1. Additional site investigations Study on long-term behavior of rock PhD project at Technische Universität München Chair of Engineering Geology Carola Wieser, Dr. Heiko Käsling hours / days / weeks

2. Background  Research project ABROCK  Improvement of penetration prediction model for tunnel boring machines (TBM) in hard rocks  Rock excavation largely dependent on rock strength

3. Background  Laboratory rock strength ≠ Rock strength at the tunnel face Rock excavation results in  relaxation of the rock mass  redistribution of stresses  deformation and cracking of the rock  time-dependent changes in rock strength → Degradation of rock quality before laboratory tests are performed

4. Site investigations Sampling: 1 240 – 1 275 m PH 105 -1084 m SECTION, VIEW TO THE EAST

5. Site investigations  Sampling immediately after drilling  Sample preparation within 1 hour Sampling PH 105 -1 084 m

6.  P-wave velocity detection in 45° angles around the sample in 3 to 4 measurement planes and along the core axis Methodology Ultrasonic Testing

7.  AE = elastic waves caused by the release of stress energy (cracking)  Acoustic Emission Testing with 8 sensors attached to the sample surface Methodology Acoustic Emission Testing Data aquisition system Pre-amplifier Drill core + Sensors

8. Results: P-wave velocity Sample 1:-1242 m Sample 2: -1257 m  Rapid decrease in v P after drilling  Stable value after about 100 – 450 hours v P II core axis v P schistosity T

9.  v P is higher parallel than perpendicular to the schistosity  Strong variation in v P in the measuring planes (A / B)  Anisotropy within the measuring planes P-wave velocity v P core axis v P II schistosity B A A B T -1257 m

10. Acoustic Emission  Rapid increase of AE after drilling  Almost stable value after several days Event rate -1257 m -1275 m

11. Acoustic Emission Event rate -1257 mp-wave velocity

12. 1 hour after drilling 147 hours after drilling Acoustic Emission Event localization

13. 1 hour after drilling v P ≈ 5.600 m/s 147 hours after drilling v P ≈ 3.800 m/s Acoustic Emission Localization error

14. Ongoing work  received samples after core logging  ultrasonic measurements  uniaxial compression tests  including acoustic emission measurements during loading  try to gain the Kaiser effect for estimating primary stress level before core extraction  thinsection analysis

15. Conclusion  v P is reduced considerably within a few hours (up to > 1 km/s)  v P reaches a stable value after about 100 – 450 hours  Stable value is different for different samples  v P varies within the samples (up to > 2 km/s)  v P is highest perpendicular to the schistosity and lowest parallel P-wave velocity

16. Conclusion  v P is reduced considerably within a few hours (up to > 1 km/s)  v P reaches a stable value after about 100 – 450 hours  Stable value is different for different samples  v P varies within the samples (up to > 2 km/s)  v P is highest perpendicular to the schistosity and lowest parallel  Rocks are anisotropic even if schistosity is not clearly visible! P-wave velocity

17. Conclusion  Event rate is reduced considerably within a few hours  Event rate will probably reach a stable value after several days  3D event localization is not possible due to anisotropy of the rocks Acoustic Emission

18. Conclusion  Rock mass degradation takes hours to days  Ends up about 100 to 450 hours after core extraction from the drilling  Rock strength determined in the lab (days/weeks after drilling) may be lower than in situ  Reason might be degradation during extraction of the rock core due to high primary stress