Example: 20 × 0.6 m trench, 1.2 m deep
In-place geometry is 20 × 0.6 × 1.2 = 14.4 m³. If a project-specific measured factor is 1.20, loose haulage becomes 17.28 m³. With an assumed usable 6 m³ per load on the same loose basis, 17.28 ÷ 6 = 2.88, rounded to three loads. The 1.20 factor and vehicle capacity are example inputs, not recommendations.
Measure the excavation, not the pipe
Trench width and depth describe the actual excavation region. Pipe diameter does not determine them by itself. Working space, support and the designed section may create a different shape, and those decisions belong to the approved excavation method.
The rectangular model fits a constant-width section or a documented average. For changing depth, record sections and lengths. If the section has sloping sides, calculate its actual cross-sectional area rather than using the bottom width as if the sides were vertical.
Keep bank and loose volume apart
The volume before excavation is often called bank or in-place volume. Material after excavation is loose and can contain a different proportion of void space. A project-specific factor may convert between these bases, but the factor depends on the material and operation.
The trench tool's percentage field is an explicit factor. Leave it at zero when only calculating geometry, then add a verified factor if you need the corresponding loose quantity. Do not enter both an over-excavation factor and a swell factor into one unexplained number and then reuse it for backfill.
Backfill is its own material balance
Backfill space is not necessarily equal to total excavation volume. Pipe, bedding, structures and other retained materials occupy part of the trench. Deduct the external displaced geometry that the backfill cannot occupy, not the pipe's internal water capacity.
Some excavated material may be unsuitable for reuse or assigned to a different layer. Measure specified imported bedding and selected backfill separately. An excavation-volume calculation does not establish compaction, suitability, disposal acceptance or a reuse allowance.
Turn a verified loose quantity into loads
Match the haul quantity to the same volume basis as the truck's usable capacity. Payload limits can reduce usable volume for heavy material. Confirm the actual vehicle, site access, destination and applicable load constraints with the haulier.
The trench tool keeps its truck-capacity field in cubic yards even when trench dimensions are metric. Read that label carefully, or transfer the metric haul quantity into the dump-truck calculator, where quantity and capacity use the same selected unit. Do not type a cubic-metre capacity into a field labelled cubic yards.
Do it in order
- Measure the approved excavation shape in sections and sum in-place volume.
- Apply only a verified conversion if loose haul volume is needed.
- Use the actual haulier's capacity on the same basis and round final loads upward.
Planning boundary
A volume calculation does not establish a safe excavation method, side slopes, support, access or underground-service clearance.
Sources checked
Can I use the pipe volume as a backfill deduction?
Internal pipe capacity is not the external displaced volume. Backfill excludes the pipe's outside geometry and other installed materials.
Is 20% swell always appropriate?
No. It is only the stated example. Use a verified material- and project-specific conversion.