Homeowner Business Infrastructure Company 0800 084 3503

Rail

Void Filling at Shugborough Tunnel on the WCML

Challenge

Hidden construction shafts and deteriorated voids behind the Victorian lining at Shugborough Tunnel posed collapse risks to the West Coast Main Line and the National Trust estate above.

Solution

Geobear designed a solution to fill the shafts and lining voids — stabilising the tunnel safely in short night possessions without grout pressure or disruption.

Background

Shugborough Tunnel, built in 1846–47 beneath the National Trust estate, carries the West Coast Main Line (WCML) — one of the busiest mixed-traffic corridors in the UK, linking London to the North West.

During construction, temporary shafts were excavated to speed tunnelling. These were capped and backfilled, but many had deteriorated or were never properly infilled, leaving voids above the tunnel lining. Inspections by Network Rail and consultants COWI confirmed the presence of hidden shafts and lining voids, creating a risk of collapse that could damage the railway below or the historic estate above.

Challenge

Several core issues presented this project with a number of challenges to overcome:

• Fragile brick lining could not tolerate the hydrostatic load of cementitious grout.
  
  
• Wet grouts risked contamination of ballast and track drainage.
  
  
• Access through National Trust estate required sensitive methods with ecological safeguards.
  
  
• All works needed to be carried out in short, planned possessions to avoid disruption to WCML services.

Client insight

Within the tunnel, there’s a number of shafts used during construction. Over time, these weren’t properly filled, leaving voids inside. If they were to settle, it could damage the railway or the estate above. On such a critical, busy route, that wasn’t a risk anyone could accept.

Joe Ward, Project Manager

Solutions

Geobear designed a bespoke geopolymer solution with two formulations: a lightweight resin to stabilise the tunnel lining, and a closed-cell resin to fill shafts.

Works were delivered in three stages:

Tunnel lining stabilisation — voids behind brickwork filled 1 m either side of each shaft. This will involve injecting a low expense geopolymer with high compressive strength behind the tunnel lining to fill the voids.

Shaft base sealing — injection through the lining into shafts, binding debris and sealing the lower 4 m.

Shaft top infill — angled drilling from surface to inject geopolymer and fill shafts completely from top-down.

Results

The project was completed successfully in 40 Saturday night possessions, maintaining full availability of the WCML. The shafts and lining voids were permanently stabilised, eliminating collapse risks and extending the tunnel’s life with a 120-year design life.

Compared with cementitious grout, the geopolymer solution delivered ~45% lower embodied carbon, reduced programme duration, and avoided the need for disruptive temporary works.

Collaboration between Network Rail, COWI, Story, and Geobear was critical to success. The project demonstrated the suitability of closed-cell geopolymers for complex tunnel stabilisation in heritage and high-demand contexts.

Ready to discuss your project?

Get in touch with our expert team today and discover how Geobear can extend the life of your critical infrastructure assets.

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