Volume 10, Issue 4 (December 1987)
Triaxial Testing of Brittle Sandstone Using a Multiple Failure State Method
The first phase of a recent research program undertaken to investigate sandstone/methane outbursts in coal bearing rocks required the use of a sandstone reference material in the development and trial of the testing procedures to be used. This was because the number of specimens of outburst-prone rocks from the affected mine was limited. Thus another goal of the first phase was to determine a triaxial testing method for characterizing rock properties that minimized the number of specimens required. The International Society for Rock Mechanics (ISRM) multiple failure state method is attractive in this regard because an approximate strength envelope can be determined from a single specimen.
In this test program however the brittle nature of the reference material made control of failure by monitoring axial strain (the ISRM method) impossible; specimens always failed at the first, low or zero confinement, stage. An alternative method of detecting imminent failure in the specimen was developed and applied, yielding results almost identical to those obtained by conventional single state testing.