An Elastic-viscous-plastic Structured Unified Hardening Model

Soils in nature have structural and temporal properties.The structural nature allows the soil to delay the development of deformation during the low stress phase,while this deformation is sharply released during the high stress phase with structural collapse.The temporal properties are mainly manifested by two phenomena: creep,which increases the degree of overconsolidation of the soil,and strain rate effect,which means that the strength of the soil is affected by the strain rate.These two properties affect the soil stress-strain relationship and may increase the risk if ignored or underestimated in the actual project.In this paper,based on the Unified Hardening model for structured soils,the moving instantaneous normal consolidation line(MINCL)is used as the reference line for calculating creep and overconsolidation parameters instead of the moving normal consolidation line(MNCL)to introduce the temporal properties into the original model.Establish an elastic-viscous-plastic structured Unified Hardening model that can describe both structural and temporal properties,and apply the transformed stress method based on the SMP criterion to extend the model into a three-dimensional model.The comparison between experimental data and model prediction data shows that the elastic-viscous-plastic structured Unified Hardening model model can reasonably describe the mechanical behavior of clay in one-dimensional compression,triaxial undrained shear,and creep with controlled net mean stress equaling constant for prediction.The model was written as a UMAT subroutine,and its validity was verified by simulating the isotropic compression and creep of the calculated unit soil.