Performance evaluation of buried uPVC pipes by numerical simulation of soil-pipe interaction

Abstract

[EN] Pipelines are the most important and valuable assets in a water distribution network. Design, commissioning and maintenance of the pipes costs a huge amount of money and effort for water supply companies. Understanding the behaviour of buried pipelines is a major concern for engineers. In this paper, soil-pipe interaction has been investigated under various conditions using the numerical simulation of in-situ pipes. A finite element model has been developed to numerically simulate the interaction of soil with pipes. More than 180 scenarios have been designed to cover the different conditions. Three segments of uPVC pipes with diameters between 160-450 mm were modelled. To cover a range of soils, three different soil types were modelled. The value of Young’s modulus was decreased in various scenarios to consider the effects of age on the mechanical properties of pipes material. Four different external loads (corresponding to light to heavy vehicles) were exerted on top of the road pavement. Also, a large external load was applied to study the pipes failure under heavy loads. A variety of internal fluid pressures from 0 to 6 bars was applied inside the pipelines and the ultimate internal pressure which would cause failure in the pipe was determined. The model domain was discretized for finite element calculations. Finer mesh sizes were selected around the pipe. An appropriate mesh size was determined by mesh sensitivity analysis. The Mohr-Coulomb failure criterion was chosen to simulate the soil behaviour. Also, an elastoplastic stress-strain relationship was considered for the uPVC material. Von-Mises stress was selected as the failure criterion. Running the finite element model, the distribution of stresses and strains in the soil and the pipe were computed. In the absence of external load, the values of axial and hoop stresses were compared with the theoretical values. The comparison of the results showed a high correlation between the computed and theoretical values. In both absence and presence of external loads, the values of shear stresses are relatively small and negligible in comparison with axial and hoop stresses. As a result, the minimum and maximum principal stresses are close to the axial and hoop stresses, respectively. This implies that, only measuring the axial and hoop stresses can provide the principal stresses with a reasonable accuracy. Both internal and external pressures in which the pipe fails are significantly higher than the usual loads on roads and water distribution networks. It justifies the fact that most of the pipe failures occur not due to exceeding the yield stress, but due to fatigue in elastic region. The results of numerical modelling of soil-pipe interaction help engineers to study the pipe performance under different conditions.