Conduction Area
During trench construction and pipe installation, appropriate measures must be taken to prevent soil, debris, or other foreign materials from entering the conduction area (12). At the same time, the movement of bedding or embedding material from the conduction area into the surrounding soil must be avoided.
The conduction area must remain stable throughout the installation process and should be protected against any foreseeable changes that could negatively affect its load-bearing capacity, stability, geometry, or position.
Potential causes of deterioration may include:
- Removal or collapse of the trench side walls;
- Infiltration or influence of groundwater;
- Excavation or other construction activities in adjacent areas;
- Movement of surrounding soil or excessive external loading.
The trench should be inspected regularly during construction, particularly after heavy rainfall or groundwater changes, to ensure that the conduction area remains stable and suitable for pipe installation.
Water Retention and Dewatering
During pipe installation, the trench must be maintained in a stable and adequately drained condition and kept free from standing water.
The selected dewatering method must not disturb the bedding, conduction area, surrounding soil, or installed pipeline. Pumping or drainage operations should be carefully controlled to prevent soil erosion, piping, settlement, or movement of the pipe.
Where groundwater is present, suitable drainage or groundwater control measures should be implemented before and during installation. Further requirements and recommendations regarding trench conditions and groundwater control should be followed in accordance with EN 1610.
Trench Width
For pipes installed using the electro-fusion socket jointing technique, large access openings or additional trench width specifically for welders are generally not required.
The trench width specified in EN 1610 or determined by the relevant structural/static calculation is normally sufficient. However, sufficient working clearance must always be provided to ensure that the electro-fusion welding equipment can be positioned and operated safely and without obstruction.
The trench should also provide adequate space for proper pipe alignment, bedding installation, compaction, inspection, and safe access for workers.
Compaction of the Conduction Area
The quality of the pipe embedding and surrounding soil has a significant influence on load distribution, pressure distribution, and the long-term deformation behavior of the pipeline.
Improper or insufficient compaction may result in excessive pipe deformation, reduced structural performance, or uneven loading. For this reason, the bedding and side-fill material must be installed and compacted carefully according to the project design and applicable standards.
For pipes with a diameter of DN/ID ≥ 1000 mm, it is recommended that the pendentive area beneath and alongside the pipe be compacted using suitable compaction equipment.
For pipes with a diameter of DN/ID ≤ 900 mm, the lateral compaction effect generated by the selected equipment is generally sufficient to achieve adequate compaction in the pendentive area, provided that the appropriate equipment and procedures are used.
Compaction Procedure
The pendentive area should be compacted carefully to provide continuous and stable support around the pipe.
- The soil alongside the pipe should be compacted using a suitable vibratory plate or other approved compaction equipment.
- In the pipe support and embedding zone, extending up to approximately 0.30 m below the pipe crown, only suitable embedding materials specified in the ATV A 127 requirements should be used where the lateral embankment width is at least 1.5 × da.
- Bedding and embedding material should be placed in uniform layers with a maximum thickness of 300 mm before compaction.
- Material should be placed on both sides of the pipeline simultaneously and in balanced layers. This helps prevent lateral displacement, rotation, or movement of the pipe during backfilling and compaction.
- Particular attention should be paid to the area directly beneath and beside the pipe, ensuring that the material fills all required spaces and provides continuous support without leaving voids.
- Compaction should be performed progressively and evenly. Excessive or concentrated compaction forces should be avoided, particularly when working close to the pipe wall.
- During the entire backfilling and compaction process, the pipeline must remain in its specified alignment, elevation, and position.
The required degree of compaction, expressed as Dpr, must comply with the values specified in the relevant static calculations and the requirements of ATV A 127.
Proper control of bedding, side-fill, backfilling, and compaction is essential for ensuring that the Krah pipe system can effectively transfer external loads to the surrounding soil and maintain its designed structural performance throughout its service life.
