In recent months we have covered Crossrail Tunneling and Tunnel Boring Machines (TBMs) quite extensively. One part of the process we haven’t really looked at in depth, however, is where the excavated material ultimately ends up.
This may seem a rather strange topic to cover, but like all mega-projects Crossrail’s impact extends well beyond the range of the area it’ll ultimately serve. Tunneling and construction will see Crossrail generate approximately 6.5m tonnes of spoil which, as anyone who has ever watched the Great Escape knows, needs to go somewhere.
In Crossrail’s case, the bulk of this spoil is clean and can be reused. On most projects, it would thus be dispersed over a number of sites, but interestingly in Crossrail’s case much of this excavated material (4.5m tonnes of it) is actually destined for one single place – Wallasea Island on the Essex coast.
Bounded to the north by the River Crouch and to the south by the River Roach and Paglesham Pool, Wallasea was mostly wetland mud flats until the arrival of Dutch settlers in the area. Flat and low lying, the construction of sea walls allowed it to be turned into farmland and it saw cultivation until the 19th Century, when periodic flooding and crashing wheat prices saw the island’s population decline. Brief agricultural resurgences during both World Wars followed, but the floods of 1953 marked something of a point of no return.
Since 1953 Wallasea has led a rather unremarkable existence. In 2006, however, the RSPB decided to embark on an ambitious scheme -the Wallasea Wetlands project. This involved taking over 115 hectares of Wallasea farmland and demolishing the surrounding sea wall. With their section of the island now flooding again at high tide, the original salt marsh and mud flats began to return, and with them the birds and other wildlife that had once been a regular feature of the Essex coast.
The RSPB’s project was a success, and with the need for mudflats and marshes growing (it is now often an EU requirement that endangered environments removed through the construction of ports and other coastal sites be replaced elsewhere), the decision was taken to embark on one of the largest and most ambitious Conservation projects yet seen in the UK – the whole of Wallesea would be taken over and turned into the largest wetlands conservation site in Europe.
Recreating 1,500 acres of ancient mudflats and saltmarsh, lagoons and pasture on Wallasea requires significant landscaping. The extensive walkways and new sea walls required to make the site accessible to visitors (and to keep differing environments separated) will require approximately 10 million tonnes of earth.
With Crossrail thus looking to dispose of 4.5m tonnes of clean spoil, and the RSPB looking to find 10m tonnes of it, a partnership seemed like a very good idea indeed.
Moving the Earth
As anyone involved in the process of spoil disposal and management will tell you, finding somewhere to put your excavated material is only half the battle. The other half is working out how the hell you get it there.
As we’ve highlighted before, in Crossrail’s case, this largely means moving spoil by rail (although early on there were some rather creative ideas about reusing the old Post Office Railway and the Kingsway Tunnel to do some of the job). All spoil from the Western Portal is taken via the Great Western Main Line, the Greenford Loop, West London Line, Clapham and Lewisham down to Northfleet, where the reinstatement of the freight rail link from the North Kent Line means access can be gained to Lafarge’s new railfreight depot at Northfleet, on the site of the old Concrete Works.
Spoil from the eastern portal has a slightly easier journey to the river – once tunneling begins it will be transported via conveyor belts to Instone Wharf.
In both cases, the spoil is then transferred to barges and taken to Wallasea.
The End of the Line
Due to the already protected nature of Wallasea’s environment, Crossrail’s actual presence on the island itself can be described minimalist at best, which presents a rather interesting contrast with the amount of material being brought in. A large jetty has been constructed by BAM Nuttall just offshore, to which the spoil can be delivered and conveyed inland.
Standing alone and kept to the absolute minimum amount of ground occupation necessary, the jetty is a surprisingly striking structure – and one that’s deceptively large.
The huge machinery onboard hints at the sheer amount of material that will pass through the jetty, as do the conveyors, which run up from both sides (to allow two ships to dock at once) and over the top onto the island itself.
Like much of the Crossrail project, the jetty feels like an impressive piece of engineering with a large task ahead. The view inland, however, manages somehow to eclipse it – and it is this image that we have saved until last. For while the engineering needed to turn this London spoil instead into a little bit of Essex is huge, nature is bigger…
…And the sight of the vast conveyor stretching off into the flatlands of Wallasea makes this large jetty actually feel like a very small and lonely outpost of technology indeed.