# Earthwork

Only three tools, but together they cover the whole cut-to-fill chain. Cut volume comes from the pit geometry, side slope and working space in bank cubic metres; backfill converts the required compacted volume into loose volume for buying or hauling; compaction checks whether the field sample passes. All three have to use the same conversion basis, or the argument about why a thousand cubic metres of excavation will not fill the hole never ends.

The key is three states: bank, loose and compacted. A typical soil bulks 1.30 when excavated and compacts to about 1.15 of its bank volume. So 1000 m³ bank comes out as 1300 m³ loose and compacts back to roughly 870 m³ — the difference is loss and settlement. Imported fill is bought by loose volume and accepted by compacted volume; mixing the two bases puts a 30% error straight into the order.

- Category page: https://jianzhujisuan.com/en/c/earthwork
- Data checked: 2026-10-25

## Tools in this group

- [Earthwork Calculator](https://jianzhujisuan.com/en/earthwork): Enter pit dimensions and slope ratio to get cut volume, backfill and spoil to remove.
- [Backfill Volume Calculator](https://jianzhujisuan.com/en/backfill): Backfill volume, soil required, surplus to remove and truck loads.
- [Compaction Degree Calculator](https://jianzhujisuan.com/en/compaction): Dry density and compaction degree from field density, with a pass/fail check.

## Questions

### How is pit excavation volume calculated?

For a regular rectangular pit use the frustum formula V = h/6 × [ab + (a+a₁)(b+b₁) + a₁b₁], where a₁ and b₁ are the bottom dimensions including working space and a, b are the sloped top dimensions. Side slope factors run 0.33 for class I soil, 0.25 for class II, 0.33-0.5 for class III and 0.5-0.75 for class IV. Working space is typically 300-800 mm per side.

### How much backfill do I need to buy?

The design backfill volume is compacted; purchased soil is loose. Loose volume is roughly compacted volume × 1.30, and estimating on that basis is usually safe. Deduct the volume occupied by foundations, blinding and buried services — that deduction is the most commonly forgotten step.

### How is the degree of compaction calculated?

Field dry density divided by the laboratory Proctor maximum dry density, as a percentage. Field density comes from a sand replacement or core cutter test. Basement backfill usually requires 0.94 or better, road subgrade 0.93-0.96, per the design. If moisture is more than 2% away from optimum, compaction will not reach the target — dry or wet the material first.