Sewer System Stabilisation – UK
A road and sewer system had experienced significant settlement of 100-200mm, initially caused by flash flooding. Consequently, washout beneath the existing sewer pipe occurred, meaning it bowed and the joints failed which caused further soil erosion. This led to an accelerated rate of settlement and loss of ground support increasing the risk of creating a localised sinkhole.
Ground conditions were classed as ‘very loose ground’ based on standard penetration testing and the requirement was to improve the ground conditions to a medium density.
The client urgently needed to stabilise the ground and reduce further settlement, in order to accommodate complete pipework repairs (re-lining).
A major difficulty for the client was the site location and options available. The traditional option would have been the full excavation of the site to around 6.5m. The area in question is a busy town road with buildings on either side and is at the junction with an access road to a large supermarket. A large amount of temporary works such as sheet piling, service diversion and a much larger road closure area would have been required, all involving heavy machinery to achieve this. This would have required many weeks to complete, meaning a lengthy road closure. Anglian Water needed to minimise disruption to the local community and in choosing a Geobear geopolymer solution only part excavation was needed.
Geobear’s solution is based on the use of ground injections that involve using a geopolymer material to stabilise the soil. It involved injecting expansive resin at various depths to densify and compact the loose or eroded soil beneath the pipes.
The Geobear engineers used Plaxis modelling to illustrate the achievable improvement in ground conditions through a geopolymer material. This data could reassure the client that the proposal was suitable and would achieve the desired outcomes.
This is the first time geopolymer technology was used on such an extensive scale to permanently treat poor ground under a sewer system.
Geobear worked with the client in the engineering design phase. The teams used BIM (Building Information Modelling) and overlaid the Geobear treatment drawings to ensure the accurate placement of injections to avoid clashes with buried services.
The incorporation of a geopolymer injection design into a BIM model is a true industry first and the demonstrable success opens countless opportunities for future works.
Geobear injection tubes needed to be inserted to depths of 7.5m, to facilitate this a working platform was required to be constructed. However, once the project commenced, the Geobear technical team concluded that the use of a working platform could be circumvented by using rod-driving. The Geobear team successfully used the rod driving method and saved five days of the programme and notable cost with this intervention.
The project was successfully delivered and the client’s expectations for improvement in standard penetration test values were met. The threat of a sinkhole was removed and full sewer repair could proceed.
The Geobear works were completed on time ahead of the original schedule due to the work platform not being required. The verified ground conditions post-treatment achieved 3 times increase in soil density as a result of the injections (see the pdf for data).
Ground conditions on site were classed as ‘very loose ground’ based on standard penetration testing (SPT) and the requirement was to improve the ground conditions to a medium density. At the treatment depth between 4.5 to 7.5 metres, the SPT results showed 0-1. Post-treatment with geopolymer, the improvement was between 5-15 exceeding the client’s requirement.
The work was completed on-site with no incidents reported.
The unforeseen circumstances presented us with a particularly challenging situation. On approaching Geobear to propose a solution their engineering team worked collaboratively with us to develop an appropriate and innovative solution to the unique conditions on the site. The site team delivering the project has exceeded expectations and Geobear has clearly met all our objectives.