Residential ground improvement
Challenge
Gradual settlement of made ground beneath a two-storey extension in Matlock caused the structure to pull away from the original property, resulting in visible cracking.
Solution
Geobear delivered a targeted geopolymer injection solution beneath the 0.5m deep strip foundations to compact and stabilise the made ground without excavation or underpinning.
Foundation depth
Injection holes
Monitoring accuracy
The site is a two-storey brick residential property built in 1970, located in Matlock, Derbyshire, featuring a two-storey rear extension. Site investigations, including boreholes and trial pits, revealed that the soils directly beneath the property consisted largely of made ground, characterised as medium compact black and brown slightly gravelly sandy clay containing brick and concrete debris. The structure was supported by strip foundations at an assumed depth of 0.5m below ground level.
The two-storey extension was actively pulling away from the original building, causing visible cracking at the rear junction. A structural assessment and site investigation confirmed the movement was not caused by clay shrink-swell subsidence. Instead, the damage resulted from the progressively gradual settlement of the underlying made ground.
The settlement was potentially exacerbated by localised water ingress from nearby defective pitch fibre and PVC drainage runs, which may have contributed to weakening within the fill materials beneath the extension.
Because the movement was attributed to the settlement of made ground rather than insured subsidence, the building insurance claim was repudiated by the loss adjuster. This left the homeowner seeking an independent, evidence-led, and cost-effective repair solution.
A further complication was the close proximity of live drainage infrastructure to the treatment area. The ground improvement works needed to be carefully controlled to avoid any geopolymer ingress into the adjacent foul drainage network.
Geobear designed a bespoke geopolymer injection programme to consolidate the settling made ground directly beneath the extension foundations. Using hand-held combi drills, technicians created a series of 12mm to 16mm diameter injection holes through the structure into the treatment zone below.
Expanding geopolymer resin and hardener were then injected via 12mm steel tubes driven into the soil. Once introduced into the ground, the material expanded up to 10–15 times its liquid volume, filling voids and compacting the surrounding granular fill and clay matrix.
To protect the adjacent drainage infrastructure, a pre-treatment CCTV drain survey was undertaken. The pitch fibre foul drains were then continuously monitored via CCTV throughout the injection process to ensure no resin ingress occurred.
Ground movement and lifting were controlled using digital monitoring equipment and a tripod-mounted spinning laser system. The injection process was immediately paused as soon as movement was detected, with lift tolerances controlled to within 0.5mm accuracy. This ensured effective ground compaction while preventing over-lift or additional stress to the masonry structure.
The Geobear solution successfully improved the made ground beneath the two-storey extension, mitigating the risk of further settlement and rotational movement.
The treatment was completed without the need for traditional underpinning, excavation, spoil removal, or heavy construction equipment, significantly reducing disruption to the homeowner and shortening programme duration.
The use of portable hand-held drilling equipment and compact 110V truck-mounted pumps enabled the works to be delivered efficiently within a constrained residential environment. Following stabilisation, the homeowner was able to confidently proceed with self-funded structural and cosmetic masonry repairs.
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