Knowledge of the in situ stress state in rock and soil deposits is very important in many problems in civil, mining and petroleum engineering and energy development, as well as in geology and geophysics. The prediction of the response of rock masses interacting with underground structures is highly influenced by the stress field. For example, as pointed out in 1, in civil and mining engineering, in situ stresses control the distribution and magnitude of the stresses around underground openings such as tunnels, mines, shaft or caverns. Stress concentrations in the excavation walls may be large enough to overstress the rock, mobilize the strength of the rock mass and induce failure. On the other hand, tensile stresses in excavation walls may open existing fractures or create new ones which could result in block stability problems.