Ground improvement works at a major commercial project in central London

Mainmark Ground Engineering (UK) was contracted to provide ground improvement solutions on a major commercial project on Finsbury Avenue, London. This enabled the client to undertake an excavation and pour a capping beam. The nature and scale of the project meant Mainmark undertook a temporary works design to create a solution. In the initial stages of the project, Mainmark’s Teretek® resin injection technology was used to increase the load bearing capabilities of the soil. Due to the large area needing to be stabilised, permeation grouting was used in the latter stages.

A secant piled wall had been partially constructed as part of the basement works for a new office building under construction at Finsbury Avenue. Surrounding the site was an existing retaining wall comprised of a reinforced concrete cantilever retaining wall supported on discrete concrete piles installed at 7.5m centres. Steel columns installed within some of the secant piles were being used to prop the existing retaining wall. A capping beam was required at the top of the secant wall. To install the capping beam, the fill material in front of the existing cantilever retaining wall was to be excavated for the installation of the capping beam. This would expose the material below the existing wall between the discrete concrete piles supporting the existing wall.

A solution was required that would allow a temporary excavation to be made in front of the retaining wall so that reinforced concrete capping could be constructed above secant piles.

Key steps included:

1. Teretek® injection: Mainmark’s proprietry resin was injected at regular intervals to compact soil and fill void to prevent it from collapsing around the area of planned excavation.
2. Temporary works design: Mainmark UK worked closely with a consultant to come up with an alternative solution and pivot the approach for the second and third phases of the project.
3. Permeation grouting: Permeation grouting was used in the latter stages as a time efficient alternative, which minimises the risk to neighbouring properties movement due to undermining of the subsurface conditions’ structures, footings or vibrations.

With the site being located in central London, and the site surrounded by other businesses and pedestrians, a minimally invasive solution was needed to minimise disruption to the property or surrounding area.

• Non-intrusive solution in a central London location: The resin injection process is minimally invasive, allowing minimal disruption to local businesses and passersby.
• Adaptive solution-based approach: Mainmark undertook research and development work prior to phase two, to switch approach from Teretek® injection to permeation grouting allowing more efficient ground stabilisation.

Mainmark successfully carried out ground stabilisation works on the major commercial project with minimal disruption to the rest of the project team. The use of the resin injection and permeation grouting reinforced the soil allowing continuation of substructure works with minimal delay, as well as minimising the likelihood of further problems with subsidence.

The project management team at Morrisroe, which carried out the demolition and basement construction on the Finsbury Avenue project, were very satisfied with the outcome and the adaptability of the Mainmark team.

Lee Henry, project manager at Morrisroe, said: “Work on demolition, substructure and superstructure construction processes can be unpredictable and it’s therefore crucial that ground engineers are on hand should you need them. Mainmark were a pleasure to work alongside, carrying out the necessary work to stabilise and strengthen the ground in an efficient manner with little disruption to our team or the project as a whole. It was clear throughout the project that we were working towards the same goal, and their input allowed us to continue our work with piece of mind.”

On a large-scale operation, Mainmark’s team were able to work effectively and efficiently to find the best solution for the client. The team showed its abilities and delivered a solution focused approach, pivoting the approach and providing the best possible result.

Services Used:

• Teretek® resin injection
• Permeation grouting
• Ground stabilisation
• Void filling

For more information on how Mainmark can help stabilise and improve ground conditions for your business, visit Mainmark UK.