Buried Installation of PE Pipes – Fundamentals
Brief Description
The installation of polyethylene pipes in the ground can be carried out using several fundamentally different methods. The choice of method depends on route conditions, the available infrastructure, depth of cover and the specific requirements of the project.
Why This Topic Is Relevant in Practice
The installation method largely determines the stresses the pipe is subjected to — both during installation and during the subsequent operational phase. A buried installation that is inadequate in terms of bedding, compaction or method selection may compromise the long-term performance of the overall system.
Technical Principles
Open-Cut Installation
In open-cut construction, a trench is excavated along the route. The pipe is placed and covered in stages. Important aspects include:
- trench geometry (width, depth, slope stability),
- bedding material (grading, compactability),
- compaction of the backfill zones (pipe zone, main backfill zone, surface layer),
- protection against point loads (stones, sharp-edged material).
Open-cut installation allows well-controlled bedding conditions, but it requires significant space and surface access.
Trenchless Installation Methods
For trenchless installation, the pipe is inserted into the ground without continuous excavation. Common methods include:
- Horizontal Directional Drilling (HDD): a steered bore followed by pull-back of the pipe string. Design considerations include pull-in forces, bending radii and buoyancy in the borehole.
- Ploughing: a cable plough draws the pipe into the ground. The method is common in rural infrastructure.
- Impact Methods: e.g., impact moling or pipe ramming. Depending on the method, these may be suitable for short crossings.
Each trenchless method imposes specific additional stresses on the pipe during installation. These must be taken into account in the design.
Rehabilitation
If existing infrastructure is to be renewed, several approaches exist:
- Pipe Bursting (Berstlining): the old pipe is burst on line whilst a new pipe is drawn in simultaneously.
- Relining / Close-Fit: a new pipe is inserted into the existing conduit.
- Renovation and Renewal: various techniques depending on the condition of the old pipe and the diameter range.
The selection of the rehabilitation method is governed by the condition assessment of the old system, soil and space conditions, and the required performance of the new system.
Typical Influencing Factors and Boundary Conditions
- Soil Type: cohesive vs. non-cohesive soils significantly affect both trench stability and compaction behaviour.
- Groundwater: waterlogged conditions can require dewatering or buoyancy safeguards.
- Existing Services: route crossings or parallel runs with other utilities determine placement and installation choice.
- Temperature: cold conditions increase stiffness and reduce permissible bending.
Standards and Regulatory References
For the design of buried PE pipe installations, the following may be particularly relevant:
- DIN EN 12201 as the system standard for water applications,
- DIN EN 1555 for gas applications,
- DVGW GW 321 and GW 322 for trenchless installation techniques,
- DWA A 139 for open-cut construction and trench geometry,
- DWA A 127 for the structural assessment of buried pipelines.
Note on Project-Specific Verification
The choice of installation method and the assessment of stresses during and after installation must always be project-specific. For approximate assessments of trenchless installations, tools such as the Bore Profile Calculator, the Pull-In Force Calculator and the Bending Radius Calculator can be used.