Breakwater (mole) is used to prevent wave invasion and form a hydraulic structure required for sheltering waters.It is located at the periphery of the port water area, and is also used to prevent the invasion of drift sand and ice slush, so as to ensure that there is sufficient water depth and stable water surface in the port to meet the requirements of ships berthing in the port, loading and unloading operations, and entry and exit navigation.The inner side of some breakwaters is also used as a wharf or installed with certain anchoring equipment, which can be used for berthing.According to its plane layout, it can be divided into jetties and island embankments;According to the section form, it can be divided into slope type, straight wall type and mixed type.
The breakwater is an underwater structure built to block the impact of waves, protect the harbor basin, maintain the stability of the water surface, protect the harbor from bad weather, and facilitate the safe berthing and operation of ships.
The breakwater can also play a role in preventing the harbor basin from silting up and wave erosion of the shoreline.It is an important part of coastal ports under artificial cover.Generally, the allowable wave height in the port is between 0.5 and 1.0 meters, which is determined according to the requirements of different parts of the water area, different types of ships and tonnage.The breakwater is usually composed of one or two breakwaters connected to the shore or unconnected island breakwaters, or both.The waters covered by the breakwater often have one or several entrances for ships to enter and exit.
Chinese name
breakwater
Foreign name
mole
Role
Impact force of blocking waves, harbor basin enclosure, etc
Classification
Heavy breakwater, light breakwater
Features
Prevent harbor basin sedimentation and wave erosion of shoreline
Breakwater (mole) is used to prevent wave invasion and form a hydraulic structure required for sheltering waters.It is located at the periphery of the port water area, and is also used to prevent the invasion of drift sand and ice slush, so as to ensure that there is sufficient water depth and stable water surface in the port to meet the requirements of ships berthing in the port, loading and unloading operations, and entry and exit navigation.The inner side of some breakwaters is also used as a wharf or installed with certain anchoring equipment, which can be used for berthing.According to its plane layout, it can be divided into jetties and island embankments;According to the section form, it can be divided into slope type, straight wall type and mixed type.[1-2]
characteristic
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The breakwater is an underwater structure built to block the impact of waves, protect the harbor basin, maintain the stability of the water surface, protect the harbor from bad weather, and facilitate the safe berthing and operation of ships.
The breakwater can also play a role in preventing the harbor basin from silting up and wave erosion of the shoreline.It is an important part of coastal ports under artificial cover.Generally, the allowable wave height in the port is between 0.5 and 1.0 meters, which is determined according to the requirements of different parts of the water area, different types of ships and tonnage.The breakwater is usually composed of one or two breakwaters connected to the shore or unconnected island breakwaters, or both.The waters covered by the breakwater often have one or several entrances for ships to enter and exit.[1]
Function
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1. Defend against the attack of waves and ice ridges, ensure the stability of the waters in the port, and provide stable and safe berthing and operation conditions for ships.
2. (Sandy or muddy coast) reduce or prevent sediment from entering the port, reduce siltation in the port, ensure that the inner side of the deep embankment in the port can be used as a wharf, or place mooring equipment for ships to dock, saving investment.
Type of embankment
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The structure of breakwater can generally be divided into two categories: heavy and light.
Heavy breakwater: It is a traditional and commonly used type of breakwater, including sloping breakwater, straight wall breakwater and mixed breakwater.
Light breakwaters: developed in recent decades, various light breakwaters, such as permeable breakwaters, floating breakwaters, jet jetties and jetties, are developed according to the characteristics of wave energy concentrated on the surface and the special needs of the project.
Sloping embankment
When the wave meets the sloping breakwater, it will deform significantly and break on the slope, bringing local concentrated hydrodynamic pressure and bottom current to the slope, and there will also be upward counter pressure on the underwater slope surface.Therefore, natural boulders, artificial concrete blocks or special-shaped blocks are often used to protect the outer slope of the embankment from wave scouring;The embankment body is generally stacked with layered and graded block stones to form a trapezoidal section;The elevation of the dike top is mainly determined according to the wave climbing height on the armour and the allowable overtopping amount.The sloping embankment is suitable for the conditions of small water depth and soft soil foundation.
