Seismic risk assessment of the major Egnatia Motorway bridges and geotechnical works, based on the new seismological data (SHARE).

Transcription

1 Seismic risk assessment of the major Egnatia Motorway bridges and geotechnical works, based on the new seismological data (SHARE). Seismic considerations in typical maintenance life cycle costs of Egnatia Motorway structures. Application case studies Panagiotis Panetsos Egnatia Odos SA, Structures Maintenance, Thessaloniki, Greece Eleni Sakoumpenta Egnatia Odos SA, Design Department, Geotechnical Discipline, Thessaloniki, Greece Manolis Charalmbakis Egnatia Odos SA, Structures Maintenance, Geotechnical Monitoring, Thessaloniki, Greece

2 Structures of Egnatia Odos 654 km of motorway 1856 Motorway Structures 650 Bridges 50 km of twin tunnels 190 km of earth cut slopes

3 Φασματική Επιτάχυνση (g) Design/construction and Maintenance of Egnatia Motorway structures A highly demanding engineering work that considered the following combination of unfavourable parameters: High seismic prone area -active seismic faults in the vicinity of some major bridges -strong peak ground accelerations 0.20g < A < 0.30g (return period of 1000 years - important factor of 1,30) -high spectral accelerations/ displacements (ductile systems or use of seismic isolation) -liquefiable soils (loose soil river bed) Οριζόντιες Διευθύνσεις Adverse geological/geotechnical terrain active landslides -severe settlements (direct or creep) -badly weathered or cracked rock Περίοδος (sec)

4 BRIDGE HEALTH MONITORING NETWORK OF EGNATIA MOTORWAY G2 G9 T3 Kristallopigi Bridge G8 Messovouni Bridge G4 G1 G7 Metsovo Bridge Egnatia Bridges Instrumented before 2008 Egnatia Bridges Instrumented after 2008 Egnatia Bridges Monitored during construction ( ) T9/T11 Bridge Old Bridges Monitored temporarily ( )

5 Egnatia Seismic hazard model Extent of the ITSAK earthquake model and seismic zones affecting the motorway, used by the Egnatia Seismic Risk software

6 F (D>DIS)y / Damage % Bridge Seismic vulnerability model Egnatia bridges were classified to 11 structurally representative categories depending on the structural type of the superstructure (box beam, slab, beams), the substructure (hollow piers, walls, frames or single massif columns) and their interconnection (monolithical or through bearings). For these 11 classes their seismic fragility curves were analytically derived. 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 SLIGHT MODERATE COLLAPSE EXTENSIVE EQUIVALENT VULNERABILITY CURVE 0,2 0,1 0,0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 PGA (g)

7 The most seismically vulnerable Bridge sections of Egnatia Motorway Using the Egnatia Risk Assessment Software the following probabilistic analysis results were derived in terms of 4 different seismic return periods: 50, 100, 475 and 1000-year in terms of probability of damage Damage ratios % 100y ReturnPeriod 200yReturnPeriod 475yReturnPeriod 1000yReturnPeriod Probabilistically estimated bridge damages (%) along Egnatia for different return periods (100y, 200y, 475y, 1000y)

8 High seismic loading is predicted within the first 50 years of service life for some bridges in high seismic prone areas resulting in minor to Table 3. Expected seismic peak ground acceleration moderate damages. for various return periods. Bridge Code Return Periods Metsovo Bridge Aracthos Bridge Polymylos Bridge Krystallopigi Bridge Mesovouni Bridge th Kavala Bypass Greveniotikos Bridge Votonosiou Bridge Nestos Bridge th Kavala bypass ravine bridge. Table 4. Expected seismic damage % for various return periods, for some major Egnatia bridges. Bridge Code Return Periods Metsovo Bridge Aracthos Bridge Polymylos Bridge Krystallopigi Bridge Mesovouni Bridge th Kavala Bypass Greveniotikos Bridge Votonosiou Bridge Nestos Bridge

9 Maintenance life cycle costs (120 years) of Egnatia bridges considering the probability of damages induced by earthquake within the first 50 years of bridge life Expected major repair of piers 20 years earlier

10 SHARE new seismic hazard model in Europe

11 Bridge management optimization software of Egnatia Odos Deterioration Models Cost models Bridge Condition Ratings Recorded In DataBase Project Level Analysis (Determination of necessary actions) Life Cycle Analysis UTILITY Of Bridges Decision trees Life Cycles Bridge Network Level Analysis (Optimization Algorithm) Optimal Capital Maintenance Programme

12 Geotechnical units along the motorway

13 Geotechnically critical areas Landslide areas Liquefiable areas Soft soil areas (mainly in river deltas) * Major structures are located in many of the above areas

14 Cut slopes along Egnatia motorway Cut total length: 191 km Cut height (h) distribution

15 Case study - Nestos bridge Seismic fault trace

16 Site investigation Boreholes SPT tests CPT tests Cross-hole tests Down-hole tests Ground improvement site test (vibro-replacement and vibro- displacement methods) Geotechnical profile and wave velocity per layer

17 Liquefaction susceptibility assessment Susceptibility degree medium low high low

18 Case study - Nestos bridge Total length: 453m No of spans: 12 Plan view Longitudinal section Bedrock (gneiss) Wheathered bedrock Silty sandy deposits (max thickness=55m) Liquefiable zone

19 Site specific design spectra

20 Plan view at pier location Soil improvement Stone columns at 2.25x 2.25 grid length = 20m Potentially liquefiable zone Cross section at pier location Piles D= 1.2m, L=35m Improved soil profile Initial soil profile

21 Kinematic load analysis Vertical effective stress

22 Flow velocity vectors Before soil improvement After soil improvement

23 Settlement analysis Additional settlement after an earthquake Consolidation settlement Pile cap Around pile cap area : 26.1 cm

24 Case study 2 Big cut landslide Geotechnical profile and landslide mechanism 275 m 325 m Sliding surface Stabilizing measures (cross-section) Counterweights Drainage tunnel

25 Case study 2 landslide characteristics Landslide characteristics Type Rotational landslide L x B Depth 560 m x 250m 80m Volume 13*10 6 m³ Geology No of instruments Rate of movement Sheared ophiolite mass with interbedded clay layers 16 inclinometers 12 piezometers (3 multilevel) Crackmeters Mean: 12mm/year Max: >18mm/month Special characteristics Brittle mechanism of failure. Danger of very fast failure without warning. Difficult approach in winter. Need of online warning system (already designed) Stabilization measures Major counterweights (3,8*10 6 m³), drainage tunnel, surface drainage, jute and vegetation

26 Proposed Research Actions The Egnatia Motorway is a major transportation infrastructure in Europe, crossing a highly seismic prone area. The design of Egnatia structures were considered old seismic hazard model as well as Greek seismic code (EAK 2000) The seismic risk assessment of major bridges and geotechnical works of Egnatia motorway considering recent seismological input (SHARE) should be carried out for: For some major bridges minor/moderate damage is predicted within the first 50 years of their service life The incorporation of seismic considerations into capital maintenance management as resulted from seismic risk assessment is necessary: Decision trees, Life cycles Prioritization of capital maintenance actions.

27 The critical geotechnical works as the active landslides, the high slope cuts and the liquefiable areas need to be assessed in terms of their seismic safety factor against new seismic hazard data (SHARE) There are many very interesting case studies to apply monitoring based methodologies developped in IRIS