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Mersey makeover

Construction of a new trade centre on a former port may have been years in the making, but the careful planning is enabling the remediation effort to achieve recycling rates of 96%. Claire Symes reports.

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Material was excavated to up to 7m below ground level and reprocessed on site

The regeneration vision for Wirral Waters on the banks of the Mersey is aiming to deliver 20,000 new jobs to the area over the next three decades. While developer Peel Land & Development may be some way off achieving this aim, work has just started on one site that Peel hopes will be a springboard for the rest of the area.

With a 150 year history as a port facility and a legacy of landfilling, turning the area known as West Float - named after the former port that occupied the site - into a site suitable for the construction of the UK’s first international trade centre was not a straightforward task. Galliford Try first started working on the £3.2M scheme in 2008 but remediation and ground improvement work only started on the site - derelict since the 1980s - last year.

“The docks, along with a number of creeks, were used for landfill until the 1980s”

Jeff Wood, Galliford Try

Although Peel is the client, the West Float Remediation Project is part financed by the North West European Regional Development Fund Programme 2007-2013. The Department for Communities and Local Government is the managing authority for the European Regional Development Fund (ERDF), one of the funds established by the European Commission to help stimulate economic development by investing in projects which will support local businesses and create jobs.

The work currently being undertaken by Galliford represents phases one and two. A further two phases of work are planned to redevelop a total area of 25ha but the Wirral Waters area covers a much larger area.

“Records showed that the area was first used in the late 19th Century as graving docks - where ships are broken up and dismantled - and for flour mills,” says Galliford Try site agent Jeff Wood. “The mills were demolished in the 1950s or 1960s and the docks, along with a number of natural creeks, were used for landfill up until the 1980s.”

This historic use and subsequent landfill meant that contamination was an issue. Site investigations undertaken by RSK showed that there was contamination from tributyltin - which is used in the treatment of ship hulls to protect them from crustaceans - as well as lead, mercury, hydrocarbons and asbestos.

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West Float Dock has been derelict for decades

Galliford Try first became involved in the project in 2008 and undertook some site clearance to remove fly-tipped material. But the main work on site didn’t get underway until April 2012 due to the lengthy planning process created by the contamination. Nonetheless, Wood attributes this planning to the project’s delivery of 96% recycling rates during the remediation work.

“None of the contaminants were present at high concentrations so, with the intended commercial use of the site, the remediation plan that was agreed for the site involved excavating down to 1m and processing the material before backfilling,” says Wood. “Hot spots of contamination were identified before this stage.”

“The building will straddle one of the old infill creeks. There was concern about differential settlement”

Jeff Wood, Galliford Try

The site was divided up into 50m by 50m cells for the excavation work. Excavated material was crushed and screened and samples underwent validation testing to prove contaminant levels met the predetermined criteria. Any material with elevated hydrocarbons was aerated and retested before being replaced.

During the work, any obstruction was removed to a depth of 2m but under the footprint of the new building, the reprocessing was extended to 7m below ground level, to the top of the natural clay that underlays the site.

“The building will straddle one of the old infilled creeks - known as Ranks Creek - and there was a concern about differential settlement,” says Wood. “In total 14,000m3 of material has been removed from this area and replaced - it was mostly demolition waste.

“All obstructions from previous structures were also removed during this work. Most were taken down to 7m but some could only be extracted to 3m below ground and the design of the vibro stone column spacings has been modified as a result.”

Ground improvement using vibro stone columns was selected over a piled foundation solution, not just because of the ground conditions but also as a condition of the funding from the ERDF. Under the funding agreement, the foundation solution had to consider any future change in land use at the site and the current development had to be done in such a way that it would not impact on this. As a result, ground improvement was seen as the best way forward.

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Keller used instrumented rigs to ensure the success of the vibro work

Keller started work on the ground improvement work in mid- September and finished installing the 3,959 columns just before Christmas.

The lengths of the 600mm diameter columns varies from 3m to 7m and spacings from 1.2m to 3m, depending on whether they will be supporting the floor slab or building footings. The columns have been designed to support a bearing pressure of 100kN/m2 for the footings and 30kN/m2 for the floor slab. The columns have been designed to minimise settlement to a maximum of 25mm and a differential settlement of 1:500.

“A 32t bottom feed vibro rig was used to install the majority of the columns, but a smaller rig was used once deeper columns were installed”

Jeff Wood, Galliford Try

“The ground improvement has gone like clockwork even though Keller had to redesign some of the columns and add 900 to the total to cope with the obstructions that couldn’t be removed,” says Wood. A 32t bottom feed vibro rig was used to install the majority of the columns but a smaller rig was used once the deeper columns were installed.”

Ground improvement work was completed before Christmas and Galliford was due to finish its work as GE went to press. According to Wood, construction of the 230,000m2 trade centre is expected to start later this year with the scheme about to be put out to tender.

 

Springboard for Asia

Peel Land and Development’s new 230,000m2 International Trade Centre is expected to provide up to 1,000 selfcontained units for companies from China, India, South Korea and other emerging economies to exhibit, sell and distribute their goods into the UK, Irish and European markets.

According to Peel, the centre will be the first of its kind in the UK and will feature exhibition and event space, serviced offices, cafes, restaurants and a conference centre that will be linked to road, rail, water and air transport.

The development is part of an one of four UK enterprise zones established by the government inMarch 2011.

Wirral Waters forms part of the Mersey Waters zone, with the other part being made up by another Peel development area called Liverpool Waters.

Tenants taking up space in the new trade centre will benefit from special initiatives from locating within an enterprise zone.

These could include a 100% business rates discount for five years. A simplified and improved planning regime replaces previous legislation to give greater flexibility in terms of changes of use of floor space within the trade centre complex. There is also government support for the provision of superfast broadband in these zones.

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