Finite Element Analysis Of Consolidation And Settlement Of Viscoelastic-plastic Foundation

Rheology is one of the most important deformation properties of geological materials,and consolidation is one of the basic research topics in geotechnical engineering.Consolidation analysis has undergone a process from the one dimensional consolidation of Terzaghi,the Biot consolidation to the elastic-plastic consolidation and rheological consolidation analysis.According to the rheological properties of geotechnical materials,rheological consolidation can be divided into viscoelastic,viscoelastic-plastic and viscoelastic-viscoplastic consolidation types.Viscoelastic consolidation does not consider the yield properties of soil,and viscoelastic-viscoplastic consolidation couples the viscoelastic and viscoplastic deformation characteristics.The plastic flow associated with the plastic strain rate is used,but the visco-plastic viscosity coefficient and other parameters are not easy to determine by experiments.The viscoelastic-plastic consolidation is coupled with two aspects of viscoelastic consolidation and conventional plastic consolidation.The calculation parameters include viscoelastic parameters and conventional plastic parameters,which are easy to determine.Both the viscoelastic behavior of the material and the plastic yield characteristics in the consolidation process are taken into account.This paper deals with the viscoelastic-plastic models which were coupled by viscoelastic consisting of basic viscoelastic elements and isotropic hardening and hyperbolic Drucker-Prager plastic model,taking into account viscoelastic strain history,based on the viscoelastic creep flexibility,the equivalent shear modulus and equivalent bulk modulus are defined,derivation of the general recurrence formula for viscoelastic stress increments,and the use of a two-step viscoelastic “prediction” and plastic “correction” algorithm to update the stress and give an fully implicit stress update algorithm and calculation formula.The UMAT material subroutine provided by ABAQUS can be used to calculate the viscoelastic-plastic consolidation.Finally,the viscoelastic,elastic-plastic and viscoelastic-plastic consolidation of the foundation were compared and analyzed.The main conclusions of the work done are as follows:(1)The strain increment was decomposed into viscoelastic part and plastic part in this viscoelastic-plastic model,taking into account viscoelastic strain history,based on the viscoelastic creep flexibility,the equivalent shear modulus and equivalent bulk modulus are defined,derived a general incremental iterative formula.Through the two-step viscoelastic “prediction” and plastic “correction” algorithms,the implicit updating of the stress is realized,and a modified completely implicit algorithm and calculation formula are given.No matter how the serial number of viscoelastic elements changes,or the viscoelastic Burgers model,there is no need to change the calculation formula or adjust the calculation program and achieve a unified algorithm and program of viscoelastic-plastic consolidation.(2)The computational analysis shows that because of the stress recursive algorithm based on viscoelastic creep flexibility,the completely implicit algorithm and the complete calculation formula,the implicit iteration can be converged after two or three iteration steps.The stress points can all be well returned to the yield surface.It shows that the algorithm and precision of this paper can satisfy the calculation requirements well and avoid the stress drift phenomenon,which provides an effective method for rheological consolidation calculation.(3)Analysis of the examples show that under the same load,the amount of settlement caused by ground creep increases.The viscoelastic-plastic consolidation settlement is the largest,the elastic consolidation settlement results are the smallest,and the elastic-plastic consolidation and the viscoelastic consolidation are in between.