Anglezarke Reservoir – Enabling Works & Cut-Off Wall Civils Support
Key Achievements
- Delivered complex enabling works within a live dam embankment
- Safely executed a 10.2m deep excavation with full monitoring and control measures
- Progressed from principal contractor (enabling works) to key subcontractor on main contract
- Supporting delivery of cut-off wall installation to restore dam integrity
- Managed civil engineering works within a live impounding reservoir environment
- Coordinated closely with specialist contractor Keller for piling and installation works.
Project Overview
GDB Civils Ltd. were engaged to deliver essential maintenance and improvement works to Heapey Embankment at Anglezarke Reservoir, located near Chorley.
Focus
The reservoir, originally constructed in 1857 as part of the Rivington Pike Scheme, had identified seepage issues within the dam core requiring remediation works.
The works
GDB initially delivered an enabling works contract directly for United Utilities, including a deep excavation within the embankment to investigate and prepare for remedial works. Following successful completion of this phase, Keller was awarded the main cut-off wall contract and subsequently subcontracted to GDB to deliver all civil engineering and earthworks support associated with the installation.
Key Challenges
- Deep excavation within a live dam embankment
The enabling works required a 10.2m deep excavation within the embankment structure, presenting significant risk due to the live reservoir conditions. - Continuous monitoring requirements
Temporary works and embankment stability required constant monitoring using strain gauges and monitoring pins. - Live impounding reservoir
All works were carried out while the reservoir remained operational, requiring ongoing vibration and stability monitoring throughout piling and earthworks activities. - Ground conditions deeper than anticipated
Variations in ground conditions during excavation required adjustments to methodology and programme - Access and public interface
Full closure of Moor road, a well-used public route, required coordination with United Utilities communications and management of pedestrian access. - Specialist subcontractor coordination
Close interface with Keller for piling operations, requiring careful sequencing of working platforms, guide walls and material handling.
Our Delivery Approach
The project was delivered in two key phases, beginning with the enabling works contract under GDB’s appointment by United Utilities.
During this phase, GDB:
- Designed and implemented complex temporary works for the deep excavation
- Managed monitoring systems to ensure embankment stability
- Delivered investigation works and reinstatement using grout
The successful delivery of this phase led to GDB being retained as a key subcontractor to Keller on the main cut-off wall contract.
For the main works, GDB:
- Established and managed the site compound and working areas
- Constructed and maintained the working platform for piling operations
- Coordinated closely with Keller to support efficient cut-off wall installation
- Managed material handling, including disposal of pile arisings
- Delivered associated civils works including guide walls, traffic management, scaffolding and reinstatement.
The approach required careful planning and coordination to ensure safe and efficient delivery across multiple work fronts within a constrained site.
Safety & Risk Management
Safety was a critical consideration throughout both phases of the project, particularly during the deep excavation within the live embankment.
Key measures included:
- Design and implementation of complex temporary works to support excavation
- Continuous strain gauge monitoring of temporary works performance
- Embankment stability monitoring using monitoring pins
- Strict adherence to method statements to protect dam integrity
- Ongoing vibration monitoring during piling operations
- Controlled working practices within a live reservoir environment
This approach ensured that all works were carried out safely while maintaining the structural integrity of the dam.
Outcome
(Ongoing Project)
GDB successfully delivered the enabling works phase, including a complex deep excavation and reinstatement within a live embankment, providing critical data and preparation for the main remediation works.
The successful execution of this phase led to GDB being retained to deliver the civil engineering and earthworks package for the main cut-off wall installation.
The project demonstrates GDB’s ability to:
- Deliver high-risk works within live infrastructure environments
- Adapt to changing ground conditions and constraints
- Coordinate effectively with specialist contractors
- Maintain safety and control across complex, multi-phase works.
Works are ongoing, with GDB continuing to support the successful delivery of the cut-off wall installation and associated reinstatement works.