Capital dredging can be defined as, “the removal from beneath water and raising through water or soil, rock or debris to create a greater depth than had previously existed”.

The optimum choice of dredger is mainly dependent on location, the type of material to be removed and the method of disposal.

On the left is shown the ‘ladder’ and cutter head of a very large ‘walking’ cutter suction dredger operating in the Middle East. The Partnership was involved with commissioning on site.

If it is required to dredge strong, wide jointed rocks, it is usually necessary to fragment the rock first by pre-treatment, most commonly by drill and blast. The type of rock and the method of extraction govern the density of blast holes, and the charge size to be used.

On the right is seen a drill & blast pontoon used to pre-treat igneous rock during harbour expansion in Ireland. After treatment the fractured rock was removed using large backhoe dredgers loading to barges. The Partnership provided specialist advice to the Client from conception to completion.

Capital dredging may also be required in soft sediments. Left is seen a Clamshell dredging a trench in soft alluvium for a sea outfall. Dredged material is loaded into barges and taken to a sea disposal site. By working from deep to shallow water, barges are able to use the new channel to continue working even at low water. The Clamshell pontoon can be seen grounded during low tide.

Not all capital works involve only dredging. The Partnership project shown right involved the reconstruction of a NAABSA (drying) berth at an oil storage terminal off the Severn Estuary in the southwest of the UK. The new rock-fill base allows ships to ground safely during discharge.