User:TP Adiwijaya/Integrated Armor System Breakwater

How Coastal Wave Impacts The Land? Wave action on a beach is a complicated natural phenomenon that constantly changes because of its irregularities. This is easily understood because waves are influenced by the wind. The complexity of the ongoing water movement in the coastal area unfortunately is not caused by the wave alone. Bathymetry, sea level changes, storm surge, long-shore currents, rip currents, tides, underflow, and geologic activities also contribute the complex movement of water in the coastal zone. Although those factors do not always present simultaneously, wave never acts as a lone ranger. The impacts of those activities to the beach can be deposition also known as accretion or abrasion which is beach erosion. The impact measured in time also varies from instantaneous, hours, days, months, years, centuries, to millennia. Subsidence and tectonic activities may change the beach suddenly or slowly in centuries. Rip currents, narrow and near-bottom seaward-flow have the ability to transport significant amount of sediment in a matter of hours during coastal storms. Storm surge is very critical to erosion magnitude in the order of hours to days. Sea level change is still poorly understood, but its effect on erosion can be observed in months to years. The currently hot issue on global warming implicitly carries subtle world-wide gigantic erosion that may come in decades to centuries. When the sea wave moves on a coastal zone, the shape is forced to experience gradual transformation by the decreasing water depth, until the wave becomes unstable and breaks. It is during breaking when a large portion of its energy is released. We can actually see the violent collision between water during this process, accompanied by loud voices. This energy can reach and scatter the sediment at the bottom and suspend it within the turbulence flow. These sediments can be carried seaward by the back flow of the wave. Some heavier materials are disposed closer from the original position while the lighter ones are moved to the farther.

The Breakwater Breakwater is a civil structures construction body built to protect certain places such as beach, road, seaport, building etc. Breakwater are constructed on coasts as part of coastal defense or to protect an anchorage from the effects of weather and long shore drift.

Offshore breakwaters, also called bulkheads, reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion. They are constructed some distance away from the coast (detached) or built with one end linked to the coast (attached). The breakwaters may be small structures, placed one to three hundred feet offshore in relatively shallow water, designed to protect a gently sloping beach.

The mechanism of breakwater is slowing the accumulated water with certain velocity by breaking it either in distance from the beach or on the protected beach. By breaking the wave, the transmitted wave will loose its abrasiveness.

The Third Generation Integrated Armor System (IAS) pioneers the third generation of cover layer design by its unique design concept.

Unlike various types of previous armor designs which emphasize on interlocking, IAS was designed based on direct simultaneous measurements of wave forces on two identical armor model arranged in tandem. The two units were placed among the surrounding rocks yet totally isolated without any contact with one another and with the rocks around them. This was necessary to measure the actual wave forces acted on them. This is a rational method to understand the characteristics of wave forces on the cover layer before designing a good and economical cover layer.

Direct wave force measurement on two instrumented unit models has quantified the simultaneous responses of the two armor models against breaking wave forces. Each model was built with exactly the same shape, dimension, and materials. A special instrument was inserted in the unit to enable the measurements of longitudinal and uplift forces simultaneously. In addition, the spinning moments about the center of mass of the unit was identified by measuring the uplift forces on two selected points.

Wasi, the inventor, found in his study that two tandem armor stones received different forces. As the wave started to attack, the front armor experienced very powerful force while the second armor behind it, at that moment, received a very weak force. It is easy to understand because the front unit acted as the shield to the rear unit at that moment. As the wave continued to move forward, the rear armor experienced an increasing magnitude of forces, but less powerful than the force on the front unit, because of energy loss.

The concept of IAS was born by distributing the instantaneous powerful force acting on that front armor to the tandem unit behind it so that the strong force magnitude on the front unit was reduced to half. This force distribution was conducted by introducing a compressive connector. The reduction of force magnitude is greatly amplified by employing a tensile connector from the front unit to another rock in front of it. This scheme would reduce the magnitude of the force on the front unit model to one third. The more armor units are interconnected in such fashion, the more force reduction is produced. As a result the dimension of the armor unit can be greatly reduced because of the presence of these unique connectors.

