Hello,

there are several types of borehole tests to estimate the direction of the principal stresses like in situ overcoring technique or the observation of borehole breakouts. But these are mostly qualitative tests.

Here is a nice overview on the topic:

http://petrowiki.org/Methods_to_estimate_stresses_and_orientation

If you need quantitative assessments you can use flat jack tests or dilatometer tests. But I'm not aware if these tests are applicable in very hard rock. Perhaps your rocks are too stiff and you don't get reliable results.

Best Regards

Thank you very much

Hi Tharanga,

Although it is not expert in this field, but I think when we talk about the metamorphism and metamorphic rocks, we are dealing with P and T. Therefore, the degree of metamorphism which can be identify on the bases of presence of special minerals in metamorphosed rocks will give an idea of possible stress that the rock has experienced.

Hi Tharanga,

I wonder whether stress can be stored after the forces acting on the material concerned have been relieved. In metamorphic rocks, release of stress acting on them may be manifested in the form of systems of fractures and joints. Particularly, in rocks exposed at the surface, one frequently comes across horizontal sets of joints which could indicate release of overlying load of rocks by erosion and weathering. Even closer to the surface, rocks could be still under stress depending on the horizontal and vertical forces acting upon them. For example, during tunneling engineers take into account the patterns of stress around a tunnel. But the idea of stress without applied forces (built-in stress) is suggested in materials like prestressed concrete. However, whether any residual stress inherited from its metamorphic history still remains within a rock appears to be the question you are looking for answers.

Hi Tharanga,

Before answering the question of residual stress, one will have to answer the questions whether stress accumulates? and if so how? and what is the evidence to suggest that stress once accumulated and then later released? Also, if stress accumulates is there the necessity to release all that stress after the metamorphic rocks reached the surface? One can argue that stress was accommodated by re-crystallization to a new mineral assemblage and ductile deformation (strain) and therefore did not accumulate. What happens if the system of stress changes? There will be new deformation and re-crystallization. Does one want to argue that stress accumulates during successive stages of deformation? or whether all that was accommodated by re-crystallization and deformation? These are questions you have to look into closely before answering your main question.