50 & 65 Harbord Square

Designing sustainable mixed-use buildings using concrete

This development provides much needed affordable housing designed to the Code for Sustainable Homes – level 4 using a traditionally reinforced in-situ concrete frame. Alongside this is a primary school, a leisure centre and an NHS health centre, all of which achieved a rating of BREEAM ‘Excellent’. The key constraints were the Jubilee Line tunnels crossing the site, the associated vent shaft and a historic ‘Graving Dock’ located on the plot boundary, just a few metres from the new buildings.

Walsh and the geotechnical team developed a scheme that ensured ground movements and risk to LUL assets and the boundary were negligible. Due to the poor soil conditions on site, piled foundations were designed to ensure that appropriate exclusion zones were maintained around all LUL assets. This was supported by a construction strategy that ensured the adjacent ‘Graving Dock’ was not adversely impacted by the new 8m-deep basement that was built just 8m away.

A detailed geotechnical analysis was undertaken to verify that potential ground movements stayed within acceptable limits throughout the project. This included both movements in the short term as pressure was relieved on the assets during excavation of the large basement, and also in the long term as the construction of the new buildings increased earth pressure.

Instead of using deep steel beams as had originally been planned, Walsh suggested using post-tensioned concrete techniques. This minimised the depth of the transfer beams which span more than 20m over a new Sports England-compliant Sports Hall in the leisure centre. This also allowed the depth of basement below to be reduced and had the added benefit that using concrete across the site made it easier for the client to procure through a single sub-contractor.

The school and health centre were designed with long clear spans, ‘soft spots’ and minimal columns which provides long-term flexibility for Tower Hamlets and the NHS to fit-out and adapt the buildings to suit their needs as they change.