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Piling is nearing completion for a high profile Bristol expansion, a project due to transform a large part of the city centre.

Bristol city centre is undergoing its biggest transformation since post WW2 reconstruction work, in a £500M regeneration project that will see the addition of a new city quarter.

The expansion will create 140,000m 2 of mixeduse development, which includes 93,000m 2 of retail and leisure space,15,000m 2 of offi ces and 250 new homes.

The magnitude of the city centre regeneration is already apparent when driving into Bristol on the M32, with drivers surrounded on both flanks by the ongoing works as they head towards the city's Broadmead shopping centre. Although the overall project is still in its early stages, the site is a hive of activity; at the centre of which are the red piling rigs of Bachy Soletanche.

Bachy won the job from main contractor Sir Robert McAlpine for the impressive new buildings due for completion in 2008.

The rigs were first mobilised late in 2005 to complete the enabling works and since then, work has gathered momentum. 'The scale of the Bristol city centre expansion is very impressive and we currently have six rigs working simultaneously on site, providing both CFA and large diameter auger piling, ' says Bachy Soletanche engineer, Drew Fraser. 'The site itself is divided into two key areas, Broadmead and Quaker's Friars, and as we have progressed with piling work we have been quickly followed by other contractors - meaning that both areas have been very busy from the start. The sheer volume of work going on has meant there is very little room for manoeuvre.'

However, amongst the forest of cranes and rigs are clearly marked areas that bustle with a different kind of activity, as the development work makes way for a range of sites of archaeological interest. The long history of the city has meant the project unearthed some intriguing artefacts; all of which are being excavated and dealt with by archaeological teams. Situated at the heart of the site, care has been taken during piling and other construction work to ensure no impact on these sites.

In addition to the archaeological interest, a Grade 1 listed building also sits in very close proximity to the foundation work on Quaker's Friars. Engineers have needed to preserve the building - a registry office that closed its doors in June.

When piling completes, Bachy will have built 1401 piles for the Bristol regeneration project, with the majority of those being CFA. In the smaller Quaker's Friars area of the development, 229 CFA bearing piles with varying diameters up to 900mm are accompanied by 136 LDA bearing piles with diameters ranging up to 1500mm.

In the Broadmead area, 102 CFA and 236 LDA bearing piles will be installed with maximum diameters of 900mm and 1800mm respectively.

In addition to the bearing piles in the Broadmead area, a contiguous wall will be formed using 20 CFA piles with a 900mm diameter, and adjacent to the Castlemead Tower the subcontractor has built a huge secant wall. This will be used as an entrance for a new car park structure, and here, 20 LDA piles with diameters of 1500mm have been completed.

Fraser says: 'The sheer scale and depth of the LDA piles in the secant wall makes for a precise and time consuming process when compared with a standard piling project. Although the remainder of the wall will be constructed using CFA, the car park entrance area of the wall requires piles of a size and strength that can only be constructed using LDA.'

The development has called for a versatile piling solution, and with foundations now reaching completion, the positive transformation of Bristol city centre looks set to continue apace.

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