WEF Discussion Forums
Any reported problems with plastic gravity sewer mains?
Our municipality currently requires DIP for sewer mains but is considering allowing plastic. Is bedding critical to plastic installation? DIP is so forgiving I'm spoiled. We're located in Northwest Illinois.
Bedding may be the most critical factor for plastic pipe installation. With plastic pipes, the structural strength comes from the surrounding soil, not the pipe itself. If the soil is not compacted correctly, the pipe will be overloaded and will go out of round.
With PVC pipes, you also need to be careful that no rocks are placed adjacent to the pipe wall. A point loading could cause the pipe to split and once PVC splits, it will continue to split all the way to the next break in the pipe.
I'm in Phoenix, AZ and we've used fiberglass pipes in very limited applications, but our standard pipe materials are clay, concrete, and DI.
See ASTM standards for pipe bedding/envelope materials AND installation. This is really no different than DIP other than, yes, It is much more critical with plastic pipe. You have been letting contractors off the hook if not following standard pipe installation methods regardless of pipe type.
Plastic pipe should have no problem achieving a 100+ year life IF installed correctly. Incorrectly the pipe could fail in less than 5.
Bid document final completion and warranty criteria should include mandrel testing and televising 1 year post installation. If the pipe was installed with inferior envelope materials and methods, it will experience egg shaping in the initial settlement period.