Tynybryn Bridge is one of the first Active Travel Bridges in South Wales to use a light-weight fibre reinforced polymer (FRP) deck solution with a localised ground improvement system of injected geopolymers to improve the ground bearing. Using Geobear geopolymer injection as a pre-construction activity rather than a post-remedial solution has not been used like this before, especially for accommodating a fast-flowing river in a highly constrained site.
Project Overview
Geobear was contracted to undertake ground improvement works for the southeast abutment of the Tynybryn Bridge in Tonyrefail. This project required specialised geopolymer injection techniques to enhance soil stability before constructing the bridge abutment.
The key objectives were:
- Improve soil stability to meet a friction angle of 30 degrees.
- Ensure the ground conditions are suitable for the new bridge abutment.
- Complete the project within a strict two-week timeline.
Client Challenges
Working adjacent to the watercourse, the client needed a solution that required limited access, no heavy plant to reduce temporary works and an environmentally inert material. Geobear provided low-carbon, ground stabilisation solutions to enable the client to fulfil their objectives.
Alternative method
The alternative for this scheme would be the complete excavation, followed by new fill construction or piling, which would have required a rig and platform. Both options would have been difficult to achieve, have long project times and be costly due to the location.
Scope of Work
The project involved injecting geopolymer into the soil at various depths up to 2.3 meters below the proposed abutment base.
Methodology
- Site Preparation:
- Conducted pre-probing to determine soil conditions and required depths for geopolymer injection.
- Set up a fully self-contained injection unit within 50 meters of the injection points; the hoses were positioned through a closed subway.
- Geopolymer Injection:
- Drilled injection holes based on the design
- Inserted 12mm injection tubes to the required depths.
- Mixed and pumped the multi component geopolymer into the soil.
- Verification:
- Conducted pre and post-dynamic probing to verify the improvement in soil stability.
Site Constraints and Considerations
- Space Requirements:
- Adequate space was necessary for the injection unit and safe operation around the injection points.
- Safety and Permits:
- Obtained necessary permits for digging and ensured the site was secure for the workforce and pedestrians.
- Coordinated with Balfour Beatty to manage any traffic and site access issues.
Project Management and Timeline
The project was delivered within one week with one injection unit. Our design schedule allowed for continuous work without interruptions, with additional charges for delays caused by external factors.
Test Results
Post-work testing was carried out at two locations over the treated area using a Super Heavy Dynamic probe (DPSH). The results were converted to an equivalent SPT N1(60) blow count to verify soil improvement.
- DP01 Test Results:
- Depth of 0.1m: 13 blows
- Depth of 1.1m: 32 blows
- Depth of 1.2m: 43 blows
- Depth of 1.3m: 59 blows
- Refusal at 1.45m with an equivalent friction angle greater than 40 degrees.
- DP02 Test Results:
- Depth of 0.1m: 17 blows
- Depth of 0.6m: 62 blows
- Depth of 0.65m: 176 blows
- Refusal at 0.65m with an equivalent friction angle greater than 40 degrees.
The high blow counts and refusal at shallow depths indicated a significant increase in soil stability, exceeding the required 30-degree friction angle.
Conclusion
Based on the validation testing using dynamic probing and empirical conversions from literature, the required design specification of achieving a friction angle of more than 30 degrees was satisfied. The post-injection results showed significant improvement in soil stability, with the probing refusal depth indicating a friction angle greater than 40 degrees.
Client Collaboration
Effective communication and coordination with the client, Balfour Beatty, was crucial for the success of this project. Regular updates and prompt responses to any site issues ensured the project stayed on track.
Furthermore, the project was shortlisted for a number of industry awards and was commended by the Chartered Institution of Highways and Transportation.
