HS2 in Bucks & Oxfordshire update: HS2 reveals the innovative slurry treatment technology supporting the Colne Valley ‘rewilding’ project
Ambitious plans to create 127 hectares of new grasslands and woodlands around the southern portal of our Chilterns tunnel have been enabled by an innovative solution to reuse the waste chalk slurry generated during the tunnel’s construction.
Two giant tunnel boring machines (TBMs) will spend three years boring out 2.6 million cubic metres of chalk beneath the hills to create the new high speed rail network’s 10-mile long twin bore tunnel. The chalk cut away by the 170-metre long TBMs will be mixed with water before being pumped out as slurry back along the tunnel to its entrance.
Slurry from boring the tunnels will be processed on site at a construction base just inside the M25 motorway – avoiding the need to transport the waste off site for reprocessing elsewhere. Once out of the tunnel, the chalk and water slurry will be separated on site in a giant, purpose-built slurry treatment plant (pictured) where it will be pressed through ever-finer filters until all the water is removed to leave behind a dry chalky “cake”.
One of the key challenges the separation process faces is preventing the thickening slurry from clogging up the filtering machinery. Working with its supplier MS, which has delivered the slurry treatment plant, our civils contractor Align opted to use a polymer specifically developed to be effective with Chilterns chalk, which will enable the entire separation process to happen in around a week.
The chalk cake will be used to deliver the Colne Valley Western Slopes project – part of our Green Corridor programme to re-establish the locally distinctive chalk valley landscape and create the right growing conditions for calcareous grassland across the site.
The initiative will be a major contributor in helping us meet our carbon reduction targets by delivering significant ecological gain in the Colne Valley, reducing road haulage, and enabling habitats to sequester carbon by replacing arable land with natural habitats. Almost 65,000 trees and shrubs comprising 32 species will be planted together with nearly 3.5km of new hedgerows. Around 90 hectares of chalk grasslands will be created and areas of historic woodland reinstated.