Work to reclaim 12 hectares of land for the Liverpool2 deep-water container terminal has passed the first stage with further infilling due to take place over the summer.
BAM Nuttall/Van Oord joint venture was awarded a 拢75m contract in 2013 for the quay wall design, crane rails, and the construction of an 854-metre quay wall. Van Oord has also dredged soft materials using a combination of its own water injection dredging technique and backhoe dredger Goliath 鈥� Europe鈥檚 largest backhoe.
The majority of 296 steel piles have now been driven into the seabed, allowing the infilling of 1.43 million tonnes of sand and silts taken from the Mersey estuary and deposited behind the new quay wall, up to a level of (+)6 metres above ordinary datum.
Liverpool2 construction director Doug Coleman said: 鈥淭here are very few projects of this kind and scale going on in the UK, especially considering the impact of the exceptional tidal range. We can only carry out the installation of anchor blocks and other infrastructure, including vibrocompaction, for a maximum of eight hours each day 鈥� two hours either side of each low tide. The one benefit is that the weight of water during high tide helps to compress the infilled material.
鈥淭he tide also means that for every million tonnes we bring in, we lose about 2.5% which is not significant in the scheme of things and is helped by our deliberate strategy of installing the new sewerage outfall pipe which acts as a barrier to minimise losses.
鈥淭hanks to the project being 鈥榓ll-weathered鈥�, the tide is the only major challenge we face from the elements, although high winds or freezing conditions inevitably mean that work has to be carried out slightly differently to minimise any consequent risks.
鈥淥verall, the first phase of infilling progressed exceptionally well and I鈥檓 generally very pleased with how all the works are taking shape.鈥�
The piling process, which began in 2014 and is due to be completed in the next few months, involves drilling from large jack-up rigs and inserting tubular piles to create the new quay wall. The area behind the wall has been dredged to bed rock to allow for virgin materials to be deposited.
The infilling process began in February with the arrival in the river Mersey of Van Oord鈥檚 Willem van Orange trailer suction hopper dredger. The vessel has a handling capacity of 10,000 m3 (21000 tonnes) and took materials from a site 20 miles away from Liverpool2, with each dredging and discharge operation taking 6.5 hours from beginning to end.
The dredger is due to return at the beginning of July to begin the second campaign of infilling, which will see a further four million tonnes of dredged material being harvested from the river.
Other significant elements of the project to date include:
- installation underway of 261 anchor blocks 3metres below the current infilled level,
- connection of the anchor block to piles with steel bars, to straighten and tension the quay wall structure
- vibrocompaction of the infill to settle it and drive out water
- 220m extension to an existing sewerage outfall through the site, towed in a single piece from Norway
- installation of drainage works directly behind quay wall
- upfill from (+)6.5 metres to (+)10 metres to cover the tie bars and anchor blocks to the top level of the piles.
As well as the further infilling, the next major phases of the work will include installation of capping beams, with bollard and fender blocks, and pocket dredging for the delivery of ship to shore cranes.
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