Trenchless Tactics: Solving Subsidence with Innovation

Challenges and Risks

The identified issues included:

1. Subsidence in the Conservatory: Affecting the structural stability and safety of the residential property’s cherished conservatory.
2. Collapsed Sewer Pipework: Both incoming and outgoing pipework in the sewer system had collapsed due to a void beneath the manhole chamber, leading to significant issues with the 100mm foul sewer system.
3. Safety Hazards: The project presented various risks, such as working in confined spaces, potential hazards in and around the residential area, and concerns related to noise and dust pollution.

Considered Options

In evaluating the best approach to resolve the complex issues identified, CBUL and PSS analysed various options, considering potential impact on cost, time, community disruption, and long-term effectiveness.

1. Traditional Excavation: Initially contemplated but ruled out due to its invasive nature, high costs, extended time frame, and potential disruption to the neighbourhood.
2. Non-Invasive Repair Techniques: Selected and implemented for the project. These techniques included innovative methods such as using Pipe Lifters to support downstream pipes, compacting QC10 material underneath the pipework to provide structural support, and re-benching the chamber (adjusting the base of the chamber) as necessary. The primary goals of these techniques were to prevent future issues with the pipes sinking or dropping, ensure that water flowed correctly through the pipes, and stabilise the ground effectively to address the subsidence problem.
3. Patch Lining and Grout Injection: As part of the repair process, a significant amount of grout (over a cubic metre) was injected into the affected areas. The purpose of injecting this grout was twofold: first, to fill any voids that may have formed beneath the surface, and second, to stabilise the ground or subsurface. By filling these voids and stabilising the subsurface, the repair aimed to ensure structural integrity and prevent further issues related to subsidence or instability in the affected area.

Innovative Solution, Lasting Stability

The selected trenchless solution demonstrated remarkable effectiveness. By opting against traditional excavation methods, CBUL and PSS successfully resolved the subsidence issue from within the manhole chamber. Innovative techniques were used to lift and support the pipework, while also filling the underlying void. This approach not only promptly resolved the immediate problem but also strengthened the area to mitigate potential future issues.

– Cost-Effective Solution: The project was completed at just over a fifth of the estimated cost of traditional excavation and piling methods.

– Swift Completion: The entire operation was finished in just 10 days, significantly faster than the projected 6 weeks required for conventional techniques.

– Minimal Disruption: By avoiding large-scale excavation, the project caused minimal disturbance to residents and the surrounding neighbourhood, preserving the tranquillity of the area.

– Long-Term Stability: The innovative techniques used provided a robust and lasting solution to the subsidence problem, effectively reducing the likelihood of future issues.

– Reduced Risks: The non-invasive methods employed minimised common excavation risks, such as interference with underground services, and significantly reduced noise and dust pollution.

Collaborative Expertise

At Cappagh Browne, collaboration with partners like PSS is integral to our approach to solving complex issues. By combining expertise and resources, we enhance our ability to deliver comprehensive solutions that exceed client expectations. This synergy allows us to foster a culture of continuous learning, tap into diverse perspectives, leverage specialised knowledge, and access cutting-edge technologies, driving us to explore new possibilities and set higher standards in our industry. Together, we achieve results that are greater than the sum of our parts, ultimately benefiting our clients with superior outcomes and sustainable long-term value.