Design of Breakwaters Rubble Mound Breakwater

Transcription

1 Design of Breakwaters Rubble Mound Breakwater BY Dr. Nagi M. Abdelhamid Department of Irrigation and Hydraulics Faculty of Engineering Cairo University 013

2 Rubble mound breakwater Dr. Nagi Abdelhamid

3 Advantages of Rubble mound breakwater: Failure of the armour layer is not sudden but gradually; It allows high energy dissipation due to its slope and transmission through porous of mound; It can be used for weak soil; Easy maintenance and construction; Small wave reflection; Minimum overtopping less than Vertical Breakwater. 3 Dr. Nagi Abdelhamid

4 Design Criteria For Breakwaters ECONOMIC LIFE Very Important Marine Structures Important Marine Structures Normal Marine Structures Temporary Marine Structure 100 years 50 years 5 years 1- years 4 Dr. Nagi Abdelhamid

5 Design Wave Height Non-Breaking Wave Condition, Hd Normal Marine Structures H1/3 Temporary Marine Structures Hm Breaking Wave Condition, Hb All Marine Structures Hb = 0.78 d Note : d is the available water depth. 5 Dr. Nagi Abdelhamid

6 Design Rubble-Mound Breakwater Structure Response The design of the rubble mound cross section includes the following: 1. design Armour (primary cover layer) of breakwater a) weight of armour (primary cover layer) W a b) Thickness of armour layer(t a ) c) Placement density ( number of units/m)nr. design Secondary ( under Layer) of breakwater a) weight of under layer W s b) Thickness of under layer(t s ) 3. design Core 4. design of Crest level and width 6 Dr. Nagi Abdelhamid

7 Design of Rubble-Mound Breakwaters 7 Dr. Nagi Abdelhamid

8 1- Design Design Of Rubble Mound Armour (primary layer) of breakwater The armour layer is probably the most important feature of a rubble mound breakwater since damage or failure can lead to failure of other parts a)weight of individual armor : Hudson Formula W 50 = γ a H 3 /{K D (S a -1) 3 Cot θ} Where: W 50 weight of individual armor unit, natural rocks or H γ a artificial concrete unit design wave height unit weight of armor unit material =.65 t/m 3 for rocks and.40 t/m 3 for concrete

9 γ w = 1.05 t/m 3 S a specific gravity of armor material, γ a / γ w θ angle between seaward structure slope and horizontal, cot θ = t armor unit stability coefficient K D b) Thickness of armour layer Where: D 50 = {W 50 / γ rock } 1/3 ta D max = K 0 D D 50 D D 50 D D 50 D min 0.15 D 50 D is the nominal size(equivalent cube); the suffix 50 refers to the percentage of stone passing that size 9 Dr. Nagi Abdelhamid

10 Concrete Armour Units Massive Bulky Slender Cube Accropode 1980 Tetrapods 1950 Dolos 1963 Depend the stability on own weight Depend the stability on own weight and interlocking Depend the stability on interlocking Dolos Cube 10 Dr. Nagi Abdelhamid Tetrapod

11 Concrete Armour Units 11 Dr. Nagi Abdelhamid

12 armour unit Concrete (Tetrapods ) 1 Dr. Nagi Abdelhamid

13 Suggested K D No-Damage Criteria and Minor Overtopping Structure Trunk Structure Head Armor Units n Placement Break Wave K D Non Br. wave Break wave K D Non Br. wave Slope Cot Quarry Stone Rough angular random Tetrapod & Quadrapod random Dolos random to 3 3 Modified Cube random Dr. Nagi Abdelhamid

14 Layer Coefficient and Porosity Armour Unit n Placement Layer Coeff., k o Porosity (p) % Quarrystone (rough) random Cube (modified) Tetrapod Quadripod Dolos Quarrystone graded random Dr. Nagi Abdelhamid

15 15 Dr. Nagi Abdelhamid

16 16 Dr. Nagi Abdelhamid

17 C. PLACEMENT DENSITY N r = A.n.K [1- P%/100].[γ u /W] /3 where: N r = number of units for a given surface area A = Surface area P% = Percentage of average porosity of layer 17 Dr. Nagi Abdelhamid

18 . Design Secondary ( under Layer) of breakwater a) weight of under layer W s W 50 =W armour /10 - W armour /15 D 50 = {W 50 / γ rock } 1/3 D max = D 50 D 85 = D 50 D 15 = D 50 D min =0.15 D 50 Filter Criteria (D 15 ) armor /(D 85 ) secondary 5 18 Dr. Nagi Abdelhamid

