Pipelines are an expensive long-term investment and their construction implies a major visible impact, particularly within urban areas - sometimes extensive open trenches are hardly tolerated anymore. No-dig methods may offer alleviations on both counts.
However, the trade-off is a loss of transparence: You don‘t see what happens in a black box. What happens to the pipe and its connections during insertion? What happens to neighboring plants? What are the drawbacks for operation, in particular for the service life of the pipeline?
These questions cannot be answered in general for all methods at once. Each method has its own risks and chances. DVGW has issued a series of standards to describe the best practice of theses methods („G“ refers to gas supply, „W“ refers to water supply):
• GW 304 Pipe Drive (Tunneling)
• GW 320-1/2 PE Relining (with/without close-fit)
• GW 321 Horizontal Directional Drilling
• GW 322-1/2 Pipe (direct/indirect) Exchange
• GW 323 Burstlining
• GW 324 Cutting & Plowing (in preparation)
• GW 325 Service Lines
• G 478 Fabric Hose Lining (to be replaced by GW 327)
• W 343 Cement-Mortar Lining
Pipes have been enhanced in various ways to cope with the additional stresses of no-dig methods. Steel and cast iron pipes with robust coatings, e.g. on cement-mortar basis, may well be used and rightfully so, considering their inherent strength.
But is has been the flexibility of polyethylene that pushed no-dig methods forward. On the other hand, that same property raises questions about its vulnerability. There appears to be a huge range of qualities that is not reflected by the crude classification PE 80 and PE 100, based on minimum required strength.
DVGW has started a three year project at the end of 2004 to assess a method for judging the resistance of PE to slow crack growth and the resistance of PE pipes to point loads. The final goal is to provide a standard for certification of PE pipes that are suitable for rough bedding conditions.“