Understanding the Dynamic Leakage Behaviour of Longitudinal Slits in Viscoelastic Pipes

Polyethylene pipes, and other polymeric materials, are a popular choice in the water industry due to their advertised but exaggerated leak resistance. When leaks do occur in this pipe material, the complex leakage behaviour (time and pressure dependent) presents a challenge in accurately modelling the representative response. The presented research aimed to quantify the leak behaviour of longitudinal slits in viscoelastic water distribution pipes, considering the dynamic interaction of hydraulic conditions and the pipe section characteristics. A methodology was developed to create synergy between novel physical investigations and numerical simulations, evaluating the synchronous pressure, leakage, flow-rate and leak area to understand the interdependence of the leakage and structural
dynamics. The synchronous leak area was confirmed as the critical parameter defining the leak response and is in turn dependent on the leak and pipe geometry, loading conditions and viscoelastic material properties. The theoretical discharge coeffcient was shown to remain constant, thereby establishing that the structural response, i.e. the change of leak area, can be determined by quantifying the leakage flow-rate and the pressure headalone. Derivation of a generalised leakage model effectively captured the dynamic leakage behaviour. However, the model may provide an erroneous estimate of the true response due to the exclusion of the influence of ground conditions. These were shown to result in a significant increase in slit face loading dependent on the specific soil matrix properties, simultaneously
altering the structural deformation and net leakage. Alongside the advances in fundamental understanding, the research also has implications for leakage management strategies. The short term behaviour may severely hinder the effectiveness of leak localisation technologies and the quantification of risk associated with contaminant ingress. However, it was shown that current leakage modelling practice over relatively long time periods are not adversely affected by the existence of such dynamic leaks.