What is soil stabilisation?
Soil stabilisation is improving the existing soil on site by mixing a binder such as lime or cement into it, so that it becomes stronger, stiffer and easier to work. Instead of digging out soft ground and carting it away, you make the soil that is already there suitable as a base for, say, a road, car park, industrial floor or site working platform.
How it works
- Lime (usually quicklime) is mainly used on wet clay. The lime reacts with water, drying the soil, and then reacts with the clay particles. The clay turns crumbly, compacts better and gains strength over time.
- Cement is mainly used on sandy and silty soils. It binds the grains into a firm layer that deforms less.
- Combined binders of lime and cement are used when the soil calls for it.
The binder is spread, mixed into the top layer with a rotavator-type stabiliser and then compacted. Mechanical stabilisation also exists: compaction, or adding aggregate and geotextile without a binder.
Application
- Start with a soil investigation. Soil type, moisture content and the bearing capacity you need determine the binder and dosage. This is established in a laboratory beforehand.
- Watch for sulfates. Soils high in sulfate can swell after treatment with lime or cement. This should be covered in the preliminary testing.
- Work in dry weather. Mixing binder into waterlogged or frozen soil produces a weak layer.
- Protect yourself. Quicklime and cement are caustic. Wear a dust mask, safety glasses and gloves.
- Small projects. For a shed or patio, soil stabilisation is usually overkill. Well-compacted crushed stone on firm, dug-out ground is often enough.
Common mistake: thinking stabilisation replaces a foundation. A stabilised layer improves the subgrade, but a building’s foundation remains a job for the structural engineer.
Related terms
- Ground improvement
- Soil compaction
- Soil investigation
- Soil type
- Quicklime
- Cement
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