Barhale has been awarded a £4.5M contract by Thames Water to install a protective liner to minimise the impact of a third party tunnel boring machine on north London’s important Middle Level Two (ML2) Sewer.

The protection liner to the ML2, part of Joseph Bazalgette’s transformative Victorian sewer system, will see civil engineering and infrastructure specialist Barhale install a 75 metre length of non-structural liner. It will protect the 2 metre sewer while the Tunnel Boring Machines (TBMs) for HS2 pass beneath.

The relining will take the form of a series of steel hoops installed at 600mm intervals internally to the existing sewer with additional supports and bracing added between.

Access to install the liner will be provided by two shafts - one existing and one new. The latter will be constructed at a point where the route of HS2 will be in closest proximity to the sewer to optimise monitoring. The shaft will be constructed as a caisson but installed using underpinning from the collar rather than by jacking so avoiding pressure on the 19th Century, brick-constructed sewer.

ML2 carries third party cables and additional measures have been put in place to ensure they are not disturbed.

Steve Hills, Contracts Manager at Barhale, said that the work was an important measure.

“The ML2 has been an important part of the capital’s infrastructure for more than one hundred years,” he said. “While it has more than stood the test of time, it is prudent to make sure that it is fully protected as HS2’s TBMs pass below.

“Every element of these works has been carefully planned and designed so that there is the least impact on the sewer through construction and the maximum protection afforded for the future.

“That design philosophy of minimising impact has also extended above ground where we have planned to minimise disruption as we negotiate an historic part of London around Regents Park.”