Ballasting and Underbase Grouting

Foundocean gained initial experience in underbase grouting on the Thistle SALM installation project in 1978. The scope of work included pumping 2,000 tonnes of hematite into the base of the structure. Foundocean have now carried out solid ballasting operations to many offshore structures in the North Sea, the Mediterranean, Africa and the Far East. In 2000, Foundocean successfully completed a project for Veba Oil & Gas, pumping some 33,000 tonnes of ballast material into the Gravity Base Structure of the Hanze F2A facility.

To meet the high technical and performance specifications of offshore clients, Foundocean will design and procure all necessary equipment and iron ore materials that may be required for the ballasting operations, with resources, capacities, production rates, etc. all focused upon achieving the client's programme. A range of specialised ballasting systems is available, and subject to ballast density, can achieve delivery rates from 200 to 1,000 tonnes per hour. High-density materials include barites, haematite and magnetite.

The ballasting equipment is highly versatile and can be assembled on a wide range of vessels and transport barges. The ballast material, in the form of a graded high-density ore, is supplied to the fluidising unit via conveyors for mixing with seawater. High output centrifugal pumps are then used to deliver the slurry via hoses to the structure. Once in the structure, the ballast material settles out of suspension with the excess water from the slurry either passing through outlets at the top of the gravity base, or being pumped out of each compartment.

During ballasting operations the quantities of sand being mixed are carefully monitored by means of the following:

• Water flow meters on the water supply lines to the wet hoppers from the submersible pumps
• Belt weighers on the conveyor belts, feeding ore to the wet hoppers

The quantity of sand delivered to each compartment can therefore be carefully monitored, to ensure that they are filled to the correct level.