Bridges, wildlife corridors, and a mega ditch: Taking a look at HS2 at Calvert

Not far outside London is a part of the HS2 railway that will also see the first passengers to pass over a newly built railway that’s not part of HS2

This is Calvert, where the HS2 railway passes along a section of the former Great Central Main Line and crosses the soon-to-open East-West Railway, which will eventually link Oxford with Cambridge via Bedford.

It’s also a location where it seems as much effort is going into building a railway as it is building roads. That’s because while there was an existing railway along the route, it was built to Victorian standards and was far too small for modern railways. That means pretty much everything that was there had to be demolished and rebuilt, including all the roads that crossed the railway.

Away with small brick arched road bridges over small railways and in with wide concrete and steel bridges built not just for HS2 but also for potential future upgrades of other rail lines in the area.

They also have to deal with a water-logged landscape, which requires a lot of new drains to be built today to reduce the cost of water damage maintenance in the future — including the aptly named “mega ditch” that will run alongside part of the railway to act as a temporary flood storage area after heavy rainfall.

They are replacing old bridges with new ones that are built for both road traffic and wildlife. At the moment, the old railway was a physical barrier between fields, but the new railway will have several green bridges that are much wider than needed to include a corridor for wildlife. These new wildlife corridors are about twice the width of the roads they will sit next to and will be planted with ground cover shrubs so that animals can safely move across this part of the landscape for the first time since the Great Central main line cut a line through the countryside.

One of the other interesting features along the railway will be next to a future public footpath, where a decorative wall has been built in the style of a giant crinkle crankle wall.

That will sit next to a new porous tunnel, through which the railway will eventually run between two woodlands. One woodland already exists, but the other is actually a large baren mound created in the past few years, as it’s a giant waste landfill site. Over time, the mound will sink down as the landfill inside decays (the methane is captured for a power plant) and will be transformed into a new woodland.

Because bats and birds are expected to fly between the two, a porous roof over the railway is being added to prevent them from flying into the tracks. It’s a very large and long wildlife protector that is almost unique in design.

In addition to the tunnel, in order to stabilise the railway as it passes through the landfill site, deep foundations and piling along its length have been needed so that future local ground movements will not affect it.

Although most of the focus has been on building the north-south HS2 railway, Calvert is also where the new East-West Railway passes over HS2, so the same contractors were also responsible for building that section as well. It would have added considerably to the complexity to have two different construction teams building two separate railways in the same location.

The East West Railway was completed a few months ago, and the new embankments are already grassing over and transforming from brown mud to green landscapes. This will eventually happen with the rest of the building site as well.

Calvert is also where HS2’s Infrastructure Maintenance Depot will be located, as it’s about halfway between London and Birmingham. It will become the primary maintenance depot for the HS2 railway.

The depot is also why the road bridges over the railway need to be much wider than expected, as they will have the two HS2 railway lines, as well as the connecting railway lines for the depot. That’s in addition to the provision of space for Network Rail tracks which may — if approved — include a spur from the East West Railway to nearby Aylesbury for services into London.

For all the fuss about the railway’s impact on the landscape, as most of it is in cuttings or porous tunnels, the biggest visual impact along this part of the line will be the road bridges.

Fortunately, a lot of thinking has gone into their design, including a very bold corten steel section with some exceptionally impressive bolts and riveting going on that, sadly, no one will ever see again when the railway opens.

It is very Victorian in appearance.

Sometimes (ok, often), armchair commentators say that HS2 would have been easier to build if it just reused the old Great Central mainline alignment. Mostly that’s not possible for reasons that have long been explained, but here at Calvert where they can reuse a small bit of it — the amount of work needed to convert the old railway to a modern one has been considerable.

While it will be some years before HS2 trains rush through the area, next year, you can catch a passenger train over an HS2-built railway — when the East-West Railway opens and passes along this part of the railway line — built by HS2.