We are working on a challenging constrained site at Tower Hill, part of the Royal Mint Gardens development in London — a masterplan of four blocks. This is the final stage of the wider development, comprising 450 aparthotel units and 79 residential units in a 12 storey concrete frame building over multiple rail assets. Constraints affect the majority of the building’s footprint.

The site is intersected by an above-ground Victorian-era heritage-listed viaduct supporting Network Rail and Docklands Light Rail (DLR) railways and shallow DLR tunnels that run directly underneath in a sweeping curve. The presence of a DLR plant room is a further challenge. The building is consequently designed for potential train impact loads. A new vent shaft, entrance for Tower Gateway Station and lift installation to platform level are included in the project.

The optimised superstructure incorporates huge steel transfer trusses for the long spans needed. To support the building over the above-ground tracks along the northern boundary, four 12m steel columns, weighing up to 13t each, are threaded through holes in the masonry viaduct (placing no weight on it) onto piled foundations formed using low-headroom piling rigs. Other piled foundations are placed where possible, with multi-storey transfer structures spanning the encapsulation of the below-ground DLR tracks. The building is isolated from ground-borne vibration using steel isolation springs at ground level, designed as an integral part of the structure.

The northern boundary transfer structures were all installed during a series of rail possesions, obtained from Network Rail and Transport for London. The trusses are up to 13m long and 3.5m high. Overall, some 1,200t of steel has been used.

A ground movement assessment using 3D finite element modelling was carried out to evaluate potential impacts on nearby third-party assets. Temporary and permanent works were considered, including piling and superstructure loading. Results showed that predicted movements remain within acceptable thresholds, indicating minimal impact on the safe operation and integrity of surrounding assets.

Our geotechnical and structures teams collaborated to ensure accurate modelling of the geometry for existing and proposed structures based on real data from 3D surveys. To enable accuracy and precision, a digital workflow was developed by both teams, reducing the time for geotechnical post-processing modelling by 50%.

Part of the design brief was to provide an additional storey within the overall height of the building. To achieve this, we designed a super-thin structure, and maximising floor heights using strategies such as sprayed ceiling finishes.

main contractor : Midgard
steel fabrication and installation : Caunton Engineering