content_image/499061.jpg
## 5.3.9.4 Foundation and Bedding 

Unless specified otherwise, pipelines shall be laid in trenches excavated in the ground conforming to the above section "Excavation for pipes in trenches". Unless unsuitable soil is encountered, trenches shall be excavated to 250 mm below the barrel of the pipe and prepared conforming to the following. 

On the trench bottom sand bedding shall be laid to a compacted thickness at least 200+(D/100)mm. The bedding sand shall comply with TS EN 1610. Pipe bedding to concrete pipes shall contain no more than 0.3% sulphate. The bedding shall be compacted to 95% of the standard maximum dry den- sity. The level tolerance for the bedding shall be 10 mm. 

For pipes over 400 mm, the height of the bedding shall be 5% of the diameter plus 250 mm. The addi- tional layer shall be shaped concentrically with the pipe along the bedding angle. Where pipes are jointed, bell holes of ample dimensions shall be formed in the bedding to ensure that each pipe is uni- formly supported throughout the length of its barrel and to enable the joint to be made. Care shall be executed to assure that the cavities under the pipes are filled with bedding material and compacted thoroughly. 

Pipes shall be laid on sufficient setting blocks only where a concrete bed or cradle is used. 

Pipe bedding material shall be imported to the site. 

The bedding material shall be spread over the full width of the foundation and lightly hand compacted to a level slightly higher than the level corresponding to the underside of the pipe barrel to allow for settlement of the pipe to the correct level. 

For embedding of pipe, sand or other approved granular material shall be placed in the trench, special care being taken to fill under the sides of the pipe to ensure full contact with the barrel of the pipe, but leaving the joint exposed for a length of approximately 200 mm on each side of the joint collar, sleeve or socket. The granular material shall then be compacted evenly on both sides of the pipe. 

Clay, or other approved impermeable material barriers shall be constructed to limit the uninterrupted length of granular bedding and backfill to a maximum of 500 m. 

According to the pipe type, the grading range must be specified according to the sieve diameters for the backfill material. Here is an example: 

## Bedding-embedding: 

For HDPE Pipes: 0-20 mm sand-gravel (well graded) (maximum 20% moisture content, suitable for compacting) 

For Concrete/Reinforced Concrete pipes and Manholes: 0-31.5 mm (gravel or boulders in fraction well graded) 

## Backfilling: 

<img src='content_image/499061.jpg'>

