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Three into one

Spotlight - Piling and foundation work along the Thames Embankment meant Westpile was presented with a unique set of challenges.

Westpile recently carried out basement piling and foundations on a £1.3M development in Battersea, south west London.

Running along the Thames Embankment and flanked by Battersea Heliport, the development of three mixed-use buildings includes 252 residential apartments, a 100-bedroom hotel and 2800m 2 of commercial space.

The scheme is unusual in that the whole basement area is common to all three buildings.

The main secant retaining wall for basement levels one and two runs parallel to the Embankment, while rectangular basement level three is set on at 20infinity to the upper levels.

For a two-basement excavation, the design would have been fairly straightforward.

However, due to the rotation of the third basement, the berm thickness to the secant wall varies at different points. At the narrowest points on opposite corners of this lowest level, the pile design would theoretically require increased diameter to accommodate the increases in lateral load caused by the deeper excavation.

But larger diameter piles were not a design option due to other site factors. To arrive at an engineered solution, Westpile worked with the client to design an innovative use of bearing piles within the construction to assist the external retaining wall at these points.

Additional problems originate from the site's proximity to the river. Groundwater levels naturally fluctuate with tidal flow. There are many old river channels coming into the River Thames. Piles must toe into the London clay, but unmapped local depressions in its horizon make it necessary to adjust pile lengths to suit the river channels.

This avoids a water path flowing beneath the piles.

The rst phase of installation at Bridges Wharf commenced in October 2006 with the installation of 290m of bored secant retaining wall, constructed using two heavy duty controlled flight auger rigs.

The wall utilises soft primary piles formed at 750mm diameter and firm piles at 900mm diameter. Pile depths are from 10m-16m below ground level.

In the second phase, due to commence next month following excavation, bearing pile installation will be from the level of the second basement. Five hundred piles will be constructed by cased rotary methods and will extend to approximately 30m depth.

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