This report concerns part 2 of a project with the aim to propose protective measures for cables and pipelines for bio and natural gas. Part 1 was previously reported in SGC Rapport 2011:239. The wish is to be able to increase the pressure in the distribution networks from 4 to 10 bar without having to retain the safety distances valid for 80 bar pipelines. Polymer, concrete and steel protective plates, and deep digging are the physical measures considered. In part 1 a survey was made, in part by an enquiry, of the frequency, causes and consequences of incidents where pipelines were hit by excavators. Further, the rules and standards were investigated in countries where 7–10 bar pipelines are already in service. Here, in part 2 the perspective was widened to include, apart from gas pipelines, also all kinds of buried pipelines and cables. Now a visit to a supplier in France is reported, as well as an vestigation of costs and environmental impacts of the different protective measures, and an analysis of the strength of protective plates and of how they can best be positioned in the ground in relationship to the pipeline. The main result from the study visit to France was that new regulations mean that both new and existing pipelines have to be satisfactorily protected. For the physical point of view these plastic protective plates play an important part, and there are commercially available building systems of plates for which the strength and durability have been verified by tests. In the full scale experiments done in, e.g., France, it can be concluded that the plastic (HDPE) plates can wit stand high loads which are applied by use of a bucket with teeth mounted on an excavator. In some cases penetration of teeth occurs, but the plates will in that case either come up and alert the operator or stay in the ground and still protect the buried cable or pipeline. Concrete plate can also break, but the pieces are held together by the steel reinforcement. The analysis of costs and environmental impacts shows that plastic plates are preferred with regard to both aspects. In addition they have a very good signalling effect being produced in a bright yellow colour. Also deep digging can be effective taking into account costs and environmental aspects, but the risk reduction will according to literature be less than for the plates. Plastic plates are shown, in the literature surveyed, by full scale experiments to have at least as good, and sufficient, resistance to impact as concrete ones. This is verified by in-house numerical analyses. The finite element analyses show that the plastic plates deforms but do not break. The arching action of the backfill protects the buried pipe, and the stresses become only somewhat higher when using plastic plates instead of using stiff plates of steel or concrete. There may be unfavourable cases when the plastic plates cannot by themself stop forces and stresses passing down through soil layers acting on the buried pipe.
2013. , 53 p.