Ground in its natural state is packed tight. Dig it up and it loosens, taking up more space. This is swell, and it's why excavation jobs so often need more skips or grab lorries than planned.
Bank, loose and compacted volume
- Bank volume: the volume of the hole, as measured.
- Loose volume: what the dug material occupies on a truck or in a pile, which is bank × swell factor.
- Compacted volume: what it occupies after rolling or tamping back into place, often less than bank.
Typical swell factors
| Material | Swell |
|---|---|
| Sand and gravel | +10–15% |
| Common earth / loam | +20–30% |
| Clay | +30–40% |
| Rock, broken concrete | +50–80% |
Pricing removal
Skips are sold by volume (yards), but most also have weight limits for heavy waste such as soil and rubble. Grab lorries usually carry about 16 tonnes. Check whether they price by load or by tonne.
Backfill
When filling, work the other way. To end up with a compacted volume, you need more loose material, typically 15–25% more for granular fill. Order accordingly.
Before you dig
Get utility plans and use a cable avoidance tool (CAT) before digging. Assume services are there until proven otherwise.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.