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The strength-dilatancy characteristics embraced in hypoplasticity

Frontiers of Structural and Civil Engineering 2013年第2期7卷 178-187页

作者： Zhongzhi FU Sihong LIU Zijian WANG Geotechnical Engineering Department Nanjing Hydraulic Research InstituteNanjing 210024China College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China

The strength-dilatancy characteristics of frictional materials embraced in the hypoplastic model proposed by Gudehus and Bauer are investigated and compared with the revised model suggested by Huang.In the latter the deviatoric stress in the model by Gudehus and Bauer is replaced by a transformed stress according to the stress transformation technique proposed by Matsuoka.The flow rule,the failure state surface equation and the strengthdilatancy relationship embraced in both models are derived analytically.The performance of the two hypoplastic models in reproducing the relationship between the peak strength and the corresponding dilation rate under triaxial compression,plane compression and plane shearing are then extensively investigated and compared with experimental results and with the predictions made by particular classical stress-dilatancy theories.Numerical investigations show that the performance in reproducing the strength-dilatancy relationship is quite satisfactory under triaxial compression stress state in both models and the predictions made by the transformed stress based model are closer to the results obtained from classical stress-dilatancy theories for plane compression and plane shearing problems.

关键词： strength dilatancy hypoplasticity frictional materials

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Calibration and performance of two different constitutive models for rockfill materials

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Water Science and Engineering 2016年第3期9卷 227-239页

作者： Lin-ke Li Zhan-jun Wang Si-hong Liu Erich Bauer Institute of Applied Mechanics Graz University of Technology Changjiang Institute of Survey PlanningDesign and Research College of Water Conservancy and Hydropower Engineering Hohai University

In this paper, two different concepts for the constitutive modeling of the mechanical behavior of creep-sensitive rockfill materials are presented. Specifically, the performance of an extended generalized plasticity model proposed by Wang is compared with a simplified version of the hypoplastic constitutive model for weathered rockfill materials proposed by Bauer. Both models can reflect the influence of the mean stress on the incremental stiffness, the peak friction angle, and the dilatancy angle. The so-called solid hardness defined for a continuum description and originally introduced by Bauer is embedded in both models. Hydrochemical, thermal, and mechanical weathering are usually caused by environmental changes and are taken into account in a phenomenological description with an irreversible and time-dependent degradation of the solid hardness. A degradation of the solid hardness is usually accompanied by creep deformation of the stressed rockfill material. It is shown that appropriate modeling of creep deformation requires at least a unified description of the interaction between the time-dependent process of degradation of the solid hardness and the stress state. In this context, the solid hardness can be understood as a key parameter for describing the evolution of the state of weathering of the rockfill material. Particular attention is also paid to the necessary procedure for determining the constitutive constants of the two different constitutive models. Finally, the performance of the two different constitutive models is demonstrated by comparing the results obtained from numerical simulations with experimental data from the creep-sensitive rockfill material.

关键词： Rockfill material Creep Generalized plasticity hypoplasticity Constitutive model

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Hypoplastic particle finite element model for cutting tool-soil interaction simulations:Numerical analysis and experimental validation

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Underground Space 2018年第1期3卷 61-71页

作者： Abdiel Ramon Leon Bal Ulrich Hoppe Thai Son Dang Klaus Hackl Günther Meschke Inustitute for Structural Mechanics Ruhr-Uniuersitdit BochunGermany Inustitute of Mechanics of Materials Ruhr-Universitit BochunGermany

This study presents numerical and experimental models for the analysis of the excavation of soft soils by means of a cutting tool.The computational model is constructed using an Updated Lagrangean(UL)velocity-based Finite Element approach.A hypoplastic formu-lation is employed to describe the constitutive behavior of soft soils.Large displacements and deformations of the ground resulting from the cutting tool-soil interaction are handled by means of the Particle Finite Element method,characterized by a global re-meshing strat-egy and a boundary identiﬁcation procedure called a-shape technique.The capabilities and performance of the proposed model are demonstrated through comparative analyses between experiments and simulations of cutting tool-soft soil interactions.The experiments are performed using an excavation device at Ruhr-Universita¨t Bochum(RUB),Germany.The main details concerning the setup and calibration and evolution of the measured draft forces are discussed.Selected computational results characterizing the cutting tool-soft soil interaction including the topology of the free surface,void ratio distribution ahead of the tool,spatio-temporal evolution of the reaction forces and abrasive wear behavior are evaluated.

关键词： Velocity-basedﬁnite elements formulation hypoplasticity Large deformations Particleﬁnite elements Cutting tool-soil interaction Excavation experiments

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Influence of pressure and density on the rheological properties of rockfills

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Frontiers of Structural and Civil Engineering 2012年第1期6卷 25-34页

作者： Erich BAUER Zhongzhi FU Sihong LIU Institute of Applied Mechanics Graz University of TechnologyGrazAustria Geotechnical Engineering Department Nanjing Hydraulic Research InstituteNanjing210029Ch Institute of Hydraulic Structures Hohai UniversityNanjing 210098China

Long-term deformations of rockfill dams can be related to the type of dam,the pre-compaction achieved during the construction of the dam,the history of loading events,the rheological properties of the rockfill material used,the seepage behavior caused by defects of the sealing,the interactions of the dam building with the foundation,and the hydrothermal phenomena of the stressed rockfill material.The present paper investigates the theological propcrtics of coarse grained rockfill materials using a hypoplastic constitutive model.Particular attention is paid to wetting deformation under different deviatoric loading states and pre-compactions.To quantify the state of weathering a so-called“solid hardness”is used in the sense of a continuum description.It is shown that an appropriate modeling of wetting deformations requires a unified description of the interaction at least between the state of weathering,the stress state,the density and the rate of deformation.The results obtained from the numerical simulations are compared with available experimental data for a rockfill material used in Xiaolangdi earth dam.

关键词： rockfills solid hardness wetting deformation hypoplasticity creep

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Hypoplastic constitutive modeling of wetting deformation of weathered rockfill materials

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Frontiers of Structural and Civil Engineering 2010年第1期4卷 78-91页

作者： Erich BAUER Zhongzhi FU Sihong LIU Institute of Applied Mechanics Graz University of TechnologyGrazAustria Institute of Hydraulic Structures Hohai UniversityNanjing 210098China

The wetting deformation of weathered rockfill materials has been attracting growing attention from both engineers and scientists.The importance of realistic predictions of wetting deformations for high earth and rockfill dams is a strong motivation to establish a suitable constitutive model.Recently,the hypoplastic constitutive model by Gudehus and Bauer was extended by introducing solid hardness depending on the state of weathering.The extended model takes into account the influence of the current density,the effective stress state,the rate of deformation,and the time dependent process of degradation of the solid hardness.In the present paper,the performance of this model is evaluated by comparing numerical simulations with experiments obtained from a water sensitive rockfill material.In particular,triaxial compression paths and creep deformation under deviatoric stress states are considered.Finally,the constitutive model proposed is used to study the influence of a degradation of the solid hardness on the long term behavior of a hypothetical fill dam.

关键词： rockfill dams weathered granular materials hypoplasticity solid hardness creep stress relaxation

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