Ground improvement is the process of making soft or inadequate subsoil fit for building by replacing, compacting, draining or strengthening the ground. The aim is to raise the bearing capacity and limit settlement, so that a foundation can be built safely and without tilting.
Methods of ground improvement
- Excavate and replace — remove the soft soil and backfill with well-compactible sand or crushed aggregate (a sand blanket). Common for shallow soft layers.
- Preloading — temporarily raise the site with extra soil so the subsoil settles (consolidates) before building.
- Vertical drains — install vertical drains that let pore water escape faster, so the soil consolidates more quickly.
- Soil compaction — densify the existing ground with vibrating rollers, drop weights or vibro techniques.
- Grouting and stabilisation — strengthen the soil with cement, lime or injection grout.
Applications
Ground improvement is used when a shallow foundation is not possible but an expensive piled foundation can be avoided. Examples:
- Preparing building sites in soft clay and peat areas
- Roads, car parks and industrial floors on weak subsoil
- Embankments and flood banks
The choice of method depends on the soil type, the thickness of the soft layer, the groundwater level and the allowable settlement. A site investigation beforehand is essential.
Related terms
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