all samples increases gradually,indicating that the impact energy makes the samples broken.The grading evolution law of quartz sand is basically similar to that of calcareous sand.(2)By comparing the change of fractal dimension with energy,the fractal behaviors of calcareous and quartz sands were studied.Compared with quartz sand,the fractal behavior of calcareous sand is more easily affected by the initial particle size.(3)According to the change of the deformation rate,the volumetric deformation of the above two types of sands can be divided into three typical stages: initial compression stage,failure stage and stability stage.In contrast to calcareous sand,quartz sand can reach a stable stage at a lower input energy.By measuring the axial deformation under impact loading,the results show that the compression of calcareous sand is more obvious than that of quartz sand.(4)Based on the measurement methods and experience of domestic and foreign scholars on the crushing degree of granular materials,the crushing degree of calcareous sand and quartz sand under impact load were quantitatively compared and analyzed.The “breakage sensitivity index” Bd,which is defined as the increment of the relative breakage index under the per unit increment of the input energy,was proposed to evaluate the breakage sensitivity of samples.The results show that the breakage sensitivity of fine particles is more significant than coarse particles.This difference between coarse and fine particles can be attributed to the difference of the coordination number.Particles with smaller coordination number bear larger impact loading,resulting in higher crushing sensitivity than particles with larger coordination number.(5)The relative breakage index is linear with the volumetric deformation.An empirical model for estimating particle crushing degree by volume deformation is proposed.Compared with other models,it has the characteristics of less parameters,convenience and effectiveness,which provides a theoretical reference for island and reef engineering construction.