Chapter 15: Failure modes andoptimisationct5308 Breakwaters and Closure Dams                                              ...
What is the most important elementof a breakwater or closure dam ??•     the        element which is the most expensive on...
failure modes for                 dike-type structures                        Failure of breakwater by earthquakeApril 12,...
failure modes for a rubble mound(Burcharth, 1992)April 12, 2012                     4
Failure modes for a monolithicbreakwaterApril 12, 2012                   5
rock fill                 overflow                 dam failure                 modesApril 12, 2012                 6
fault treeApril 12, 2012   7
fault tree for closure dam (crosssection)April 12, 2012                      8
fault tree for closure dam(equipment)April 12, 2012               9
fault tree for construction planningApril 12, 2012                         10
equipment                 utilisation in                 relation to                 fault treeApril 12, 2012             ...
The Dilemma• A strong and heavy breakwater does not require  maintenance                   … but is very expensive to cons...
Wave Height H       Probability of    (m)              Exceedance         4                 (times per annum)             ...
development of damage             Actual Wave Height H    Damage in % of armour layer                    H < Hnd          ...
Cost of construction                  Initial cost   for armour units:          € 1320 * Hd                               ...
annual riskHnd               1 < H < 1.3 Hnd             1.3 Hnd < H < 1.45 Hnd                 H > 1.45 Hnd              ...
average annual risk           Hnd                                s = Σ(Δp.Δw)                 Full repair of partial   Onl...
capitalised maintenance cost           Hnd                               Capitalised risk S                    Full repair...
total cost        Hnd                                  Total cost I + S                 Full repair of partial   Only repa...
total cost for various strategies                 50000                 45000                 40000                 35000 ...
Conclusions for Rubble MoundBreakwaters• There is an optimum design wave height• Accepting regular maintenance is the best...
differences in breakwater type• In case of overload a Rubble mound breakwater will  suffer from some damage, which can be ...
Vertical wall breakwater                                    400000                                    350000            to...
Conclusions                         50000                                                           50000  total cost per ...
Conclusions (2)• Rubble mound breakwaters are less sensitive to  uncertainties in wave data• If there is no overload, a Ve...
Including “secondary damage”• When a breakwater is damaged, the port cannot  function well• The cost because of loss of pr...
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Breakwaters and closure dams 15

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Breakwaters and closure dams 15

  1. 1. Chapter 15: Failure modes andoptimisationct5308 Breakwaters and Closure Dams Sri Lanka, Kudawella Tsunami damage of breakwaterH.J. Verhagen 2004April 12, 2012 1Faculty of Civil Engineering and GeosciencesVermelding onderdeel organisatieSection Hydraulic Engineering
  2. 2. What is the most important elementof a breakwater or closure dam ??• the element which is the most expensive one• the section which is the most costly one• the element which is the most unreliable one• the element which is the most sensitive to variations in the boundary conditionsApril 12, 2012 2
  3. 3. failure modes for dike-type structures Failure of breakwater by earthquakeApril 12, 2012 3
  4. 4. failure modes for a rubble mound(Burcharth, 1992)April 12, 2012 4
  5. 5. Failure modes for a monolithicbreakwaterApril 12, 2012 5
  6. 6. rock fill overflow dam failure modesApril 12, 2012 6
  7. 7. fault treeApril 12, 2012 7
  8. 8. fault tree for closure dam (crosssection)April 12, 2012 8
  9. 9. fault tree for closure dam(equipment)April 12, 2012 9
  10. 10. fault tree for construction planningApril 12, 2012 10
  11. 11. equipment utilisation in relation to fault treeApril 12, 2012 11
  12. 12. The Dilemma• A strong and heavy breakwater does not require maintenance … but is very expensive to construct• A light breakwater is much cheaper to construct … but requires a lot of maintenanceApril 12, 2012 12
