Process of pipe laying and jointing

Laying of pipes should be done carefully so that the line is watertight, correct in line and level, and safe from damage.

Steps in pipe laying

1. Survey and setting out: the alignment and levels are marked on the ground from the drawings.
2. Excavation of trench: width = pipe diameter + 0.3–0.6 m; depth gives a cover of 0.75–1.0 m (more under roads). The trench bottom is graded as per the pipe gradient. Dewatering and timber shoring are used in loose or wet soil.
3. Bedding: a 100–150 mm layer of sand or fine gravel is laid and compacted at the bottom.
4. Handling and lowering: pipes are inspected for cracks, cleaned inside, and lowered carefully by ropes or cranes, not dropped.
5. Laying: pipes are laid from the lower end to the upper end, with sockets facing up the slope, to the correct line and grade, checked with boning rods or a level. Air valves are placed at high points and washouts at low points.
6. Jointing: the joints are made as per the pipe type: socket-spigot with lead and yarn, flanged with gasket and bolts, solvent cement for PVC, fusion for HDPE/PPR, collar or screwed for GI.
7. Anchorage: concrete thrust blocks at bends, tees, dead ends and valves to resist the thrust.
8. Testing: after joints cure, sections of about 500 m are filled with water, air is released, and a hydrostatic test is done at 1.5 times the working pressure for a few hours. Leaks are repaired.
9. Backfilling: sand around the pipe, then soil in 150–200 mm layers, compacted; no stones near the pipe.
10. Flushing and disinfection: the line is flushed and disinfected with chlorine (about 20–50 mg/L for 24 hours) before the supply starts. Finally the surface is restored.