Four dynamic centrifuge tests were conducted to study the performance of a newly developed countermeasure technique against soil liquefaction: "desaturation by air injection". In the experiment, liquefiable foundation soils below lightweight structures were desaturated by the air injection technique and base shaking was imparted to the models to obtain a comprehensive set of response data. In this study, numerical simulations of these experiments were conducted by using a two-phase (solid and fluid) fully coupled finite-element code, Coupled Analysis of Liquefaction (LIQCA-2D), to validate the numerical procedures. The mechanical properties of the soil in the saturated and desaturated zones in the models were exactly the same, with the exception of the degree of saturation. The simulation attempted to examine the desaturated models by changing the compressibility of the pore fluid, in which all input parameters for saturated and desaturated models were the same except for the bulk modulus, K f . Numerical results were comparable with the test results in terms of excess pore pressures and settlement of structures for both saturated and desaturated models. This validates the numerical procedure and further assures the effectiveness of desaturation by the air injection technique as a liquefaction countermeasure.
During large earthquakes, soil liquefaction has repeatedly damaged many buildings with shallow foundations. Many researchers have continuously worked to develop more reliable countermeasure techniques apposite to the foundation soils of existing buildings. However, most countermeasure techniques available in the current practice are either too expensive or applicable only to new construction sites. Lowering the degree of saturation by artificially injecting air is a newly developed, innovative technique that significantly improves the liquefaction strength of soil. This paper describes a series of centrifuge tests for evaluating the effectiveness of this technique by applying it to the foundation soil underlying shallow foundations of relatively light structures, such as residential buildings. Models of saturated medium dense sand beds with shallow foundations were shaken in a centrifuge. Except for benchmark models, air was injected into the soil in-flight before the shaking event, which lowered the degree of saturation of the soil in the desaturated zone from 100% before air injection to approximately 85%. The test results show that air injection effectively reduced both foundation settlement and pore pressures generated below the foundation.
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