Over the last 40 to 50 years laboratory experiments have been conducted in order to quantify the conditions under which a wide range of materials might fail. Figure 19 is an illustration of a typical triaxial stress experiment. During the experiment, confining pressure and temperature are commonly held constant while s1 is progressively increased until failure occurs or some other critical experimental threshold is reached.
Mohr circles can be used to "map" the values of normal and shear stresses at failure (Davis and Reynolds, 1984), failure being the loss of cohesion of a material when the differential stress (s1-s3) exceeds some critical value that varies with different types of Earth materials.