CASE STUDIES FOR OIL TANK ON LIQUEFIABLE SANDY GROUNDSUBJECTED TO EXTREMELY LARGE EARTHQUAKES ANDCOUNTERMEASURE EFFECTS BY COMPACTION

摘要

Liquefaction-induced settlements of storage tanks on liquefiable sandy ground have been observed in pastearthquakes. These problems can be mitigated by improving potentially liquefiable layer, but it isimpossible to prevent occurrence of liquefaction completely under extremely large earthquakes. Thereforeit is necessary to carry out performance-based design by considering the allowable displacement for aparticular type of structure. In practical design, reliable analytical procedures are necessary to predictliquefaction-induced settlements of structures, not only qualitatively but also quantitatively.This paper presents the effects of countermeasure against liquefaction by compaction such as sandcompaction pile method by considering a storage oil tank founded on the improved ground, comparing theseven liquefaction analysis codes mostly used for practical design in Japan. These codes are based on theprinciple of effective stress analyses based on elasto-plasticity theory, effective stress analyses based onmulti-mechanism theory and static equilibrium analysis with decreased shear modulus due to liquefaction.Same conditions such as tank and ground dimensions, soil profiles, undrained cyclic resistance of sand,and boundary conditions were used for analyses. The effect of input wave amplitude and configuration ofcompacted soil cross section were studied.Analytical results showed that although there are differences among codes in vertical displacementquantitatively, almost reasonable tendencies on input wave amplitude and the effectiveness ofcountermeasure were confirmed qualitatively. These data may be useful to determine the countermeasureconfiguration in cross section for storage tank foundations.