Uniaxial compression tests
Specimens from drill cores are prepared by cutting them to the specified length and are thereafter grinded and measured. There are high requirements on the flatness of the endsurfaces in order to obtain an even load distribution. Recommended ratio of height/diameter of the specimens is between 2 and 3.
The specimens are loaded axially up to failure or any other prescribed level whereby the specimen is deformed and the axial and the radial deformation can be measured using a special equipment, see figures below.
Specimen inserted in the testing machine between the loading platens with deformation measurement equipment attached on the specimen.
Examples of results from an uniaxial compression test including the post-failure response are shown below. Radial and axial strain versus axial stress are shown in the graph together with volumetric strain and crack volume strain versus axial stress.
The pictures below show that spalling has occured on several locations on the specimen.
The results and pictures are taken from:
Jacobsson, L. Forsmark site investigation, Borehole KFM02A, Uniaxial compression test of intact rock. SKB-P04-224, Svensk Kärnbränslehantering AB, 2004.
This and many other reports on unixial compression tests, conducted at SP, are published on SKB.
Examples of standards
ISRM 1979, Suggested methods for determining the uniaxial compressive strength and deformability of rock materials. Int J Rock Mech Min Sci Geomech Abs 16(2), sid 135-140.
ISRM 1999, Draft ISRM suggested method for the complete stress-strain curve for intact rock in uniaxial compression. Int J Rock Mech Min Sci 36(3), sid 279-289.