Secondary Development And Application Of Super-loading And Sub-loading Yield Surface Model For Natural Cohesive Soils In ABAQUS

The study of deformation response characteristics of natural clayey soils under load and the study of intrinsic model has been one of the main problems in geotechnics.It is important to evaluate the deformation and safety of many geotechnical projects on natural clay foundations in a reasonable and effective way.In this paper,we focus on the Over-consolidation and structural properties of natural cohesive soils,and use ABAQUS FEM software to develop a secondary user material subroutine for this principal structure model:1.Based on the ABAQUS finite element software,a second development of the Umat subroutine was carried out for the Sub-loading yield surface modified Cam-clay model,and a sub-step iterative stress point integration algorithm with autom atic error control was introduced to improve the calculation accuracy in the process of writing the user material subroutine.The subroutine was used to verify the correctness of the subroutine’s description of the mechanical properties of normally consolidated remodeled soils through single-unit triaxial undrained tests;the simulation of multi-unit triaxial tests using the subroutine demonstrated the stability of the program for multi-unit analysis,and the computational accuracy of the program was verifi ed by comparing with the indoor test data;The mechanical properties of cohesive soils with different Over-consolidation ratios are also simulated using the subroutine and compared with the calculation results of the modified Cambridge model built in ABAQUS to show the superiority of this procedure in describing strong Over-consolidation;finally,the calculation results are compared with those of the explicit Euler integration algorithm to show the necessity of adding the sub-step iterative algorithm to improve the calculation accuracy.2.The influence of structural properties is introduced on the basis of Over-consolidation of the soil,and the parametric relationship between the contribution of plastic volume strain incrementdε_v ~p and plastic shear strain increment dε_s ~p is established to modify the hardening law of Over-consolidation and structural properties.In addition,the modified Cambridge model was developed based on the ABAQUS numerical simulation platform,and the Over-consolidation and structural properties were verified by triaxial tests.Comparing the calculation results of the Super-loading and Sub-loading yields surface subroutines with those of the Sub-loading surface subroutines,it is found that the Super-loading and Sub-loading yields surface modified Cambridge model can also accurately describe the stress-strain relationship of Over-consolidation soils,especially the strain-softening characteristics of severely Over-consolidation soils;based on the calculation results of the Super-loading and Sub-loading yields surface subroutines for different structural undisturbed soils,it is found that the stronger the structural soil is the higher the peak stress intensity of the cohesive soil,but with the damage of structural damage,its final strength tends to be the same;Finally,the calculation results of Umat subroutine are compared with the indoor data of Shanghai in-situ soils to verify the calculation accuracy of the Super-loading and Sub-loading yields surface subroutine.3.The Umat subroutine was further applied to the engineering case study.The calculation results of the subroutine are compared with the measured values in the engineering case,and the results show that the calculation accuracy and correctness of Umat can be well verified,which shows that the written subroutine will have good practical significance and application value for such engineering cases.