Geobear was contracted to deliver ground improvement works at multiple locations of an out of town retail park, Woodfields in Bury. The site had become severely undulated and a solution was required to stabilise the access road, car park and service area. See photos 1&2.
The current site was constructed in the 1990s on a former landfill tip. A number of reports were compiled from structural engineers and a ground investigation company which included boreholes, standard penetration tests and drainage surveys.
The results of those reports and a visual survey revealed that throughout the site there had been poor compaction of the sub-base due to the construction on an area that has been subject to a historical, random deep landfill. The borehole data indicated the landfill was between 3m-6m depth and given its non-homogenous nature, the area was subject to non-linear displacements and undulations as it was loaded.
Consequently, settlement occurred across the site and localised settlement was evident across the car park which created ponding during periods of wet weather and settlement below the wheels of parked vehicles.
The service yard was affected by settlement affecting dock levellers and access steps. The condition of these areas and the extent of settlement posed a health and safety concern due to the high usage of the area for servicing of units.
A further contributory factor was the foul and surface water drainage having significant defects, with major undulations apparent to the car park surfacing along the drainage run.
The traditional solution available to the site owner was excavating the existing construction, replacing the fill material at a greater depth and installing new road surfaces and walkways. Woodfields is a busy out of town shopping centre with major stores such as Tesco on-site, the prospect of significant construction works was inconceivable.
Geobear uses a geopolymer injection solution to improve weak, compromised soil, fill and sub-base. On this project, we worked on the client’s design in terms of depth and area to treat and selected the geopolymer type and amount to install.
In this instance, the design covered 5,576m2 of the car park and entrance roundabout. We predominantly installed material at 1m depth (to treat to 1.5m), part of the roundabout was installed at 1m and 2m. Furthermore, the service yard dock leveller, used for loading and unloading of delivery lorries required void filling and lifting to return it to datum levels.
The engineering design for the treatment to the car park would require Geobear to inject specialist geopolymer material to a depth of 2.0m in some locations. This depth of treatment was required due to the presence of the landfill and the weakness of the ground in those locations.
The installation process would see drilling to the required depth and insertion of a precut steel injection tube that would transfer the geopolymer material into the required depth. The geopolymer is pumped directly from a Geobear injection unit adjacent to, or within 80m from the injection location.
The geopolymer material is processed on-site. It is created by combining two components that react to form an expanding geopolymer that exerts pressure in the ground compacting the existing soils or fill.
The process of injections follows the same pattern for differing vertical depths, all at 1m intervals. The roundabout approach, which required treatment up to 2m, would require 2 injections per location. The complete area requiring improvement is marked out in a grid pattern with a one-metre horizontal matrix. Each point on the matrix was subject to the required depth of injections.
With respect to the dock leveller in the service yard, Geobear injected material at 1m centres beneath the treatment area and used laser monitors to register the lift. Using a different geopolymer material we could lift the dock leveller by 150mm back to its datum level.
The Geobear works at the site took seven weeks to complete. Once an area is treated it could be handed straight back to site operators for continued use. This meant that the number of shoppers at the site was barely impacted by our works. Only 6-12 parking bays would be restricted whilst the work was completed.
The verification of the work was completed using CBR testing completed by the client.