Research On Bearing Characteristics Of Coral Reef Sand Foundation Based On Multi-Scale FDM-DEM

Coral reef sand was widely found in islands and reefs in the South China Sea and along the coast.As an important area for the development of marine resources in the South China Sea,coral reef sand is important to national defense and energy development,and the research on marine island reef construction become more important in recent years.Coral reef sand is composed of calcareous sand,coral reefs,shellfish and other impurities.It has the characteristics of large pores,irregular shape and high breakage.These characteristics make it quite different from terrigenous standard quartz sand,and exhibit the special mechanical properties when coral reef sand was appiled to foundations,slopes and different conditions.Therefore,explore the bearing characteristics of coral reef sand foundation is of great significance.In this manuscript,the coral reef sand foundation is taken as the research object.Simulated hydraulic reclamation and foundation bearing tests were carried out,several numerical models were established for analysis.The main work was listed as follows:(1)There was a stratification phenomenon with uneven distribution of gradation in the coral reef sand foundation after hydraulic reclamation.Different gradation of coral reef sand will cause changes in the mechanical properties.The uneven distribution and inhomogeneous gradation changes of coral reef sand under the hydraulic sorting were explored through the hydraulic reclamation model test.Relying on the simulated model test,the uneven distribution of the foundation was simplified,and the bearing capacity model tests were carried out.The test results show that the two-layer inhomogeneous horizontal distribution has the largest ultimate bearing capacity,and the ultimate bearing capacity will be weakened when the ground has non-horizontal stratification.(2)A coupled inhomogeneous coral reef sand foundation simulation model was established using the finite-discrete coupling method,and the simulation results were compared with the experiment model to confirm the rationality of the simulation.Different numerical models of inhomogeneous coral reef sand foundations were established with the same parameters to investigate how the heterogeneity distribution change the coral reef sand foundation on its ultimate bearing characteristics and microscopic distribution.The movement and force distribution of coral sand particles in the inhomogeneous coral sand foundation are more concentrated,the strong-weak force chain and displacement nephogram explain the distribution changes affecting the ultimate bearing capacity.Based on the test and simulation results,the equivalent friction angle considering the depth correction factor was proposed,and the calculation results were compared with the results in the specification.The calculation results of the equivalent formula considering the depth correction factor and reduction factor were closer to the experimental and numerical simulation results(3)Using the coupled inhomogeneous non-horizontal coral reef sand foundation model,the numerical simulation and experimental results were compared.A inhomogeneous non-horizontal coral reef sand foundation model with the same parameters and different conditions were established,and the changes of its microscopic distribution were analyzed.The particles in the non-horizontal foundation will slip along the direction of uneven distribution,weakening the ultimate bearing capacity of the foundation.The calculation results of the equivalent method considering depth correction and reduction factor were compared with the experimental and numerical simulation results.The influence of different inclination conditions which were considered into Hansen’s methods on the ultimate bearing capacity is discussed.