Background
At a property in the South West UK subsidence had become evident after cracks appeared in the walls. Geobear was contacted in March 2019 to inspect the damage that was affecting the front left corner of the property and where cracks opened rapidly during the autumn of 2018. Geobear arranged a site investigation which revealed that clay soils had been subject to shrinking exacerbated by nearby trees.
Birds eye view of house and trees
Trees in close proximity to properties on shrinkable clay soil often cause clay shrinkage subsidence. Damage is not always uniform, as tree roots radiate to locations where nutrients (water/minerals) are available and in this instance, roots were clearly taking advantage of conditions around the front left corner alone.
The primary damage to the property was:
Lateral separation of the gable at the front facing (FF) bedroom window head (~25mm vertical crack)
Vertical (~15mm) cracking at the (FF) bedroom window cill (from downward movement of the front left corner foundation)
Lateral separation of the gable at the (GF) lounge window head (~25mm)
Repair solution
Geobear used its clay shrinkage subsidence solution to stablise the front end and gable wall of the property. The process involved the injection of a specialist geopolymer into the soils beneath the foundations. The material expands into the clay fissures and minimises any seasonal movement caused by shrinking of the clay soil.
The material expands into the clay fissures and the result is a reduction in permeability which creates a loss hospitable soil environment beneath the foundation so that roots from trees or other vegetation can no longer extract moisture from the area. This then minimises any seasonal movement caused by summer shrinkage or winter re-swelling of the clay soils.
Damage to rear of property
The property owner contacted Geobear again in October 2022 as there had been structural movement to a different area of the property. The new damage was again caused by roots of trees now withdrawing moisture from the soils at the rear of the property. This is likely to have been caused by the dry summer in 2022 and the inhospitable (relatively impermeable) soils to the front half of the property.
The damage to the rear of the property was:
Diagonal cracks indicating separation of the gable (2 No. ~10mm cracks)
Vertical <3mm internal separation cracking between gable and internal cross wall
Geobear repaired the rear of the property (see diagram 3) with its clay shrinkage solution. The principle of ground injection remained the same, but the lateral and vertical interventions were dictated by the area of movement.
Importantly, where a subsidence treatment has been implemented, there often needs to be appropriate masonry reinforcement or similar repairs to the superstructure, to prevent any minor movement in future that can result in hairline cracks in plasterwork. Geobear can advise on any such requirements. Click here to view our masonry repairs document
