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Further development in logistic process of dredging for Dubai coastal developments

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Author(s): Gerrit Jansen, Project Engineer, Van Oord, Rotterdam, The Netherlands

In Dubai several large land reclamation projects are going on for the expanding tourism business in this part of the Middle East. The ‘Palm Jumeirah’, ‘The World’,  ‘Dubai Maritime City’, ‘Deira Corniche’ and ‘Palm Deira’ are the most striking examples. Van Oord is putting a lot of effort in creating the dreams of Dubai, carrying out the dredging works, using an ‘army’ of dredgers and coastal construction equipment.

In 2005 the project ‘Palm Deira’ was awarded to Van Oord by the premier real estate developer ‘Nakheel’. This project needs a quantity of sand of over one billion m3, to be constructed within a period of eight years. (See article in Port Technology International 27th edition, autumn 2005 for more details.)

Logistic process

Due to the high demand and short turn around time for large infrastructural and land reclamation projects, Van Oord, has developed another view on the logistic process of dredging.

The basic cycle of dredging with a hopper dredger is the pumping of the soil into the hopper, transport of the dredged soil from place A to place B, discharging the soil from the hopper and sailing back to the winning area. In this process the ‘winning’ and the ‘transport’ of the soil is combined within one piece of equipment.

By separating the function of winning and transport Van Oord has developed a significant increase of scale in sand transport. This development is a system to load large hopper barges, offshore with a jumbo trailing suction hopper dredger for which existing techniques have been used. Solving the classic problem of offshore
transshipment of the dredged soil was especially quite a challenge.
 

Barge loading

Loading barges is not a new idea in dredging. Smaller barges are often used in combination with cutter suction dredgers or with backhoe or clamshell dredgers in coastal waters. This method is more or less a stationary working method and has a limited dredging depth. Barge loading with a trailing suction hopper dredger is different.

A trailing suction hopper dredger sails with a low speed while filling its own hopper. While loading barges, the hopper dredger has to sail as well, which means that the barge has to be towed alongside the hopper while dredging. Trailing suction hopper dredgers can nowadays dredge the sand at water depths of over 100 m.

As the dredging areas are offshore where wave heights are up to 3.5 m, the combination of hopper dredger and barge are exposed to rather high dynamical forces. Van Oord’s jumbotrailer Volvox Terranova was selected to be fitted with a barge loading installation.

The Volvox Terranova was delivered to Van Oord in 1999 by IHC Holland N.V. and has one suction pipe on starboard; this suction pipe is fitted with a 6,000 kW underwater pump which pumps the dredged mixture directly inside the hopper. The trailer can discharge its load via bottom doors or via the bow coupling or rainbow nozzle with two discharge pumps with a total available pump power of 13,900 Kw and has a hopper capacity of 20,000 m3.

As the Volvox Terranova does not have a suction pipe on portside there is enough space available for mooring a barge along portside hull. Instead of filling its own hopper, the underwater pump pumps the mixture towards the spray pipes from which it is sprayed into the hopper barges.

The hopper barges have a capacity of 8,000 m3 and therefore by employing three barges more than doubling the capacity of the Volvox Terranova. The barges including pusher tug are over 140 m long and 26 m wide. The pushers are connected to the barges with a special articulated connection.

At the beginning of 2006 Van Oord started developing a barge loading system for the Volvox Terranova. The barge loading system mainly consists of two spray pipes through which the mixture is sprayed into the barges. The hopper barges are moored alongside the Volvox Terranova which is protected by floating fenders;
during dredging the barge is kept alongside with wires at the front and aft ship.


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Edition 34

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