The scaling effect on rock behaviour by comparing compressional wave velocities measured in the lab and field

• Main Authors: M. Sehizadeh, M. H. B. Nasseri, R. P. Young
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-08-01
• Series: Advances in Geosciences
• Online Access: https://www.adv-geosci.net/45/167/2018/adgeo-45-167-2018.pdf
• ISSN: 1680-7340; 1680-7359

<p>A careful comparison of rock behaviour at different scales is essential to determine if laboratory experiments can be useful for understanding the field scale. This research aims to investigate the scaling effect on rock behaviour by comparing P-wave velocities passing through rock at different scales in field and laboratory experiments. Field P-wave velocity was measured at specific ray paths in a fairly homogenous pegmatitic zone located at the third experimental hole ONK-EH3 of the POSE tunnel at OLKILUOTO site, Finland. Three true-triaxial experiments were carried out on pegmatite samples taken from the POSE niche to duplicate the stress path that was believed to exist at the most critical region around the ONK-EH3. Ultrasonic surveys were carried out during these experiments. Initially, reproducibility of the true-triaxial experiments was investigated and a good match was observed among the three samples. The evolution of the stress tensor around the ONK-EH3 was calculated and used in an ellipsoidal model to estimate P-wave velocities for all the points located on the ray paths in the field. Calculated field P-wave velocities along the ray paths were in reasonable agreement with those measured in the field. A linear trend was observed between absolute error per unit length of a ray path and it's average distance to the highest stress zone. This study corroborates the stress path dependency of rock behavior at different scales and the usefulness of the true-triaxial experiments in this regards.</p>