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Prepare to meet thy monster

FOUNDATION CONTRACTS

IMPENDING ARRIVAL of a monster ship meant the Port of Tyne had to assemble some monster berthing facilities.

The 300,000t floating production storage and operation (FPSO) vessel Bonga was built by Samsung in South Korea and was due to arrive at Wallsend on the River Tyne on 12 October.

Adverse winds and tides delayed its first attempt at berthing and optimum conditions were not expected again until late last month.

The Bonga has a beam of 75m and is 32m high from keel to main deck - the same height as a 10storey building. Once berthed it will be fitted out by Amec before going into service for oil company Shell off the African coast.

Work began on the new berthing facilities in July. The £1.7M contract for the Port of Tyne Authority required three mooring structures to enable the vast ship to tie up. In its design Mott MacDonald had to provide adequate fendering systems to absorb the energy of the docking vessel, without damaging its hull.

Contractor Harbour & General began by installing an array of steel tubular piles for the two berthing points.

Vertical, 914mm diameter fender piles 16mm thick and 32m long are supported by an arrangement of 30m long, 508mm diameter circular hollow section struts with 12mm thick walls.

The struts are in a v-shaped configuration on plan, each bearing against a pair of massive concrete thrust blocks.

Each strut runs through a concrete block cast near mid-length to provide restraint against buckling, with the ends welded to a plate which bears directly against the thrust block.

The heavily reinforced concrete blocks are about 9m by 7m in plan and 4m deep, and are founded on an array of 32m long tubular steel piles raking at 1 in 2.5, generally 508mm diameter, with 12mm thick sections, providing both compressive and tensile resistance.

Ground conditions are between 5m and 10m of fill over clay, with some contamination from the site's old shipyard days.

Forces in the piles are massive, as would be expected given the size of the vessel, with working loads in the thrust block piles of 200t provided by skin friction, giving more than 2,000t per block.

A vibrating hammer was used to drive the first 12m length of pile. Once that was in, extensions were welded on and driven in.

The bollard blocks are similar to the thrust blocks, each housing three 200t mooring bollards anchored by 50mm diameter bolts cast into the reinforced concrete block.

These are unpiled, relying on the blocks' mass alone to provide anchorage. The vertical fender piles, good for 90t in compression, support a 10m by 4m rectangular steel fender panel covered with a proprietary rubbing surface against which the Bonga will come to rest.

To reduce the energy of the berthing impact, the vessel will be winched into place rather than hitting the berth at speed. The berthing energy will be absorbed by rubber elastomeric fender units bolted to the back of the fender panel, and fixed to the fender pile.

Inspections during fendering work revealed concerns about the existing quay wall. Harbour & General therefore installed a sheet-piled combi-wall in front of the wall, consisting of Larssen LX32 piles forming box sections with a pair of straight LX32s in between.

The wall is anchored by tie bars cast into a new concrete block behind the capping beam at the edge of the existing quay.

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