An important aspect of any tunneling project is the preliminary investigation of rock cores from reconnaissance drilling in order to determine the rock quality along the tunnel axis.
Characterization of rock cores is made on one hand by the direct observation and appreciation of the collected materials on site. On the other hand, analytical procedures performed in the lab are used to derive geotechnically relevant parameters.
We present in this contribution results of classical investigations from geology and rock mechanics performed on cataclastic rock samples from various petrologies.
Most of these techniques are destructive. An interesting alternative analytical technique would therefore be the indirect characterization of the rock cores by means of X-Ray Computed Tomography (XRCT). XRCT analyses on geotechnical rock cores provide important textural and structural evidence on a 3D basis. This evidence can be interpreted and tracked in a specific sample before and after submitting it to a deformational experiment. In this sense, XRCT is used as a "bridge technique" allowing a better use of structural geology and mineralogy in the mechanical interpretation of tri-axial results
Although geotechnical rock cores would -because of their size- need a powerful X-ray source to perform micrometric investigations, we used a medical XRCT scanner that performs fast analyses at a good spatial resolution of about 0.5 mm. This allows minimal manipulation on fragile cataclastic cores from geotechnical drilling operations. We see therefore medical XRCT as an important complimentary method to use hand together with classical analytical techniques in order to better constrain the rock mass that will be met underground and better understand its geotechnical implications.
