Underground application of photographic and GPR techniques for discontinuity survey

The survey of the geometric characteristics of discontinuities in a rock mass is fundamental for the evaluation of potential detachable blocks. However, in particular contexts, such as ornamental stone quarries, traditional survey could lead to inaccurate and incomplete results, due to the conditions of faces and excavation environment. To overcame, at least partially, such limitations, more and more frequently non-contact survey techniques are used, based on digital photography for mapping traces and on digital photogrammetry or laser scanner for surveying discontinuity planes. Also geophysical techniques, such as georadar, can be coupled to them. In this research, the applicability of these techniques inside Cava Piastreta, an underground marble quarry in the Apuane Alps, has been evaluated. Ground penetrating radar was found to be particularly effective. due to its performances on perfectly smooth excavation faces: results were fund to be coherent with those obtained form traditional survey. Conversely non-contact surveys suffered from limitations imposed by faces conditions.