This paper deals with the short term and long term failure strength of rocks, and with a general criterion introduced to describe both limiting conditions. It is also shown how the criterion can be extended to take into account the effect of time and of specimen scale. Applications of the criterion are illustrated using various experimental data taken from the literature.
The mechanical strength of rock is influenced by numerous factors, such as geometry of loading, defect population characteristics, specimen size, and time. This renders difficult the proper expression of a failure criterion, as its formulation and corresponding parameters depend on these factors.
As a general rule, it can be expected that material strength decreases with increased scale, time and defect density, but these effects are sometimes tedious to quantify and difficult to introduce into criteria used for stability calculations.
In this paper, the authors present a general criterion that can be used to define the short term and long term strength of intact rock. It is also shown how to establish, in a simplified manner, the material strength as a function of time. The effect of scale is equally treated, so that the criterion can be applied to a variety of situations. A discussion follows.
