Failure Range

Failure Envelope Range option is available in Define Material Models for Mohr-Coulomb and Generalized Hoek-Brown strength failure criterion. It has a direct effect on the equivalent Mohr-Coulomb parameters for non-linear failure envelopes. If you change the stress range, you will obtain a different Mohr-Coulomb fit.

Application

The appropriate stress range (maximum sigma3 or sigmaN value) over which equivalent Mohr-Coulomb parameters must be obtained depends on the application, i.e. the type of geotechnical excavation being designed or analyzed. There are four possible selections: General, Tunnels, Slopes and Custom.

• • For details about the Mohr-Coulomb fitting procedure, and the significance of the Failure Envelope Range option, click here to view the Hoek, Carranza-Torres and Corkum (2002) paper. (See section 4: Mohr-Coulomb Criterion, and section 6: Determination of Sigma3 max). Based on the principles outlined in this paper, RocData estimates maximum sigma3 values for Tunnel or Slope design applications.
  • The General option is available only for the Generalized Hoek-Brown criterion. When the Failure Envelope Range option is set to General, sigma3max will automatically be set to sigci / 4. This is based on the empirical observation that the stress range associated with brittle failure, occurs when sigma3 is less than about one-quarter of sigci.
  • When the Failure Envelope Range option = Custom, you may enter any value of sigma3max or sigNmax. TIP: this can be used to customize the stress range of the failure envelope plots, even if you are not interested in the equivalent Mohr-Coulomb fit.
  • NOTE: the Failure Envelope Range has NO effect on the calculated parameters of a non-linear failure envelope.