The underground installation of polyethylene pipes is similar to the installation of other flexible pipes. The performance of the pipe depends on the quality of its installation. Most polyethylene pipes are considered flexible, which means that pipes installed for non-pressure purposes are partially dependent on the retention of the overlying soil. Installing flexible pipes is often different than installing rigid pipes, but the general requirements are the same for both types of pipes. The thin trench minimizes the load on both types of pipes. Both types of pipes require a firm and stable bed and uniform support under the back strap. The main difference between these two types of pipes is that non-compressive flexible pipes require lateral support, while rigid pipes do not. Lateral support is the result of placing strong and stable materials on the side of the pipe. In most cases, these materials are the same materials that are used next to rigid pipes, with the difference that these materials must be compacted in flexible pipes. Sufficient space should be provided along the length of the pipe to compress the lining material. The embankment of the trench that is placed on the pipe should be implemented with the same method in flexible and rigid pipes. The more dense the material on the pipe, the smaller the load will be on the pipe.

Polyethylene pipes have beneficial interactions with the topsoil. The viscoelastic properties of polyethylene pipes and most soils are the same. When the pipe is bent, most of the earth load is transferred to the soil around the pipe due to the buckling action. Therefore, next to the pipe, we need stable soil. Rigid pipes are usually made of materials that are not compatible with soil deformation. As the soil settles, the load accumulates on the rigid pipes. If this load exceeds the breaking capacity of the primary material of the pipe, the pipe will be damaged by bursting or breaking suddenly. Polyethylene is a tough material that can withstand. Polyethylene pipes deform under excessive loads without cracking. The amount of deformation is often sufficient to release the amount of accumulated stress, so pipe performance is not impaired.

Bending is usually the primary criterion for judging the performance of flexible gravity flow pipes. The amount of bending of polyethylene pipes installed in pressurized applications is usually not an important consideration, unless the pipes are deep in the embankment and have a high aspect ratio. Pipes that have the ability to bend have 2 advantages over rigid pipes: (1) bending causes the release of accumulated stresses and the occurrence of buckling, which in turn causes the uniform distribution of earth pressure around the pipe and (2) Bending can be used as an easy way to inspect the quality of the installation – in general, the less bending, the better the installation.