School of Public Health, Imperial College London

DAWSON-WAM (DW) was contracted by Graham Construction in 2021 to construct a new basement for the new School of Public Health at the White City Campus of Imperial College London.
The project involved the installation of 600mm diameter CFA piles to depths of up to 30 metres. A secant pile wall was constructed to provide effective earth retention and groundwater control, ensuring stability for the excavation and surrounding structures.

The basement construction was delivered using a carefully considered mixed cantilever and propped secant pile wall. The southern section of the excavation was designed as a cantilever wall in the temporary condition, allowing for congestion-free construction of the core and improving overall buildability and programme efficiency.

The basement excavation extended generally to a depth of 4.7m, with localised deepening around 7.9m for a tank base.
Retention was achieved using a hard-hard secant pile wall formed using 630mm diameter piles, designed not only to retain the ground but also to support vertical and column loads from the superstructure.

A key challenge on the project was the presence of an underground sewer and a gas main running along two sides of the basement footprint. To mitigate risk and comply with asset protection requirements, the construction of the secant pile wall was undertaken using our Cased CFA system, which enabled us to meet Thames Water guidelines while eliminating vibration risks typically associated with conventional piling methods, thereby safeguarding the adjacent utilities and ensuring a safe and controlled installation.