Vertical wall embankment
The positive wave will be completely or partially reflected in front of the straight wall embankment, forming standing wave (standing wave).The complete standing wave height is about twice the original wave height, and the wavelength is unchanged;The wave crest and wave trough appear alternately at the half wave length of the wall and in front of the wall, which is called the antinode;The water surface almost does not move at one quarter of the wave length in front of the wall, which is called wave node.In this way, the vertical wall will bear the pressure and buoyancy of standing waves, so it is often usedreinforced concreteCaisson or concrete block construction, wooden cage can also be used when the wave is small, or largePipe stringThe structure of the arrangement.The straight wall embankment is suitable for rock foundation or relatively dense foundation. A layer of crushed stone foundation bed is often paved at the bottom of the wall. The surface of the foundation bed outside the embankment is paved with facing stones as required, and the inside of the embankment can also be used as a wharf.When overtopping is allowed, the elevation of the dike top can be reduced, and sometimes chamfered top covers and caissons with wave dissipating chambers are used to reduce standing wave pressure.The directional spectral component of oblique wave or irregular wave is reflected in front of the straight wall to form a three-way wave, with peaks and valleys alternately appearing in a chessboard shape. To determine the combined pressure of waves along the breakwater line, the effect of vertical wall segmentation needs to be considered.
Mixed embankment
The upper part isconcreteThe vertical wall and the lower part of the breakwater are mixed with slope type riprap and protruding foundation bed.According to the different elevations of the sudden foundation bed top, the critical depth of wave breaking in front of the vertical wall varies from 0.8 to 1.7 times the wave height.On the premise of meeting the bearing capacity of the foundation, the lower protruding foundation bed shall be used as far as possible to make the water depth in front of the straight wall greater than the critical water depth to form standing waves.If the sudden foundation bed is too low and the water depth in front of the vertical wall is less than the critical water depth, wave breaking will inevitably occur. The vertical wall will bear wave breaking pressure that is much greater than the standing wave pressure, which directly affects the stability of the vertical wall.Therefore, under the condition of wave breaking, the higher foundation bed should be used as far as possible to break the waves on the foundation bed without directly impacting the straight wall. At this time, the straight wall bears the wave pressure of some waves or wave breaking currents.Large stones or artificial blocks shall be used for surface protection and shoulder pressing outside the outburst bed.The inner side of the embankment can also serve as a wharf.
Permeable dyke
The upper wave protection structure is installed on piles and column supports to form a permeable breakwater at the lower part.It is uneconomical to build heavy breakwater in waters with small waves and deep water.According to the characteristics that wave energy is concentrated on the surface of sea water, this kind of light permeable breakwater can be used.Since more than 90% of the wave energy is concentrated in the surface water depth of 3 times the wave height, the wave protection structure can play the role of wave protection when it extends into the underwater wave height of 2~2.5 times.The structural types include empty boxes, one or two straight baffles, inclined plates, flat plates, etc., and the boxes and plates can also be made permeable.The pile, column and other supports are hollow structures, and the lower wave energy can still pass through.The permeable embankment is a structure with baffle plates fixed on both sides of the pile abutment, one side is used for wave prevention, and the other side can be used as a wharf.The permeable breakwater shall be designed according to wave load.
Floating dike
It is a breakwater composed of floating body and anchoring equipment, which can reduce surface wave energy.Floating structures include raft, air bag, empty box or other special structures, and iron anchors are often used to tie them to caissons.Each floating dike must have sufficient width. Sometimes several floating dikes are required to effectively prevent waves. In addition, the mobility of its structure often requires consideration of plane layout.The floating dike is easy to move and can be used in many places.The floating dike structure has many limitations and is mainly used in the water area with large water depth and small waves or some places where temporary wave protection facilities are required.
Jetty and jetty
utilizeAir compressorJet jetty is the device that forms air curtain and circulation on both sides by ejecting bubbles through perforated pipes placed at the bottom of the water to block and reduce waves;The jetty is a device that uses a water pump to spray water through a nozzle placed on the water surface to reduce wave energy.Both are easy to move and suitable for temporary works such as construction and maintenance. Jet jetties are also used to protect against blast waves.Jet jetties and jetties consume a lot of electricity, are prone to corrosion and biological attachment, and there are many specific problems in practical application.
All the light breakwaters mentioned above are suitable for steep wave conditions, with poor shielding effect for long waves, and weak points such as thin structure, easy damage and high maintenance requirements.