19 b. Thickness of under layer(t s ) where: t s n K t s = n K [W rock /γ rock ] ⅓ = total thickness of layer = number of layers of protection units = layer coefficient γ rock = unit weight of material W rock = weight of individual protection unit in layer 19 Dr. Nagi Abdelhamid

20 3. Core Design W 50 =W armour /00 - W armour /6000 D 50 = {W 50 / γ rock } 1/3 D max = D 50 D 85 = D 50 D 15 = D 50 D min = 0.15 D 50 Filter Criteria (D 15 ) secondary/(d 85 ) core 5 0 Dr. Nagi Abdelhamid

21 4. DESIGN OF CREST LEVEL AND WIDTH 4.1 Crest width B 3 K [W/γ u ] 1/3 Where: B = crest width Note: Controlled by construction method and maintenance equipment. 1 Dr. Nagi Abdelhamid

22 4. CREST LEVEL CL = DWL + R Where: CL = Crest Level of Breakwater DWL = Design Water Level R = Wave Run-Up Dr. Nagi Abdelhamid

23 Wave Run-Up R Where: R H d a 1 b a = b = for Quarry Stones = = for Tetrapods = = for Quadripods = = for Tribars tan gt H d Surf 3 Dr. Nagi Abdelhamid similarity

24 Overtopping Discharge: Q g Q H * 3 e o d tanh 1 hd R Where: = ln (sin ) h = structure height d = water depth R = wave run-up * Q o Q overtopping coefficien t overtopping discharge, 4 Dr. Nagi Abdelhamid L/s/m For pedestrians

25 Typical crest structures for rubble mound breakwaters 5 Dr. Nagi Abdelhamid

26 Typical crest structures for rubble mound breakwaters 6 Dr. Nagi Abdelhamid

27 Toe details for rubble mound breakwaters 7 Dr. Nagi Abdelhamid

28 Given: Example A rubble mound breakwater with two-diameter of rock armour layer: Find: Crest level = +4.5 m (LCD) Side slope of sea-side = 1: Design water level = +3. m (LCD) Significant wave height at sea-side =.0 m Mean wave period = 4.4 s Overtopping Coefficient = 0.0 Mean overtopping rate of the rubble mound. 8 Dr. Nagi Abdelhamid

29 Solution: H d.0 m T 4.4 s a b for Quarry stones tanθ 0.5 for side slope1: ζ tanθ π H g T d 0.5 * π * 9.81*(4.4) Dr. Nagi Abdelhamid

30 R CL α H d 1 DWL ln ( sin θ ) ln ( sin aζ bζ R * * m Case of 30 Dr. Nagi Abdelhamid CL ( 4.5 m) overtopping ) 1.77 m

31 h d R 4.50 m 3. m 1.77 m Q * o 0.0 Q ) g Q * H 3 o d 1 e 0.17 tanh α 1 hd R ) 9.81*0.0* e 0.17 tanh m /s/m 9. l/s/m 31 Dr. Nagi Abdelhamid

32 Design of Ruble Mound Breakwaters Mid Term May 011 A trunk cross-section with side-slope :1 has to be designed based on breaking wave condition, where the wave period is 8s. The cross-section is located at 9m water depth where the crest level is 5m above water level. (a) Design the sea-side rock armor and secondary layers, and estimate wave run-up. (b) Re-estimate wave run-up if Tetrapods armor-units are used. Data Trunk Breaking Condition t = T = 8s d = 9.0m h-d = 5.0m 3 Dr. Nagi Abdelhamid

33 Rock-Armor Layer H = 0.78 d = 0.78 * 9.0 = 7.0m W 50 = γ r H 3 /[K d (γ r /γ w -1) 3 cot θ] =.65(7) 3 /[3.5(.65/1.05 1) 3.0] 33t t = n K (W/γ r ) 1/3 = 1.15(33/.65) 1/3 = 5.3m D50= (W/γr )1/3 = (33/.65) 1/3 =.3m D15 = D50 = = 0.9m Secondary Layer W50 = Warmor /10 Warmor /15 = 33/10 = 3.3t t = = 1.15(3.3/.65) 1/3 =.47m D50= (W / γ r) 1/3 = (3.3/.65) 1/3 = 1.1m D85 = D50 = =.m Check: (D15) armor / 33 (D85)secondary = 0.9/. = Dr. Nagi Abdelhamid OK

34 Wave Run-up for Rock-Armor Layer ζ R tanθ π H g T d 0.5 * π*7 9.81*(8) 1.9 Wave Run-up for Tetrapod-Armor Layer aζ H 0.775*1.9 d 1 bζ *1.9 R 1.01* *1.9 aζ H 4. 9 d 1 bζ 34 Dr. Nagi Abdelhamid