Since their abandonment in the 1920’s, salt mines beneath Northwich had deteriorated to such an extent that the possibility of their collapse presented a threat to life and property. As a result, no new development was permitted in the town centre and property values and economic activity were depressed. Vale Royal Borough Council applied to English Partnerships, as part of the government’s Land Stabilisation Programme, for grant funding to carry out the work necessary.
The project involved the infilling of four salt mines to ensure the future stability of the town centre. It was the largest project of its kind in the world, with 780,500m3 of void filled at depths of 90m below ground. 32ha of surface land has been released for regeneration.
The grout mix used to fill the mines was made sustainable and cost effective by utilising Pulverised Fuel Ash, a waste product from power stations. To ensure its durability and to avoid solution of the rock surrounding the mine the grout for this scheme was made using brine. This was the first time this has been done and required extensive research and analysis.
In all more than 97% of the material put in the mine was or would have become waste.
Grout was delivered to the heart of the town via a 470m directional drill bore made beneath a navigable river and adjacent to a Site of Biological Interest (SBI). This not only reduced the impact to the town centre and SBI, but also considerably reduced cost, time and health and safety risk.
The work broke new ground and overcame many technical challenges while being completed on time and within the budget. The project was fundamentally sustainable from objective to implementation, allowing the long standing planning moratorium to be lifted from the centre of the town. Vale Royal Borough Council and their partners are now free to implement their vision for the sustainable development of a new town centre that will bring jobs, housing and refreshed activity to the area.
Since completion, the Northwich Salt Mines Stabilisation project has won the following awards:
Ground Engineering Sustainability 2008
ICE North West Merit 2008
Regional Monitor Excellence 2007
Most Innovative Remediation Method, Innovation in Remediation 2006