SYMPOSIA PAPER Published: 01 January 1999

Laboratory Evaluation of Mechanical Properties of Rock Using an Automated Triaxial Compression Test with a Constant Mean Stress Criterion


A computerized, servohydraulic test system has been used in the laboratory to perform axisymmetric, triaxial compression tests on natural rock salt using a load path that maintains constant mean stress. The constant mean stress test protocol illustrates that modern test systems allow a nonstandard load path which can focus on a particular aspect of rock characterization; namely, the onset of dilation. Included are discussions of how the constant mean stress test could be used to investigate material anisotropy and determine elastic moduli. The results from the constant mean stress tests are compared to test results from a traditional test method used to investigate dilation of rock salt. The comparison verifies that the constant mean stress protocol may be preferable to the more traditional test method. The paper also addresses system calibration concerns and the effects of pressure changes on the direct-contact extensometers used to measure strain.

Author Information

Mellegard, KD
RE/SPEC Inc., Rapid City, SD
Pfeifle, TW
RE/SPEC Inc., Rapid City, SD
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Developed by Committee: D18
Pages: 247–258
DOI: 10.1520/STP13320S
ISBN-EB: 978-0-8031-5400-1
ISBN-13: 978-0-8031-2493-6