A time capsule containing a Covid-19 mask, a smart phone, maps and a sample of water from the Thames has been buried 60 metres underground as part of the super sewer project.

The Tideway team at Blackfriars in the heart of London recently completed excavation of a giant 65m-deep cylindrical pit that will link to London’s new sewer.

One of the final pieces of work needed to build the shaft is to pour the concrete base – a thick slab that will strengthen the bottom.

But before the concrete is poured, the team excavated a small 65cm hole in the bottom for the time capsule.

Burying a time capsule is an old tradition on construction projects, with Wembley Stadium, the O2, the Design Museum – and even Cleopatra’s Needle, erected on the banks of the Thames in 1878 – all standing over a sealed container full of relics.

The contents of Tideway’s capsule sought to reflect the unique events of 2020 with a facemask to reference the pandemic, but also a sample of today’s Thames water, so future generations will be able to test how much cleaner their river is thanks to the super sewer – due to open in 2025.

Viv Jones, Project Director of Tideway Central, said: “It’s been a turbulent and uncertain year for everybody, but our teams have made fantastic progress despite this.

“It’s pertinent that we’re commemorating the bottoming out of Tideway Central’s ninth and final shaft with this time capsule given the historical significance of the time we’re living in.

“We’re building this infrastructure to last well into the next century and hope future generations appreciate our engineering in the same way we appreciate Bazalgette’s 150 years on.”

Photos of Tideway’s central-London sites, a Tideway-branded hardhat, a selection of hand tools and a cube of concrete from the project were also buried in the capsule.

The completion of the excavation of the shaft itself represents a significant milestone on the Tideway project, allowing the central teams to begin secondary lining more of the main tunnel in the coming months.

Four of Tideway’s six tunnel boring machine have now finished, leaving the 5km eastern stretch to be bored, as well as a connection tunnel between Greenwich and Bermondsey, which is also underway.