ABSTRACT
Geomechanics is the study of motion and the causes of motion in soil or rock. Ordinarily, the interest is in deformation. Deformation can be volumetric or distortional. The onset of large deformations, usually associated with plasticity, is defined by yield criteria or yield envelopes. The shear stress leading to excessive deformation is the shear strength of the material. The shear strength may be expressed in terms of a friction angle. Deformation can be expressed in terms of a dilatancy angle. Stresses in soils and rocks result from the self-weight of these materials and from boundary loads.
