Rini Kusumawardani, - Influence of mis-assignment of groundwater level on liquefaction assessment of soils. Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering.

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Abstract

This paper discusses unexpected influences of the miss-assignment of groundwater table in the analysis of soil lique- faction. In viewing that the groundwater table (GGGGGG0) during subsurface exploration for evaluating cyclic resistance ratio (CCCCCC) of soils is sometimes mistakenly assumed the same as the groundwater table (GGGGGG) for computing cyclic stress ratio (CCCCCC) due to seismic shaking, the results of liquefaction analysis may thus be erroneous. If the GGGGGG0 is assigned higher than the actual level, than the CCCCCC, and the associated factor of safety (FFLL), would be overly predicted. Alternatively, if the GGGGGG0 is assigned lower than its actual one, than the CCCCCC and FFLL would be underestimated. If the groundwater table during exploration is mistakenly assigned as the groundwater table for computing cyclic stress ratio (i.e., GGGGGG0 = GGGGGG; or “one-groundwater, 1-GW, scenario”), then the variation in groundwater tables will lead to the changes in CCCCCC and CCCCCC in the same sense. Owing to different rates of change, however, the computed factor of safety (FFLL = CCCCCC/CCCCCC), and the associated liquefaction potential index (LLLLLL), may sometimes result in an unexpected situation. Namely, an increase in the groundwater tables would cause an unanticipated increase in the com- puted factor of safety and a decrease in the associated liquefaction potential index. Based on results of current study, the LLLLLL could be reduced by 10~30% if 1-GW scenario is assumed and GGGGGG0 is 3m higher than the actual level; or alternatively, the LLLLLL would be increased by 5~45% if GGGGGG0 is 3m lower than the actual one.

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