New Constitutive Models in FLAC3D 6.0

Plastic-Hardening (PH) Model

The Plastic-Hardening (PH) model is a shear and volumetric hardening constitutive model for the simulation of soil behavior. When subject to deviatoric loading, soils usually exhibit a decrease in stiffness, accompanied by irreversible deformation. In most cases, the plot of deviatoric stress versus axial strain obtained in a drained triaxial test may be approximated by a hyperbola. This feature was discussed by Duncan and Chang (1970) in their well-known “hyperbolic-soil” model, which is formulated as a nonlinear elastic model. The new PH model is formulated within the framework of hardening plasticity (Schanz et al. 1999), allowing the removal of the main drawbacks of the original nonlinear elastic model formulation (e.g., detection of loading/unloading pattern, nonphysical bulk modulus). This constitutive model is also easy to calibrate using either lab tests or in-situ tests and uses familiar properties, names, and conventions in civil engineering. For more information, please review these papers.


Swell Model

The swell model is based on the Mohr-Coulomb constitutive model. The difference is that the wetting-induced deformations are taken into account by means of coupling wetting strains with the model state prior to wetting. The wetting-induced strains are assumed following logarithmic or linear function of normalized compressive stress in the user-defined principal swelling direction.

Ubiquitous-Anisotropic (CANISO) Model

This ubiquitous joint model with anisotropic (transversely isotropic) elasticity accounts for the presence of an orientation of weakness (weak plane). The plane of weakness has the same orientation as the plane of elastic isotropy. The criterion for failure on the plane, whose orientation is given, consists of a Mohr-Coulomb envelope with tension cutoff. This model can be useful in simulation of the behavior of layered (laminated) materials.

Mohr-Coulomb-Tension (MOHRT) Model

This model requires the same material parameters as the conventional Mohr-Coulomb model. It assumes that a zone can have up to three mutually perpendicular cracks. Each crack completely cuts throughout a zone. If the tensile strength (which is initially isotropic) is exceeded, a crack is formed perpendicular to the principal tensile stress. The tensile strength (which becomes anisotropic) perpendicular to the crack is set to zero, as a result of instantaneous softening. Cracking opening and closing are tracked internally. After the crack closes, the model behaves as if the crack does not exist, except that the tensile strength perpendicular to the crack is zero.

Cap-Yield (CYSOIL) Model, Updated

This model is a strain-hardening constitutive model for soil characterized by a frictional and cohesive Mohr-Coulomb shear envelope and an elliptic volumetric cap, associated with a shape parameter. The model features include: a cap hardening law, to capture the volumetric power law behavior observed in isotropic compaction tests; a friction-hardening law, to reproduce the hyperbolic stress-strain law behavior observed in drained triaxial tests; and a compaction/dilation law to model irrecoverable volumetric strain taking place as a result of soil shearing.

Compared to the model implemented in FLAC3D 5.0, these features are all built into the updated version. The updated model retains the capability to substitute, by means of tables, alternative user-defined hardening/softening laws for the built-in laws. When a table is declared for a specific model property of friction, dilation, cohesion, tensile strength, or cap-pressure, the associated user-defined law takes precedence over the corresponding built-in law.

Power-Mohr-Ubiquitous Creep (CUPOW) Model

This creep model (requires the creep option for FLAC3D) combines power law creep, Mohr-Coulomb failure, and ubiquitous joint effect. The model simulates the viscous-elastic-plastic mechanical behavior of ubiquitous joint rock with power-type creep occurring in a rock matrix.

C++ User-Defined Material (UDM) Model

Microsoft Visual Studio templates are included with the C++ Plug-in option. Creating C++ User Defined material models (UDM) has never been easier.