Levee reliability analysis considering different failure mechanisms - A case study (Gueishan Levee) in Southern Taiwan

Because Taiwan is located in a subtropical area, it is unavoidable to encounter severe disasters induced by typhoons during the summer season. On August 8,2009, Typhoon Morakot invaded Southern Taiwan and many levees and revetments in southern Taiwan were damaged during this event. In this study, the uncertainty of the parameters was considered in stability analyses of one of the failed levees, the Gueishan Levee, under different flood return periods to examine the effect of the extreme weather conditions. Analysis results have shown that the slope sliding safety factor coefficient of variation (C.O.V.) is more influenced by the change of water level difference and less influenced by the change of flood return period. As the water level difference (WLD) coefficient increases, the safety factor is more concentrated and exhibit less uncertainty. The C.O.V. of sliding and overturning of retaining structure are both influenced by the variations of flood return periods and the WLD coefficient. As the flood return period increases, the two failure mechanisms associated with retaining structure exhibit less uncertainty under a long flood return period. On the other hand, as the WLD coefficient increases, the response of the two failure mechanisms related to retaining structure exhibit more uncertainty. It is therefore recommended to consider the water heights and possible scouring depths from hydrologic analysis of floods, and empirical equations in the levee stability analysis. If a specific levee is more important (more lives and properties are expected to be influenced), possible failure mechanisms may need to be considered under the effect of extreme weather condition, and thus the design can be reexamined and redesigned as a countermeasure to face the extreme weather conditions in the future.