Testwork: Point load index

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Testwork: Point load index

Point load index is a standard measurement of rock competency and is often used as a proxy for the Unconfined compressive strength which is used to determine rock mass rating (RMR) and slope stability for pit walls.

The test is a 'per-specimen' test where individual specimens of drill core are hand-picked by the test operator and placed into the apparatus. Typically several specimen is chosen at regular intervals down a section of core are aggregated to represent a sample and the result reported may include subjective comments like "good fracture" or "invalid-fracture failure".

Sample Requirements

The test requires multiple cylindrical pieces of large or small diameter (NQ, HQ or PQ) drill core, minimum length 60 mm.

Test Inputs

Not applicable.

Test Outputs

SAGMILLING.COM uses only metric units of "MPa corrected to Is50". If the laboratory reports PLI in other units (such as psi), convert the results before entering.

The laboratory will report the following information:

  • N° specimens: The number of specimens tested (typically 10-20)
  • min The Is50 value, MPa, of the specimen with the lowest result (if applicable)
  • max: The Is50 value, MPa, of the specimen with the highest result (if applicable)
  • stdev: The standard deviation of value of all the specimens (if applicable)
  • pli: The arithmetic average of the Is50 as MPa of all the specimens

Extra field available for modelling

  • synthetic indicates whether this is a real test result, or just a synthetic one that should only be used for modelling. If this column contains a value of '1' (boolean=true) for a test, then that test is understood to not be a real test result and is therefore not shown on the testwork comparison charts. Synthetic values are available when running circuit model simulations and do show up in the list of model results.


Point load index is not used directly in any SAGMILLING.COM models. Literature suggests it can occasionally be used as a proxy for the Bond crushing work index if a suitable calibration sample set exists for an ore.

The PLI reflects the energy requirement to break rocks in the coarse size range, from >100 mm down to about 10 mm - 20 mm.