Abstract
ABSTRACT As one of activities of the 1977-fiscal year for the R&D project of offshore oil storage system being conducted under the supervision of Japan Ocean Industries Association and in the budget of Ministry of International Trade and Industry, a series of experimental study on the liquefaction of sand foundation have been performed to investigate the aseismatic stability of offshore oil storage tank of gravity type. Acceleration of shaking table, tank model, sand bed, pore-water pressure of sand bed and settlement of tank model etc. are measured to describe experimentally the phenomenon of liquefaction and study the liquefaction potential in relation to the stability of structure. Excess pore-water pressure can be expressed with equations to a good degree of accuracy and liquefaction potential of ground is assessed on the basis of soil test in laboratory. In addition to the improvement of physical information of ground for better assessment of liquefaction potential, prevention of liquefaction and anti-liquefaction design of structure are the problems for further discussion to be solved according to situations. The results will be reflected upon the recommendations for the aseismatic design of offshore oil storage system prepared by Japan Ocean Industries Association (JOIA). INTRODUCTION Quantitative observation of liquefaction of sandy seabed is performed by means of experimental study of offshore oil storage tank model of gravity type in order to study liquefaction potential of seabed and stability of overlying structure. The influence of existence of structure and sea water around structure upon liquefaction potential of seabed are also discussed. There are such problems of the ground underlying structure as shear failure, settlement due to consolidation, sliding of structure and liquefaction. The studies on these for conventional structure have been applied to the design and construction of marine structure and contributed to the improvement of safety. Liquefaction of ground has been well known in earthquake region as such phenomena as blowup of sand, unusual settlement of structure, etc. The study on liquefaction has been gradually promoted up to date. However, it is scarcely performed on the liquefaction of seabed for offshore structure of gravity type. The structure of this type are going to be constructed in earthquake region and the liquefaction of seabed will be one of the important items for discussion. Rise of pore-water pressure due to seismic shake causes reduction of vertical effective stress, leading up to liquefaction of ground when such damages as settlement of overlying structure and surfacing of embedded structure will occur. Liquefaction of ground was already taken up for study by Taylor(l) and Mogami et al(2) in the 40's and 50's. Sunami(3) made a detailed observation of liquefaction and settlement of sand bed in a shaking box. Seed(4) tried to predict liquefaction of ground with applying the result of cyclic triaxial compression test.
Published Version
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