A Study on Damages of Lifeline Facilities due to Soil Liquefaction

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Damages of lifeline facilities during earthquakes due to soil liquefaction were studied based on shaking table tests and analyses.1. Damages of lifeline facilities caused by soil liquefaction during the 1964 Niigata Earthquake and the 1983 Nihonkai-chtibu Earthquake were reviewed. It was clarified that buried pipelines had possibilities to be broken not only due to dynamic ground displacements during shaking but also due to permanent ground displacements which occur after liquefaction.2. Shaking table tests and laboratory cyclic shear tests were conducted to know the mechanism of occurrence of the permanent ground displacements. The displacements did not occur at the boundary between the liquefied layer and the non-liquefied layer, but occurred with a constant shear strain on liquefied layer. And, the elastic modulus decreased tip to about 1/1000 due to liquefaction. Based on these test results, a simplified procedure for the analysis of the permanent ground displacement due to liquefaction was proposed.3. Pull out tests of a model buried pipe in the model ground were conduct to know the friction strength between the pipe and the ground. The friction was measured under various excess pore pressure ratio, and reached LIP Lo 1/20 in liquefied state.4. The deformation and stress of various kinds of buried pipes was analyzed by using a numerical method, the "response displacement method", considering the test results. Then the relationships between the damage of pipes and the dynamic ground displacements and the permanent ground displacements were discussed.