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Case Study - Manhole Rehabilitation in Confined Space

Sealing and repairs works on a grease bin consisting of rebuilding base damage and sealing fiberglass unit using structure injection and reinforcement.

Equipment used:

  • CityFlex® jet-vac unit
  • Variation of chemicals
  • Injection device
  • Compressor
  • Hand tools
  • Communication equipment
  • Protective personal equipment


The grease bin was emptied of all liquid and solid content and a bypass system was put in operation. A submersible pump was used. Once the unit was satisfactorily sealed from ingress, works commenced.

The unit was cleaned thoroughly using high pressure jet wash. Any difficult deposits were removed using a wire scraper (to clear the aggregate on the surface). Lose parts of fibreglass were broken away and the edges on the base of the tank were evened to ensure the adhesion was formed correctly at the remediation stage.

Once the walls were cleaned, the rebuilding support of the base floor commenced using a variety of chemicals. This application was applied using a concrete injection device where adhesive packers were attached to the solid surface under the unit and the chemical formula was pumped through the device to create a bonding with the existing shale base. Once the adhesive had set, the void was filled using quick set mortar.

To seal the tank to the new base, a fibreglass compound was used.  The raw fabric fibreglass was folded into three layers. The entire base and up to 250mm of the walls was treated to ensure that a seal was formed.

On completion of the tank, a static test was carried out to ensure that the sealing had been successful, and a report was issued to our client.

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