Upper-bound limit analysis of cutoff wall-reinforced embankments subjected to fluctuating reservoir levels

As subsurface barriers, cutoff walls are used to reinforce embankments to prevent instability induced by reservoir seepage during water level fluctuations. This paper analyzes the stability enhancement provided by cutoff walls using the framework of limit analysis upper-bound method combined with a rotational log-spiral failure mechanism. Verification on unreinforced slopes shows that there is a high degree of consistency between the proposed upper bound results and existing analytical and numerical solutions. It was shown that the slope has a higher safety factor as the stabilizing effect of the cutoff wall strengthens. In addition, the critical sliding surface tended to be shallower with an increase in the external water level coupled with a decrease in the internal water level. Due to combined stabilization from soil self-weight and hydrostatic pressure, the stabilizing effect of the cutoff wall is not always necessary under all water level conditions; only when the wall is positioned within a critical normalized distance from the crest could the reinforcing effect of the cutoff wall be fully exerted, enhancing the long-term sustainability of embankment slopes.