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The proper method of investigating the applicability of a failure criterion, through laboratory results of uniaxial and tri-axial compressive strength tests, is presented. The influencing factors and conditions have been discussed individually. The role of each factor has been shown using the experimental results obtained by the author.
The main factors on selecting laboratory data are as follows: brittleductile transition in rocks, the minimum number of data of each data set, the range of confining pressure in tri -axial tests and finally the size and shape of tested specimens.
This paper is the outcome of a critical review of investigation methods of other researchers in this field, pointing on the weak points of previous works and suggesting solutions to the previous shortcomings.
It has been shown that neglecting the importance of the influencing factors leads to wrong conclusions.
The paper introduces the proper way of producing or selecting laboratory data to those who are interested or involved in the research works relating to the mechanical properties of rocks.