How to use it
- Enter the trench length, depth and bottom width.
- Enter the side slope as horizontal per 1 vertical, or 0 for vertical sides with shoring.
- Enter the pipe's outside diameter, the bedding under it and the surround above it.
- Set the bulking factor for your soil; 25% suits most common soils.
Worked example
A 50 m trench, 1.5 m deep and 0.6 m wide with vertical sides, holds a 160 mm pipe on 100 mm of bedding with 300 mm of surround above. The excavation is 0.6 × 1.5 × 50 = 45.0 m³. The pipe zone is 0.56 m deep, so it takes 15.8 m³ of bedding material after subtracting the pipe. Backfill above it is 28.2 m³. With 25% bulking, about 56 m³ of loose soil comes out, and 21.0 m³ of it is surplus to haul away.
Bank and loose volumes
Soil in the ground is called bank volume. Once dug, it loosens and takes up more space, which is the loose volume you pay trucks to move. Compacted backfill ends up smaller than the loose volume again, so the calculator reports the trench volumes in bank terms and the spoil in loose terms.
Frequently asked questions
How wide should a pipe trench be?
Wide enough to place and compact the pipe surround on both sides. Many specifications use the pipe outside diameter plus 300 to 600 mm, with a practical minimum for the excavator bucket and for workers to enter safely.
When does a trench need shoring or sloped sides?
Rules vary by country, but trenches deeper than about 1.2 to 1.5 m (5 ft in the US under OSHA) generally need a protective system such as shoring, a trench box or sloped sides, unless in stable rock.
What is the swell factor of soil?
It is how much soil expands when dug. Sand and gravel swell around 10 to 15%, common earth around 25%, clay 30 to 40%, and blasted rock 50% or more.
What material is used for pipe bedding?
Usually a clean, granular material such as sand or small single-size gravel, placed and compacted around the pipe. The pipe manufacturer and local specification set the grading and thickness.