# block analyze-stability command

Syntax

block analyze-stability free-face s <keyword>

Primary keywords:

Analyze the block stability considering an “isolated rigid body.” The method for block creation is determined by the first keyword used. The free-face keyword is used to specify the face group name for the free faces of the block (faces to which the boundary stress relaxation will be applied).

The joint properties can be defined using the following keywords. If not defined, the properties are derived from the properties of the contacts.

block-extra i

Specify the extra variable slot to store mean block factor of safety. The mean block FOS is calculated from the face FOS values. If the block-extra keyword is not given, mean block FOS is not stored with the blocks (but is still printed to the screen).

cohesion f

Specify the cohesion for block faces. If not defined, the property is derived from the contact properties.

friction f

Specify the joint friction for block faces. If not defined, the property is derived from the contact properties.

stiffness-normal f

Specify the normal stiffness for block faces. If not defined, the property is derived from the contact properties.

stiffness-shear f

Specify the shear stiffness for block faces. If not defined, the property is derived from the contact properties.

Input needed prior to the command

‐ Define a block model and mesh it (zone meshing) ‐ Define in situ stress ‐ Define joints properties (stiffnesses, cohesion, friction angle) ‐ Give a face group name to the “free” faces of the block

Output of the command

Blocks having faces touching the tunnel free face are identified. These blocks are stored in different groups in the slot “isolated_blocks.” Joined blocks are put in a single block group.

For these groups, the following results are computed:

• Displacement at every gridpoint of the block
• Forces on the faces
• Factor of safety per zone face

The list of block groups having a free face are given in the console with the following information:

Group ID     Number of blocks     Volume     FOS-Min     FOS-mean


Note that “FOS-min” is defined as the minimum factor of safety value per group, and “FOS-mean” as the mean value.

The following results can be plotted:

• Factor of safety per block face
• Block – Face Block – Contour – Kinematic FOS
• Displacement vectors on gridpoints
• Block -Vectors – Type = Displacement
• Block displacement contour (magnitude, x-component, y component or z component)
• Block – Color By Contour- Value = Magnitude, x-component, etc
• Final boundary forces on block faces
• Block -Vectors – Type = Out of Balance Force