« Back
  • Improving guidelines on installing caisson breakwaters

    Caisson motion scoping study
  • Caisson motion scoping study
  • Caisson motion scoping study
  • Caisson motion scoping study
  • Caisson motion scoping study

Caisson motion scoping study

Increased demand for large new marine terminals, often require offshore island breakwaters in locations exposed to swell conditions, making installation of caisson breakwaters difficult and time-consuming.

Due to the locations of these terminals, many are exposed to swell conditions, making installation particularly difficult and time consuming.

The installation of caisson breakwaters is expensive, with high daily mobilisation cost; the cost of marine installation plant can cover £2,000—£150,000/day for small to large plant, with very large specialist crane barges up to £500,000/day (Hawkswood & Allsop, 2009). In most cases, delays carry heavy penalties. Survey of literature has suggested that most delays in installation of caisson breakwaters are caused by difficult wave conditions and unexpected problems during lowering.

Present guidance for designers or contactors is very limited with no clear methods for predicting the motion response of the caisson or mooring loads during sinking (Hibbs et al, 2009), particularly when influenced by near-bed effects. Guidance available is primarily of experiences reported by contractors, or suggestions that appropriate numerical model / physical model studies should be used. Some of the contactors experiences are generic, i.e. finding problems with the behaviour of the caisson during final touch down on the seabed.

A detailed literature search was undertaken in an attempt to find references in the public domain which discusses issues concerning the installation of caisson units. In relation to the volume of material found concerning the permanent installation of caissons, only very few covered the lowering of caissons to the seabed.

The majority of information is given as general guidance without detailed analysis methods for the prediction of caisson response/behaviour or specific design approaches to be used during installation. For example, Japanese construction regulations specify that work should stop when the wave height is higher than 1 m, and it is understood that contractors generally follow this rule (Miguel et al, 2009).

Reported wave conditions during successful, problematic and suspended installation have been found in three publications from three different parties installing caissons: Yoneyama (2002), Díaz-Rato (2009) and Hibbs et al (2009). These results suggest that installation is achievable in wave heights between Hs = 1 and 1.5m when wave periods are less than Tp = 10s.

The principles controlling the floating response of caisson fall under Archimedes principle of buoyancy and the rules that govern the stability of a floating body. Equations of motion, which include moments of inertia, added moment of inertia, damping coefficients, mass of floating object, righting lever and excitation forces are well-established methods within the offshore and naval architecture industry.

Caisson physical model data was compared with an established numerical model and results suggest that overall, offshore / naval architecture motion prediction tools should give a good starting point in the evaluation of the response of caissons when floating, but it may not be accurate enough when predicting near-bed response.

The study findings suggest that further investigation into the floating behaviour of caisson during installation would prove useful to the engineering community. Further research will use Froude scale physical model experiments and/or numerical models to investigate a range of caissons geometries, measuring motion response during various stages of sinking and at near contact with the seabed.

Authors

John Alderson, William Alsop

Keywords

caisson breakwater installation, floating response

Completed

2008

References

Miguel E, Hiroshi T & Tomoya S (2009). Methodology For The Simulation Of The Construction Of A Breakwater Taking Into Account Climate And Construction Accident Risks, Coastal Engineering Journal, Volume 51 – Issue 1 – Page 49, 2009.

Yoneyama H(2002), Development of an automatic installation system of breakwater caissons, PIANC Bulletin No. 109, 2002.

Díaz-Rato JL(2009), Innovation in the Extension to the Port of Gijón, Coasts, Marine Structures and Breakwaters 2009, 16 – 18 September 2009, Edinburgh.

Hawkswood M & Allsop W (2009), Foundations to Precast Marine Structures, Coasts, Marine Structures and Breakwaters 2009, 16 – 18 September 2009, Edinburgh.

Hibbs W, Bowers P, Young M, & Dingwall J (2009), Innovation Installation of Caisson Breakwater at Costa Azul, Mexico, Coasts, Marine Structures and Breakwaters 2009, 16 – 18 September 2009, Edinburgh.T

Read more information at

"Study findings suggest that further investigation into the floating behaviour of caisson during installation would prove useful to the engineering community."

Contact

Giovanni Cuomo

Giovanni Cuomo

Research Director

+44 (0)1491 822 414

Send an email View profile

Project information

Related projects