Probabilistic design fault tree and reliability analysis of flood defences

Probabilistic design, Fault tree and reliability analysis of Flood defences Cong MAI VAN, PhD Water Resources University, Hanoi, Vietnam Emails: CONG.M.V@wru.edu.vn & C.MAIVAN@yahoo.com June 7, 2013 WRU Water Resources University Contents • • • • • Background: overview flood risk Reliability analysis: deterministic vs probabilistic Probabilistic design: Fault tree & reliability analysis Calculation tools: VaP; OpenFTA Exercise: reliability analysis of a simple flood defence system June 7, 2013 Background • • • • Recent floods in the world Probabilistic design/flood risk analysis, approaches Flood defences system: questions Focus: reliability analysis of existing flood defences (a part of risk assessment) June 7, 2013 Background Last years: - New Orleans is still recovering - River floods in the UK and Eastern Europe - Serious Floods in Bangladesh, Parkistan; thousands fatalities In Europe: • Government taskforce prepares emergency as well as longterm management for floods (e.g FLOODsite project); • Safety chain concept is introduced with more preference for other types of measures: insurance, evacuation, internal- or compartiment dikes, etc.; debase is going on => Much more attention for reducing flood risk 1953 flood, Holland 1953 flood, Holland Flooding due to huricance Katrina 2005 Flooding in Vietnam 2005 - 2007 Reducing flood risk, how? Risk = {Probability} x {Consequence} Scenario 1: Relief centered approach Reducing consequence: e.g rescuse people and livestock; accept economic damage =>Evacuation plan; flood proof; spatial planning ect.; Scenario 2: Prevention centered approach Reduce probability of inudation: e.g a sufficient strong and reliable flood defence systems June 7, 2013 Reducing flood risk, how? Engineers are challanged to go for Scenario This requires: • Good estimate of extreme conditions of nature in terms of its value and frequency (e.g River discharge, HW, sea surges and waves 1/100, 1/250, 1/500, 1/1.000, 1/10.000 per year); • Acceptable safety level (required) for a certain protected region; => target safety • Reliable design given a target safety June 7, 2013 10 Exercise A dam system comprise of sections; reliability of section & is known (i.e Pf-sect2=0.0002; Pfsect3=0.0005 per year ) while reliability of section is unknown Failure of the dam system happened mainly due to overflowing; instability of revetment amour units, instability of inner slope and piping Loads and strength parameters of the dam section are given in the below table Safety standard of protected region is 1/100 per year Question: what is the actual safety of the dam system? June 7, 2013 53 Failure mechanisms • Overflow: Z=Zdc –Zwl June 7, 2013 54 Failure mechanisms (contd.) • Instability of amour layers: Z= (Hs/∆D)R-(Hs/∆D)S Hs  S  [ ]R = 8.7 P 0.18   ∆Dn 50  N ξ − m Van der Meer formula Z={8.7*P0.18*(S/N0.5)0.2*(tanα α/SQRT(S0))-0.5 } - {Hs/∆ ∆/D} June 7, 2013 55 Failure mechanisms (contd.) • Macro instability of dike’s slopes Z = ∑ R M − ∑ SM • Z= S.Fbishob – [S.F.]