The Elastoplastic Soil Material feature is used to model stress-strain relationships which are nonlinear even at infinitesimal strains. It is available in the Solid Mechanics interface. This material model requires a Geomechanics Module license (see https://www.comsol.com/products/specifications/).

By adding the following subnodes to the Elastoplastic Soil Material node you can incorporate other effects:

Add an External Stress node in case you need to define a pore pressure in a porous soil. The Pore pressure pA is user-defined by default. The default value is 1 atm, but you can change it to another value or expression for the pore fluid pressure. If there are other physics interfaces (like Darcy’s Law) in the model that make a pressure variable available, such variables will be available in the list.

The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate systems that the model includes (except boundary coordinate systems). The coordinate system is used when stresses or strains are presented in a local system. The coordinate system must have orthonormal coordinate axes, and be defined in the material frame. Many of the possible subnodes inherit the coordinate system settings.

Select a Material model from the list: Modified Cam-Clay, Modified Structured Cam-Clay, Extended Barcelona Basic, or Hardening Soil.

All elastoplastic soil models have density as an input. The default Density ρ uses values From material. For User defined enter another value or expression.

If any material in the model has a temperature dependent mass density, and From material is selected, the Volume reference temperature list will appear in the Model Input section. As a default, the value of Tref is obtained from a Common model input. You can also select User defined to enter a value or expression for the reference temperature locally.

The Modified Cam-Clay options adds the equations and interface for defining the material properties for the modified Cam-Clay soil model.

From the Specify list, define the elastic properties either in terms of Poisson’s ratio or Shear modulus.

The defaults for the Poisson’s ratio ν or the Shear modulus G, Density ρ, Slope of critical state line M, Swelling index κ, Compression index λ, Initial void ratio e0 , and Void ratio at reference pressure eref are taken From material. For User defined enter other values or expressions

Enter a value or expression for the Reference pressure pref, and the Initial consolidation pressure pc0.

From the Specify list, define the elastic properties either in terms of Poisson’s ratio or Shear modulus.

The defaults for the Poisson’s ratio ν or the Shear modulus G, Density ρ, Slope of critical state line M, Swelling index for structured clay κs, Compression index for destructured clay λd, Angle of internal friction φ, Initial structure strength pbi, Destructuring index for volumetric deformation dv, Destructuring index for shear deformation ds, Plastic potential shape parameter ξ, Initial void ratio e0, Void ratio at reference pressure for destructured clay erefd, Additional void ratio at initial yielding Δei, and Critical equivalent deviatoric plastic strain edcp are taken From material. For User defined enter other values or expressions.

Enter a value or expression for the Reference pressure pref, and the Initial consolidation pressure pc0.

The defaults for the Poisson’s ratio ν or the Shear modulus G, Density ρ, Slope of critical state line M, Swelling index κ, Swelling index for changes in suction κs, Compression index at saturation λ0, Compression index for changes in suction λs, Angle of internal friction φ, Weight parameter w, Soil stiffness parameter m, Plastic potential shape parameter bs, Tension to suction ratio k, Initial void ratio e0, Void ratio at reference pressure and saturation eref0, and Initial yield value for suction sy0 are taken From material. For User defined enter other values or expressions.

Enter a value or expression for the Initial suction s0, Suction s, the Reference pressure pref, and the Initial consolidation pressure pc0.

The defaults for the Reference stiffness for primary loading E50ref, Reference stiffness for unloading and reloading Eurref, Elastoplastic compression modulus Kc, Poisson’s ratio ν, Density ρ, Stress exponent m, Cohesion c, Angle of internal friction φ, Dilatation angle ψ, Ellipse aspect ratio R, and Initial void ratio e0 are taken From material. For User defined enter other values or expressions. The Ellipse aspect ratio R can also be defined from the Coefficient of earth pressure at rest k0nc.

Enter a value or expression for the Failure ratio Rf, the Reference pressure pref, and the Initial consolidation pressure pc0.

Select the Include dilatancy cutoff check box if needed. The defaults for the Maximum void ratio emax is taken From material. For User defined enter other value or expression. Enter a value or expression for the Initial volumetric strain εvol0.

The default is None. Select Implicit Gradient to add nonlocal regularization to the equivalent plastic strain. Enter a value for the:

If a study step is geometrically nonlinear, the default behavior is to use a large strain formulation in all domains. Select the Geometrically linear formulation check box to always use a small strain formulation, irrespective of the setting in the study step.

When a geometrically nonlinear formulation is used, the elastic deformations used for computing the stresses can be obtained in two different ways if inelastic deformations are present: additive decomposition and multiplicative decomposition. The default is to use multiplicative decomposition. Select Additive strain decomposition to change to an assumption of additivity.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.

Select the Calculate dissipated energy check box as needed to compute the energy dissipated by Creep, Plasticity, Viscoplasticity, or Viscoelasticity.

This section is available with the Implicit gradient nonlocal plasticity model. Select the shape function for the Nonlocal equivalent plastic strain εpe,nl — Automatic, Linear, Quadratic Lagrange, Quadratic serendipity, Cubic Lagrange, Cubic serendipity, Quartic Lagrange, Quartic serendipity, or Quintic Lagrange. The available options depend on the order of the displacement field.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.

Select the Reduced integration check box to reduce the integration points for the weak contribution of the feature. Select a method for Hourglass stabilization — Automatic, Manual, or None to use in combination with the reduced integration scheme. The default Automatic stabilization technique is based on the shape function and shape order of the displacement field.

Control the hourglass stabilization scheme by using the Manual option. Select Shear stabilization (default) or Volumetric stabilization.

When Shear stabilization is selected, enter a stabilization shear modulus, Gstb. The value should be in the order of magnitude of the equivalent shear modulus.

When Volumetric stabilization is selected, enter a stabilization bulk modulus, Kstb. The value should be in the order of magnitude of the equivalent bulk modulus.

Physics tab with Solid Mechanics selected: