North Eastern port of Japan, facing the Pacific Ocean Construction started in 1983 Length of some 1800 m Partially completed by beginning 1991, but also part under construction In February 1991 high waves struck breakwater during winter depression (968 mbar), i.e. not by a typhoon. Damage at three locations along the breakwater H s = 6.9 to 7.6 m H max = 12.1 to 13.2 m T1/3 = 13 s Method: Goda γ sliding = 1.35 – 2.16 γ overturning = 2.60 – 4.54 Damage (finished section) Caissons displaced (some up to 6 m) Caisson walls broken Wave dissipating blocks scattered and inside caisson! Scour Damage (part under construction): 17 caissons displaced some up to 5 m Measured waves: H s = 9.94 m, T 1/3 = 13.4 s. Cause of damage: Waves beyond design wave Scattering of wave dissipating blocks
What is Breakwater? Breakwater is a structure that protects the area within it from waveattack.What’s the Need of Breakwater?To provide shelter from waves.Through this shelter, to manipulate the littoral/sand transport conditions andthereby to trap some sand entrance inside the Anchorage Area.
Availability of materials of construction. Depth of water at site of construction. Nature of natural foundations. Equipment available for construction. Funds and time available for construction.
Rubble mound breakwaters (Conventional Type)Vertical wall/front breakwaters ( Widely Used)Reef breakwaters Rarely used (Based on the MaterialsPiled breakwaters Available on Nearby Site)
Objectives :- To be able to make an assessment of hydraulic loads against caisson breakwater To be able to make a preliminary design of a caisson breakwater (length, width, height) To be able to compare caisson breakwater against rubble mound breakwater ie, on basis of material usage
TYPES(breakwaters with vertical and inclinedconcrete walls) Conventional type The caisson is placed on a relatively thin stone bedding. Advantage of this type is the minimum use of natural rock (in case scarce) Mutsu-Ogawara (Japan) Wave walls are generally placed on shore connected caissons (reduce overtopping)
TYPES (continued) Vertical composite type The caisson is placed on a high rubble foundation. This type is economic in deep waters, but requires substantial volumes ofAlgeciras (Spain) (small size) rock fill for foundation
TYPES (continued) Horizontal composite type The front slope of the caisson is covered by armour units Gela (Sicily, Italy) This type is used in shallow water. The mound reduces wave reflection, wave impact and wave overtopping Repair of displaced vertical breakwaters Used when a (deep) quay is required at the inside of rubble mound breakwater
TYPES (continued) Block type Alderney (Guernsey, UK) This type of breakwater needs to be placed on rock sea beds or on very strong soils due to very high foundation loads and sensitivity to differential settlements
TYPES (continued) Piled breakwater with concrete wall Piled breakwaters consist of an Manfredonia New Port (Italy) inclined or vertical curtain wall mounted on pile work. The type is applicable in less severe wave climates on site with weak and soft subsoils with very thick layers.
TYPES (continued) Sloping top The upper part of the front slope above still water level is given a slope to reduce wave forces and improve the direction of the wave forces on the sloping front. Overtopping is larger than for a Napels (Italy) vertical wall with equal level.
TYPES (continued) Perforated front wall The front wall is perforated by holes or slots with a wave chamber behind. Dieppe (France) Due to the dissipation of energy both the wave forces on the caisson and the wave reflection are reduced
TYPES (continued) Semi-circular caisson Well suited for shallow water situations with intensive wave breaking Miyazaki Port (Japan) Due to the dissipation of energy both the wave forces on the caisson and the wave reflection are reduced
TYPES (continued) Dual cylindrical caisson Outer permeable and inner impermeable cylinder. Low reflection and low permeable Nagashima Port (Japan) Centre chamber and lower ring chamber fills with sand
TYPES (continued) “Combi-caisson” Sloping top Semi-circular/perforated Perforated front wall Perforated rear wall
What is needed? Proper understanding of functional requirements Proper understanding of loads and resistance Insight in failure modes Understanding of breaking/non-breaking waves
Vertical Wall Breakwaters - Loads and resistance Failure modes (local) Instability of mound Erosion of seabed Partial InstabilityErosion Scour U
Example overall failure: Mutsu Ogawara Port, East Breakwater (Japan)
Example local failure: Catania Breakwater (Sicily, Italy)
Advantages:- Disadvantages:-Easy to repair. Construction cost is high.Protects the shore. Can be easily displaced by waves.Functions after minor damage. Don’t absorb all energy due to the gapsDon’t disturb the shoreline. between breakwater. Aesthetically seems to be bad.
Protection of the Ports or Harbors from the Natural Calamities such asTsunami is essential. But exact prediction of Natural Calamities is notpossible, but some extent of it can be prevented by BreakwaterConstruction.Protection of the Ports or Harbors from the Siltation & Wave Action isdone by providing a economical & suitable type of Breakwaters.Instead of using Armor Blocks the Sand Bags may be used to Protect orSafe Guard the Shores to some extent . Shore Protection in Quatar
Indian Standard Code of practice for planning and design of ports andharbours part 4 general design considerations [Third Revision of IS 4651 (Part4)].PIANC; Breakwaters with Vertical and Inclined Concrete Walls, Report WG 28,2003.US Army Corp of Engineers. 1985. Shore Protection Manual. Washington,D.C., US Army Corp of Engineers.