The International Information Center for Geotechnical Engineers

Wednesday, 09 May 2018 07:32

Don't Let Your Rock Strength Results Come Up Short Specimen Preparation is Key

If your project requires rock compression testing by ASTM D7012 Methods A through D then end preparation by ASTM D4543- Preparing Rock Core as Cylindrical Test Specimens and Verifying Conformance to Dimensional and Shape Tolerances MUST be performed to produce suitable specimens.

If tests are performed on specimens without preparing the core to ASTM D4543 tolerances, the results are not considered reliable and will produce lower values of compressive strength than a properly prepared sample.Each specimen must be machined to produce flat and parallel ends with perpendicular sides.

At GeoTesting Express, we always provide a report verifying the compression test specimen's conformance to the dimensional and shape tolerances required by ASTM D4543. This provides you with the assurance that your results are as accurate as possible. Underestimating rock compressive strength can result in specifying the wrong equipment, increased excavation time or advance rates and change of condition claims.Having the testing done correctly the first time can make a big difference in keeping project costs down.

 Below is an example comparing the results of a properly prepared sample vs saw cut ends.

  1. Compressive strength measured on six specimens of the same rock.Three specimens were saw cut specimens with no additional machining and three were prepared in accordance with ASTM D4543.
  2. The unconfined compression results for the saw cut specimens meeting the ASTM D4543 tolerances had an average unconfined strength in the range of 30,000 psi with a standard deviation of only 200psi.
  3. The unconfined compressive results for the specimens meeting the ASTM D4543 tolerances had an average unconfined strength in the range of 30,000 psi with as standard deviation of only 200psi. 
  4. Comparing the results shows the importance of quality end preparation.The specimens meeting the ASTM D4543 tolerances were 50% stronger than the saw cut specimens (30,000 psi vs 20,000 psi).

 Unconfined Compression strength is one of the most important characteristics you can determine from the rock you are working with.Without the correct value, all other calculated properties and determinations are flawed.

Source: Geocomp

Read 298 times Last modified on Wednesday, 09 May 2018 14:30

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