= S.Fbishob – 1.15 S.Fbishop= N (1.35, 0.1) June 7, 2013 56 Failure mechanisms (contd.) • Piping: happens when both conditions occur - Condition 1: Rupturing Z1= ρcgd-ρwg∆H - Condition 2: Sand Flowing Z2= mLt/c - ∆H June 7, 2013 57 Fault tree June 7, 2013 58 Dam system failure Fault tree Failure of Section Overflowing Cond June 7, 2013 Piping Failure of section Sliding of inner slope Failure of section Instability of slope protection Condt 59 Use VaP and openFTA June 7, 2013 Failure mode Pf by VaP Overflowing 0.00233 Piping 0.0816 Piping 0.0783 Instability of inner slope 2.87e-07 Instability of amour units 0.0527 60 June 7, 2013 61 Example of a fragility curve Slope m1=4 Slope m1=4,5 Probability of failure (per year) 0,9 Existing old dike system, constructed before 1992 0,8 0,7 0,6 Actual dike system, constructed after 1992 and upgraded after 1998 0,5 0,4 Newest sea dikes in Hai Hau, after Damrey 2005 0,3 0,2 0,1 1/20 safety require 4,5 5,5 6,5 7,5 8,5 9,5 Dike crest level (m) June 7, 2013 62 Reliability based design Excessive wave overtopping Slope stability 10 Piping analysis for Nam Dinh dike 10 outer-slope 1:3.5 outer-slope 1:4.0 outer-slope 1:4.5 d actual d=1.0 m d=0.1 m -2 10 -1 Failure probability [1/year] Failure probability [1/year] 10 -2 10 -4 10 -6 10 -3 10 -8 10 -10 10 -4 10 5.5 June 7, 2013 6.5 Dike crest level Hk [m] 7.5 30 35 40 45 50 55 60 Mean value of seepage length [m] 65 70 63 75 Design of flood defences – integrated model Design Risk-based design Reliability-based design Evaluation of limit states Description of boundary conditions June 7, 2013 64 Failure modes Limit State Eq Component/system reliability analysis; Safety assessment (Pfi; Pfsys) Damages/ consequences: inventory/model RSAM PDF & CDF of sea loads (Hs Tp, water levels) Strength boundary: alternative geometries Input model ReOM RiOM Reliability based design model: optimal geometry given [Pf] {from component to system level} Risk-based design model: optimal level of protection [Pf] {system level} June 7, 2013 65 Output Optimal CFDS Literatures • • • • • • • • Allsop, N.W.H., 2006 Failure modes report Technical report FLOODSite Task 4, final draft verion Bakker, W.T and Vrijling, J.K., 1980 Probabilistic design of sea defences Proceedings International Conference on Coastal Engineering 1980 Barlow, R.E., 1998 Engineering reliability Philadelphia, USA: SIAM Ditlevsen, O., 1979 Narrow reliability bounds for structural systems Journal of Structural Mechanics, pp 453-472 Oumerarci, H., Allsop, N.W.H., Groot, M.B de, Crouch, R., Vrijling, J.K., Kortenhaus, A., Voortman, H.G., 2001 Probabilistic design tools for vertical breakwaters Balkema, Rotterdam, 2001 Vrouwenvelder, A.C.W.M and Vrijling, J.K., 1987 Probabilistic Design (in Dutch: Probabilistisch ontwerpen) Delft University of Technology, Faculty of Civil Engineering, Delft, September 1987 Vrijling, J.K and van Gelder, P.H.A.J.M., 2002 Probabilistic design in Hydraulic Engineering Lecture notes CT5310 Delft University of Technology Mai Van Cong Probabilistic design of coastal flood defences in Vietnam PhD thesis Sieca Repro, the Netherlands (2010) ISBN: 978-90-9025648-1, 249p June 7, 2013 66 • PhD thesis: Google me by title Probabilistic Design of Coastal Flood Defences in Vietnam; Direct available for download: http://repository.tudelft.nl/view/ir/uuid%3Aa7171f8444f4-4453-82d8-c7ec864cf954/ • Email: c.maivan9@Gmail.com & Cong.M.V@WRU.Edu.vn Subject: CHVB ……name June 7, 2013 67 ... overview flood risk Reliability analysis: deterministic vs probabilistic Probabilistic design: Fault tree & reliability analysis Calculation tools: VaP; OpenFTA Exercise: reliability analysis of a... failure of filter layers 23 Reliability &Fault tree analysis • • • • Reliability of a element Levels of calculation Reliability of a system Fault tree analysis Failure of dike section # i OR Overtoping... of failure modes to the system failure June 7, 2013 47 Reliability & Fault tree analysis - Investigation of all possible failure mechanisms, Estabilishment of LSE and fault- tree Calculation of