All flexible pipes require the passive support of the surrounding soil to prevent excessive ovalization under the vertical loads; it is, therefore, important to define the correct installation procedure.
In general the pipe must be uniformly supported by a well graded and compacted bed made of 150-200 mm of granular material like sand or gravel. The same material shall also be used to fill the sides of the trench.

Trench cross section

The compaction of the backfill is very important because, regardless of the stiffness of the pipe, it is the soil that limits the ovalization. The entire pipe must be surrounded by sand or gravel. The dimension of the largest grain must not exceed the thickness of the pipe.

When the pipe is installed in unstable soils it is a good practice to provide a foundation of coarse gravel under the bedding

Installation method 1

The vertical deflection - ovalization - of the pipe must be frequently checked and must not exceed 3% of the pipe diameter.
When the pipe protrudes from a rigid structure such as an anchor block or an inspection manhole a bell and spigot joint must be placed within 2 pipe diameters as shown on the following figure:

PLAN

Rubber band

Increased bed thickness
SECTION

This will provide enough flexibility to prevent that the pipe is damaged by differential settlement.

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