Abstract

The popularity of the elasto-plastic Hardening Soil (HS) model is based on simple parameter identification from standard testing and empirical formulas. The HS model is implemented in many commercial FE codes designed to analyse geotechnical problems. In its basic version, the stress–strain behaviour within the elastic range is subject to the hypoelastic power law, which assures the barotropy of the elastic stiffness. However, a proper modelling within the small strain range, i.e. strain-induced stiffness degradation and correct reproduction of the hysteretic behaviour, was one of the most important drawbacks in the HS formulation. The first small strain stiffness extension to the HS model was proposed by Benz (Small strain stiffness of soils and its numerical consequences, 2007), and the new model was called Hardening Soil Small (HSS). Despite the simple isotropic formulation, its applicability was proved in various numerical simulations in geotechnics. However, the HSS formulation exhibits a serious fault known in the literature as overshooting, i.e. uncontrolled reset of the loading memory after tiny unloading–reloading cycles. The authors' main aim was to retain the set of material parameters for the HSS formulation and to propose a new small strain extension to the HS model without overshooting. The new proposal is based on the Brick model which represents the concept of nested yield surfaces in strain space. The implementation aspects of the new HS-Brick model are described, and its performance is presented in some element tests and selected boundary value problems by comparisons with the HSS formulation.

Highlights

  • The basic version of the elasto-plastic Hardening Soil (HS) model was developed by Schanz et al [36] and implemented into the Plaxis FE code [7]

  • It is implemented in many commercial FE codes due to clear parameter identification based on the standard laboratory and field tests or empirical formulas

  • Since it is convenient to keep the control of small strain stiffness within the strain space, we have followed the original version of nested yield surfaces in strain space proposed by Simpson [38, 39] in his BRICK model

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Summary

Introduction

The basic version of the elasto-plastic Hardening Soil (HS) model was developed by Schanz et al [36] and implemented into the Plaxis FE code [7]. The HS model has become a standard in geotechnical engineering computations It is implemented in many commercial FE codes due to clear parameter identification based on the standard laboratory and field tests or empirical formulas. The main framework of the HS model may be explained by drawing the contours of yield surfaces on the plane of Roscoe’s stress invariants p-q The first small strain stiffness extension to the HS formulation was proposed Benz and co-workers [5, 6], and the new model is called Hardening Soil Small (HSS). The primary aim of this paper is to propose a new small strain extension without the overshooting and to retain the main modelling assumptions of the HSS formulation together with its set of material parameters. We describe the implementation aspects of the new HS-Brick model and present its performance by comparisons with the HSS formulation in some element tests and selected example boundary value problems

Summary of the basic HS model
Deviatoric plastic mechanism
Volumetric plastic mechanism
Stiffness barotropy
HSS formulation
HS-Brick formulation
General implementation scheme
Algorithmic treatment of barotropy
Elastic stress predictor in the HS-Brick model
Multi-surface stress return in the principal stress space
NJACT Dkk
Element tests
Triaxial drained compression with small unloading–reloading loops
Triaxial hysteretic behaviour
Simple geotechnical boundary value problems
Loading case—shallow foundation
Unloading case—excavation
Dynamic case—earthquake induced shearing of a soil layer
Findings
Conclusions
Full Text
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