Victorian giant – modern tunnel: protecting Bazalgette’s mid level 2 sewer for HS2

Imagine working on a Victorian engineering masterpiece just metres away from the route of a modern megaproject that will race beneath London. As HS2 advances its twin tunnels under the capital, the route threads perilously close to the historic Thames Water mid level 2 (ML2) sewer – part of Sir Joseph Bazalgette’s 160-year-old legacy. Diverting a live, critical interceptor in a dense urban setting is costly, risky and slow. Protecting it – reliably, quickly and with minimal interruption to London’s daily life – demands a different mindset. On behalf of Thames Water, Barhale designed and delivered an innovative, rapidly deployable internal rib solution that preserved hydraulic capacity and structural integrity, allowing the HS2 tunnel boring machines to pass just 3.46 m from the sewer (downline) and 5.46 m (upline). The ML2 reinforcement project was a success on three levels: it met the immediate engineering needs of HS2 and Thames Water; it maintained use of the existing sewer structure, saving new build costs and building resilience; and it has been delivered through a sustainable build programme that demonstrated consideration for the environment and community, yielding value for the client.