Study On Softening Calculation Of Cemented Soil And Mechanism Of Grid Sensitivity

Grid sensitivity has always been a difficult problem in geotechnical numerical simulation.Only by systematically studying the mechanism of grid sensitivity can we accurately describe the macroscopic mechanical properties and deformation characteristics in practical engineering.But often sensitivity of strain localization can bring grid,so this article from the generation mechanism of strain localization shear zone,constructed to reflect cemented damage constitutive model,simulation cementation and damage softening and dilatancy softening of strain localization shear zone,to reveal the mechanism of grid sensitivity,in this paper,the main work and research results were as follows:A constitutive model is constructed to reflect the damage softening characteristics of cemented soil.The model involves seven constitutive parameters and three state quantities of cemented soil.The physical significance of the model is clear and the value is simple.The formation mechanism of strain localization shear band was investigated.It is verified that the compactness of soil plays a decisive role in dilatancy and softening of sand.For cemented structural soil,two cementing parameters have a great influence on soil softening.The initial cementing force can significantly increase the peak strength of soil,and the damage coefficient of cementing force determines the speed of the loss of cementing force.By comparison,it is found that strain localization occurs in both dilatancy softening and cementation damage softening,and the change of boundary constraint conditions only affects the distribution of strain localization,but does not affect its occurrence.The causes of grid sensitivity are analyzed.The mesh sensitivity mainly occurs in the samples with softening characteristics,which is mainly reflected in the softening stage.For specimens exhibiting hardening properties,the effect of sensitivity is negligible.The specimen with softening characteristics must have strain localization phenomenon,and the existence of strain localization shear band has a greater effect on the mesh sensitivity of deviator-stress curve than on the mesh sensitivity of volumic-deformation curve.Under the condition of cementation damage softening,the specimen exhibits volume shrinkage,while under the condition of shear dilatancy,the specimen exhibits obvious volume dilatancy.In addition,the mesh sensitivity caused by the cement damage softening is relatively weak under the condition of volume contraction,while the mesh sensitivity caused by the shear dilatancy softening is relatively strong under the condition of bulk dilatancy.The conclusion is supported by laboratory triaxial test.The cemented structural soil with different strength and strength and remolded soil with different cement content were prepared.The remolded soil does not produce strain localization in triaxial test and the mesh sensitivity is weak in simulation.Cementation damage and softening will occur in cemented soil samples,leading to the formation of strain localized shear bands,which in turn will lead to the occurrence of mesh sensitivity.