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Screen and clean

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

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Dirty dock: The site contains pollutants left over from its time as a harbour

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.

“The remediation plan that was agreed for the site involved excavating down to 1m and processing the material before backfilling”

Jeff Wood, Galliford Try

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.

Although Peel is the client, the West Float Remediation Project is part financed by the North West European Regional Development Fund (ERDF) Programme 2007-2013. The Department for Communities and Local Government is the managing authority for the fund, 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 Try 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.

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.

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

“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,” he says.

“Hot spots of contamination were identified before this stage.”

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 elevatedhydrocarbons was aerated and retested before being replaced.

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

Jeff Wood, Galliford Try

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, “adds Wood.

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.

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.

“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 Try was due to finish its work last month.

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 to 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 in one of four UK enterprise zones established by the government in March 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 by 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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