Risk analyses and risk management slope instabilities in alpine environments

Transcription

1 Risk analyses and risk management slope instabilities in alpine environments Stefan Eder (ILF Consulting Engineers Co. Ltd.) Gerhard Poscher (p+w geo-zt Ltd.) Christoph Prager (alp-s)

2 Contents Introduction General remarks on risk management of rapid slope movements such as huge catastrophic rockfalls Case study 1 Eiblschrofen rockfall Case study 2 Creeping slope Zintlwald Conclusions

3 Mass movements in Tyrol and surrounding temporal and spatial distribution Zintlwald Innsbruck Eiblschrofen

4 Prominent examples of huge catastrophic mass movements in Tyrol Comparison of project areas with reference systems as a part of the risk management process

5 Standards, geotechnical environment and authorisation procedures for land-use in Tyrol (Austria) regarding geohazards No defined standards for the risk estimation of geohazards Implementation of the geohazards in the so called Alpen-Konvention (Convention of the Protection of the Alps, Protocol on Soil Protection) and introduction of a checklist by the Geological Department of the Tyrolean government (Heissel et. al., 2004), which must be used for designs Geohazards like rockfalls are indicated in the land-use regulations only marked in brown, but without legal consequences, in contrast to areas marked in red which is an indication for floods and avalanche threats Design-events are defined by expert groups individually

6 Land-use and Standards (examples) TIRIS Unstable rock-masses (scarp area of the large Tschirgant rockslide)

7 Case study 1 Eiblschrofen rockfall (summer 1999) Eiblschrofen - scarp, accumulation areas and localities of retention dams

8 Mitigation measures - Protection dams Heigth: 25 / 15 m Dam Volumes: / m³ Retaining capacities: / m³ Gradient of 60 under the crest to reduce ski-jumping-effects

9 Mitigation measures - Monitoring systems Laser Scanner

10 Geologic profile base for event scenarios Schists Dolomite, Database: ILF Consulting Engineers on behalf of WLV Tyrol Autumn 1999: Protection dams erected, End of dam evacutations Monitoring system still activ Some remaining questions regarding land use and possible additional events

11 Conceptual model for the failure (event) scenarios Pult-plains Database: Gruppe Felsmechanik (GFM), 2003 Expert group Rock mechanics, on behalf of the WLV Tyrol.

12 Influencing factors Debris Volume of the event scenario evaluated with a 3D-Modell geo-byte Salzburg on behalf of WLV Tyrol Disintegration factor Exampleof thevolumeof themovingrock-mass with a disintegration factor of 1,5 Scenario Section Volume (m³) 1 East Middle West Sum East Middle West Sum 3 Sum East Middle West Accumulation geometry (accumulation scenarios) 4 East Middle Retention capacity (m³) minimal accumulation middle accumulation maximum accumulation Sum West Main dam East Middle Western dam Sum West Sum

13 Damage scenarios No damage the whole rockfall-debris is retented by the dams Stray boulders interaction of blocks in the rockfall mass may cause steep flight paths - some boulders can probably overcome the barrier dams Overflow of the dams this main hazard scenario has been evaluated by a comparison of the rockfall volumes and the retention space (- retaining capacity) of the dams Residual retention space [m 3 ] at: Failure Scenario Min. Acc. Scenario 1,054, , ,000-1,005,000-2,584,500 Medium Acc. Scenario Max. Acc. Scenario 2,504,500 5,124,500 1,810,000 4,430,000 1,102,000 3,722, ,000 3,065,000-1,134,500 1,485,500

14 Event tree conceptual model

15 Comparison with well-investigated reference systems Comparisons to reference systems (geological and legal aspects) regarding the land-use show the need for the definition of design events. It is not common legal practice to use worst-case scenarios as design events, This has been verified by reference-projects regarding the authorisation aspects. It is based in the land-use-laws that expert groups (in Austria: WLV, Institution for Torrent and Avalanche control ) can decide whether land-use should be allowed or not, even in restricted areas. In similar projects the design events have been defined by expert groups for the dimensioning of measures and further land-use.

16 Case study 2 Creeping slope Zintlwald (summer 2005) Dr. G. Poscher, p+w geo zt, Pictures taken from Poscher, G., Mattle, B. & Henzinger, J. (2006): Hangbewegung Zintlwald: Geologisch-geotechnischer Bericht.- Unveröffent. Bericht i.a. des Amtes der Tiroler Landesregierung.

17 Investigation of damaged infrastructure Deformation rates (dm/d up to 1.3 m/d) Dr. G. Poscher, p+w geo zt, Pictures taken from Poscher, G., Mattle, B. & Henzinger, J. (2006): Hangbewegung Zintlwald: Geologisch-geotechnischer Bericht.- Unveröffent. Bericht i.a. des Amtes der Tiroler Landesregierung.

18 Measurements on-line Monitoring System Highly active area Slowly creeping land slide, deep creeping process Smaller events like local rock-falls Highly active area Smaller events at the bank of river Rosanna Dr. G. Poscher, p+w geo zt, Pictures taken from Poscher, G., Mattle, B. & Henzinger, J. (2006): Hangbewegung Zintlwald: Geologisch-geotechnischer Bericht.- Unveröffent. Bericht i.a. des Amtes der Tiroler Landesregierung.

19 Conclusions The presented risk analyses are based on different scenarios for the failure mechanisms, accumulation of debris volume and damage Semi-quantitative assessments have been used for the risk analyses Design-events should be defined by expert groups like foreseen in the landregulation-laws Worst-case scenarios have not been considered a design-event and are therefore neither a basis for measures, nor for decisions regarding future land-use Also reference systems regarding geology and authorisation processes should be taken into account Also the naturally occurring basic geohazards should be considered for a specific environment for a sustainable geohazard management Multidisciplinary automatic monitoring systems with alarm values are a powerful tool for this sustainable risk management

20 Thank you very much for your attention! Tschirgant ( G. Poscher, p+w geo zt gmbh) stefan.eder@ibk.ilf.com