Groundwork Excavation Calculator — Volume, Swell & Lorry Loads

Swell (bulking) factor is the increase in volume when soil is excavated and loosened. Typical working values: topsoil about 25% (factor 1.25), clay about 30% (1.3), sand/gravel about 15% (1.15), chalk about 40% (1.4), and rock about 50% (1.5). Bulking is genuinely variable — it depends on moisture, plasticity and the dig method — so treat these as mid-range figures (cross-referenced to BGS Civils bulking data) and verify for your site material. You need to account for swell when calculating lorry loads and disposal volumes, as the loosened material takes up more space than it did in the ground.

Loads are limited by whichever fills the lorry first — VOLUME or WEIGHT — so this calculator takes the greater of the two counts. A standard 8-wheeler tipper holds about 8 m³ of spoil and carries up to ~20 tonnes (GVW 32t); a 6-wheeler about 6 m³ / ~16 tonnes; an artic about 12 m³ / ~29 tonnes. For a typical 50 m³ clay excavation: 50 × 1.3 swell = 65 m³ swelled. Volume path: 65 ÷ 8 = 9 loads. Weight path: 50 × 1.9 t/m³ = 95 t, 95 ÷ 20 = 5 loads. The greater is 9, so you need 9 loads in an 8-wheeler. Heavy, dense soils can make the weight path govern on smaller tippers. Always round up to whole loads.

These are effective rates (loading and repositioning included), not peak machine rates. A mini digger (1.5-3 tonne) excavates approximately 5-8 m³ per hour in normal conditions. A larger 8-tonne excavator can manage about 15-20 m³ per hour effective. Peak rates are higher (a 6-10 t machine can dig 20-40 m³/hr before applying the usual 50-83% efficiency factor), but productivity also varies with soil type (rock is slower), depth, access, and weather. Allow extra time for setting up, moving equipment, and loading lorries.

Disposal costs in the UK vary by soil type and location. Clean topsoil/subsoil: £150-250 per lorry load. Contaminated soil: £350-600+ per load requiring specialist disposal. Landfill tax adds significantly to costs. If the soil is clean, consider offering it free for collection or reusing it on site to reduce disposal costs. Need to bring in fresh topsoil? See our Topsoil Calculator.

Soil density varies by type: topsoil approximately 1.6 t/m³, clay 1.8-2.0 t/m³, sand/gravel 1.8 t/m³, chalk 1.7 t/m³, rock 2.0-2.5 t/m³. These are in-ground densities — the weight per cubic metre matters for lorry payloads. An 8-wheeler tipper carries up to about 20 tonnes, so with clay at 1.9 t/m³ that is roughly 10.5 m³ by weight; in practice a tipper body holds around 8 m³ of spoil, so volume usually fills the lorry before weight does on lighter soils.