At the Porce III Hydroelectric Project site there is a lack of information concerning the natural stress tensor field. Only three USBM overcoring measurements were performed during final-design explorations at the exploration powerhouse chamber branch gallery. In this article is explained how the natural stress tensor field was assessed by considering these few measurements and a stress inversion analysis based in a slip analysis with discontinuity data collected at the powerhouse chamber site. Even tough, there is no a clear evidence to validate the estimated natural stress tensor field, the obtained results was helpful to reduce the uncertainty about the natural stress tensor field at the site and exhorted to the stakeholder to be afraid in performing state of the art and state of the practice stress estimation programs, for any future project in the region.
The natural stress tensors field (NSTF) refers to a continuous volume forming the crust, in where every infinitesimal point is loaded by stress actions coming from the current or past activity of the crust. The estimation of NSTF in rock mass is a central concern within the geosciences, for understanding basic geological processes, for the study of plate tectonics, earthquakes and for rock mechanics, this last for the designing process of surface or underground structures. Concerning this later application, the NSTF was attempted to assess for the Porce III Hydroelectric Project located in Colombia-South America, more specifically for the underground powerhouse complex which is 260m below the surface, inside a metamorphic good quality rock mass. Knowing the natural stress tensor field at this hoisting rock mass was an essential condition to develop any further stress-strain study.
Natural stress tensor field can be assessed by three different scales: regional scale, local scale and punctual scale.