Effect of repeated rise and fall of water level on seepage-induced deformation and related stability analysis of Princeville levee

摘要

The Princeville levee, and flooding associated with Hurricanes Floyd and Matthew, is used as a case study in which the analyses are focused on the effect of repeated rise and fall of water levels (representing severe storm cycles) on the stability of the levee and the risk of failure. The analyses included strain-based and strength reduction approaches and are conducted using the finite element program Plaxis 2D. The limit equilibrium stability software "Slope/W" was also used for comparative study. The strain-based limit state approach considers the uncertainty of soil properties and is used to characterize the levee performance under repeated storm loading in terms of damage levels (or limit states). The strain-based analyses results show a progressive development of plastic shear strain zone within the levee as the number of storm cycles is increased. The accumulation of such shear strain leads to increasing the probability of exceeding a given performance limit state. As more flooding cycles are introduced, the shear strain values increase by a factor of 3.5 from cycle 1 to 6, and therefore reflect the increasing level of failure risk. In parallel, the deterministic stability factor of safety obtained from limit equilibrium method remains unchanged and slightly changes for strength reduction method with an increased number of rises and falls of the water level. The consideration of "rapid" drawdown conventionally used in limit equilibrium stability analyses (where no consideration for time is included), instead of more realistic rate based on drawdown hydrograph leads to conservative estimate of factor of safety. The analyses results demonstrate the increase in risk with repeated hydraulic loading.