Research On The Secondary Development Of ABAQUS Based On The Twin-shear Unified Strength Theory And Its Application In Geotechnical Engineering

In order to overcome the corner singularities of the twin-shear unified strength theory,and make them be used in the finite element,the Drucker-Prager series yield criterion considering the influence of the intermediate principal stress is derived,and then based on the derived criterion,the secondary development of ABAQUS material subroutine is carried out.Firstly,the relationship between the strength parameters of the twin-shear unified strength theory and the shear strength parameters is determined by the method of mathematical derivation.Two methods for calculating the flow vector are proposed,namely formula method and definition method.With reference to the traditional calculation method of foundation bearing capacity based on the Mohr-Coulomb yield criterion,the twin-shear unified strength theory is used as the yield failure criterion of the soil.The parameter substitution method and the theoretical derivation method for calculating the foundation bearing capacity are proposed,and the process of second method is encapsulated into F-C function using MATLAB software.By mathematical derivation and MATLAB symbolic function solving,a series of circles with a special position relationship with the limit line of the unified strength theory are obtained,namely the twin-shear outer corner circumscribed circle DDP1,the twin-shear inner corner circumscribed circle DDP2,and the twin-shear inscribed circle DDP3,twin-shear equal area circle DDP4,twin-shear non-associative matching circle DDP5,twin-shear intermediate corner circumscribed circle DDP6.Then,the three software,namely finite element software ABAQUS,the Fortran operating environment Microsoft Visual Studio,and the Fortran compiler Intel Parallel Studio XE are linked.According to the theory of elasticity and elastoplasticity,a constitutive model of the material is established.Using the method of computer programming,a method is proposed to use the improved Euler method and classic Runge-Kutta method to update the stress in the elastoplastic stage,and use the Newton iteration method to calculate the scaling factor for transition from the elastic phase to the elastoplastic phase.Through Fortran language and the material secondary development interface Umat provided by ABAQUS,Umat subroutines are written based on the deduced criteria and established constitutive model.Finally,the Umat subroutine is used to carry out a stress analysis of a plate with holes,the results show that the stress analysis results under the developed Umat subroutine and ABAQUS’s own Mises yield criterion are consistent.ABAQUS calls the Umat subroutine for slope stability analysis,the results shows that the slope stability coefficient increases with the increase of the intermediate principal shear stress influence coefficient b,the influence of intermediate principal stresses cannot be ignored in slope stability analysis.The unified shear strength parameters are used to calculate the foundation bearing capacity,and the results show that the foundation bearing capacity value is positively correlated with b.The above results show that the Umat subroutine written is correct and reasonable,and it can be used for numerical simulation of geotechnical problems;The intermediate principal stresses contribute to the strength of the material,and its influence on the yield failure of the material cannot be ignored;Compared with Mohr-Coulomb theory,the twin-shear unified strength theory can give full play to the strength potential of materials and guide engineering practice more correctly.