Summary
Geobear was approached by Story Contracting to design a solution to fill the voids in and around the shafts and behind the tunnel lining of the West Coast Mainline Shugborough Tunnel in Stafford. The 1847 tunnel had deteriorated over time and there was a significant risk of collapse.
Introduction
Indicative section of the hidden shaft
Shugborough Tunnel, a 710m tunnel carrying the West Coast Mainline, was built in 1846-47 and is located beneath the National Trust’s Shugborough Estate in Colwich, Staffordshire.
During the construction of the tunnel, its temporary works included a number of unlined construction shafts along its length to create multiple excavation fronts. On completion of the works these were capped with timber baulks and decking and backfilled to re-establish the pristine appearance of the Shugborough Estate. The shafts had deteriorated over a number of years since they were constructed so Network Rail made this one of their priority schemes by investing heavily so that the risks from any possible collapse of debris onto the tunnel lining puncturing the lining and falling into the tunnel itself were removed.
Network Rail engaged experienced engineering consultants COWI to locate and investigate the shafts. During tunnel lining test drilling, a void was identified between brickwork and rock caused by the original timber temporary lining rotting away over the life of the tunnel, leaving the tunnel’s lining at risk from rock fall from the conglomerate sandstone through which the tunnel had been constructed. COWI’s solution was to drill and grout each shaft infilling the void between the rock and the masonry lining. Story Contracting was awarded the contract.
An initial proposal used a water-based foam grout for the shaft infill. However, the loading of dense wet grout on the tunnel lining could have caused catastrophic damage. The tunnel lining void solution of cementitious grouting also used dense slow curing materials that continue to flow following injection, this could have resulted in grout entering trackside drainage and ballast causing permanent damage to the trackbed.
Identifying an alternative solution was vital.
Geobear’s Solution
Drilling into tunnel annulus
Geobear designed a lightweight geopolymer solution to fill the void around the lining beneath each shaft and the first metre of the shafts themselves, with a different geopolymer used to fill the rest of the shafts. The controllability of geopolymer injection and its rapid curing – 5 minutes, made it ideal for short possession railway works.
Work began in May 2020 and was delivered in standard ‘rules of the route’ Saturday night possessions. Access to the shaft-tops across National Trust land was established using aluminium trackway and work platforms to avoid damage to the National Trust’s land.
The works were delivered in three stages. Firstly, the void behind the brick lining was filled 5m on either side of the shaft to stabilise the rock face around the tunnel lining and prevent any rock from being displaced by later activities. Secondly, holes were drilled through the lining into the shaft and further geopolymer was injected to seal the bottom 4m of the shaft and bind any debris sitting on the lining. Finally, from the surface level, a machine standing well back from the shaft, to prevent the risk of loading the shaft walls, drilled at 45o into the shaft top to inject further geopolymer in a single pour, filling the shafts to the finished level.
Benefits of the Geobear System
Geobear’s geopolymer was used as a game-changing alternative to traditional grouts due to the lightweight, rapid curing and lower carbon footprint. The fragile tunnel lining was at risk of collapse and traditional cementitious grouts or water-based foams would have created significant loading on the tunnel linings risking a full collapse or requiring significant temporary works and major possession windows to install the solution and allow it to cure.
Optimising the efficiency of maintenance regimes and minimise the impact of maintenance on the operational railway
Injection of geopolymer material
Our Geopolymer’s curing speed and absence of cementitious material eliminated the risk of contamination of track drainage and ballast and allowed the work to be carried out in “rules of route” possessions on Saturday nights without the need for extended possessions. This maximised asset availability preventing disruption to rail services. The lightweight equipment and rapid installation also minimised disruption to the National Trust during the injection of the geopolymer into the shafts from ground level.
Deployment of smart asset management systems such as remote condition monitoring and/or predictive maintenance models
Geobear’s engineering team modelled the solution for the tunnel injection ahead of undertaking the works to ensure that the loadings to the lining were minimised and the risk of collapse was eliminated. Modelling our solutions enables us to ensure the most efficient design and the selection of the correct geopolymers from our range. Each geopolymer has specific engineering properties and this enabled us to use different materials for the void between the lining and the rock and a lighter weight material for the shafts further reducing the mass of the repair materials loading the fragile masonry lining.
