Worked example — French drain (trench filled with gravel) — Trench length 20, Trench width 40, Trench depth at the high end 60
Excavation: 5.600 m³ · Total fall over the length: 0.20 m · Pipes to buy: 4 · Gravel: 5.987 m³ · Geotextile: 40.00 m²
Drainage Quantities (trench, gravel, pipe)
Enter the length, width and depth of the trench and the fall of the pipe. PRAXAO works out the excavation (the trench deepens towards the outlet), the gravel, the soil backfill when the pipe sits in a gravel surround, the geotextile and the number of pipes. The drawing shows the trench in 3D, its section and its profile along the fall. Widths, depths, surround, overlap and compaction are starting values to replace with the drawings.
Enter the dimensions to see the drawing.
Calculation results
Fill in the fields to see the result.
Preliminary estimate from the values entered: not a structural validation and not an execution plan. Check the local rules and the manufacturers’ data.
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Results are provided for information. Check tax rates and legal requirements that apply to you.
How to use it
- Choose a French drain (all gravel) or a pipe in a gravel surround.
- Enter the length, width and depth of the trench, the fall and the pipe size.
- Replace the starting values (bed, cover, overlap, compaction) with the drawings’.
- Read the excavation, gravel, backfill, geotextile and pipes to buy.
Examples
Frequently asked questions
Does it size the drain?
No. It counts what a set of dimensions requires. The pipe size for a flow, the fall suited to the soil, the outfall and the geotextile choice come from the engineer.
Why is the excavation deeper than the depth entered?
The depth is taken at the high end. The pipe falls towards the outlet, so the trench is deeper there by the total fall; the volume uses the average depth.
How is the gravel counted?
It is the volume it fills minus the volume of the pipe, increased by the compaction allowance. In a French drain it fills the whole trench; with a pipe it fills the bed, the pipe and the cover.
Guides to go further
BUILNORA
How to count a drainage trench: gravel, pipe and geotextile
Excavation, gravel, backfill, geotextile and pipes of a drainage trench: the method, with an example.
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