Dynamic UH Model For Soils

There are complex deformation behaviors for saturated sand under cyclic loading conditions or complex stress paths.There are particle breakage phenomena for saturated sand under high confining pressure.Stress-strain relationship is affected through volume compression behavior,characteristic state stress ratio and peak stress ratio.There are three research results in the paper:(1)Applicability of generalization methods on dynamic model is analyzed.Taking Zhang's model for example,it is more reasonably to generalize Zhang's model using Transformed Stress(TS)method than that using g(?)method.(2)A dynamic UH model for sand was proposed on the basis of UH model.The Umat program based on the proposed model is developed and embedded into FEM software.(3)A dynamic UH model considering particle breakage is proposed based on the particle breakage phenomena and cyclic mobility behavior under cyclic undrained loading conditions.Generalization of dynamic model: Application of generalization methods to elastoplastic model is analyzed.If the Modified Cam-Clay(MCC)model were revised using TS method,the lowest stress point on yield surface is not coincident with the critical state point under triaxial extension condition.The increment of negative plastic volume strain is caused on critical state under triaxial extension condition.If anisotropic model were generalized using g(?)method,the discontinuous yield surface would be caused in p-q space under triaxial extension condition.The above problems can be avoided using TS method.Taking Zhang's model for example,Zhang's model is generalized using TS method.Simulation results using original model and generalized model are compared with test results respectively.Comparison demonstrates that the generalized model's prediction is more consistent with the test results.Dynamic elastoplastic constitutive model can be generalized using TS method reasonably.Dynamic UH model for sand: Stress-strain relationship is analyzed under dynamic cyclic loading conditions for saturated sand.A dynamic elastoplastic constitutive model for saturated sand is proposed on the basis of overconsolidated UH model.There are three aspects revised.(1)The ratio of the value of long axis to that of short axis for ellipse yield surface is defined as the function value for rotational axis which can be used to reflect stress-induced anisotropy.(2)The rotational hardening rule is introduced into the proposed model to reflect stress-induced anisotropy.(3)The unified hardening parameter is established by coordinating rotational hardening rule and critical state behavior.Comparison between model prediction and test results demonstrates that the proposed model can be conveniently used to simulate stress-strain relationship under dynamic loading conditions for sand.Transformed Stress(TS)method is adopted to generalize the proposed model.Dynamic constitutive model is also embedded into FEM software.The cyclic loading process on unit and foundation under drained condition and undrained condition are simulated respectively.The results of simulation using dynamic UH model with FEM indicate the simplicity and reasonability of the proposed model which can be used to describe the stress-strain relationship for sand under dynamic loading conditions.Dynamic UH model considering particle breakage: Based on particle breakage phenomena and dynamic constitutive relationship for sand,a dynamic constitutive model considering particle breakage using TS method is proposed on the basis of UH model.There are three aspects developed in the proposed model.(1)The shape of yield surface in UH model changes accompanying with the change of current stress state.The yield surface in ordinary stress space is transformed into the ellipse yield surface in TS space.(2)Rotational hardening rule is adopted.The position and the shape of ellipse yield surface are determined based on the slope of rotational axis.The mixed hardening parameter considering isotropic hardening and rotational hardening is established.(3)Relationship between reference yield surface and current yield surface is established using stress ratio R in TS space.The value of parameters can be obtained according to the current pressure and density of particle.Dynamic constitutive relationship under large scale of confining pressure can be described using the proposed model.There are fewer parameters in proposed model,which is very practical.