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Bolt Failure Modes

There are four bolt failure modes which can be reported in RocSlope2:

  1. Pullout
  2. Tensile
  3. Stripping
  4. Shear

In the event that a bolt cannot be equated to any of the above modes, bolts can also be defined as any of the following:

  1. User-Defined
  2. Simple Force
  3. Unknown

The failure mode is also indicated when you display the Force Diagrams for the bolts. This can be done using the Force Diagram Visibility Toggle in the Results menu. The different modes will be color-coded when Show Bolt Force Diagrams is toggled ON, and a legend will be displayed to the right of the Results Grid.

The term "Failure" as used here, does not necessarily mean that a bolt has actually failed. It really refers to the potential failure mode of a bolt, if block failure occurs. Remember that the RocSlope2 analysis is a limit equilibrium analysis. The actual stresses and deformations of the bolts are not computed.

Pullout / Tensile / Stripping

Pullout, Tensile, and Stripping are all tensile failure modes. They are determined by the Bolt Force Diagram and the point at which a block face intersects the bolt. For examples of bolt force diagrams, see the Force Diagram topic, and the topics for the individual Bolt Types in RocSlope2 (e.g., Mechanically Anchored, Cable Bolt, etc.).

bolt failure modesbolt failure modesbolt failure modes
Pullout, Tensile and Stripping Bolt Failure Modes

Shear

The Shear failure mode will only be reported if:

  • The Use Shear Capacity option is selected, for a given bolt type.
  • The bolt intersects a sliding plane of a block (as opposed to a dilating plane).

See the Use Shear Capacity and Bolt Implementation topics for more information.

Shear Bolt Failure Mode
Shear Bolt Failure Mode

User-Defined

If a bolt failure mode is reported as User Defined, this simply means that the bolt (tensile) properties have been defined with a User-Defined bolt type (i.e., the user creates an explicit Bolt Force diagram, rather than entering various capacities). For more information, see the User-Defined Bolt topic.

For a User-Defined Bolt type, it does not matter where a block plane intersects the Bolt Force Diagram. The failure mode will simply be reported as User Defined. The specific modes of Pullout, Tensile or Stripping are not reported.

Simple Force

If a bolt failure mode is reported as Simple Force, this simply means that the bolt (tensile) properties have been defined with the Simple Bolt Force type. For more information, see the Simple Bolt Force topic.

For a Simple Bolt Force type, it does not matter where a block plane intersects the Force Diagram. The failure mode will simply be reported as Simple Force. The specific modes of Pullout, Tensile or Stripping are not reported.
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