Buried pipe systems

Last updated on Tue, 11/06/2012 - 15:06

Buried Pipe system

The SMU - Ensign Plus pipes can be used in below ground applications.
Buried pipes are subject to mechanical strain due to the weight of grounds and possibly wheel loading when they are laid under a circulating area.

The mechanical performance of a buried pipework is to be considered as a pipe/ soil system: the interaction of the pipes with the surrounding soils depends on their stiffness or flexibility, and the selected type of laying condition.
The choice of bedding and backfilling depends on the depth at which the pipes have to be laid, the size and the strength of the pipes. The standard EN 1610 “Construction and testing of drains and sewers” applies to drains normally buried in the ground and normally operating under gravity.

You will find below the hypothesis for rigid pipes retained for the calculation of allowable depth of cover.

  DN 100 à DN 300
Modulus of Young 110 000 N/mm²
Poisson's ratio 0.25
Max stress 350 N/ mm²
Strain coefficient 1.5
Buckling Coefficient 2.5
Geometrical defect 1,2 + DN/2000 mm

Installation parameters are laid down according to:

  •  Soil type (see groups below)
  •  Quality of compaction of the embedment
  •  Behaviour of the pipe (rigid for cast iron)
  •  Presence of wheel loads or not
  • Particular conditions (groundwater table…)

Backfilling recommendations from DN100 to DN300, with or without traffic loads (according to EN1610)

Two main solutions have been retained out of the EN 1610 recommendations, taking into account both ease of installation and knowledge from experience of rigid pipe systems. For compaction, the more adverse hypothesis was retained.
These solutions maximise the advantage from cast iron’s mechanical properties: depth of cover they can withstand, possible backfilling with native soil removed, thereby limiting the damage to the environment…

   

Dimensions are in mm.

* Detrimental materials = stones; tree roots; rubbish; organic material; clay lumps (>75 mm); snow and ice.

From our experience in buried pipe systems and the French origin of our company, we have retained French Fascicule 70 calculation model (recommendations for sewage pipe systems according to the pipe material).

The table below gives values for depths of covers according to the Fascicule 70 calculation, considering rigid pipes.

    Depth of cover values (m)
    Without traffic loads With traffic loads
Solution 1 Min** 0,3 (1) 1
  Max 3,2 2,4
Solution 2 Min** 0,3 (1) 0,3
  Max 6 (or 9) 6 (or 9)

** does not take into account the frost free arrangements
(1) The calculation allows shallower depth of cover, but this figure includes safety margin / ground surface proximity and related hazards.

Other precautions:

  • Clearance at each joint between the couplings and the granular bed to allow sufficient space and to prevent the pipe from resting on the joints. (see EN1610 §8.5.4)
  • Testing for pipe system leak tightness according to EN1610 §13.
  • Identification of the pipeline with a netting for example.
  • Furthermore, check that these specifications do not contravene to other local or national regulation or recommendations for installation.

For any other case, other diameters and buried systems under the bottom slab, please refer to the technical support.