UCS

Test Overview

This test determines the axial compressive strength of intact rock specimens under unconfined conditions. It is commonly used to assess the mechanical competence of rock materials for design and classification purposes.

Standards

The “Uniaxial Compressive Strength” (UCS) test is regulated by the following standards:

• ASTM D7012 [1]

• ASTM D2938 [2]

Common Data

A geotechnical engineer commonly works with laboratory reports from UCS tests. These reports typically include essential specimen information sucha as:

Parameter	Description
Borehole ID	Identifier of the borehole from which the rock core specimen was extracted.
Sample No.	Laboratory-assigned identification number for the tested specimen.
Depth From [m]	Starting depth of the sample interval, referenced to the borehole.
Depth To [m]	Ending depth of the sample interval.
Diameter	Core diameter, typically corresponding to standard drilling sizes (e.g., HQ).
Density [g/cm³]	Bulk density of the specimen prior to testing.
Failure Load [t]	Maximum axial load applied to the specimen at the moment of failure.
UCS [MPa]	Uniaxial compressive strength computed from the peak failure load and the specimen’s cross-sectional area.

Sample Size Influence

As mentioned by Hoek [3], the uniaxial compressive strength, \(\sigma_{cd}\), of a rock specimen with a diameter of \(d\) mm is related to the uniaxial compressive strength, \(\sigma_{c50}\), of a \(50\) mm diameter sample by the following relationship:

\[\sigma_{cd} = \sigma_{c50} \cdot \left( \frac{50}{d} \right) ^ {0.18}\]

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GeoAssistant Implementation

UCS Test Object

GeoAssistant handles UCS tests by means of the UCS

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References

[1]

ASTM International. Astm d7012 – standard test methods for compressive strength and elastic moduli of intact rock core specimens under varying states of stress and temperatures. https://www.astm.org/d7012, 2020. ASTM International, West Conshohocken, PA.

[2]

ASTM International. Astm d2938 – standard test method for unconfined compressive strength of intact rock core specimens. https://www.astm.org/d2938, 2020. ASTM International, West Conshohocken, PA.

[3]

Evert Hoek. Practical rock engineering – chapter 11: rock mass properties. https://www.rocscience.com/learning/hoek-s-corner, 2018. Rocscience publication.