Development And Implementation Of Modified Duncan-Chang Model Considering Intermediate Principal Stress Based On ABAQUS

As one of the most comprehensive large general finite element software system in the world,ABAQUS is widely used in geotechnical engineering.Due to its good openness,users can extend the function by secondary.One of the secondary development methods is creating new constitutive models to expend its material library,which is a currently important research direction.The Duncan-Chang E-V and E-B model are commonly used in describing the constitutive relationship of soils.Currently,the user material subroutine(UMAT)based on Duncan-Chang model on ABAQUS software has been redeveloped.However,in the existing literature library,there is a lack of research on the development of the Duncan-Chang model UMAT subroutine considering the influence of the principal stress on the strength and deformation.The three-dimensional unequal stress state is one of the most commonly faced situation in engineering practice,and the influence of moderate principal stress can not be ignored.In this paper,we focus on the following aspects:(1)On the basis of existing research,a new Duncan-Chang model updating method is discussed and explained in physical sense.Based on the Duncan-Chang E-B model,the method does not add new model parameters,and uses the method of modifying the elastic modulus and Mohr-Coulomb failure criterion to consider the effect of intermediate principal stress.It provides a new idea for the application of Duncan-Chang model under complex stress conditions.(2)Three existing Duncan-Chang correction models considering the effect of principal stress and the new correction methods discussed in this paper are compiled into corresponding UMAT subroutines by using Fortran language,and the complete program code is given.(3)By comparing the stress-strain curves obtained from conventional triaxial tests with the results obtained from finite element model,the feasibility of UMAT subroutines for each modified model when the middle principal stress ratio B is 0 is verified.The results obtained from different UMAT subroutines are compared with the data of true triaxial tests in existing literatures.The applicability of the modified models are analyzed when the ratio B is 0.25,0.50,0.75 and 1.00.It is found that when the middle principal stress coefficient is small,each correction method can reflect the influence of the middle principal stress to varying degrees.However,when the main stress is large,the correction method proposed by Skermer will show obvious distortion.The new correction method can better reflect the stress-strain relationship of soil at different intermediate principal stress levels.(4)The UMAT subroutine is applied to engineering cases.The three-dimensional excavation of foundation pit is simulated by modeling,and the simulation results are compared with the measured data,which verifies the rationality of the new correction method.