| With the in-depth advancement and continuous pragmatism of the strategy of "Powering the South China Sea",calcareous sand is used as a natural raw material for the infrastructure of island reef engineering.The complex marine environment and special biological causes make it have the characteristics of irregular shape,easy breakage,easy cementation,and many internal pores,showing different engineering mechanical properties from ordinary terrigenous sand.A large number of studies have shown that the special mechanical properties of calcareous sand originate from its particle breakage.At the same time,the deformation characteristics of calcareous sand directly affect the safety of island reef structures.Therefore,understanding the particle crushing mechanism of calcareous sand and the factors affecting its deformation characteristics have become the key to ensuring the safety of reef engineering.Understanding the causes of calcareous sand particle breakage and the meso-deformation characteristics is a necessary condition for the steady advancement of the "South China Sea Power" strategy.It is of great practical and strategic significance to study the crushing mechanism and meso-deformation characteristics of calcareous sand particles.In this paper,a calcareous sand sourced from an island reef in the South China Sea is taken as the research object,and the laboratory test results are used as the benchmark,and a numerical model that can reproduce the results of the calcareous sand laboratory test is proposed.The bond strength between particles is improved to simulate unbreakable particles,and the large principal stress theory proposed by PETERS et al.The evolution process of calcareous sand,and the advantage of using internal contact force of particles at any time,explore the causes of calcareous sand particle breakage,and reveal the generation mechanism of the macroscopic mechanical properties of calcareous sand.Its main research contents are as follows:(1)Through the indoor triaxial consolidation drainage test,it is found that the confining pressure has an important influence on the macroscopic mechanical properties of calcareous sand.Using the two contact models of linear bonding and bonding in PFC,a biaxial numerical test model was established using the BPM particle breakage simulation method.A large number of biaxial numerical experiments were carried out,and the controlled variable method was used to explore the influence of different mesoscopic parameters on the macroscopic response of the simulated experiments.The meso-parameters were repeatedly adjusted according to the results of the laboratory test,and a biaxial test model that was consistent with the trend of the results of the laboratory test was proposed.(2)Using the large principal stress theory proposed by PETERS et al.to identify the force chain,a series of biaxial numerical experiments with different confining pressures were carried out,and the high stress particles and force chain particles of calcareous sand were systematically analyzed under biaxial compression conditions.The law of evolution,and the numerical test results of the unbroken model and the broken model were compared and analyzed,and the force chain distribution,length,quantity and probability in each direction of the two models under different confining pressures were analyzed to reveal the mechanism of particle breakage.(3)Using the advantages of discrete elements,the rotation,displacement,and internal contact force of the two models during loading under different confining pressures were analyzed.Impact.The evolution of the position and quantity of particle breakage with axial strain is analyzed,and it is found that the confining pressure affects the form and location of particle breakage.The mesoscopic deformation of calcareous sand is mainly related to particle breakage and confining pressure. |
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