The contractor says that its piling methods have saved time on excavation works for the development.
The Portal West development is being built by O’Shea Construction for City & Docklands Property Group. It is a mixed-use development in North Acton, consisting of four blocks rising between nine and 42 storeys. The highest, called One West Point, will be the tallest residential building in west London.
The towers will be set around communal courtyard gardens and sit on top of a six-metre deep communal basement. When complete, the new development will provide 578 new homes as well as new pedestrian routes, public open space, commercial premises and new amenities for the local community.
Central Piling is installing the contiguous piled wall that will facilitate the excavation of the basement, and also the large-diameter bored piles for the deep-piled raft that will support the high-rise buildings.
The company was brought in at an early stage by O’Shea Construction as the piling specialist subcontractor, enabling it to help choose the piling solutions.
Central Piling began work on the £1.25m geotechnical contract in November 2018, with construction of the embedded basement retaining wall, which is formed of 600mm diameter continuous flight auger (CFA) piles. The installation of the rotary-bored bearing piles began soon after, with the entire contract scheduled to be complete by the end of February 2019.
Steve Hadley, managing director of Central Piling, said: “High-rise buildings such as this require large-scale foundation systems capable of transferring the loads to suitable ground. The 1050mm diameter bored piles, with depths of 35 metres, are a first for us and our Soilmec SR-45 and SF-75 rigs are working to their maximum capacity.
“Given the magnitude of the compression loads, we undertook a preliminary pile load test on a 750mm diameter pile loaded to over 10MN which produced satisfactory results. This validated both the design assumptions and the installation technique proposed for the bearing piles.”
Central Piling also dug an additional 44 metre deep borehole to complement the site investigation works and to obtain more information about the ground conditions.
Despite the six-metre deep excavation being surrounded by such buildings as the Algerian consulate, the wall design allowed for a cantilever solution for the construction stages, with a minimum amount of locally-installed temporary props and a significant programme saving on the excavation works.
The optimum solution of a temporary cantilever retaining wall formed of 600mm at 750mm centres and large diameter 1050mm and 750mm rotary-bored piles for the piled rafts was the result of a significant amount of pre-construction and design work.