A Study on Damages of Lifeline Facilities due to Soil Liquefaction

通过振动台试验和分析，研究了地震作用下，由于土壤液化引起的生命线设施的破坏.回顾了1964年新泻地震和1983年日本海地震中由于土壤液化而造成的生命线设施的破坏。阐明了埋地管道不仅在地震过程中由于地面的动态位移而断裂，而且在地震后由于地面的永久位移而断裂的可能性.通过振动台试验和室内循环剪切试验研究了永久位移的产生机理。位移不发生在液化层和非液化层的边界处，而是发生在液化层上的恒定剪应变处。并且，由于液化，弹性模量最高降低到约1/1000。在此基础上，提出了液化引起的永久位移分析的简化方法.为了解埋地管道与地面之间的摩擦强度，进行了模型埋管在模型土中的拉拔试验。在不同的超静孔压比下测定摩阻，液化状态下摩阻达到LIP Lo 1/20.结合试验结果，采用“响应位移法”数值计算方法，对各种埋地管道的变形和应力进行了分析。分析了地下管线损伤与地面动位移和永久位移的关系。

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.