Home » Projects » A47 Bretton Subway, Peterborough


Several pavement defects were present on the eastbound and westbound dual carriageways in the vicinity of a pedestrian subway which passes underneath the A47 at junction 16. A ground investigation was undertaken along a 50m stretch of the carriageway to obtain data regarding the ground and ground water conditions at the site in order to investigate the cause of the defects and to provide information enabling remedial works to be designed.

Five window sample boreholes and twelve super heavy dynamic probes were undertaken. The investigation revealed the road construction was supported by up to 3m of made ground. The dynamic probes revealed that the made ground was loose, and it was determined that the loose made ground was resulting in the carriageway surface being not adequately supported by the ground beneath which was allowing settlement and defects to occur.

Client issues

The client required a solution in order to increase the allowable bearing capacity of the soil to a depth of 3.0m beneath the carriageway surface to 150kN/m2 prior to resurfacing of the carriageway. The affected section of road was 446m2 in area, covering sections of road on either side of the pedestrian subway behind 2 abutments and between 4 wing walls on both the East and West bound carriageways.  

A solution was required on site to deliver repairs with minimal construction works in a short a timescale as possible. Geobear was contacted to propose an injection solution to stabilise and strengthen the ground to ensure no further movement occurred and to allow resurfacing of the carriageway on completion.

A key concern for the client was that precise  levelling had to be undertaken throughout the treatment procedure to monitor heave/settlement of the ground and also the subway wing walls and abutments to monitor lateral movement during treatment. The structural elements had no tolerable movements and could not be affected by the zone of influence of treatment, it was essential that that no movement occurred to any structural elements during the works. If any movement was to occur then works would have to cease and advice be obtained from the overseeing organisation before recommencing.

Geobear Solution

treatment plan image

Treatment plan highlighting injection points

The Geobear solution would see our geopolymer material injected at multiple points and of depths to 3.0m across the treatment area behind each abutment and the between the wing walls as shown on the treatment drawings.

Monitoring was undertaken of the structural elements as part of the Geobear works and Geobear  specified a specific geopolymer to carry out the treatment. This was in order to complete the works successfully and also to ensure a high level of control so the structural elements would not be affected by the geopolymer.

Injections points were as close a 1.5m to the abutments and wing walls, however Geobear were able to ensure that the injected geopolymer would not migrate away from the region of soils being targeted and thus not impact the structural elements. Geobear also utilised a set trigger time per injection to ensure that the process remained fully controlled.

The work was completed successfully within 2 weeks under night time lane closures. Throughout the works the structural elements were monitored and there was no movement. On completion of the works the carriageway was handed back to the client in preparation for resurfacing.


Homeowner Contact Form

  • This will help us as we can look at local site conditions.
  • This field is for validation purposes and should be left unchanged.

Contact Us

Please use this contact form or navigate to the contact us page and send us a message. We will respond to you within 24hrs.

Alternatively please call us on 0800 084 3503 and speak to our customer services team. Calling from Ireland please go to the contact us page.

We deliver projects on any sort of building or structure – from conservatory extension problems to 80,000m2 warehouses and road infrastructure. In most cases we will have the best solution, so get in touch today.

  • This field is for validation purposes and should be left unchanged.