Damage Mechanism of Large-Diameter Ductile Iron Pipes Used to Supply Water during the 2018 Earthquake in Osaka, Japan

In 2018, a moderate earthquake occurred in northern Osaka, Japan, that damaged large-diameter ductile iron pipes used to supply water. The pipe body had large cracks, and the water supply to residents in the surrounding area was stopped. This failure mode is unexpected based on the ductile material properties of the pipes. In this study, tensile and bending strength tests were conducted on damaged and new pipes, and microscopy was used to observe the tensile fracture surfaces to clarify the material properties. The results showed that the excavated pipes did not meet the material strength standard of current ductile iron pipes and exhibited brittle properties. The finite element method was used to simulate the seismic response of a large-diameter pipe along its cross-section. The generated section forces of pipes with different wall thicknesses were compared according to the material strengths obtained from the above tests and current standards to clarify the damage mechanism.