Project London, United Kingdom

1 Broadgate

Sector: Buildings

Technical specifications

Secant pile wall

made of 558 piles

Secant Wall Retained Height: 10.5m to 16.0m multi-level propped

Challenge & Solution

In order for the Client Sir Robert McAlpine to realise maximum saving on programme, it was established during the planning stages that if piling works could commence during the demolition stages, then two thirds of secant piled wall box could be formed within the existing extents of the basement.

Available headroom within the basement in the first visit to site was generally between 3.9m and 5.5m meaning Martello MP4000 series rigs were perfectly suited for this working environment to install 600mm, 750mm and 900mm dia. piles forming the first part of the Secant Piled Wall.

London Clay Formation was encountered at approximately 3.5 - 4.5m below Piling Platform Level within the existing basement, meaning temporary casing was required to support the pile bore during construction. Martello MP4000 rigs were able to install temporary casings to seal in to the clay layer to form large diameter bored piles.

Restricted Headroom Martello Rigs used were MP4002, MP4003, MP4004 and MP5003 which were able to work within the limited headroom with the use of spliced full length cages across the secant piled wall extents.

Engagement with Sir Robert McAlpine’s sustainability team meant we were able to include for high GGBS content within the concrete mixes (and up to 95% within the female unreinforced piles) which was beneficial towards SRM’s sustainability targets on the project.

The combined approach of Martello Piling and return visit for Bluesky (unrestricted) piles meant that the overall project duration was reduced by 16 weeks, with piling being complete by June ’22 as opposed to initial antipated finish date of September ’22.

Project details

Project name

1 Broadgate

Area(s) of expertise

Commercial

Techniques

Restricted access bored piling, Continuous flight auger pile (CFA)

Contract type

Build

Location

London, United Kingdom

Client

Sir Robert McAlpine

Building Period

2022 - 2022

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