The tunnel lining was monitored with lasers throughout the work to ensure there was no movement.
The Geobear process focuses on the use of technology to ensure that our design and installation are optimised to meet our client’s exact requirements. Technology also ensures that our product is mixed to the precise specification requirements to meet the specific structural requirements of the project. All work is then recorded through our I-Auditor system and the locations logged using the What-3-words app to ensure that each injection hole can be precisely located and that the volume of material and void size at that location is recorded for as-built pu
rposes.
Value engineering and innovative thinking
Geobear’s involvement in this critical infrastructure project enabled all members of the project Network Rail, COWI and Story to collaborate on a design solution that had never been used for this application before, working from first principles to identify all the issues which required addressing we were able to create a bespoke solution which created benefits for the client and key stakeholders. The rapid implementation process meant that rail traffic was not disrupted, the small plant and minimal impact of the works meant that we were able to work unobtrusively on the National Trust estate without disturbing the wildlife or creating visual intrusion. The lightweight materials we utilised created a solution which not only filled the voids in the shafts and around the critical tunnel lining but with a 120-year design life have created a permanent solution, minimising future disruption.
The lightweight materials and rapid curing times also removed the need for extensive temporary works within the tunnel further improving the overall cost-benefit of the solution.
Geobear’s design solutions are founded on the principles of reduced operational and environmental impact for stabilisation works. Our determination to create more sustainable solutions has led to a grouting efficiency of between 500 and 700% for our geopolymer products with no risk of unplanned flows due to the rapid curing and easy control of material spread. This efficiency when compared to the traditional grouting efficiency of 25% clearly shows the reduction in material required. When we look at the carbon footprint of the geopolymer and the cementitious grouts the picture is equally compelling. With 1 tonne of Geopolymer the equivalent to 65 tonnes of grout the Carbon footprint of the two products is clear, the Geopolymer creates just 1.18T CO2e whilst the equivalent cementitious solution would generate 12.35 Tonnes of CO2e (DoT Analysis of Carbon footprint of construction materials No 2013)
Attention to the trade-offs between maintenance and renewals and the opportunities to deliver minor enhancements;
Shortlisted for BCI Award
Geobear is committed to providing the best solutions for every one of our clients. Our work on critical infrastructure across the UK has given us a unique insight into the benefits of holistic design and installation, avoiding trade-offs by identifying the optimum solution for the assets future performance. Geobear’s geopolymer solutions have a design life of 120 years meaning that having stabilised the shafts and voids no further work will be required on these areas. Collaboration was at the heart of our project solution, by collaborating with Story Contracting, COWI and Network Rail and carefully considering primary stakeholders National Trust, train operating companies and the travelling public we were able to minimise the project cost and duration whilst creating a high-quality solution with a 120-year design life without the need for trade-offs between best practice and efficient use of the possession periods. The longevity of our product also means that the works will not need to be revisited further reducing ongoing maintenance requirements to the tunnel without increasing project costs.
Adherence to budget and timescales.
All work on the project was undertaken within the required timescales, both in relation to individual ‘rules of the route’ possessions and the overall project duration. The work was also carried out within the agreed budget and with Zero safety incidents.
Summary of the Scheme Benefits
Shortlisted for Construction News Award
Shugborough Tunnel is a first of its kind use of Geobear’s game-changing geopolymer for the protection of a nationally important piece of Historic Rail Infrastructure. The geopolymer was used as an alternative to traditional grouts due to the lightweight, rapid curing and significantly lower carbon footprint. The fragile tunnel lining was at risk of collapse and traditional cementitious grouts or water-based foams would have significantly loaded the tunnel linings risking a full collapse or requiring significant temporary works and major possession windows to install the solution and allow it to cure.
Our geopolymer’s curing speed and absence of cementitious material eliminated the risk of contamination of track drainage and ballast and allowed the work to be carried out in “rules of route” possessions on Saturday nights without the need for extended possessions. This maximised asset availability preventing disruption to rail services. The lightweight equipment and rapid installation also minimised disruption to the National Trust during the injection of geopolymer into the shafts at ground level. The project was delivered on time and within budget in full collaboration with Network Rail, Story Contracting, COWI and the National Trust.
