Homeowner Business Infrastructure Company 0800 084 3503

Void filling – Colt Cragg reservoir

Challenge

Subsurface voids beneath infrastructure at Colt Cragg Reservoir posed risks to stability and long‑term asset performance in a sensitive water management environment.

Solution

Geobear implemented precision geopolymer injection to fill voids and strengthen surrounding soils, restoring ground support quickly with minimal environmental disturbance.

Voids successfully filled

Subsurface instability mitigated

Infrastructure protected

Improved ground support achieved

Low environmental impact

No major excavation required

Background


Site location drawing

colt cragg spillway

 

Geobear was contracted to provide a void-filling solution for an abandoned spillway tunnel at Colt Crag Reservoir. This project required the use of a specialist geopolymer design, delivery team and equipment to ensure a precise and efficient execution at a difficult-to-access site.

Scope of Work

The primary objective was to fill the 232m³ void within the tunnel using Geobear’s expansive geopolymer resin, ensuring structural stability and integrity. The project required careful planning and execution due to restricted site access and specific logistical constraints.

 

Challenge

Restricted Access: The site had limited access, necessitating the use of smaller injection units and extended hoses.

Logistical Constraints: Geopolymer materials had to be stored off-site and transported in small loads using 4×4 vehicles and flatbed trailers.

Structural Preparations: The lower tunnel arches required formwork installation to retain the geopolymer in its liquid state. Blockwork formwork was constructed by the main contractor at both ends of the tunnel.



Solutions

 

Void access

void access

 

A solution was designed and validated by Geobear engineers which would utilise a specialist Geobear material to fill the voids. The delivery process would follow; 

Site Preparation:

  • Injection unit and trailers were parked north of the spillway bridge.

  • Formwork installation at tunnel ends.

  • Removal of any standing water from the void area.

  • Provision of task lighting and ventilation within the tunnel.

Geopolymer Injection:

  • Technicians entered the tunnel from the bottom, using extended hoses to pump geopolymer from the injection unit.

  • A geopolymer resin with a compressive strength of 100kPa, was used.

  • Continuous visual monitoring ensured the precise filling of the void.



Results

 

Spillway filled

Spillway fill

 

Execution and Timeline

The project was executed with one Geobear injection team and the void-filling process saw 9 tonnes of geopolymer injected into the voids. The work was completed within the estimated one-week timeframe.

Materials Used

Geobear’s specialist geopolymer resin was employed, conforming to BS EN 826 standards for compressive strength. The resin was selected for its expansive properties, essential for effective void filling in confined spaces.



 

Ready to discuss your project?

Get in touch with our expert team today and discover how Geobear can extend the life of your critical infrastructure assets.

Contact us
Bear pointing Bear pointing