Approaches To The Triple-Shear Subloading Surface Models For Saturated Clayey Sands

Taking Saturated Clayey Sands as the research object,it is particularly crucial to study its deformation characteristics under dynamic and static loads,especially the Mansing effect and ratchet effect under dynamic loads.There are many constitutive models for studying soil mass.The sub-loading surface model can well predict the deformation nonlinearity,continuity and smoothness of the stress-strain curve of soil mass under load.It can also better reflect the accumulation characteristics of plastic deformation and plastic strain of soil mass under asymmetric stress-controlled cyclic loading.There is no need to determine the plastic modulus by complicated trial and error or even function interpolation.In this paper,the failure stress ratio is determined by using the Three-Shear strength criterion which can better describe the strength characteristics of soil.By introducing the failure stress ratio into the model of the secondary loading surface,a Three-Shear loading surface model of saturated sand with mud,which is suitable for the unidirectional movement of normal yield surface under static and dynamic loads,is proposed.In order to reflect the complex and special stress state,a Three-Shear loading surface model of saturated sandy soil with mud and normal yield surface moving in multiple directions is proposed based on the yield surface moving in one direction.In addition,in the actual soil deformation,if the soil density is large and the load is small,the soil deformation relative to its initial size may conform to the mechanical characteristics of small deformation.Then,the elastic-plastic mechanical analysis method based on the small deformation theory can be considered for its deformation analysis.The model of this method is relatively simple and the calculation workload is small.If the soil mass is relatively weak or the load is large,the deformation of the soil mass relative to its original size may not conform to the characteristics of mechanical small deformation.Therefore,the analysis method based on the small deformation theory will cause a large calculation error,so the finite deformation theory with higher calculation accuracy is adopted.However,the constitutive model based on the finite deformation theory is relatively complicated,and the calculation workload is large,especially in the finite element analysis.Based on the theory of small deformation and finite deformation,this paper systematically studies the Three-Shear loading surface model of small deformation and finite deformation of saturated sand containing mud under the condition of unidirectional and multidirectional movement of normal yield surface.The S-R decomposition method is adopted in the analysis of finite deformation,which is characterized by that the method does not need to consider the order of deformation and rotation when analyzing the deformation of soil element.Thus overcome the shortage of polar multiplication.On the basis of putting forward a variety of models,the soil particle screening test,conventional dynamic and static triaxial test and compression rebound test are done for saturated sand containing mud to determine the soil parameter values,and then explore the corresponding parameter law of different compactness and different mud content.The experimental data are used to verify the accuracy of the theoretical calculation results of the Three-Shear small deformation and finite deformation sub-loading surface model with unidirectional movement of normal yield surface.In terms of true triaxial test verification,the influences of different intermediate principal stress influence coefficients on the calculation results of the model were analyzed first,and then the PFC3 D model of saturated muddy sand was compared with the theoretical model.The research work and achievements are as follows:(1)Taking the Three-Shear strength criterion as the strength criterion of the constitutive model in this paper,the Three-Shear failure stress ratio of saturated soil is derived by using this criterion.Considering the dilatancy characteristics of sandy soil,the phase transformation stress ratio combined with the Three-Shear unified strength criterion is introduced to characterize the dilatancy state of sand,and the fixed failure stress ratio in the modified Cambridge model is replaced.In addition,based on the small deformation elastic-plastic theory,A small deformation constitutive model of three shear loading surface of saturated sandy soil with mud is proposed for unidirectional movement of normal yield surface and multidirectional movement of normal yield surface.The unidirectional motion constitutive model of normal yield surface is suitable for predicting soil deformation behavior under normal and true triaxial stress conditions,while the multi-direction motion constitutive model of normal yield surface is suitable for complex and special stress states.When the soil force is small and the compactness is large,the theory of small deformation is accurate and simple,and the calculation work is small,which can bring great convenience.(2)When the soil mass is relatively loose or the load is large,the deformation of the soil mass relative to its original size may not conform to the mechanical characteristics of small deformation.At this time,in order to more accurately predict the stress-strain relationship of saturated sand soil containing mud under large deformation,the Three-Shear loading surface model is combined with the finite deformation S-R decomposition theory.A Three-Shear finite deformation sub-loading surface model with unidirectional movement of normal yield surface and multidirection movement of normal yield surface is proposed.From the perspective of theoretical system,this model inherits the advantages of the former model and can predict the deformation of soil under load more accurately.(3)The soil particles required by the sample were determined by the soil particle screening test,and the cohesion and friction Angle values corresponding to different compactness and mud content were determined by the conventional static triaxial test.The dimensionless parameters,dimensionless parameters,compression index and spring back index were determined by compression and spring back tests.Finally,the rule of the above parameters under the conditions of different density and mud content was explored,and a curve was drawn.(4)The conventional triaxial and true triaxial monotone loading and cyclic loading and unloading test programs corresponding to the theoretical model were written with Fortran language.The conventional static triaxial test and conventional cyclic dynamic triaxial test were used to verify the correctness of the theoretical model of Three-Shear small deformation and finite deformation sub-loading surface with unidirectional movement of normal yield surface,and the numerical results of various theoretical models were compared with the simulation results of PFC3 D numerical test program,and then the characteristics of different models in simulating the constitutive relationship of saturated sandy soil with mud were analyzed.In the true triaxial numerical test,it is found that at the end of the experimental deformation,the finite deformation theory is closer to the PFC3 D simulation test than the small deformation theory simulation results.