In Visualizing Stress select File from the main menu and then Open. In the Open File dialog box select the file BereaSandstone.txt and then click enter Enter. Plot the Mohr diagram for the sandstone from Berea, Ohio. With these data plotted, a failure envelope can be drawn. Select the menu item Graphics and then select Mohr Envelope from the No Pore Pressure menu group. The failure envelope is the best-fit line representing the locus of shear and normal stresses at failure for the sandstone from Berea, Ohio under the given experimental conditions (Figure 20).
From the above a diagram we would predict that for stress states below the failure envelope, the sandstone from Berea would be stable. However, if the stress state yielded shear and normal stresses plotting above the envelope, then such a condition would be unstable and failure would be likely to occur.