Project overview
Anglian Water Services Limited commissioned the emplacement of a 4.5 km foul water flood relief tunnel along Clacton seafront. The project posed significant geotechnical challenges, particularly regarding the stability of the London Clay cliffs, which were prone to slope failure. Additionally, local residents expressed strong opposition, increasing the need for robust technical analysis to address their concerns.
Our approach
We conducted a comprehensive site investigation, including:
- 150 cable percussion boreholes, most equipped with piezometers, to assess subsurface conditions.
- Identification of a water-bearing granular deposit (channel scour) along the proposed tunnel route.
Our analysis revealed that while slope failure of the cliffs was inevitable, the tunnel’s construction would not impact cliff stability. This conclusion provided assurance to Anglian Water and local residents that the tunnel could be safely constructed below the toe of the cliffs.
Geotechnical solutions
- A detailed settlement analysis was performed to refute potential compensation claims related to structural movement.
- Pre-emptive surveys of nearby structures were conducted to ensure rapid responses to any allegations.
- Extensive instrumentation was installed, including:
- 140 inclinometers
- 70 pneumatic piezometers
- 450 crack gauges
These instruments monitored cliff stability before, during, and after construction as part of a long-term monitoring programme.
Outcome
Our thorough geotechnical analysis and monitoring provided critical evidence that the project would not compromise the stability of Clacton’s cliffs. This allowed the sewer emplacement to proceed safely, alleviating local concerns and ensuring the project’s success.
Key details
- Client: Anglian Water Services Limited
- Cost: Not disclosed
Our work combined technical expertise and community engagement, ensuring the safe delivery of this critical infrastructure while addressing the concerns of all stakeholders.