Excavation, bedding and backfill

A trench must not affect the stability of the building. Trenches should not be open too long in advance of pipe laying and should be backfilled as soon as possible. Trench widths should be as narrow as practicable, but not less than the 410mm to allow adequate sidefill to be placed.

Deeper excavations should ideally incorporate a sub-trench.

Bedding is the layer of material underneath the pipe. The in-situ soil (as dug material) may be suitable, but it must be inspected to ensure there is no sharp material (i.e. broken bricks) or a particle size which is more than 20mm.

If the as-dug material is not suitable, a granular material with a nominal 10mm particle size to BS EN 1610 should be used.

When the pipes are to be laid in rock, compacted sand or gravel, or in very soft or wet ground the bedding should be a minimum of 100mm.