Hydraulic Effects on a Large Piping System During Strong Earthquakes

Liquid in a large piping system could become a resonance column under axial excitations. A 1000-m long closed-boundaries pipeline with pressure wave propagation velocity of 1000 m/s would have the fundamental liquid resonance frequency of 0.5 Hz. Then, some hydraulic transients might occur during strong earthquakes. If dynamic pressure amplitude exceeds the value of system stationary pressure, then vaporizing at negative pressure, and after that, cavity or liquid column separation and reconnection can be produced. One of the effects of these behaviors would be equivalent damping of dynamic response, and the other an impact force on pipe structural system. The latter effect is considered as one of potential damage factors of a large liquid piping system. In this paper, an analytical method of earthquake-induced hydraulic transients of piping system is applied to a real underground large piping system subjected to a strong earthquake motion which has occurred in Japan. The results of the analysis have shown that the occurrence of earthquake-induced negative pressure in liquid column is possible. Further, the analysis has explained the difference between two long straight pipelines buried in the same route, one failed by axial cracking and the other had no damages.