Homeowner Business Infrastructure Company 0800 084 3503

Utilities

Relevelling of manholes during dewatering

Challenge

Severe settlement beneath a Renfrew pumping station caused by sewer-induced ground loss and water ingress threatened manholes, pipes, and nearby homes — excavation or underpinning was impractical.

Solution

Geobear stabilised the site with geopolymer injection, sealing recharge flows, densifying silty sands, and re-levelling manholes — maintaining operations and avoiding deep excavation or structural risk.

14 ejector wells

installed — 17 m deep, 20 m diameter

~60 mm

settlement induced, soils consolidated to design density

Zero service disruption

interruption or property movement recorded

Background

A pumping station at Provost Driver Court, Renfrew, experienced severe settlement — up to 500 mm — due to a broken pipe drawing Clyde alluvial silty sands into the sewerage network.

Over time, groundwater and soils were pumped out, leaving very loose ground beneath the station and associated manholes.

Urgent stabilisation was required to protect both the pumping station and nearby infrastructure, including manholes, services, and residential properties at the end of a cul-de-sac. Conventional underpinning or deep excavation was ruled out due to scale, disruption, and insurance implications.

Challenge

The project faced multiple geotechnical and operational challenges:

  • Progressive ground loss: The sewer network was actively removing silty sands from beneath the site, leaving very loose soils and driving continued settlement.
  • Controlled densification: Engineers needed to accelerate settlement in a controlled way via dewatering to re-compact soils, while keeping the pumping station operational.
  • Infrastructure risks: Dewatering created risks of manhole tilt, chamber movement, and even settlement of nearby houses. Protecting these assets was critical.
  • Water ingress management: Recharge flows entered the ejector wells along existing pipe bedding, undermining dewatering efficiency and requiring additional sealing works.
  • Community interface: The works were carried out adjacent to homes and public roads, requiring constant monitoring and stakeholder engagement.

Precision, control, and safety — Geobear stabilised Renfrew’s pumping station without excavation, sealing leaks and protecting homes above fragile alluvial ground.

Solutions

Geobear was engaged to provide ground stabilisation and water-sealing using expansive geopolymer resins.

  • Injection beneath manholes: Injection tubes were installed beneath local chambers to allow controlled lifting and re-levelling during dewatering. This kept manholes within pre-agreed tolerances and aligned with surrounding strata.
  • Pipe sealing: When recharge flows began to overwhelm the dewatering system, Geobear injected fast-reacting geopolymer around pipe bedding gravel, sealing leakage paths and consolidating soils to stem water inflows.
  • Void filling: Expansive resin was injected into identified voids. Verification included volume calculations, resin rise density checks, and pump back-pressure monitoring to confirm void closure.
  • Risk mitigation: Geobear’s precision injection method (using 12 mm diameter tubes, accurate to 0.25 mm) was available on standby to remediate houses if movement exceeded thresholds. In practice, careful monitoring meant no intervention was required.
  • Material selection: A geopolymer resin was specified for wet soil conditions, with high expansion and rapid gel time to minimise washout and allow efficient placement.

This flexible methodology allowed the scheme to adapt as challenges emerged, providing reassurance to both the client and local residents.
Provost date with Geobear

Results

  • Settlement controlled: Dewatering induced ~60 mm of settlement, bringing soils to design density.

  • Ground improved: Probe testing confirmed consolidation of loose alluvial soils beneath the pumping station.

  • Manholes re-levelled: Geopolymer injections successfully stabilised and adjusted chambers to tolerance.

  • Water inflows sealed, preventing recharge from undermining dewatering.

  • No service disruption or property damage, with continuous monitoring throughout.
  • Carbon savings: By avoiding underpinning, cutoff walls, or deep excavation, the geopolymer solution delivered a lower carbon footprint and faster programme.

 

Michael Purkis, Principal Engineer, Donaldson Associates:

“The pumping station presented us with very loose soils and high uncertainty. Having Geobear on board allowed us to manage the risk, knowing their injection system could stabilise manholes, seal leaks, and even remediate nearby houses if needed. Their flexibility on site solved unforeseen problems and was key to delivering the project safely and on programme.”

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