Barhale to protect sewer from HS2 tunnelling

Barhale will install a 75m length of non-structural liner to north London’s Middle Level Two (ML2) sewer to protect it while HS2’s TBMs pass underneath.

The relining will comprise 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 HS2 route will be in closest proximity to the sewer to optimise monitoring. The shaft will be built as a caisson but, to avoid pressure on the Victorian brick sewer, it will be installed using underpinning from the collar rather than by jacking.

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

Barhale contracts manager Steve Hills said the work was an important measure.

“The ML2 has been an important part of the capital’s infrastructure for more than 100 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 there is the least impact on the sewer through construction and the maximum protection afforded for the future.”

He added that the objective of minimising impact had also been applied above ground where there will be minimal disruption as Barhale negotiates area around Regents Park.