Based on the relationship between the current yield surface and the reference yield surface, a new model, called the three-dimensional unified hardening model for overconsolidated clays (the UH model), is proposed in this paper. A current yield surface is used to describe overconsolidated behaviour, and a reference yield surface to describe the yield characteristics corresponding to normally consolidated clays. The UH model can model many characteristics of overconsolidated clays well, including stress-strain relationships, shear dilatancy, strain-hardening and softening, and stress path dependence behaviour. The key feature of the model is the adoption of a unified hardening parameter that is independent of stress paths. Based on the SMP criterion and the corresponding transformed stress method, the proposed model can be applied conveniently to three-dimensional stress states. Compared with the Cam-clay model, the UH model requires only one additional clay parameter, the slope of the Hvorslev envelope. The validity of this new model is confirmed by data from triaxial drained and undrained compression and extension tests for clays with different overconsolidation ratios, true triaxial tests with different Lode's angles, and cyclic loading tests.

UH model: three-dimensional unified hardening model for overconsolidated clays

A Simple Elastoplastic Model for Normally and Over Consolidated Soils with Unified Material Parameters

Explanation of cyclic mobility of soils: approach by stress-induced anisotropy

The spheropolyhedra method has been used earlier for efficient and accurate molecular dynamics simulations of granular matter with particles with complex shapes. Also the Voronoi construction is a tool of proved utility for the virtual representation of powders and grains. In this paper a technique that combines the two methods and provides a framework for the study of the three-dimensional mechanical behavior of granular matter is proposed. In order to understand the capabilities of the new method, a number of computer simulations of the cubic (true) triaxial test, measuring the mechanical behavior of packing of particles, is carried out. Results from tests with packing of complex-shaped particles represented by "Voronoi particles" are compared with corresponding results of packing of spherical particles. Features such as the saturation value for the macroscopically observed coefficient of friction, as reported in the literature, are compared for the packing of spheres and for the packing of "Voronoi particles," showing that the difference in shape strongly affects the results. The proposed technique and simulation results can be used to help understand how the individual shape of grains affects the macroscopic mechanical behavior of granular matter such as cohesionless soils.

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Molecular dynamics simulations of complex-shaped particles using Voronoi-based spheropolyhedra.

The critical state concept has been widely used in soil mechanics The purpose of this study is to apply this concept in the framework of multi-mechanism elastoplasticity The developed model has two yield surfaces: one for shear sliding and one for compression In this model, the location of the critical state line is explicitly considered and related to the actual material density to control the peak strength and the phase transformation characteristics The stress reversal technique is incorporated into the model for describing clay behavior under complex loading including changes of stress direction The determination of the model parameters is discussed; it requires only one drained or undrained triaxial test up to failure with an initial isotropic consolidation stage The model is used to simulate drained and undrained tests under monotonic loading with different over-consolidation ratios on various remolded and natural clays, including true triaxial tests with different Lode’s angles Drained and undrained tests under cyclic loadings are also simulated by using the set of parameters determined from monotonic tests The comparison between experimental results and numerical simulations demonstrate a good predictive ability of this new simple model

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Masaya Hinokio

Papers

A Simple Elastoplastic Model for Normally and Over Consolidated Soils with Unified Material Parameters

Influence of surface loads and construction sequence on ground response due to tunnelling

Ground Behavior Due to Tunnel Excavation with Existing Foundation

3D effects on earth pressure and displacements during tunnel excavations

Ground Densification Due to Sand Compaction Piles