Cracks where the building rotates
Background
A property investor purchased a four-storey building, including a basement, in Hamilton Park, Islington, London, with the intention of converting it into four apartments. The building suffered from significant structural issues due to clay shrinkage, causing subsidence, rotation, and separation from the neighbouring property.
The client required a solution to improve the ground beneath the foundations and re-level the property for planned renovations. With a challenging site and multiple constraints, the investor sought an efficient solution that minimised disruption while ensuring long-term structural integrity.
Alternative Options
Before selecting Geobear’s geopolymer solution, the client considered two main alternatives:
- Traditional Underpinning
- Required extensive excavation, street licenses, and prolonged work durations.
- The process would take approximately 9 to 11 weeks due to the need for staged excavation, hydraulic jacking, and concrete curing.
- Significantly higher costs due to labour, materials, and extended project timelines.
- Complete Rebuild
- Would have been the most comprehensive but financially prohibitive.
- Required extensive permits, demolition, and reconstruction, adding months to the project timeline.
Phase one injections to improve ground
After careful evaluation, Geobear’s geopolymer injection method was chosen for its non-disruptive, engineered solution, offering a reliable alternative to traditional underpinning.
Geobear Solution
Geobear implemented a two-phase geopolymer injection strategy to improve the ground and re-level the structure.
Phase One: Ground Improvement
- A site investigation included three boreholes (5m deep) and a full-day drain survey.
- Identified desiccation reaching 4.8m below the basement level and a poor drainage system requiring prior structural repairs.
- The soil-bearing capacity was improved through geopolymer injections to 4.8m below ground, mitigating future clay shrinkage effects.
- Work was completed in 5 days with minimal disruption.
- A temporary steel structure was installed to support the building and allow controlled lifting.
- 38 injection points were placed around the front, rear, and outrigger over a 19m treatment length.
- Laser monitoring ensured structural stability throughout the process.
Steel frame to shore up building
Phase Two: Structural Lifting
- Engineering data from a brick course survey was used to design the lifting solution.
- Geopolymer injections were performed at 1m intervals around the full internal and external perimeter.
- The terrace-end wall, which had settled the most, received multiple targeted injections to restore alignment.
- The foundation (at 0.5m to 0.8m depth) was lifted using dual-material geopolymer injections.
- Laser monitoring confirmed a lift of up to 42mm.
- The property was restored to its original position in only 4 days.
Results and Key Benefits
Structural integrity was restored, preventing further movement and detachment from the adjacent local authority building.
Geobear completed the work in 9 days, compared to an estimated 9 to 11 weeks (45 to 55 days) for underpinning. This saved over 80 per cent of the project time, allowing renovations to begin much sooner.
Injections for lifting around frame
The project achieved significant carbon savings, reducing emissions by 1,481.48 kgCO₂e compared to traditional underpinning. This resulted in a 25.52 per cent reduction in carbon emissions by avoiding heavy excavation, concrete, and steel reinforcements.
Minimal disruption was ensured, as no excavation was required, allowing other trades to commence work immediately after lifting was completed.
Geobear provided full technical support, conducting multiple surveys and meetings to guide the client and structural engineer through the process.
The investor was highly satisfied with the outcome, impressed by Geobear’s expertise, innovative technology, and efficient project execution.
