Materials

The Materials section defines the physical and mechanical properties necessary for simulations.

Number of Phases

The material behaviour depends on the number of phases present:

1: Solid-only simulations.
2: Solid-fluid interaction (e.g., fully saturated soil).
3: Solid-air-water interaction (e.g., unsaturated soil).

Note that the number of active phases affects some of the subsequent commands. For more details please click here

Density

Defines the density for each phase:

Phase 1: Density of Soild phase.
Phase 2: Density of Fluid phase (e.g., water).
Phase 3: Density of Second fluid phase (e.g., air).

Kindly make sure that all input values use consistent units (e.g. \(g/cm^3\)). For more details, click here

Stress-Strain Models

The Stress-Strain section defines the material's constitutive behaviour under mechanical loading. Various models are available, each suited to different material behaviours and loading conditions. This section outlines the available options:

Linear Elasticity
HCA Linear Elasticity
Mohr-Coulomb
Mohr-Coulomb-2
Hypoplastic+IGS
HCA-Hypoplasticity
Hypo-ISA
HCA Hypo-ISA
SANISAND
HCA-SANISAND
Modified-Cam-Clay
Barotropic Elasticity
Matsuoka-Nakai
AVHP (Anisotropic Visco-Hypoplasticity)

Reducible Strength

The Reducible Strength parameter is used to model materials whose strength diminishes with progressive deformation, a behaviour commonly seen in brittle materials or soils undergoing strain-softening. By default, reducible strength is disabled. When enabled, this feature allows the material's strength, such as cohesion or internal friction angle, to decrease as a function of deformation or plastic strain. For more information, refer to the detailed description of reducible strength

Rayleigh damping

Rayleigh damping is used to simulate energy dissipation in dynamic or transient simulations, helping to stabilize vibratory responses. When enabled, it incorporates mass damping and stiffness damping coefficients, which control the dissipation of kinetic and strain energy, respectively. This is particularly beneficial in preventing unrealistic oscillations in dynamic analyses. By default, Rayleigh damping is disabled but can be activated as needed. Users should carefully calibrate the damping coefficients (𝛼 for mass damping and 𝛽 for stiffness damping) to ensure that the damping behaviour aligns with the physical characteristics of the material and the simulation's objectives. Proper tuning of these parameters ensures realistic and stable results in simulations involving dynamic loading. For more information please click here

Stabilization Parameters

Additional controls for numerical stabilization and improved simulation accuracy. These include:

Minimum Pressure: This parameter prevents unrealistic negative pressures in numerical calculations. It can be activated or adjusted by specifying a threshold value. It is particularly useful for materials that are prone to tensile instability, ensuring that the simulation remains physically realistic. For more information please click here
Mechanical Viscosity: This introduces numerical damping to stabilize simulations involving high strain rates. For more information please click here
Phantom Elasticity: This feature adds artificial elasticity to stabilize poorly constrained simulations. It should be enabled only when necessary, as it can potentially reduce the accuracy of the simulation results. Use this option judiciously for situations where other stabilization measures are insufficient. For more information please click here
Hourglass Stiffness: This parameter is critical for stabilizing under-integrated elements by counteracting zero-energy deformation modes. It is particularly useful when working with reduced-integration elements, as it helps avoid spurious deformations. Users can enable this feature and adjust the stiffness value as required to ensure stability and accuracy. For more information please click here

Permeability

Permeability defines the ease with which a fluid can flow through a porous medium. Users can configure this property to simulate various fluid flow conditions in geotechnical applications.

This option is applicable only when the number of phases is set to 2 (solid-fluid interaction) or 3 (solid-air-water interaction). Ensure that the phase setting in the material definition aligns with this requirement.

Model

Isotropic: Assumes uniform permeability in all directions, commonly used for homogeneous materials.
Kozeny-Carman: Implements the Kozeny-Carman equation, suitable for materials where permeability is a function of porosity and grain characteristics.

Value Specify the permeability value

Bulk Modulus of fluid phases

The Bulk Modulus of Fluid Phases defines the compressibility of the fluid phases in multi-phase systems. This parameter is essential for accurately simulating the behaviour of fluids under pressure changes, especially in saturated or partially saturated conditions. Please refer to Bulk modulus for more information. This option is applicable only when the number of phases is set to 2 (solid-fluid interaction) or 3 (solid-air-water interaction). Ensure that the phase setting in the material definition aligns with this requirement.

Dynamic viscosity of fluid phases

The Dynamic Viscosity parameter defines the resistance of fluid phases to flow, a critical property for simulating fluid behaviour. Please refer to Bulk modulus for more information. This option is applicable only when the number of phases is set to 2 (solid-fluid interaction) or 3 (solid-air-water interaction). Ensure that the phase setting in the material definition aligns with this requirement.

Saturation-Suction

Saturation-Suction defines the relationship between the degree of saturation (\(S_w\)) and matric suction (\(\varphi\)) in porous materials. This property is essential for modeling unsaturated soils in geotechnical applications where the interaction between air, water, and the solid skeleton is critical. Please click here for more information. This option is applicable only when the number of phases is set to 3 (solid-air-water interaction). Ensure that the phase setting in the material definition aligns with this requirement.

Model

Van Genuchten: Commonly used for fine-grained soils, offering flexibility in describing the soil-water retention curve.
Brooks & Corey: Best for coarse-grained soils and soils with well-defined air entry values.

Permeability-Saturation

Permeability-Saturation defines the relationship between the degree of saturation and the relative permeability of a porous medium. This property is crucial for modeling unsaturated soils in geotechnical applications, where the fluid flow depends on the saturation level. Please click here for more information.

This option is applicable only when the number of phases is set to 3 (solid-air-water interaction). Ensure that the phase setting in the material definition aligns with this requirement.

Model

Van Genuchten: Commonly used for fine-grained soils, offering flexibility in describing the soil-water retention curve.
Brooks & Corey: Best for coarse-grained soils and soils with well-defined air entry values.

Bishop Effective Stress

The Bishop Effective Stress parameter is used to define the effective stress in unsaturated soils by incorporating the effects of matric suction and saturation. Please click here for more information.

This option is applicable only when the number of phases is set to 3 (solid-air-water interaction). Ensure the phase setting aligns with this requirement.

Model

Saturation:
Crude-Switch:
Liakos: