Breakwaters and closure dams 8

1,311 views
1,066 views

Published on

Published in: Education, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,311
On SlideShare
0
From Embeds
0
Number of Embeds
327
Actions
Shares
0
Downloads
54
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Breakwaters and closure dams 8

  1. 1. Chapter 8: Dynamic Stabilityct5308 Breakwaters and Closure DamsH.J. VerhagenApril 12, 2012 1Faculty of Civil Engineering and GeosciencesVermelding onderdeel organisatieSection Hydraulic Engineering
  2. 2. What is dynamic stability ?• Do not design on “damage”• Try to make the breakwater in such a way that it gets a “stable” form• Extra material is needed• “Natural” dynamically stable breakwaters seem to exist on Iceland• However, these breakwaters are not permeableApril 12, 2012 2
  3. 3. Types of berm breakwaters• Statically stable non-reshaping structures In this condition only some few stones are allowed to move similar to a conventional rubble mound breakwater• Statically stable reshaped structures In this condition the profile is allowed to reshape into a profile, which is stable and where the individual stones are also stable• Dynamically stable reshaped structures In this condition the profile is reshaped into a stable profile, but the individual stones may move up and down the slopeApril 12, 2012 3
  4. 4. Selection process for rubble mounds• Is it economical to design an conventional rubble mound ? Can all quarried material be used ?• If not all material can be used, and Hs < 2, use stable non-reshaping berm breakwater. If 2 < Hs < 3 m this might be a good option in case of dedicated quarry.• If the stones are too small, use statically reshaped type• If this also is not possible, use more stone and make dynamically stable berm breakwaterApril 12, 2012 4
  5. 5. Types of berm breakwatersDynamically stable Statically stable reshaped BB non-reshaping BB• Two stone classes • Several stone classes• Homogeneous berm • Berm of size-graded layers• Wide stone gradation • Narrow stone gradation• Low permeability • High permeability• Reshaping structures • Non-reshaping structures• Allowed erosion < berm width • Allowed recession < 2*Dn50• More voluminous • Less voluminous• No interlocking • Interlocking prescribedApril 12, 2012 5
  6. 6. Berm breakwaters in the world Country Number of berm Year first breakwaters breakwater was completed Iceland 27 1984 Canada 5 1984 USA 4 1984 Australia 4 1986 Brazil 2 1990 Norway 4 1991 Denmark (Far Oer) 1 1992 Iran 8 1996 Portugal (Madeira) 1 1996 China (Hong Kong) 1 1999 Total 57 Data from Pianc report on berm breakwaters 2003April 12, 2012 6
  7. 7. schematised profile for sand andgravel beaches lc = 0.041H sTm g Dn50 ls = lr =1.8lcApril 12, 2012 7
  8. 8. Influence of wave climate on a bermbreakwater profileApril 12, 2012 8
  9. 9. Berm breakwater Berlevåg (Norway)April 12, 2012 Figure from Jacobsen et al, PIANC congress 9 2002
  10. 10. Reshaped profile of BerlevågbreakwaterApril 12, 2012 10 Figure from Jacobsen et al, PIANC congress 2002
  11. 11. Reshaping calculations• Van der Meer (1988 - 1990 Breakwat• Van Gent (1995) Odiflocs• Archetti and Lamberti (1996) (See Copedec Cape Town)• new research by Tørum (1998, 2001)April 12, 2012 11
  12. 12. Recession according to Tørum (1)Special parameter for recession: H0T0 Hs Ho = ΔDn 50 g T0 = Tz Dn 50 Tz is mean periodApril 12, 2012 12
  13. 13. Recession according to Tørum (2)Rec = A(H0T0 )3 + B(H0T0 )2 + C(H0T0 ) − (−9.9 f g2 + 23.9 f g −10.5) − fhdn50A = 2.7 10−6B = 9 10−6C = 0.11 gradation factor f g = dn85 / dn15 1.3 < f g < 1.8 ⎛ h ⎞ depth factor fh =− 0.1⎜ ⎟ + 3.2 ⎝ dn50 ⎠ April 12, 2012 13
  14. 14. Recession according to Tørum (3) Place of the intersection of profiles: hf h h = 0.2 + 0.5 for 12.5 < < 25 d50 d50 dn50April 12, 2012 14
  15. 15. Longshore transport of stone• apply same type of formula as longshore sand transport• to prevent excessive transport, apply Hs ≤ 4.5 ΔDn50• for heads use a value of 3• Curve fitted transport formula: ⎛ Hs g ⎞2 S ( x) = 0.00005⎜ Tp − 105⎟ ⎜ ΔD Dn50 ⎟ ⎝ n50 ⎠April 12, 2012 15
  16. 16. cross section of the Sirevåg breakwater Stone class Wmin-Wmax (tonnes) I 20-30 II 10-20 III 4-10 IV 1-4 € 20.000/m (2000/2001) April 12, 2012 16
  17. 17. Design conditions• 100 years return period Hs = 7.0 m, Tp=14.2 s (based on hindcast + refraction study)• Storm of December 1998: Hs=7.0 m, Tp=14 s• Storm of February 1999: Hs=6.7 m, Tp=15 s• Storm of January 2002: Hs=9.3 m at deep water (450 m offshore) Hs=7.9, Tp=10 s •Damage to breakwater: 8 stones removed, 6 stones movedApril 12, 2012 17
  18. 18. Prototype and modelApril 12, 2012 18
  19. 19. Stone classes and Quarry yieldSirevåg Stone Wmin-Wmax Wmean Wmax/Wmin dmx/dmin Expected Class quarry yield I 20-30 23.3 1.5 1.114 5.6% II 10-20 13.3 2.0 1.26 9.9% III 4-10 6.0 2.5 1.36 13.7% IV 1-4 2.0 4.0 1.59 19.3%April 12, 2012 19
  20. 20. Sirevåg yield cureApril 12, 2012 20
  21. 21. Sirevåg breakwaterApril 12, 2012 21
  22. 22. Sirevåg breakwaterApril 12, 2012 22
  23. 23. Sirevåg breakwaterApril 12, 2012 23

×