Ground Stabilisation Work at Shildon Coal Drops
The Grade 2 listed Victorian-age masonry retaining wall, known as the Shildon Coal Drop, is located in the town of Shildon, County Durham. The retaining wall was originally used as a locomotive refuelling station, and the Timothy Hackworth Museum Railway line runs along the toe of the retaining wall.
Constructed in 1847, it is believed that the site, known locally as the ‘coal drops’, was the first-ever attempt to mechanise the process of refuelling steam locomotives in the UK.
The structure is leaning towards the railway line, and historical intervention in the form of masonry buttressing is present in front of the wall. Within the last decade, further movement of 100 mm has occurred.
The Darlington Heritage Railway is planning to run trains down the line adjacent to the drops, and the primary concern was the potential for vibrations from the trains to cause movement in the wall, risking the structural integrity of this historic site.
Geobear was contacted to use its geopolymer injection process to stabilise the historic wall and protect the asset from further movement caused by stresses from a live track.
Solution & Execution
The project involved injecting geopolymer material beneath the foundations of the wall to increase the bearing capacity of the soil and minimise the impact of vibrations that could lead to movement. The process was carefully planned, with injections targeted below the foundation, where the soil was identified as being particularly soft. The foundation depths ranged from 500 mm to a metre, and the wall spanned 120 metres, making the task both extensive and intricate.
A key challenge encountered during the project was the softer-than-expected soil in the top layers, leading to adjustments in the injection process. The project team and engineers illustrated the versatility of the Geobear solution by modifying their design on-site to counteract the soft soil.
Geobear’s technicians conducted pre-tests and post-tests every 15 metres along the wall to ensure the desired bearing capacity was achieved.
Method, Low Carbon & Alternatives
Geobear’s solution emits significantly less carbon than traditional alternatives. A major excavation and underpinning or piling scheme would, based on Carbon Footprint reports of similar projects, emit up to 75% more carbon.
Geobear’s method requires minimal plant, typically one mobile unit. Our site team of eight people used hand-held drills to drill holes for injection tubes to the required depths beneath the foundations. The tubes are then installed, and injections of geopolymer resin are made into specified locations. The tubes are removed and disposed of, leaving the site with no spoil or notable signs of major works.
Outcome & Future Prospects
The project successfully increased the bearing capacity of the soil beneath the wall, securing the structure’s stability against potential vibrations from the heritage train line. The Shildon Coal Drops site is now poised for its next chapter, serving as a heritage site where visitors can experience the historic train route, with the assurance that the structural integrity of the wall is preserved for future generations.
Conclusion
The stabilisation work at Shildon Coal Drops stands as a testament to the importance of preserving historical sites, the challenges involved in such endeavours, and the technical expertise required to address these challenges effectively.
The project not only preserved a piece of history but also ensured that it could be safely enjoyed and appreciated by future generations. The success of this project serves as a benchmark for similar heritage conservation efforts, highlighting the importance of thorough planning, adaptability, and precise execution in the field of structural stabilisation and preservation.
