Depth of cover

Technical solutions

The minimum and maximum depth of cover depend on the pipe characteristics and the laying conditions.


By convention, manufacturers make a distinction between:

  • the backfill area. ;
  • the careful backfill area comprised of:
    - the trench bottom and pipe surround backfill up to at least 0.10 m above the assembly crown for flexible pipes;
    - the trench bottom and surround up to the horizontal diameter for rigid pipes
  • the extant soil.

The backfill zone conditions the pipe stability and/or protection. Its execution must meet variable demands depending on:
- the pipe characteristics (rigid, semi-rigid, flexible);
- the external loadings (depth of cover, wheel loads);
- the more or less rocky or heterogeneous nature of the ground.

The backfill zone varies according to the area involved (rural, semi-urban or urban), and has to take road stability into account.

Other constraints also affect the laying conditions:
- keeping the pipe frost-free (minimum depth of cover),
- passing through critical safety areas (railways, motorways, etc.), which require special arrangements,
- current regulations and local requirements applicable to roadways.

See also

Ductile iron pipelines and unstable ground
Earthworks laying recommendations.
The various types of pipes can be divided into three categories, depending on their performance.