Construction And Verification Of Constitutive Model Of Elastoplastic Damage Of Calcareous Sand Particles

With the rapid development of the global economy,the demand for resources in various countries is increasing,and the exploration and development of land resources have become increasingly tense.In particular,although China has a vast land territory,the per capita resource ownership has been lagging behind the world.China’s largest and deepest sea contains rich resources and outstanding national defense status.Since the "Sixth Five-Year Plan",Chinese scholars have devoted themselves to the study of the South Island Reef,and in the study of the South Island Reef,it is inevitable to face the problem of calcareous sand geology.Calcareous sand is a special geotechnical medium of marine biological origin and calcium carbonate content greater than 50%.Due to its high calcium carbonate content,the strength of calcareous sand particles is much lower than that of general land-based sand(quartz sand,etc.)The pores between the particles are also relatively large,so that the calcareous sand particles will break when the particles are under a lower stress.When the particles are broken,the compressive and shear strength of calcareous sand will obviously decrease,leading to various cracks,collapses,and bearing capacity of pile foundation caused by changes in the strength of calcareous sand particles in engineering practice.Insufficient engineering problems.Therefore,how to effectively simulate the change of calcareous sand geological strength when subjected to large stress,provide a more scientific geological bearing capacity reference for the development and utilization of the South Island Reef,and eliminate the engineering caused by the breakage of calcareous sand particles Hazard has become an important issue that must be solved for the development of the South China Sea.Based on this background,the paper carried out the following main work:(1)In view of the characteristics of calcareous sand particle breakage under load conditions,the physical characteristics of mixed calcareous sand samples and the three conditions of different confining pressures(200k Pa,400 k Pa,800 k Pa,1200 k Pa,1600 k Pa)were developed.The stress-strain characteristics of the calcareous sand under low confining pressure and high confining pressure stress are obtained,and the relevant physical characteristics and mechanical property parameters are obtained.(2)By sieving calcareous sand samples after triaxial shearing under different confining pressures,the content of different particle size groups after calcareous sand shearing and crushing is obtained,and the relevant gradation curve is drawn,and reference is made to the previous For the measurement method of the degree of crushing of granular materials,the degree of particle crushing after calcareous sand shear failure is calculated.Finally,through controlling variables,the effects of mineral composition,particle size,stress level and gradation on calcareous sand particle breakage were discussed.(3)Under the condition that the relative density is consistent,the calcareous sand sample that has undergone the first triaxial shear test is subjected to the same secondary shear to obtain the stress-strain curve of the secondary shear,Based on the damage theory,the stress-strain behavior of the two shear tests is studied,and the calcareous sand damage evolution function that can reflect the law of calcareous sand particle breakage is obtained.The model provides the basis.(4)Based on the definition of sensitivity in the constitutive model of the upper and lower load surfaces,the damage evolution function is embedded in the constitutive model of the upper and lower load surfaces through the relationship between actual physical meanings,and a fracture damage of calcareous sand particles is established.The elastoplastic constitutive model of the calcareous sand sample shows that the model can better characterize the particle crushing damage of the calcareous sand sample,and the model is compared through the simulation of the indoor load plate test.The difference in bearing capacity calculation with the classic Mohr Coulomb model further verifies the accuracy of the model.