EFFECTIVE STRESS SIMULATION OF LIQUEFACTION-INDUCED BUILDING SETTLEMENTS

Earthquake-induced liquefaction has long been recognized as one of the most serious seismic hazards. Damages to residential houses and commercial buildings have been observed following major earthquakes, such as the 2010-2011 Canterbury Earthquake sequence, as a result of loss in bearing capacity of the foundation ground induced by soil liquefaction. These damages include building settlement and foundation tilt (or differential settlement), which are known to affect the function of these structures. In this paper, numerical modeling and analyses were performed to examine liquefaction-induced settlement of buildings and to investigate the effects of various parameters in inducing settlements. The finite element effective stress analysis software FLIP, developed in Kyoto University, was used for this purpose. The primary objectives of this paper are: (1) to evaluate the settlement and tilt of buildings due to earthquake-induced liquefaction through numerical simulation; and (2) to quantify the effects of different parameters, such as the aspect ratio, the peak ground acceleration, and the thickness of the liquefiable layer on the magnitude of settlement. Firstly, the models adopted were validated through the results of centrifuge tests available in the literature. Next, various parameters which were deemed to contribute to the magnitude of total and differential settlements were analysed for a specified earthquake motion, with emphasis on the mechanism which induced the damage. These include building height, footing width, peak base acceleration and thickness of liquefiable layers. From the results, clear variation trends of building settlements and foundation rotation/tilt were observed as functions of the above parameters. The trends were expressed in terms of empirical formulas to describe the relationships of the most significant parameters and the resulting building movements. The results of the parametric study illustrated that taller buildings undergo stronger rocking and generate larger vertical deviatoric stress than shorter buildings and, with the increase in building height, liquefaction-induced building settlement and foundation rotation are exacerbated. Both vertical settlement and foundation rotation decrease with the increase in building width. In addition, while the normalised settlement increases linearly with the peak base acceleration, both the maximum and residual foundation rotations appear to increase dramatically with the peak base acceleration. Finally, using the results obtained, the earlier results available in the literature showing the relation between normalised building settlement and normalised foundation width were re-assessed and new chart was proposed.