Compaction information from Electronic Blueprint for architects

Soil compaction is;

• the application of energy to loose soil,
• to consolidate it, and to remove air voids,
• thus increasing its ability to support vertically applied loads without settlement.

Loose soils consolidate and settle when subjected to vertical pressure from buildings, retaining walls or vehicles. When a heavy load is applied to a soil, there may be some elastic deflection (i.e. the soil partly springs back to its original position after a load is removed). However, most of the settlement is irreversible and results from the expulsion of the air and water from within the soil.

The purpose of mechanical compaction by rollers, plate vibrators and the like is to reduce the air voids during construction, increasing the in-situ density. This has the following beneficial effect.

• Increasing the bearing capacity;
• Reducing the incidence of further in-service consolidation and settlement;
• Reducing the shrink / swell effect in reactive soils.

Architects should ensure that designs and specifications make proper provision for adequate compaction, and that tender prices allow for the level of compaction specified in these documents.