Extension of constitutive model for unsaturated soil on DEM analysis

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By the distinct element method analysis in three-dimensional state, simulations of the true triaxial test for spherical granular material was carried out In this analysis, the influence of meniscus water, which is mainly cause of the complicated behavior of unsaturated soil, is expressed by introducing a constant intergranular adhesive force that acts perpendicular to the tangential plane at contact point. The influences of the intergranular adhesive force on the failure criterion and shear deformation are examined. The obtained results are summarized as follows.1. The internal friction angle and the adhesion for triaxial stress state increased with the intergranular adhesive force. This result corresponds to the triaxial test results obtained for unsaturated soil, and shows the effectiveness of introducing the intergranular adhesive force for DEM analysis to study the mechanism of unsaturated soil and the other granular materials with cohesion.2. The Lade failure criterion on the π plane explained well the failure stress state regardless of the intergranular adhesive force. This result means that the Lade failure criterion is able to use the failure criterion for unsaturated soil and the other granular materials with cohesion.3. The residual stress points on the π plane distribute around the SMP failure criterion. This result means that the SMP failure criterion is able to use the contractive material like normally consolidated clay.The counters of shear strain show the similar shape with the Lade failure criterion at near to failure state. This result shows that the Lade failure criterion should dominate the shear deformation of expansive granular materials with cohesion.