Collapsible soils: sudden settlement on wetting
Some dry, loosely structured soils are stable until they get wet. Water from leaks, irrigation or a rising water table then breaks the bonds between grains, and the ground collapses under load.
How it is recognised
- Dry, low-density silty or sandy soils, common in arid regions.
- Collapse potential measured in laboratory tests when samples are wetted under load.
- A history of settlement near leaking pipes or landscaped areas.
Why it matters
Collapse settlement is sudden and can be large and uneven. It often appears years after construction, when water first reaches the soil.
Methods usually considered
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DC
Dynamic Compaction
Deeper collapsible layers over open areas.
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RIC
Rapid Impact Compaction
Shallow-to-moderate depths, with closer control.
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HEIC
High Energy Impact Compaction
Near-surface layers over large areas, sometimes with moisture conditioning.
Which method fits depends on the site investigation and the performance requirement. More than one may be combined.
How the choice is made
- Depth and thickness of the collapsible layer.
- Measured collapse potential.
- How likely the soil is to be wetted during the life of the structure.
- Size of the area and neighbouring structures.
How the result is verified
Treatment is verified by in-situ tests before and after and, where specified, by laboratory collapse tests on samples from the treated ground.
Tests typically used
Other ground problems
Have this ground problem on your site?
Share the site investigation report and the performance requirement.