The mixed-use scheme near Liverpool Street Station in the capital is being developed by a joint venture between Brookfield Property Partners, Concord Pacific and W1 Developments.
Bauer got the main piling works contract after completing an early works package, where it installed 25 piles, 1200mm and 1500mm diameter and more than 50 metres deep, in secant pile walls. These piles have a combined structural function as bearing piles for a 50-storey residential tower and as retaining walls for a new Network Rail ‘eight-track’ corridor.
The installation of the early works required working next to live Network Rail assets on a designed steel gantry structure, constructing piles under bentonite. Working on a steel gantry required bespoke piling rig configurations and rigorous adherence to agreed method statements. The early works scope also included coring of sub surface obstructions, forming guidewalls and the installation of 1800mm diameter bitumen coated, permanent steel liners.
With an overall contract value of £5m, including the early works, the main works scope requires Bauer’s BG40 and BG30 piling rigs to construct 27 bearing piles under bentonite for the main 50-storey residential tower. These piles are 1350mm and 2000mm diameter and 14 of them are large section ‘plunge’ columns. For the smaller structures Bauer will install 880mm rotary piles – 26 of them – while the adjacent 15-storey residential building will be founded on 36 x 900mm diameter, 27-metre deep continuous flight auger (CFA) bearing piles. As the project will be constructed using a ‘top down’ method to form three levels of basement, the 150 linear metre site boundary is supported by a load bearing 880mm diameter secant bored pile wall.
The installation of ’plunge’ columns under bentonite in bored piles demands the use of a temporary guideframe and, says Bauer, “careful execution of robust work plans at all stages of construction to achieve extremely tight tolerances”. As part of the deployment, Bauer will use an ‘on-top reaming’ tool. This is a new drilling tool developed on a previous Bauer project overseas that is designed to maximise pile diameter where temporary casings are used.
The Principal Place Residential project, which started with early works in July 2015, is expected to be substantially complete by 2019.
Bauer Technologies managing director Martin Blower said: “This is an exciting and prestigious project for Bauer in the London Private Residential market. It requires us to construct piles to extremely tight tolerances in difficult ground conditions. The many challenges that the project presents also give us an ideal opportunity to demonstrate the capabilities of Bauer and our newly developed ‘on top’ reaming tool.”
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