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Blikra - vajont 2013
- 1. DMS DMS Lars Harald Blikra & Lene Kristensen, Åknes/Tafjord Monitoring Centre Mario Lovisolo, Centro Servizi di Geoingegneria (CSG), Italy Åknes/Tafjord Beredskap IKS
- 2. Risk related to large rockslides in Norway Åknes Tafjord 1934 Loen 1905 og 1936 Åknes/Tafjord Beredskap IKS
- 3. Monitored rockslides in Norway Handled by two monitoring centres funded by government/NVE, municipalities and counties: • Åknes/Tafjord Beredskap (technical and geological) • Nordnorsk fjellovervåking (technical) Åknes/Tafjord Beredskap IKS CONTENT Requirements Subsurface investigations & instrumentation Åknes and Jettan case Conclusions
- 4. Regulations in Norwegain building code • The population safety needs to be taken care of by realtime monitoring, warning and evacuation • The warning time shall not be shorter than 72 hours and the evacuation time shall be maximum 12 hours • A system for daily continuous monitoring of the conditions, e.g. by measurements of displacements • Independent monitoring instruments and backup communication and power systems • Sufficient technical and geo personnel/competence for safe and reliable monitoring and warning Åknes/Tafjord Beredskap IKS
- 5. (1) Investigations • Surface • Subsurface (2) Monitoring systems • Surface • Subsurface • Driving mechanisms Åknes/Tafjord Beredskap IKS
- 6. Geophysics were possible Core drillings Borehole logging – televiewer and other sensors Borehole displacements Åknes/Tafjord Beredskap IKS
- 7. INSTRUMENTATION Inclinometer probe – manual readings ? Long columns with continuous records Considerations • • • • • Åknes/Tafjord Beredskap IKS High cost of boreholes Robustness Characterization vs real-time warning Resolution Flexibility
- 8. • Robust technology • Leading technology • Large economic savings in a long-term perspective The DMS borehole instrumentation: • Documented to have survived more than 70 cm movements Conventional methods: c. 3 cm Åknes/Tafjord Beredskap IKS DMS
- 10. Method: Differential monitoring system (DMS) 1 m modules Åknes/Tafjord Beredskap IKS
- 11. Differential monitoring system, DMS – “Snake” Real-time , continuous measurements Steel modules with sensors Flexible centralizers fixed to the borehole casing Flexible junctions Åknes/Tafjord Beredskap IKS Subsurface LAB: • 2D Inclinometer (0,4 mm resolution) • Pietzometer • Temperature sensor • Digital compass • One systems of 150 m length, total of 304 sensors
- 12. Example: Åknes Deep drillings Åknes/Tafjord Beredskap IKS
- 13. SEE ALSO POSTER: GB INSAR MEASUREMENT AT THE ÅKNES ROCKSLIDE, NORWAY Åknes/Tafjord Beredskap IKS
- 15. Deep core drillings – 200 m deep Åknes/Tafjord Beredskap IKS
- 16. N E Televiewer image of the sliding plane Sliding zone Åknes/Tafjord Beredskap IKS S W N
- 17. 2 years of displacements 2011and 2012: Direction towards SW Sliding plane 2009 - 2013: • Total of 9 cm movements on 2 sensors Åknes/Tafjord Beredskap IKS Accumulated total Differential Movement for each individual sensor
- 18. DMS time series: 49-51 m depth Åknes/Tafjord Beredskap IKS
- 20. Time line for sensor at 49-50 m depth. • Displacement • Water level • Temperature Internal changes/ dynamics of the rockslide controls the hydrological system and the deformations Åknes/Tafjord Beredskap IKS
- 22. Aktive back fracture: 20-25 m deep, 2,5 cm/year Åknes/Tafjord Beredskap IKS
- 26. Clay in sliding zone: 45 m depth Åknes/Tafjord Beredskap IKS
- 27. Borehole instrumentation to measure movements, temperature and water Åknes/Tafjord Beredskap IKS
- 28. DMS movements at 45/46 m depth: 1th of May – 3rd of October E Åknes/Tafjord Beredskap IKS
- 29. Time series February – August 2013 May 2013 Åknes/Tafjord Beredskap IKS
- 31. Volume: Probably 5-6 mill. m3 Åknes/Tafjord Beredskap IKS
- 32. DMS and Real-time warning • Each sensor have threshold values for displacements • Can follow directly the critical sliding zones • Sms thresholds: 1 mm/day • Threshold values for different hazard levels • Trustable and robust system • Little noise compared to surface measurements Åknes/Tafjord Beredskap IKS
- 33. Norwegian building codes has strong requirements for monitoring and permanent handling of the EWS Subsurface data gives a knowledge platform for early-warning and key data for geological models/volumes needed for evaluation of runout/tsunamis (RISK) Borehole instrumentation is a vital part of real-time monitoring DMS instrumentation is a robust in-situ laboratorium: • Direct displacement at sliding planes with directions • Water pressure vs movements • Temperature/permafrost vs movements Åknes/Tafjord Beredskap IKS
- 34. Important that the geoscientific community clearly tells the government what knowledge is needed for reliable monitoring and EW Åknes/Tafjord Beredskap IKS