Geobear has successfully remediated a chronic track defect on the Dublin-Cork mainline using geopolymer ground improvement technology, eliminating excavation requirements and avoiding prolonged line closures, according to Engineers Ireland.

UBC 4 is a single-span bridge carrying the railway over Sarsfield Road in Dublin. The bridge deck sits at a skew to the track direction, creating a long-standing twist and warp fault at the transition zone. Differential settlement at the abutments had progressively distorted the rail and fastening systems, requiring frequent maintenance interventions.

Geobear designed a targeted ground improvement solution to progressively increase trackbed stiffness across the transition zone. The design aimed to achieve a starting stiffness of 50-80 megapascals, increasing towards the bridge abutments across a 13.8-metre transition zone.

The engineering process included ground model validation using image correlation analysis of passing train footage, identifying 5.4 millimetres dynamic deflection, corresponding to a subgrade modulus of 11.7 megapascals. PLAXIS modelling confirmed that more than 90 per cent of strain occurred within 1.5 metres below the subgrade.

The final treatment design specified 528 injection points across four depth levels, with geopolymer volume increasing progressively toward the abutments. Approximately 10 tonnes of geopolymer material were injected to strengthen the trackbed soils.

All works were completed over 19 limited night-time possessions during November and December 2024, with no safety incidents. Post-treatment Dynamic Cone Penetrometer testing confirmed that stiffness targets were achieved at 11 of 12 locations at the transition start, rising to 100 per cent compliance at the transition end.

Track monitoring demonstrated significant improvements, including 59-69 per cent reduction in twist and warp at monitored rail positions, with 75 per cent of previously defective locations downgraded from red fault to yellow or green condition.

Geopolymer ground improvement has broad applicability across railway assets, including embankment stabilisation, bridge abutment settlement remediation and subgrade strengthening.

Explore comprehensive technical details on the Dublin rail bridge remediation project in the complete report.