Design of large twin-wall cofferdams for ship impact

When constructing large geotechnical structures in a river, such as shafts, buried culverts or new sections of river wall, a temporary works cofferdam is needed to create a dry and safe worksite within which the permanent works can be constructed. There is a risk that an errant vessel could strike the cofferdam. If the cofferdam were to fail, the consequences would likely be catastrophic, with collapse and flooding causing multiple fatalities as well as the potential for flooding of a shaft or tunnel being constructed from within the cofferdam. Therefore, the cofferdam, or a protection structure in front of it, needs to be designed to absorb the kinetic energy of an errant vessel. This paper will provide a recent example of design and numerical modelling of ship impact into a twin-wall cofferdam, describing the design methodology and results.