Accropode

Accropode

Accropode blocks are man-made unreinforced concrete objects designed to resist the action of waves on breakwaters and coastal structures.

History

The Accropode is the first single-layer artificial armour unit developed by Sogreah in 1981. The Accropode is robust, has a high hydraulic stability and is therefore reliable. Accropode concrete armour units are applied in a single layer. It is the most widely used single layer interlocking concrete block in coastal structures.

Sogreah's ancestor the Laboratoire Dauphinois d'Hydraulique was the inventor of the Tetrapod block in 1950-53. This block was the first interlocking monolithic concrete block used for breakwaters. It enabled structures to be protected with much larger blocks than before, when only natural rock was used (with a unit weight of up to around 10 tons) or concrete cubes. The Tetrapode was used all over the world, especially in Japan. The Tetrapod was used in a double layer with a unit weight of up to around 50 tons.

The Ecopode armour unit with a rock-like appearance was developed by Sogreah to enhance the natural appearance of concrete armourings above low water level A patent application was filed for in 1996. The color and type of rock-like appearance can be selected to match the surrounding landscape. In 1999, Sogreah modified the original Accropode shape by chipping away excess materials and adding friction features in the form of small pyramids. A patent application was filed for this modified shape. In 2004 further modifications to the 1999 shape were done to reveal the new Accropode II. The shape modifications are intended to increase interlocking.

According to the developers the modified shape results in factors comprising minimised rocking and settlement, maximised energy dissipation, reduced wave reflection and run-up/overtopping, and improved structural strength. Widely used, the Accropode technology has been applied on over 150 breakwater and seawall projects worldwide.

Design

Hydraulic stability

Specified stability coefficients at design stage:

  • Hudson’s design KD values:
    • 15 on trunk sections (16 for Accropode II)
    • 11.5 on roundheads (12.3 for Accropode II)
  • Van der Meer stability number:

NS = HS/(∆ Dn50)= 2.7 (2.8 for Accropode II)

where: HS = significant wave height ∆ = relative mass density Dn50 = nominal diameter These coefficients are valid for armour slopes from 3H/2V to 4H/3V and for seabed slopes up to 3%. The uneven surface of the Ecopode improves interlocking by friction, thereby increasing hydraulic stability.

Implementation

Fork-lifting is effective for handling the small to medium size units, whereas large units are handled by sling. The units can be stored one on top of the other, and placed in a random attitude to obtain the specified packing density. The proper packing method provides an adequate coverage on breakwater slopes.

The use of a remote-release hook is used for placing the unit, while underwater placements may be enhanced by GPS, adhering to a theoretical grid, and allowing for reliable QA/QC procedures.

References

See also

Gallery

External links

Concrete Layer Innovations

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