Why compact?
- Compaction strengthens the fill and the road. It reduces the risk of fill movement or settlement on steep or unstable slopes.
- It reduces the amount of road metal needed as road subgrade is stronger.
- It helps protect or “seal off” earthworks from water penetration.
- It can reduce repair and maintenance costs.
Which compactor for the job?
- Compactor selection depends on the material.
- Sheep or wedge foot rollers are the most useful in formation construction.
- Vibrating drum rollers (smooth) are useful for sealing aggregate.
- Heavy compactors work better.
- Loaded metal truck wheels compact.
- The correct compactor – a vibrating sheepfoot – has been used.
- Optimum moisture content ensured good compaction. This varies depending on the material.
- It is compacted in layers. The layer thickness is right for the material – it should not be more than 300 mm.
- The material is not over-compacted.
- Wide tracked machines apply low ground pressure even though they are heavy.
- Dozers (and excavators) are not compactors.
- Track rolling only gives minor compaction, but it tightens the fill by breaking down larger material.
- The metal is being compacted with the correct compactor – a vibrating steel drum.
- The aggregate is compacted in layers less than 150 mm.
- Excessive vibrating rolling has brought moisture to the surface and hasn’t improved the result.
- Do not try to compact wet or very dry materials, as these may become liquid.
- Correct the moisture content by blending in other material or using a water cart for dry material.
- Penetrometers are useful for identifying subgrade weaknesses.
- They are good for finding problem areas along roads and tracks before grading.
- They also show that the subgrade has met compaction standards.
- Lack of compaction led to this major road failure.
- Water will enter the tension cracks and make the fill even less stable.