UH Model Based On The Anisotropic Transformed Stress Method And Its Application

Soils are generally anisotropic.As an important property of soil,anisotropy can not only render different strength and deformation behaviors along different directions,but also bring some special phenomena to the stress-strain response of soil,such as non-coaxiality and the plastic deformation during principal stress rotation.In practical engineering,if the effect of anisotropy is ignored,the design tends to be relatively dangerous,or unnecessary waste could be made.It is of great theoretical importance and practical significance to study soil anisotropy.This paper starts from the microstructure of soil which is regarded as the origin of anisotropy,and proposes a new method to describe the anisotropic behavior.Then anisotropic model is developed based on some classical failure criteria and the unified hardening(UH)model.Furthermore,the new model is applied to simulate some more complex properties caused by anisotropy.The main content is summarized as follows:1.Anisotropic transformed stress method is proposed.Firstly,in order to consider the effect of anisotropy,the relative magnitudes of stress components along different directions are adjusted according to the fabric tensor,and a modified stress tensor is obtained.In the modified stress space,the anisotropic soil can be equivalent to an isotropic one.Secondly,a transformed stress tensor is derived from the modified stress tensor to consider the effect of intermediate principal stress.In the transformed stress space,yielding behaviors under different values of intermediate principal stress coefficient are identical.After these two steps of mapping,the description of the coupled effects of material anisotropy(internal factor)and complex stress state(external factor)becomes simplified.2.Anisotropic failure criteria and UH model are established.Using the anisotropic transformed stress method,many classical isotropic failure criteria are extended to be anisotropic,and different criteria can be expressed by a simple and unified formula in the transformed stress space.Meanwhile,anisotropic UH model is established through replacing the stress tensor in the UH model by the transformed stress tensor.The form of the model formulas and the physical meaning of the parameters remain unchanged.Efficiency of the anisotropic unified strength criterion and UH model is fully verified by the test results of many soils in different loading conditions.3.The anisotropic UH model is applied to simulate the effects of non-coaxiality and principal stress rotation.From the view of the mobilized plane,anisotropy is proved to be the foundational reason that causes the non-coaxiality of soils.It is then analyzed that the mapping in the anisotropic transformed stress method implies non-coaxiality,so that the anisotropic UH model is adopted for its prediction,and consequently,good results are obtained.During the simulation of principal stress rotation,a fabric evolution equation is introduced to reflect the effect of stress-induced anisotropy and ensure that the critical state line is unique while the critical state fabric reaches a stable value.Therefore,the plastic deformation induced by principal stress rotation can be predicted within the framework of elastoplastic theory.In conclusion,the work in this paper contains the proposal of basic approach,establishment of constitutive model and application of theoretical achievement,so that a research system about soil anisotropy is preliminarily formed.