• Excavation: 
  it is important to take precautions against trench collapse. Do not open 
  trenches too far in advance of pipe laying. Support the sides of trenches
  that are deeper than 1.2 meters.
  Keep trench width as narrow as practicable but not less than 300mm wider 
  than the pipe diameter, i.e. 150mm clear each side of the pipe to allow
  proper compaction of the side fill. 
  Excavation for Manholes and Inspection Chambers.
  Additional excavation is necessary for : 
  I. Traditionally constructed  manholes.
  Ii. 750mm Manhole base.
  Installation note:
  The information included in this section is based on the recommendations 
  given in BS5955: part 6: 1980 "code of practice for plastics pipe work".
  (Installation of unplasticised uPVC pipe work for gravity drains sewers).
  Laying of pipes: 
  General: all pipes fitting and valves shall be carefully lowered into the 
  trench using suitable equipment in such manner as to prevent damage to pipe
  and fittings. Under no circumstances shall the pipes be dropped or dumped 
  into the trench. 
  Pipe and fittings should be inspected for defects prior to lowering into 
  the trench. Any defects or damage must be replaced before lowering the
  pipeline into the trench.
  The open ends of the installed pipes should be closed to prevent entrance
  of foreign materials in the pipeline.
  
  Bedding and back filling:
  General:
  the flexibility of uPVC pipes and joints help them to withstand damage 
  resulting from ground movement or from other differential settlement. 
  They derive and important part of their strength from the support of 
  bedding side fill. The horizontal resistances of the side fill limits
  any horizontal deflection of the pipe caused by the vertical load.
  A state of equilibrium is reached when the horizontal reaction corresponds
  to the transmitted vertical load. The recommendations which follow will
  ensure that, should deflection occur, it will cease at an acceptable 
  level and be limited to less than 5% of the pipe diameter.
  Excavated "as-dug" material may be suitable, otherwise a non-cohesive
  material is needed bedding and back filling must be as follows:
  Bedding sequence:
  
  Bed and backfill as follows:

1. Trim excavated base, removing projections and hard spots.

2.  If the "as-dug" material is suitable for use as bedding, trim the bottom 
   of the trench to from the pipe bed.Reloosen bedding along the pipe and its 
   coupler. Then lay the pipes, holding them in position with a small banking 
   of bedding material. Do not use bricks, blocks or timbers.

3.  if the "as-dug" material is unsuitable, over dig trenches to allow for a 
   minimum 100mm bedding. If the ground is wet or very soft more it may be 
   necessary to allow for more bedding. If the ground is wet or very soft more
   it may be necessary to allow for more bedding. Use imported granular 
   material. It should be thoroughly compacted and true to gradient 
   over the whole width of the trench.

4. Place suitable side fill material evenly on each side of the pipe 100mm 
   layers. Pay particular attention to the area under the lower quadrants of 
   the pipe. Hand tamp, well at each layer up to the pipe crown. Leave the 
   pipe crown exposed.

5. if "as-dug" material is free from stones exceeding 40mm. Imported granular 
   material is not needed above the pipe crown. Cover the pipe crown with a
   minimum of 300mm of compacted "as-dug" material.
   If "as-dug" material contains stones larger than 40mm or the pipe is deeper 
   than 2 meters in poor ground, extend the imported granular material for at 
   least 100mm above the crown. Continue hand tamping until a finished layer
   of 300mm has been placed over the pipe.

6. "A-dug" material may be backfield in 300mm layers and mechanically tamped.
   Dampers or other vehicles must not be driven along the pipe tracks as a means 
   of compacting.
   
   
   

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