LAYING Of PIPE

While designing  the  pipeline  systems,   the  level  and  depth  of the trench is calculated depending on factors such as terrain and  the  usage  to  which  the  pipeline  is  to be put. Excavation and pipe laying must take place simultaneously as  leaving  open  trenches for too  long  makes  them unsuitable  for use. As  pipe  laying advances,  trenches  must  be blackfilled immediately.

The  pipe jonts, however, should  be   left  exposed  until  later  the  pipeline  system   has been tested.  The  minimum  width  of  the  trench must be equal to the pipe diameter plus 300-mm. At the crown of the pipe, the  trench width  must not  exceed  the  pipe  diameter plus an additional 600-mm. There are two types of trench formation:

Direct Laying:

The fornation of the trench  must  consist  of  stable,  uniform  and  smooth  soil  devoid of irregularities  for  direct  laying  of  pipes.  The  bed  of  the trench should be smoothed out evenly to provide uniform support to the pipe laid. There will be some extra excavations to enable adequate jont assembly and pipe support.

Pipe laying on Bedding:

Pipe laying, where soils are unsuitable  for direct pipe laying , trenches must be excavated to an additional depth of 100mm at  the  minimum  and  suitable bedding, as detailed later, must be utilized for pipe  laying, under  serve  conditions  it  may  become  necessary  the depth of the bedding even further.

Bedding Material:

It should be stable and have  a granular texture, free from impurities such as stones or other debris. Bedding which might change its properties under conditions such as  stones or other debris. Bedding which might change  its  properties under conditions such as water seepage or freezing must be avoided.  Preference  must  be  given  to  free  draining sand or nominal single  size  gravel  with  rounded  or angular  partical  size 100mm or  even  5mm  to 10mm graded. After placing the bedding material in the trench it should be  compacted  by  hand to provide  the most  even support. Special  care  needs  to  be  taken  for  sockets holes  and proper compaction in this area must  be  ensured.  When backfilling a trench make sure that there are no foreign material left inside.

Backfill:

Pipe laying and back filling  must take  place  simultaneously and installed pipeline systems must not remain exposed for longer periods than is absolutely necessary. The backfill  must be  devoid of   irregularities  like  debris  and  stones  and  should  be  compacted  by  hand. Mechanical  compaction  should  take  place  only  when  a  buffer  of 30cms has been built between the uPVC pipes and the surface being compacted. At least 76cms  of cover should be allowed over the pipeline system in case vehicular traffic is  expected  to cross  over  the pipeline location at a later stage.  Wherever extra protection to the pipeline is   required, it  is a good idea to provide concrete slabs on a cushion of granular fill. Extra protection may also be made possible by passing the pipe through an extra pipe duct of greater diameter. This is necessary  only  if  the  cover  depth  is  less  than  60cms.  For cover depths of  more than 60cms, well-compacted granular fill serves the purpose adequately. Under no circumstances is a concrete encasement of the  pipeline desirable  since  it  lessons the flexural strength of the pipeline system.