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Critical Probabilistic Values

In a Probabilistic Analysis, thousands of runs are performed on a single block, resulting in the same number of results. Instead of looking at all the results, only the critical extreme values are reported for important block results.

The following critical probabilistic values are reported in RocSlope:

  • Min. Factor of Safety: minimum Factor of Safety of all sample runs for the given block
  • Max. Weight: maximum block Weight of all sample runs for the given block
  • Max. Required Support Pressure: maximum Required Support Pressure of all sample runs for the given block
  • Max. Failed Depth: maximum Failed Depth of all sample runs for the given block
  • Probability of Failure: sum of all failed samples (i.e., Factor of Safety < Design Factor of Safety) / total samples for the given block
  • Total Failed: sum of all failed samples
  • Total Removable: sum of all removable samples

These values are listed in Block Information or can be contoured in Contour Blocks option.

Probability of Occurrence

The probability of occurrence for any block can be computed as:

Probability of Occurrence = Total Removable / Number of Samples

Probability of Sliding

The probability of sliding for any block can be computed as:

Probability of Sliding = Total Failed / Total Removable

Probability of Failure

Failure can only occur if the block is removable and can slide. Therefore, the probability of failure can be computed as:

Probability of Failure = Probability of Sliding x Probability of Occurrence Total Failed / Number of Samples

In a Probabilistic Analysis, the Results Set definitions are as follows:
  • All Valid Blocks: same as deterministic.
  • Removable Blocks: probabilistic inputs can affect Factor of Safety and therefore removal of blocks in Successive Removal. For the purpose of Probabilistic Analysis, a block is considered Removable if any sample runs result in the block being Removable.
  • Failed Blocks: probabilistic inputs can affect Factor of Safety. For the purpose of Probabilistic Analysis, a block is considered Failed if any sample runs have Factor of Safety < Design Factor of Safety (in other words, if Min. Factor of Safety < Design FS).
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