Leakage characteristics of high performance unplasticized polyvinyl chloride buried pipeline in urban

The underground pipeline network is an important infrastructure for urban development and also serves as a “lifeline” project for cities. However, due to various factors such as pipeline aging, construction activities, uneven sand settlement, and external loads, underground pipelines often experience leak, leading to water loss. Studying the leakage characteristics can help evaluate the actual degree of leakage loss within the pipeline network. This article considers the influence of three media—sand, water, and air—on the leakage characteristics of pipelines. Initially, leakage simulation experiments were conducted on three different types of leaking pipelines, each exhibiting different leak shapes. Second, the experimental results were compared and analyzed based on existing theoretical models. Subsequently, the Fluent module of ANSYS software was utilized for finite element analysis, ultimately deriving the theoretical formula for the leakage flow rate. The results showed that pipeline leakage led to the formation of an “inverted-cone” sand-water mixing zone and a “semi-elliptical” erosion pit with cracks in sandy media, causing surface oscillations in water media and the formation of water columns spraying outward in air media. The leakage flow rate increases with increasing pressure, and the order of its values under different leakage forms is axial crack > circular hole > circumferential crack. The International Water Association (IWA) model and the fixed and variable area discharges (FAVADs) model can be used to approximate the calculation of the leakage flow rate. Under identical conditions, the leakage flow rate increases on the order of S1, S2, S3, W, and A with changes in the medium and decreases with an increase in burial depth H. The final deformation of each leakage port in the pipeline is approximately elliptical. The value of m increases approximately linearly with the increase in pipeline outer diameter, approximately exponentially with the increase in leakage port size, and approximately exponentially decreases with the increase in pipeline wall thickness and elastic modulus. The FAVAD model is more consistent with finite element results than both the Torricelli (TOR) model and the IWA model. The improved FAVAD model and the S.S.A model provide ideal and reliable calculation results, which can be applied to calculate the leakage flow rate in buried pipelines.