Excavation and muck-away calculator

How much comes out of the ground once it's dug: the volume in the ground, the bulked volume by soil type, the tonnes, and the skips or grab lorry loads to take it away.

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Worked example

A foundation trench 14 m long, 600 mm wide and 1 m deep in clay:

10.92 m³ to take away once dug

8.40 m³ in the ground × 1.30 bulking for clay
About 16.8 tonnes
2 × 8 yard skips, or 2 grab lorry loads (about 16 t each)

How the sum works

The volume in the ground is length × width × depth. Once dug, soil loosens and takes up more room: that's bulking. The calculator multiplies by a typical bulking factor for the ground you choose (about 1.25 for topsoil, 1.3 for clay, 1.15 for sand or gravel, 1.4 for chalk, 1.3 for mixed made ground and 1.5 for soft rock). If you know your own figure, type it in.

Tonnes come from a typical in-ground density for each type (about 1.9 to 2.1 t per m³ for most soils). Skips hold about 4.6, 6.1 or 9.2 m³ for 6, 8 and 12 yards; a grab lorry is counted at about 16 tonnes a load.

Before you book it

Bulking factors and densities vary with the ground and how wet it is, so treat the figures as a good estimate. Skip firms limit the weight as well as the volume, and many won't take heavy soil in a big skip: ask before you book. Spoil kept on site must be stored away from the edge of the excavation (see HSE on excavations), and muck-away needs the right waste paperwork.

Guides that go with it

When does an excavation have to be inspected under CDM 2015?When a competent person must inspect an excavation under CDM 2015 regulation 22, when the report is due, and the main risks and controls for builders.What is the waste duty of care for builders in England?Waste duty of care for builders in England: your own waste, checking carriers, waste transfer notes, hazardous waste notes and what householders do.How to calculate how much concrete you needFree concrete calculator for slabs, footings, trench fill and round piers, in m3 with extra for waste and the number of bags. Worked examples and ordering ready-mix.

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