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Bookham Road Underbridge Wingwall Stabilisation Project

Project Overview

Client: Dyer & Butler

Location: Bookham Road Underbridge, Surrey


A bridge wingwall in Bookham, Surrey had experienced movement and the client needed a fast non-disruptive solution to stabilise the asset. The site comprises a single-span underbridge (Bookham Road under rail) and is located immediately to the south of the M25.

Site investigation data revealed the soil beneath the structure was weathered London Clay Formation and had a medium plasticity.

Scope of Work

The project aimed to stabilise the south-eastern wingwall of the underbridge due to weak ground conditions caused by fines washout within reworked London clay. 

Geobear designed a stabilisation solution using its geopolymer injection method. The delivery process required the following tasks:

  1. Trench Digging: Dig a trench along the wingwall to the existing foundation level (approx. 750mm below ground level) and 300mm wide.
  2. Drilling and Injection: Geobear to drill four locations 1m apart to a depth of 0.5m below the foundation level and inject specified quantity of Geobear geopolymer at each location.
  3. Pre and Post-Testing: Conduct pre and post-dynamic Cone Penetration (DCP) tests to assess the soil stabilisation.
  4. Backfilling: Backfill the trench after the injection process is complete.



  1. Site Establishment:
    • Establishment of site facilities and traffic management systems
    • Setting out and hand digging of the trench by GT Services.
  2. Drilling and Injection:
    • Geobear to drill four holes through the wingwall foundation at specified locations.
    • Injection of Geobear geopolymer using specialised geopolymer technicians and equipment.
    • Monitoring of wingwall stabilisation via DCP tests.
  3. Backfilling and Finalization:
    • Backfilling of the trench by GT Services post-injection.
    • Site clean-up and demobilisation of equipment.

Challenges and Resolutions

  • Ground Conditions:
    • The weak ground due to fines washout within reworked London clay required precise geopolymer injection to ensure effective stabilisation.
  • Site Access and Logistics:
    • Managing traffic and ensuring safe access to the site for the equipment and personnel required efficient coordination between Dyer & Butler and Geobear.
  • Weather Conditions:
    • Any delays or disruptions due to weather conditions were planned to be managed by maintaining flexibility in the project timeline and ensuring adequate site drainage and flood prevention measures.


The Bookham Road Underbridge Wingwall Stabilisation project was successfully delivered over two days and demonstrated effective collaboration between Geobear and Dyer & Butler. Despite the challenges posed by ground conditions and site logistics, the project was completed within the stipulated timeframe and budget, ensuring the structural integrity of the wingwall and safe passage for rail vehicles.


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