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Stout work in west London

Piled reinforced soil embankments, abutments and walls are key to construction of new infrastructure for the redevelopment of part of the Guinness Park Royal brewery in west London.

Brewing processes have changed considerably since Guinness's first brewery outside Ireland, the massive red brick Park Royal complex in west London, was built in 1934-36.

In recent years much of the production plant has been rebuilt outside the original buildings, some of which were designed by Sir Giles Gilbert Scott, architect of Battersea Power Station, Bankside Power Station (now the Tate Modern gallery) and Britain's famous red telephone boxes.

This, combined with the firm's need for a new office to bring together staff scattered over the site in seven buildings, led to the decision to redevelop part of the area as an office park.

Developer London & Regional Properties is carrying out the scheme, which has a total 'built out' value of nearly £350M. Nine offices will be created - one occupied by Guinness - around a landscaped area of lakes and weirs which will cost more than £3M.

New infrastructure to serve the development is also being built, plus a hotel, a new Underground station, restaurants and housing, in a bid to create jobs and revitalise this area of the capital.

The brewery is near Hanger Lane, the frequently gridlocked junction of the A40 with London's North Circular inner ring road. The main element of the infrastructure work involves building a link from the eastbound carriageway of the A40 to Coronation Road, which runs along the southern edge of the brewery.

Main contractor Norwest Holst Construction (NHC) and its subsidiary Norwest Holst Soil Engineering (NHSE) began work in March 2000.The £15M infrastructure work, supported by a £12M grant from the Government's Single Regeneration Budget, includes cycle paths, a bus interchange and a new Central Line station and a 'U-turn' junction to the east that will allow traffic to join the westbound carriageway of the A40.

Travelling north from the A40, the eastbound link road has to bridge two railway cuttings separated by an 'island' of raised ground. One cutting holds a surface section of London Underground's Piccadilly Line, while the other is shared by a surface section of LU's Central Line and a mainline track (see map).

Reinforced soil is being used extensively.The eastbound link road will run on a reinforced soil embankment alongside the A40 before crossing the cuttings on two bridges, supported by reinforced soil abutments at each end and by a reinforced soil embankment in the island between. The road will then drop down to a roundabout on the realigned Coronation Road.This is being raised by up to 4m and is also supported by reinforced soil embankments.

NHC project manager for civils and infrastructure, Tony Hogan, says reinforced soil was chosen, because it offered a 'very competitive' solution to the problem of forming structures next to the railway lines, minimising craneage and piling equipment.

Consultant Mott Macdonald is responsible for outline design of the scheme and detailed design of the foundations. Geosynthetic supplier Tensar International carried out detailed design of all the reinforced soil structures and supplied construction materials for its £300,000 subcontract.

All the reinforced soil structures have been piled to reduce the risk of settlement in the underlying London Clay and most have vertical or near vertical faces.They are built using crushed concrete demolition fill from a site near King's Cross station, reinforced with Tensar geogrid and faced with its TW Idry-laid block wall system. The exception is the 45degrees embankment near the A40 which will have a vegetated face. Some 3,000m 2of walls will be built for the project.

NHSE is carrying out the piling, which began with extensive pile testing on the new office plot. Test results were used for the final design of both the building and the infrastructure works, explains NHSE director David Donovan.

Four CFA test piles were installed.Three were 600mm diameter and 6m, 10m and 14m long, the 10m pile fitted with two arrays of extensometers, used for the reinforced soil structure design.The fourth was 450mm diameter and 22m deep, used to replicate the pile behaviour for the bridge structures. Donovan says more information was obtained when the expendable piles for three tower cranes were installed.

The vast majority of the infrastructure piles are CFA, except near the A40, where bored piling was used - partly because of design and partly because of rig availability, Donovan explains. He adds that CFA was used because NHSE's site investigations found varying ground conditions near the A40.'CFA gives a bit of insurance, 'he says.The piling equipment is also stable, essential when the firm is working close to railway lines.

In all, 500, 600mm diameter piles are being installed for the infrastructure work. These are between 6m and 14m long beneath the embankments, and about 20m long for the bridge abutments. Piles for the roundabout on Coronation Road start at 14m around the edge of the structure and get shorter and more widely spaced towards the centre. Hogan explains that it was important to minimise settlements where the roundabout is close to new buildings - its north west wall will eventually form part of the underground car park for the new Guinness building. This is the first wall to be built and will be up to 8m high.

The walls, being constructed by subcontractor Keller Comtec, are built up in stages. First, a concrete strip is cast along the base of the face and the first row of TW Iblocks fixed on to it. Subsequent courses are dry-laid. Typically, three or four courses of the blocks are laid, before crushed concrete fill is placed and compacted behind. A 300mm thick gravel drainage layer is placed directly behind the blocks and runoff is channelled to a drain at the base of the wall. A layer of geogrid is then put down, fixed to the wall using polymer connectors and pulled tight.

Up to three strengths of Tensar geogrid are being used in the embankments, depending on the loading requirements, explains Tensar International area civil engineer Geoffrey Carter.The strongest, T120RE, is used at the base, with T80RE and T55RE used higher up in the structures - the amount and grid strength varying with loading requirements. Typically, there is a 450mm vertical gap between geogrid layers, although the spacing is tighter where loadings are higher, Carter says. The length of geogrid used depends on wall height, he adds - 'For example, a 6m high wall uses 5m long strips'This does vary to some degree at the top of the walls, because of planting, for instance.

Carter says most of the structures have no load transfer platforms, with the crushed concrete simply tipped on to the piles and compacted. However, beneath the reinforced embankment island between the cuttings, which includes two bridge abutments, a Tensar Basetex load transfer platform will be used.

Piling for the new office building has now been completed. Some 700 bored piles of 400mm diameter have been installed to an average depth of 20m for the building and the adjacent piazza.

Construction of the Central Line station and the hotel should begin in the next 12 months, says Hogan.The first stage of redevelopment is due to be completed by autumn 2002.

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