| As one of the world's most advanced large-scale general finite element software,ABAQUS has been widely used in various industries,but its existing function cannot fully meet the various industries some requirements of the advanced users,such as the program existing models of geotechnical material is limited or has some defects.Therefore,in this paper,based on its secondary development platform,using Fortran language and backward euler implicit integration algorithm a number of user material subroutine(UMAT)has been developed and applied to the case analysis,the main research work is as follows:(1)If there are sharp corners or singular point of the yield surface used in finite element calculation,then the plastic flow direction is non-uniqueness,making the numerical calculation of locked and slow convergence,even no convergence.For singular yield surface of Mohr-Coulomb and Tresca criterion,the circular arc is used to instead of the original yield surface nearby the sharp angle,namely "circle".The circular arc that yield function expression is deduced,and the plastic potential function is adopted the similar expression,so it can take into account associated flow rule,to make up for the lack of ABAQUS embedded Mohr-Coulomb model only considering non-associated flow rule.(2)Due to the embedded Mohr-Coulomb model can not consider the associated flow rule,therefore according to the new derived modified Mohr-Coulomb yield criterion equations,the corresponding subroutine UMAT has been compiled,and using indoor conventional triaxial tests and a classic 2D excavation project adopted by geotechnical benchmark to demonstrate the validity of the program.On the basis of the UMAT,further considering the change of rock and soil mass modulus along with the change of pressure or the depth,and the modified UMAT was used for numerical simulation pile groups test subjected horizontal lateral load,compared with the measured data to verify the correctness and applicability of the program.(3)Currently in the process of geotechnical slope analysis,the tensile properties of rock and soil is often ignored,but when the slope close to instability,derived from the surface down to certain depth range of rock-soil mass is often subjected to stress,therefore in this paper,according to a modified Mohr-Coulomb function which can consider the tensile strength a scholar suggested,and the UMAT was compiled,and used for a classic 2D clay slope calculation and analysis.It can obtain that when considering tensile strength of soil mass,slope safety factor is less than the results of no considering the tensile properties of soil.This shows that the tensile strength of soil in the slope stability analysis is necessity,especially for structural loess slope which has a larger tensile strength.(4)Under a small load,stress-strain relationship curve of soil is nonlinear,the linear elastic state can be neglected.The embedded Mohr-Coulomb model is an ideal elastic-plastic model,thus Duncan-Chang model can well reflect the nonlinear elastic properties of soil.According to the advantage of the two,nonlinear-ideal plasticity model is set up,in order to realize the soil in the elastic stage soil stress-strain relationship is nonlinear,and after the yield,the plastic phase ideal plasticity model are adopted to simulate the plastic deformation of the soil.The correctness and applicability of the corresponding UMAT was verified based on indoor triaxial compression test datas.And it was applied to a practical 3D excavation fundation pit excavation process simulation,a considering interaction of frame structure shallow foundation optimization design,and impact analysis of the uplifts between the two adjacent depth and shallow foundation excavation. |
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