DEM Simulation And Experimental Study On The Size Effect Of Single Particle Crushing Of Calcareous Sand

As the most common coral reef geotechnical material in island infrastructure construction,calcareous sand has different mechanical properties from ordinary terrestrial sand due to its special biogenesis.The construction experience of calcareous sand applied to engineering is difficult to obtain from other geotechnical material tests,and the in-situ test or proportional test is a huge test of time cost and economic cost.Therefore,it is necessary to carry out the microscopic mechanical properties test and simulation study of calcareous sand.By further clarifying the size effect of the crushing strength of calcareous sand particles,understanding the crushing behavior of a single particle is helpful to analyze the mechanical response of particle combination crushing,and has certain guiding value for the design of efficient geomechanical analysis.Exploring the influence of microscopic parameters on the size effect is important for the construction of multiscale intrinsic structure models of brittle granular materials and the relationship between particle size and the macroscopic mechanical response of materials.In this paper,a series of experimental and discrete element simulation studies of single-particle crushing were carried out with the calcareous sand on an island in the South China Sea as the research object,and the main contents and results are as follows.(1)The particles of calcareous sand were selected and grouped into six particle size groups with a particle size span of 2 mm and analyzed statistically using two shape indexes:elongation(EI)and flatness(FI).Based on the previously proposed Fourier analysis 3D particle reconstruction method,180 irregular single particle 3D templates were constructed based on the statistical shape parameters of the calcareous sand.(2)Based on the single particle crushing test of calcareous sand,the relevant studies on the particle crushing mode and the size effect of particle crushing strength were carried out.The experimental results show that the force-displacement curves of single particle crushing of calcareous sand can be roughly classified into four categories: multi-peak type curves before the main peak,multi-peak type curves after the main peak,parallel peak type curves and single peak type curves.The types of force-displacement curves are closely related to the forms of particle crushing.The single particle crushing strength of calcareous sand can well conform to the Weibull distribution and exhibits an obvious size effect,with Weibull modulus values m between 1-2 for different sizes of calcareous sand.There is a negative linear relationship between the crushing energy per unit volume of the particles and the particle size.(3)Single-particle crushing simulations using discrete element method and fracture network model to investigate the causes of size effect and analyze the effect of microscopic initial cracks size on single-particle crushing strength distribution and size effect.The results demonstrate that the discrete element method can well simulate the shape characteristics of irregular particles and the macroscopic mechanical behavior of brittle materials.The fracture network model can successfully reproduce the size effect of the fragmentation strength of brittle particles,while verifying that the essential cause of the size effect is the internal microscopic initial cracks of the material.With the increase of the initial microscopic crack size,the single particle crushing strength of the same particle size group decreases,the dispersion increases,the Weibull modulus decreases,and the size effect is more obvious.According to the Weibull distribution model of particle crushing strength,the discrete assignment of particle strength characteristics can be effectively realized through inverse function calculation.