Geobear designed a mass void filling approach using a lightweight geopolymer to establish contact within the vault geometry and provide a continuous filled mass to the crown of the arch, helping reduce void-related settlement risk and limiting further moisture-driven deterioration.
Temporary shuttering/formwork was installed by the contractor at vault openings and propped back to provide safe containment. Geobear then introduced geopolymer through small access holes, enabling controlled placement in confined spaces without the need for large concrete pumping equipment.
Five vaults were filled in total. Recorded vault volumes were approximately 16.8 m³, 16.8 m³, 8.4 m³, and 10.9 m³, with a further vault excluded (approx. 20.75 m³) due to late scope change. Total filled volume was approximately 56 m³, achieved using approximately 2 tonnes of geopolymer. The material was described on the project as offering typical confined bearing performance on the order of ~100 kPa (and ~50 kPa unconfined), with the additional practical benefit that it can be excavated in future if required.
