Definition of Hoek-Brown model parameters in Plaxis

ApplicationPLAXIS 2D
VersionPLAXIS 2D
Date created29 March 2012
Date modified29 March 2012
In rock mechanics, it is common to express E, σci and σψ, in the unit MPA (megaPascal = MN/m2), whereas the input values in PLAXIS are given in standard units as defined in the project properties, which by default are set to kPa (kiloPascal = kN/m2).

The Hoek-Brown model is the most used failure criterion for rock masses. With the release of the PLAXIS CONNECT Edition, a side panel of the Parameters tabsheet of the Hoek-Brown model has been introduced to assist with the definition of each of the material parameters.

The pre-procession tool can be used to guide the determination of the Hoek-Brown parameters:

hoek-brown side window

Figure 1: Uni-axial compressive strength of the intact rock  (σci) for Hoek-Brown model on the side panel

Uni-axial compressive strength of the intact rock (σci)

One of the input parameters of the Hoek-Brown model is the uni-axial compressive strength of the intact rock (σci). Users should be aware that, although normally expressed in [MPa], the unit used for σci in Plaxis is based on the global project units. When the global project units are set to [kN] for Force and [m] for length, this uni-axial compressive strength of the intact rock (σci) will be expressed in [kPa] = [kN/m2]. These global project units are used consistently throughout the program for e.g. stress, strength and stiffness, therefore be sure to enter the correct value here.


hoek-brown sigma_c_i

Note that it is also possible to change the displayed units within the material dataset. The material database will then convert the values internally to the defined project units. To change this, click on the unit icon at the top:

See also