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 | | STENT SUPPORTS THE REVIVAL OF ELEPHANT & CASTLE | | | Balfour Beatty Ground Engineering (BBGE) | | 15/07/2008 | | | Construction of 43m deep bearing piles under polymer support fluid.
Stent, part of Balfour Beatty Ground Engineering (BBGE) has just completed the piling work for Brookfield Construction Ltd’s latest contract, the Castle House Development. This is a prestigious redevelopment in London’s Elephant & Castle, involving the construction of two buildings on the former site of Castle House, a six-storey structure belonging to the South Bank University. The project, due for completion in December 2009, is set to be the catalyst for the regeneration of Elephant & Castle.
The development consists of a massive 42-storey tower some 147 metres high, with a smaller 5-storey pavilion alongside it, which together will feature retail units and residential units including affordable housing. On top of the main tower will be three 9-metre turbines supplying enough electricity to light the entire building.
Stent was subcontracted by Brookfield to provide bearing piles and sheet piling for the entire project, which was a particularly challenging job due to the location of the site. To the north is a major road, a railway viaduct is on the eastern side of the site, a day-care centre to the south and a large office block to the west, all of which posed problems relating to accessibility, noise, vibration and health and safety.
Stent first had to construct the 37 large bearing piles, the primary support for the tower. The piles were constructed to depths up to 43 metres in unstable Thanet Sand, typical of this area. This unstable substrate meant that a pile bore support fluid was needed when boring the piles and on this project Stent opted for a vinyl polymer support fluid. Stent has been using vinyl polymers increasingly since 1999 and finds them particularly useful on smaller projects, as they require less plant and storage areas than traditional bentonite. The polymer support fluid is also more environmentally friendly; a cleaning agent can be added after use to turn the fluid pH neutral, which allows it to be disposed of in the municipal sewer system.
Stent was also commissioned to install sheet piling to create a retaining wall and enable the construction of a cruciform-shaped slab under the tower core. Stent used a Kowan ZU-100 Still Worker from Watson & Hillhouse to install a total of 142 AZ18 section sheet piles. This is the first time the machine has been used in the UK and it was the perfect tool for the job. The ZU-100 produces very little noise and vibration, key when installing piles in such close proximity to an existing railway viaduct. Reduced noise was also important considering the offices and day-care centre nearby.
Adding to the challenge a section 61 order was in place for this project, meaning contractors and the Local Authority had agreed on working hours before construction in an effort to reduce local noise and disturbance. The restriction on daily working hours meant that Stent couldn’t start and finish the deep bearing piles in one day, instead the boring and concreting had to be spread over two days. The time pressures for this project were compounded by the fact that a limestone band at 19 metres proved extremely difficult to bore through. Stent had reduced the time it took to break through this band from over five hours to just one through refining technique.
Thanks to Stent’s expertise, multi-technique capability and state of the art equipment they were able to finish the project on time and on budget. | |
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