Excavation and trench volumes with the working space included
Calculating excavation for trenches and pits including working space, which is usually larger than the structure itself.
The engineering question
Who pays for the soil that has to be removed to get to the structure? How is excavation volume actually measured on site?
Worked example
The figures below were produced by running the Trench Excavation & Bedding Calculator with the same inputs .
These figures are worked by the published method rather than executed at build time, because this tool is a self-contained page calculator without a programmatic engine.
- Trench volume is length × width × depth, using the excavated width rather than the pipe or service width.
- Working space either side, plus any batter, is part of the measured excavation and not a separate item.
- Spoil volume then follows from the bulking factor applied to the in-situ volume.
Sanity check
A 25 m trench 1.5 m deep at 0.6 m wide is 22.5 m³. If the commercial measure is materially larger, the extra is working space — which is a real cost and should be priced.
Tools for this problem
These are the EngiMetric calculators that compute the numbers in this topic. Each one shows its formula, its units and its limits rather than returning a bare result.
References & standards
- BS 6031 — earthworks
- UK DMR 3.2 — ground investigation
Related problems
Balancing cut and fill, and what happens when the volumes do not match
How excavation, compaction and bulking change the numbers, and why a balanced site is almost never balanced on paper.
Checking a retaining wall will not overturn, slide or sink
The three limit states every retaining wall must satisfy, and which one usually fails first on a narrow base.
Also: Geotechnical