### Material Properties

Strength and elastic properties of materials (rock or soil) are entered in the Define Material Properties dialog. If you are considering groundwater in your model, then the material hydraulic properties are entered in the Define Hydraulic Properties dialog. Material properties are assigned to different regions of the model with the Assign properties option.

To read more about the new constitutive models available in RS2 version 9.0, see the Constitutive Modeling article from the Fall 2014 RocNews.

Strength Properties
The following material strength models are available in RS2:
• Mohr-Coulomb
• Hoek-Brown (original criterion)
• Drucker-Prager
• Cam-Clay
• Modified Cam-Clay
• Mohr-Coulomb with cap
• Softening/hardening models
• User-defined constitutive model
• Non-linear isotropic elastic model

If you set the Material Type = Elastic, then the material is assumed to have unlimited strength (i.e. it will not yield or fail). The material response will be linear elastic, regardless of the stress magnitude. You may still define strength parameters, but they will only be used for the calculation of strength factor (i.e. degree of overstress).

If you set the Material Type = Plastic, then the material can yield and exhibit non-linear stress-strain behaviour, if the stress exceeds the strength envelope. For Mohr-Coulomb, Hoek-Brown and Drucker-Prager models, you may specify peak and residual strength parameters. Residual strength will be applied if the peak strength is exceeded. If residual = peak, this defines an elastic-perfectly plastic material. If residual strength = 0 this defines a brittle material.
Elastic Parameters
The following elastic models are available in Phase2:
• Isotropic
• Tranversely Isotropic
• Orthotropic
• Duncan-Chang Hyperbolic

By default in Phase2, materials are assumed to have Isotropic elastic properties. This means that the elastic properties are not dependent on directionality, and are defined by a single value of Young's modulus and a single value of Poisson's ratio.
Parameter Calculator
For the Generalized Hoek-Brown strength criterion, a special parameter calculator is available by selecting the GSI button. This allows you to estimate the Hoek-Brown parameters mb, s and a, from the rock mass parameters GSI, mi and D, using the dialog shown below. The rock mass elastic modulus can also be estimated.

From the parameter calculator dialog, assist dialogs are available to help with the selection of values for UCS, GSI, mi and D. These are accessed by selecting the Pick button beside the input parameter edit box.
Staging
The properties of a material can be modified at different stages of a multi-stage model, by using the Stage Properties option in the Define Material Properties dialog. Any of the material parameters can be increased or decreased by user-defined factors at different stages. This allows the user to simulate changes in material stiffness or strength (for example) as staging progresses.
Datum Dependent
The Datum Dependent option allows you to define material properties which vary linearly with depth from a user-defined datum elevation.