Study On Intrusion Volume Due To Negative Pressure Events In Water Distribution Systems

As an important infrastructure of the city,urban water supply systems shoulder the important responsibility of providing necessary water resources for people's daily life.However,the problem of urban water supply safety is prominent,and the leakage and water pollution incidents happen frequently.When there is a defect in the pipe of the water supply system,the leakage of water happens.When a negative pressure event occurs in the pipe,the contaminants outside the pipe may enter the pipeline through the defect,causing water pollution and endangering the public water safety.In these events,the amount of pollutants is one of the most important indicators to evaluate the degree of risk.Therefore,it is of great significance to study the intrusion volume of intrusion events.What is more,understanding the degree of pollution damage timely is also very important for water supply safety protection.First of all,this study measures the intrusion volume in steady overflow conditions.This experiment expended the upper limit ratio of defect size and pipe diameter from 15%to 38%and found a different law.The experiment studied the influences of different sizes and shapes of the leakage points and found circular defect have more the intrusion volume.The experiment was carried out under different external pressures,flow velocities,sizes and shapes of the leakage points to simulate as many as possible intrusion conditions.The negative pressure events are generated by the sudden closure of a special valve,and then explore the influencing factors of the intrusion volume.Secondly,a closed tank is used as an experimental device to study the intrusion volume.According to the comparison of the data obtained from different devices,it is found that the intrusion volume of the tank type device is significantly larger than that of the branch type intrusion device.It shows that the branch pipe intrusion device underestimates the intrusion volume when transient events happen.In addition,the experiment of soil covering and the influence of different particle sizes on the invasion volume were also included.Through comparative analysis of submerged experiment and soil cover experiment,the soil has strong inhibitory effect on water invasion.The influence of different sizes of sand on the invasion of pollutants is also studied.It is found that the inhibition effect of small size sand on water invasion is stronger.Finally,dynamic volume factor method is used to calculate intrusion volume and the results are in good agreement with the measured values.It provides a reference dynamic calculation method for calculating the invasion volume under transient negative pressure.The influence of various factors on the volume of intrusion is systematically analyzed.Sensitivity analysis of various factors is made by range analysis.It is found that intrusion volume is most sensitive to the diameter.