Mistake to Avoid
Ensure adequate gradient for pipe runs. In certain circumstances oversized pipes may be used at shallower gradients. The depth of the drain is thus reduced, saving on excavation and allowing more economical installation. However, adequate velocities should be maintained and the additional costs of pipework considered.
Make sure that there is adequate depth of ground cover of protection over pipes.
Avoid long lengths of unvented drain. Install junctions so that they continue in the direction of flow.
Space manholes at maximum centers as they are expensive. uPVC pipes are flexible in concrete unless engineering requirements make it necessary. Although concrete does not harm uPVC, surrounding pipes with concrete is wasteful and changes a flexible pipeline into a rigid beam which may fracture under ground movement.
Make sure all sockets and spigots are clean before jointing. Before backfilling, make sure that all temporary supports, hard bricks and other objects are removed from the trench. Never leave them under or at the sides of pipes. Always test pipes before backfilling.
PROTECTING UNDERGROUND PIPES FROM LOADS
As uPVC pipes are flexible they can accommodate ground movement and pressure without damage. However, if the pipe needs protection, e.g. when laid with a cover of less than 1.2 meters under roads, concrete may be used above the pipeline as a protective raft, provided a cushion of fill is laid between the pipe crown and the raft. This will prevent unacceptable deflection of the pipe.
PIPES UNDER BUILDINGS
Do not surround pipes with concrete if they run under of through buildings unless building engineering requirements make it essential as this effectively converts a flexible pipeline into a rigid beam with little flexural strength. Instead, bed the pipe as normal and continue the surround and backfill up to the underside of the oversite concrete or floor slab. Where a pipe passes through a wall, install a suitable pipe sleeve and lintel, complete with two Couplers on either side of the wall. This will compensate for any settlement of the building or made-up ground. Alternatively, form a lintel or relieving arch in the structure to leave 20mm clearance above the crown of the pipe. Fill this clearance with suitable material which is compatible with uPVC, non-cracking and resistant to moisture and gas.
USE OF CONCRETE
If pipes must be surrounded with concrete, make sure they do not float when the concrete is poured. Filling the pipes with water will generally provide enough ballast but side restraint may be needed to maintain alignment.
To maintain a certain degree of flexibility, insert 13mm of compressible material, such as fiberboard or polystyrene, around the pipe joints. These boards must be at least the width of the concrete surrounds. Protect pipe joints from the ingress of cement by wrapping them with polyethylene sheet or adhesive tape.
All lengths of sewer and drain pipe and all manholes and inspection chambers must be inspected for straightness, abstractions and for ground water infiltration.