“IAS – AN AMALGAMATION OF STRENGTH, ECONOMIC EFFICIENCY, AND BEAUTY OF COVER LAYER FOR BREAKWATERS”

''The Strength '' The strength of IAS is best illustrated as series of train wagons. One cannot push or pull one wagon without moving all of the wagons in the chain. Each wagon represents the individual IAS block. The train hook represents the IAS connectors. If any push is applied to any intermediate wagon in the series, that force will be transmitted to the rest of the wagons via the hooks. The hooks will transmit to all of the wagons in front of that intermediate wagon by a “push” force. All the hooks behind that intermediate wagon will transmit that initial push force by “pulling” all the wagons behind the intermediate wagon. In the same way if any pull force is applied to the intermediate wagon, that pull force will be distributed to all the wagons in the chain in a reverse manner. The difference between the illustration and the IAS interconnection is in the separation of functionality. The push or compressive connector is carried out by a capsule concrete shaped connector. The pull or tensile connector is performed by a steel rod connector. The two connectors were designed carefully to ensure their unique function. The conventional cover layer design does not have such mechanism. The interlocking that exists between the armor blocks is limited in scope, and it is highly depends on how they are placed. It is through the interlocking that wave force is distributed to the surrounding rocks. The breaking of the units after continual loading like what we can read in many cases shows that such interlocking has produced the strain limit of the material. The rolling of an armor unit from the slope that leads into the collapse of the structure also indicates that random placement can be very expensive!

The Economic Efficiency

The use of connectors distributes the powerful wave forces to all of the IAS blocks arranged in the chain. This distribution greatly minimizes the force on each block. Since the reduced force in a block becomes small, the block does not need a large dimension such as when the block has to withstand the force alone! The stable size in the conventional design requires a huge mass of rock that must be stable in it self. The interlocking is added as safety. This is the contrast between the IAS and the previous design. The economic of IAS is not hard to count, because IAS design greatly reduces the stable mass of each block.

The Beauty

The best way to describe a beauty is by looking at it. IAS provides excellent aesthetic values that may increase tourism. (The sketch are provided in http://www.facebook.com/?ref=home#!/pages/IAS-Breakwater/225730354335?ref=ts).

"IAS – Earthquake Resistant Cover Layer Design" Earthquake force on breakwaters works differently than the way the waves attack them. Firstly, earthquake vibrates the structures from the bottom up, whereas powerful wave force is concentrated around the contact between SW (static water level)L and the seaward slope. Secondly, the direction of the earthquake induced force combined with the inertial force produced by its acceleration causes the armor rocks to move horizontally leaving the body of the breakwater both sides, the seaward and the landward slopes. This can be easily observed by piling up rocks on a table and then shake the table. The direction of wave attack typically starts with one powerful blow directed to the body of the structure at the seaward slope, followed by backwashing with the opposite direction. Thirdly, the changing of the direction of earthquake force from left to right or vice verse is very rapid with relatively constant magnitude for a period of seconds (yet for so many cycles!). The alteration of force direction by wave is very slow, in comparison to the earthquake case, but with a rapid depletion of force magnitude because of quick energy loss. Fourthly, earthquake force attack on a breakwater is massive and simultaneously on the whole body of breakwater starting at the bottom, while the wave force attack on relatively a short distance. The wave crest may be very long, but it usually breaks at different times at different points. The differences can be investigated further, such as wave is much more continual rather than earthquake, earthquake can generate powerful tsunamis, etc, but the point is that the design of a good cover layer deserves careful earthquake resistant consideration, because earthquake force on breakwaters works differently to wave action.

The heavy mass of rubble-mound armors in the conventional design is needed for the stability of the structure. However, it poses some danger when it is shaken by a powerful quake. Loose and poor interlocking among the rubble mound has to be avoided because it provides no resistance against earthquakes.

The creation of various shapes armor blocks has significantly improved the interlocking among the units of the cover layer materials. When the placement of these armors is properly arranged, it provides a strong resistant to wave attacks. Such placements, however, is very challenging because of the extreme difficulties to systematically arrange the units under constantly moving sea surface. This may result in interlocking irregularity either locally in a few spots or worse. This irregularity can be a fatal cause of structural failure under severe wave force. Still worse, a greater damage can be expected when the structure is shaken by powerful earthquake forces.

The two types of connectors employed in IAS serve not only as force distributor but it also connect the IAS units arranged in layer to work together as a horse paddle sitting on the breakwater surface. These connectors provide a very powerful means to protect the separation of an armor unit from the body of the structure under wave attack or earthquake vibration.