Laying

Laying - B

What are the bedding requirements for PE pipe?

Customers normally advise that trench bottoms should be excavated to provide a reasonably even bed along the pipe length and free of sharp stones or other objects that could damage the pipe. Sand for pipe bedding should be used where possible and soil containing sharp, angular gravel or cobbles should not be used for bedding of PE pipe. The depth of the trench should be suitable to provide the required cover when reinstated.

PE pipes having a protective outer sheath (multi-layer) may be laid in heterogeneous ground without sand bedding thus allowing a wide range of excavated materials to be re-used.

Where the pipe is to be laid through rock or ground of variable consistency, customers normally advise that the trench should be excavated approx. 75mm below its normal depth, and a bedding material placed before the pipe to provide a bed of suitable consistency.

Where the pipe is to be laid through contaminated ground then the soil should be checked to determine if it would bechemically aggressive to PE. If necessary the aggressive material should be removed and imported bedding and backfill should be used.

What levels of productivity can be achieved in PE pipe installation?

PE can normally be installed much more quickly than most other pipe materials.

The productivity of laying PE, from excavation to reinstatement and commissioning, depends on a number of factors; environment (urban or rural), ground type and condition, surface reinstatement (road or unpaved), etc. The most important influence is the installation technique employed;trenchless techniques and chain trenching in particular can increase productivity significantly.

Factors that improve productivity are:

Ease of site handling of PE pipe due to its flexibility and low weight
Use ofcoils andlong lengths of pipe, minimising the number of joints
Ease of jointing bybutt fusion or electrofusion
Ability of pipe to be jointed above ground to provide long pipe strings
Use of narrow trench techniques
Use of trenchless or minimum excavation techniques

In urban environments using conventional open cut techniques, laying rates (excavation to reinstatement and commissioning) are typically in the following ranges:

100m per week per installation team for larger diameters
200m per week per installation team for smaller diameters.

The equivalent rate for Ductile Iron or Steel in similar circumstances is typically 60m per week per installation team. Generally for open cut installation there is at least a 50% increase in installation productivity for PE compared with Ductile iron or Steel for the equivalent pipe sizes and environments.

Using alternative installation techniques, for example trenchless techniques and chain trenching, which are ideally suited to PE pipes, the laying rates can be significantly increased with up to 500m per week per installation team easily achievable in certain conditions.

The increased productivity also leads to lower cost of installation. This cost advantage of PE is more significant at smaller diameters.

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