Break Water in Harbor

!!Find your way to know the Harbor basic concept like Breakwater which play a crucial role in that system!!

Basic Definations

Breakwater→

The protective barrier construct to enclosed harbors and to keep the harbor water undisturbed by effect of heavy and strong seas called Breakwater.It is mainly used for safe Anchorage for ships and also to facilitate loading of cargo

Trestle→

They are lighter peir design to withstand vertical loads as principal forces.In location where trestle not subjected to earthquake forces and height above firm bottom is less than 8m batter pile are omitted.In shallower water trestles constructed by overhead method.

Mole→

Inner side of break water is constructed for Quay for cargo handling and so known as Mole.Mole found economical than trestles when water depth less than 3m.In no case mole height exceed 8m.The top of mole should not be 4m to 5m more above low water

Wall acting as a breakwater

Classification of Breakwater:-

Breakwater are mainly classified into three types

1. Heap or mound breakwater
2. Mound with superstructure
3. Upright wall breakwater

Breakwater with Mound

1) Heap or mound breakwater :

It is the mixture of rubble undressed stone block , rip rap ,large blocks of huge bulk and weight the whole being deposited to form mound  acting as breakwater.As it is the simplest type so by dumping large number of stones block into sea till the mound will emerge out of water and thus safety protected from waves by certain side slope.

As the quantity of material depends on

1. Depth
2. Rise of tides and waves and their exposure

The disturbing action of waves is more between high and low water level.As for this protection is necessary to top of mound or the exposed face.

Method of Protection

1. Dumping heavy blocks of concrete on top and on front face.As this method resist flattening action of waves which is having the blocks weight of 25 tons to 30 tons and are laid with ends towards the ends of waves and by this minimum area of impact is provided against overturning
2. The upper part of mound being paved by granite blocks on the level of water.

Mound Formation

Mound are formed by means of weight of varying proportion and are placed according to the sizes such that the core is made with lightest material and also size of stone increase gradually outward.By this method waves from outside is resisted by hard or bigger stone while the core material is protected by lighter one.

As usual when rubble block placing is not suitable then concrete block has been used and by this substitute considerable economy in space and material being achieved.

1)Mound with superstructure founded at low water

The parapet is constructed to protect the solid superstructure Quay on top of rubble mound

Advantages:

1. Provide platform for handling cargo
2. Protect the top of mound
3. It reduces the mass of rubble due to slope of batter change from 2.8:1 to 1:1.

2)Mound with superstructure founded below low water level 

As this method has large advantage in founding the superstructure wall below level of disturbance so that there will be no disturbing effect on low levels and as usual it is the most economic method 

Mound Stability 

The upper portion of the mound has low quality in shape and section and they remain at equilibrium at the slope of 45 to 50 degree. The cause for the maximum disturbance is found between HWL and LWL and then the block of weight of 30 tons is deposited at a slope of 1 in 1 in that region. 

Mound Overview
Source: Professional Memoirs, Corps of Engineers, United States Army, and Engineer Department at Large, Vol. 10 

Mound Construction 

As we know mound are placed in different layers so that the small size material formed at the base and larger at the top

Such process being carried out in 3 types :

1)Barge Method :

This method has the advantages of offering opportunity for uniform depositing simultaneously over large area. 

2)Staging Method :

Series of piles of 15' to 20' are used. Connected by longitudinal runners which form tracks for the wagon. So such track are above high sea level and at about 25' to 35' centres. 

Main precaution to be taken when withdrawing staging piles from the area where mound has been completed. 

3)Low level Method :

This method naturally restrict scope of multisection attack but has advantages of consolidating the mound formed by traffic of loaded wagons 

WALL BREAKWATER

Their design is being made in order to prevent break water from failure like:

1. By overturning
2. By uplifting 
3. By fracture
4. By shearing of bed joints

So their prevention measure is being listed out to overcome the failure

Wall breakwater

1)Prevention of overturning :

To prevent this failure structure such as ordinary wall should be constructed to keep the resultant of weight and horizontal pressure within the middle third of base to avoid tension stress in the foundation. Permissible compression stress taken as 12 tons/sq.ft The horizontal force causing this overturning effect is marked at maximum value of about 2.8 tons/sq.ft at MSL with average wave size of 26'

2)Uplifting :

It occur on structure due to the action of waves underneath the mass and this force can be overcome by opposing force i.e weight of masonry 

3)Fracture 

As this effect does not directly result from wave action. But it cause due to dislocated blocks knocking against each other and thus breaking the joint causing the fracture in structure ans such effect can be eliminated by proper bonding in masonry by dowel joint etc. 

4)Shearing of Bed Joints 

It is prevented by resistance offered by adhesive force of morter joint in which 1:3 cement morter is used having strength in adhesion upto 6 to 7 tons/sq.ft

Note: Again when depth is not great and bottom is firm Upright Wall breakwater is built. 

Advantage :

1. It reduces amount of material 
2. Avoid settlement in case of mound 

Disadvantage : 

1. Involves building a good height of wall under water
2. Call for special care and this method is costlier

METHOD OF CONSTRUCTION IN WALL BREAKWATER 

1)Staging Method :

In this system piles are erected with regular staging provided by braced gross girder. Staging carried over by head moving gantries to carry huge blocks of construction. The blocks are shaped to form dovetail masonry in plan. Heavy joggle formed to prevent lateral movement of blocks under impact of waves.