  13. 13. Wave Height H Probability of (m) Exceedance 4 (times per annum) 1.11 Wave climate -1 5 1.58*10 -2 5.2 8.4*10 -2 5.5 7.62*10 wave exceedance -2 5.8 3.8*10 -2 10 6 2.47*10 -3 6.5 7.35*10 w ave height (m) 8 -3 7.15 3.0*10 -3 6 7.25 2.63*10 -4 4 7.8 9.0*10 -4 7.98 8.0*10 2 -4 8.7 1.5*10 0 1 0.1 0.01 0.001 0.0001 exceedance (times per year)April 12, 2012 13
  14. 14. development of damage Actual Wave Height H Damage in % of armour layer H < Hnd 0 Hnd < H < 1.3Hnd 4 1.3Hnd < H < 1.45 Hnd 8 H > 1,45 Hnd CollapseApril 12, 2012 14
  15. 15. Cost of construction Initial cost for armour units: € 1320 * Hd for core: € 8620 Design wave height Initial cost Initial cost Amour Hnd breakwater Layer “C” “A” (m) (€) per running meter (€) per running meter 4 13900 5280 5 15220 6600 5.5 15900 7280 6 16540 7920April 12, 2012 15
  16. 16. annual riskHnd 1 < H < 1.3 Hnd 1.3 Hnd < H < 1.45 Hnd H > 1.45 Hnd n = 4% damage n = 8% damage Collapse Δp Δw Δp.Δw Δp Δw Δp.Δw Δp Δw Δp.Δw(m) (1/year) (€) (€/year) (1/year) (€) (€/year) (1/year) (€) (€/year) 4 1.02 420 430 4.6 10-2 860 40 3.8 10-2 13900 530 5 1.5 10-1 530 80 4.7 10-3 1060 5 2.6 10-3 15220 405.5 7.4 10-2 580 40 2.2 10-3 1160 - 8 10-4 15900 10 6 2.4 10-2 630 15 7.5 10-4 1260 - 1.5 10-4 16540 3 Δp probability of occurrence of the wave height Δw cost of repair of the armour layer (2nA) respectively cost of replacement (C)April 12, 2012 16
  17. 17. average annual risk Hnd s = Σ(Δp.Δw) Full repair of partial Only repair of serious No repair of partial damage damage(>8%) damage (m) (€ per year) (€ per year) (€ per year) 4 1000 570 530 5 125 45 40 5.5 50 10 10 6 18 3 3April 12, 2012 17
  18. 18. capitalised maintenance cost Hnd Capitalised risk S Full repair of partial Only repair of serious No repair of partial damage damage(>8%) damage (m) (€) (€) (€) 4 30000 17100 15900 5 3750 1350 1200 5.5 1500 300 300 6 540 90 90 lifetime of 100 years; rate of interest 3.33%April 12, 2012 18
  19. 19. total cost Hnd Total cost I + S Full repair of partial Only repair of serious No repair of partial damage damage(>8%) damage (m) (€) (€) (€) 4 43900 31000 29800 5 18970 16570 16420 5.5 17400 16200 16200 6 17080 16630 16630 6.5 17300 Adding up initial cost plus capitalised maintenance costApril 12, 2012 19
  20. 20. total cost for various strategies 50000 45000 40000 35000 30000 full repair cost 25000 partly repair no repair 20000 initial cost 15000 10000 5000 0 3.5 4 4.5 5 5.5 6 6.5 H-designApril 12, 2012 20
  21. 21. Conclusions for Rubble MoundBreakwaters• There is an optimum design wave height• Accepting regular maintenance is the best option• This implies that the design also should allow a “repairable” breakwaterApril 12, 2012 21
  22. 22. differences in breakwater type• In case of overload a Rubble mound breakwater will suffer from some damage, which can be repaired.• In general for Rubble mounds: the amount of repair costs increase linear with the amount of overload: cost = B * (Hstorm - Hdesign)• In general for Vertical wall breakwaters: you have always a given fixed amount of damage, not depending on the amount of overload: cost = A + B (Hstorm - Hdesign)April 12, 2012 22
  23. 23. Vertical wall breakwater 400000 350000 total cost per m eter 300000 building cost 250000 yearly repair 200000 capitalised repair 150000 100000 total 50000 0 5 7 9 11 Hs (design wave) damage cost = 4000 + 1500*HsApril 12, 2012 23
  24. 24. Conclusions 50000 50000 total cost per meter 40000 total cost per meter 40000 30000 30000 total 20000 20000 repair 10000 10000 0 0 5 7 9 11 5 7 9 11 Hs (design w ave) Hs (design w ave) Rubble mound breakwater Vertical wall breakwaterApril 12, 2012 24
  25. 25. Conclusions (2)• Rubble mound breakwaters are less sensitive to uncertainties in wave data• If there is no overload, a Vertical wall breakwater requires less maintenance• If there is overload, Vertical wall breakwaters cause much more problemsApril 12, 2012 25
  26. 26. Including “secondary damage”• When a breakwater is damaged, the port cannot function well• The cost because of loss of production should be included in the calculation• In general secondary damage will not change the tendency of the conclusion before, but make them more even more stronger: • The optimum for a rubble mound breakwater is allowing quite some damage, and doing a lot of repairApril 12, 2012 26
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