OLIVEIRA, D. G. G. de. Optical televiewer in boreholes – methodological proposal for implementation and application in underground work. 2015. 187 f. Dissertação (Mestrado) – Instituto de Geociências, Universidade de São Paulo, São Paulo,...
moreOLIVEIRA, D. G. G. de. Optical televiewer in boreholes – methodological proposal for implementation and application in underground work. 2015. 187 f. Dissertação (Mestrado) – Instituto de Geociências, Universidade de São Paulo, São Paulo, 2015.
The rock mass characterization is an essential step in engineering geology, providing the possibility of performance prediction of this massive due to numerous requests of any work to be done. In the case of urban underground works, such as subway lines, for example, geological and geotechnical characterization of rock masses is critical for identifying geological conditions linked to its stability, being effective in determining the geotechnical parameters that influence the design of massive excavation, whether by the conventional method (NATM), or mechanized, using tunneling boring machines (TBM).
Structural features such as foliation planes, folds, faults and fracture systems deserve special attention as they are associated with weakness zones in addition to all the geomechanical characteristics of the massif. In urbanized areas, such as São Paulo Metropolitan Region (RMSP), geological, geomorphological and occupation hinders exposure and identification of these features on the surface. In this context, new techniques have been developed to facilitate access to the above features. Among these new techniques is the optical televiewer (OPTV, OTV), which aim to obtain 360° images of the borehole walls, providing what might be considered a virtual core of a borehole.
The optical televiewer has been a technology introduced in Brazil since 2001, but only recently has been published in ABGE Borehole Manual (2013), however, there are no specifications on the acquisition methodology, interpretation and application possibilities. This paper presents suggestions for the acquisition of these images, their interpretation and suggestions of applications in engineering works, taking as an example the design in projects of underground works of the São Paulo Metro.
In the specific case of urban underground excavations ground knowledge is essential, since its construction is an activity to be developed within the urban context, which could cause significant interference with the community, resulting in a high risk to neighboring population. Added to this is the fact that a little-known mass can result in oversized contention, increasing the cost of the work or undersized, increasing its risk.
As mentioned in ISRM (1978), as the descriptions of rock masses and discontinuities become more complete and unified, it will be feasible to design engineering structures in rock reducing the costs and increasing the reliability of the interpretation and extrapolation of the results.
Keywords: Optical televiewer, geological-geotechnical investigation, rock massif characterization, urban underground excavations.