Analysis of Pressure Fluctuation in a Pipeline under Seismic Conditions

1.Background and purpose

In recent years, magnitude 7-class major earthquakes have frequently occurred in Japan and several damages have been reported, that water supply pipelines burst. For example, the Great East Japan Earthquake (March 11, 2011) causes several air valves to be broken, that were installed at the pipelines of the Kasumigaura Water Facilities in Ibaraki prefecture.

Hydrodynamic pressure due to ground shaking is probably one of the major causes. However, there has been a limited number of studies that tried to find the mechanism of the hydrodynamic pressure and the measurement data under seismic conditions is apparent lack.

This paper aimed to obtain a deeper understanding for the hydrodynamic pressure due to affecting a seismic wave to a long distance pipeline.

2.Method

In order to elucidate the mechanism of hydrodynamic pressure change when earthquakes occur, we measured seismic waves and hydrodynamic pressure on the pipelines of Kasumigaura Water Facilities in the several earthquakes during one year from November 2015 to October 2016. Furthermore, we conducted a one-dimensional transient analysis on hydrodynamic pressure in the pipeline at the time of the measured earthquake. The numerical solution of this analysis was based on the Characteristics of Method commonly used in the water hammer analysis and seismic waves were given to pipelines.

3.Result

We found two features from the measured values for the hydrodynamic pressure due to affecting a seismic wave to a long distance pipeline. First, the peak of hydrodynamic pressure fluctuation appears later than that of seismic acceleration. The second, the peak of the frequency of the hydrodynamic pressure in the pipe is different from that of the seismic acceleration. Moreover, we compared the analysis result with the measured values and confirmed that these two features in this measurement can be reproduced also in the analysis result.