Accropode

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

History

File:Accropode.jpg

Accropode (1981)

The Accropode is a single-layer artificial armour unit developed by Sogreah in 1981. Accropode concrete armour units are applied in a single layer.

Ecopode (1996)

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 in 1996. The color and type of rock-like appearance can be specified to match the surrounding landscape.

File:Accropode2.jpg

Accropode II (2004)

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 made, resulting in the Accropode II. The shape modifications are intended to increase interlocking.

Design

Hydraulic stability

Specified stability coefficients at design stage:

• Hudson’s design K_D values:
  • 15 on trunk sections (16 for Accropode II)
  • 11.5 on roundheads (12.3 for Accropode II)

• Van der Meer stability number:

N_S = H_S/(∆ D_n50)= 2.7 (2.8 for Accropode II)

where:

H_S = significant wave height

∆ = relative mass density

D_n50 = 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.

3D simulation of wave motion near an accropodes.

Implementation

File:Offshoreworks.jpg

Large Accropode units are lowered into a position offshore by aid of a crane.

Fork-lifting is effective for handling the small to medium size units, whereas large units are handled by sling. Placement for breakwaters generally requires a crane or a barge-mounted crane.

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.

File:Idmer underwater inspection.jpg

Diver inspecting blocks

See also

• Breakwater (structure)
• Erosion control
• Riprap
• Artificial reef
• Coastal erosion
• Ocean surface wave
• Seawall
• KOLOS
• Xbloc

External links

• Ciria-CUR (2007) - Rock Manual - The use of rock in hydraulic engineering.[1]
• K. d'Angremond (2004) - Breakwaters and closure dams.
• N.W.H. Allsop (2002) - Breakwaters, coastal structures and coastlines.
• J.W. Van der Meer (1988) - Rock slopes and gravel beaches under wave attack.
• Delft Hydraulics Laboratory (1987) - Stability of rubble mound breakwaters - Stability formula for breakwaters armoured with Accropode (report H 546).
• U.S. Army Corps of Engineer Waterways Experiment Station (WES) - Shore Protection Manual (1984) - Hudson formula based on Hudson's extensive work in the fifties.

Gallery

• Accropode Breakwater.jpg

  Accropode blocks on offshore breakwater roundhead.

• Accropode block storage.jpg

  Storage of Accropode II blocks.

• 

  Accropode II on forklift.

• Acctruck.jpg

  Accropode on truck.

• Accropode offshore.jpg

  Placing Accropode blocks from land.

• Accropodedigue.jpg

  Accropode blocks on breakwater.

• Placing with a crane.jpg

  Placing with a crane

• AccropodeMonitoring.jpg

  Monitoring

• Idmer underwater inspection.jpg

  Idmer underwater inspection

External links

• Concrete Layer Innovations
• MEDUS (Maritime Engineering Division University Salerno)
• Specialized Company for ACCROPODE(TM) and one layer armouring breakwaters IDMER.NET