4. Behavior and mechanical properties of rocks

4.1 General

The mechanical properties of rocks can be classified into two broad categories:

• deformability, reflecting a rock's ability to change shape under the action of mechanical or other stresses, and characterized by instantaneous or delayed deformation moduli;

• strength, i.e. the stress a rock can withstand under a certain type of mechanical stress: tension, uniaxial compression, triaxial compression, etc. Strength cannot therefore be reduced to a simple intrinsic value, and the values obtained under different stresses can be used to define failure criteria (cf. § 4.6