Ultimate Client: Western Power Distribution
Contractor: O’Connor Utilities Ltd
Duration: 4 shifts
Solution Provided: Structural Void Filling using Geopolymer 2640
Background & Challenge
A 100-year-old culvert running beneath Sowter Road in Derby was identified as a potential risk due to uncertainties regarding its load-bearing capacity. The culvert’s structural integrity was of particular concern as a new 100-tonne transformer was scheduled to be transported over it to a nearby substation.
Derby Council required the culvert to be filled with a suitable material that:
- Could support the heavy transformer load
- Could be removed easily in future if necessary
With an estimated void space of 280m³ (after accounting for silt removal), a robust and efficient filling method was required to meet the council’s needs and ensure the safe delivery of the transformer.
Injection design drawing
Alternative Methods Considered
A number of alternative methods were evaluated for filling the culvert, but each presented significant limitations:
Concrete Infill:
Drawback: Permanent and difficult to remove if future access is required.
Compacted Aggregate Fill:
Drawback: Would require extensive excavation and compaction, adding time and disruption to the project.
Given these constraints, Geobear’s Geopolymer 2640 was selected as the optimal solution due to its lightweight, expansive properties, strength, and future removability.
Geobear’s Solution
Geobear designed a void-filling solution using Geopolymer 2640, a high-performance expanding resin with a free-rise compressive strength of up to 150 kPa. The injection process was designed to ensure the complete filling of the culvert while maintaining controlled expansion to prevent unnecessary stress on surrounding soil and infrastructure.
Execution & Methodology
Site Preparation & Dewatering:
- The culvert was dewatered and suspected water ingress points were sealed.
- Sandbag shuttering was installed at 5–6m intervals to contain the material during injection.
Location holes for injection and monitoring
Drilling & Injection Process:
- Three 16–30mm holes were drilled per section from the road surface into the culvert.
- One hole was used for Geopolymer injection, while the other two facilitated camera observation.
- Two injection units and two teams operated simultaneously to complete the process efficiently.
- The filling was conducted in two stages:
- The first stage involved injecting a 1m deep layer to create a uniform support base.
- The second stage filled the remaining void space, ensuring full coverage. During this stage, injections continued until a flicker of lift was detected on a sensor placed on the road surface, ensuring the culvert was fully filled and supported.
Material Use & Verification:
- Approximately 10 tonnes of geopolymer material was installed over the four shifts
- Camera monitoring was used to confirm proper dispersion and void elimination.
- A laser sensor was placed on the road surface to monitor movement or uplift during the final phase of injections; this verified the material had filled the void.
Project Outcome
The culvert was successfully filled in accordance with Derby Council’s requirements.
- The void fill provided the necessary structural support for the 100-tonne transformer without impacting underlying soil conditions.
- The material’s design allowed for future removability if necessary, ensuring long-term flexibility for the site.
- The project was completed within the allocated timeframe of 4 shifts, minimising disruption and ensuring the scheduled delivery of the transformer.
This project reinforced Geobear’s expertise in infrastructure ground improvement and demonstrated the efficacy of geopolymer technology in ensuring structural integrity while maintaining long-term site adaptability.
