This study investigates the probabilistic stability of embankment slopes subjected to water level drawdown using the random field finite element method (RFEM) with strength reduction technology. The shear strength of soil properties was controlled by cohesion and internal friction angle for the slope shear failure. The cohesion and internal friction angle were modeled by a random field following the log-normal distribution. The factor of safety (FOS) for the embankment slope with random soil is calculated by strength reduction technology. During the numerical simulation, the limit analysis upper bound and lower bound method are applied to the finite element method, respectively, to obtain the upper bound and lower bound value of the FOS. Seepage action is also considered during the water drawdown by setting five different water levels (WLs). A total of 1000 Monte Carlo simulations are performed for each work condition, resulting in histograms of the FOSs. The results show that the FOSs obtained by the random field model are all lower than those by the deterministic method. Even if the FOSs obtained by the two methods are close, there still exists the possibility of slope failure. Compared to the deterministic results, the RFEM method is more reasonable for evaluating slope stability.

Backward erosion piping, a soil erosion phenomenon induced by seepage, compromises the stability of water-retaining structures such as dikes. During floods, the seepage in the dike body increases due to high water levels, which directly affects the progression of the piping channel. The formation of the piping channel then impacts the stability of the dike. In this paper, an improved piping model that considers the impact of seepage in the dike body is proposed based on Wewer’s model. Specifically, we added a seepage field of the dike body to the original model to account for the impact of dike-body seepage on the evolution of piping. The seepage field of the dike body is solved using Darcy’s law and the continuity equation for unsaturated porous media. In addition, this approach also incorporates the coupling effect of seepage stress. The accuracy of the model was verified through comparing the calculated results with the IJkdijk experiment and Wewer’s results. The effects of BEP on dike stability were investigated using the proposed improved piping model. The two major conclusions of the study are that (1) the incorporation of unsaturated seepage enhanced the performance of the piping model, allowing it to more accurately simulate the development of pipe length and the changing of pore pressure; and (2) the formation of the pipe impacted dike stability, leading to a substantial reduction in the safety factor of the dike slope.

For the risk assessment of flood defense, a comprehensive understanding of risk factors affecting dike failure is essential. Traditional risk assessment methods are mostly based on experts’ experience and focus on just one type of failure mode of flood defensive structures. The risk resources, including the analytical factors and non-analytical factors, were summarized firstly according to the general experience of dikes. The uncertainty of the resources that affect dike safety can be quantified by membership degree. Hence, a fuzzy influence diagram based on fuzzy mathematics was proposed to assess the safety of the dikes. We evaluated the multi-failure modes at the same time by a fuzzy influence diagram. Taking a dike as an example, the expected value of the dike failure was 6.25%. Furthermore, the chance of damage to this dike was “very unlikely” according to the descriptive term of the Intergovernmental Panel on Climate Change (IPCC). The evaluation result was obtained as a probabilistic value, which enabled an intuitive perception of the safety of the dikes. Therefore, we provided some reasonable suggestions for project management and regular maintenance. Since the proposed method can account for uncertainties, it is well suited for the risk assessment of dikes with obvious uncertainties.