Double Yield Surface Model of Calcareous Sand Considering Particle Breakage

Coral islands is mainly composed of calcareous sand with characteristics of irregular shape, multi porosity, high compressibility and friability. During the ecological development and construction of coral island, due to the particularity of calcareous sand, it is necessary to study the constitutive model of calcareous sand considering the particle breakage, to provide references for the design and construction of coral island engineering. To obtain the stress-strain and grading curves of calcareous sand, the triaxial tests with different confining pressures were carried out and the particles were screened. The test results showed that the calcareous sand with the same gradation and density had different degrees of strain softening and dilatancy under different confining pressures, especially under the lower confining pressures. In the range of confining pressure with strain softening and dilatancy, with the increase of confining pressure, the axial strain corresponding to the peak point of deviatoric stress and the critical expansion point increases. Calcareous sand had different degrees of particle breakage under different confining pressures. The higher confining pressure is, the higher degree of particle breakage is, and the more content of fine particles is. At the same time, to accurately describe the stress-strain relationship of calcareous sand, the tangent deformation modulus and tangent volume ratio of Nanjing Hydraulic Research Institute (NHRI) double yield surface model were modified. Based on the fractal theory and Mohr-Coulomb theory, the index considering particle breakage was established to modify the internal friction angle. Finally, the constitutive model of calcareous sand considering particle breakage was established, and the significance of each material constant was clarified. Fortran language was used to simulate the modified constitutive model, and the results were compared with the experimental results, which were in good agreement. Combined with the relevant experimental data in the references, the established constitutive model of calcareous sand considering particle breakage was extended and verified. The results showed that the model could accurately reflect the strain softening and dilatancy of calcareous sand under different confining pressures. © 2021, Editorial Department of Advanced Engineering Sciences. All right reserved.