Flow failure assessment for dams and embankments

A procedure is proposed to assess whether a liquefied strength should be applied to a zone of non-plastic silt, silty sand, and (or) clean sand in a static or seismic stability analysis to assess the flow failure potential of dams and slopes. The procedure consists of the following five main steps to assess flow failure potential: (1) assess static liquefaction potential of segments along a potential failure surface; (2) assess seismic liquefaction potential by calculating the factor of safety against liquefaction (FoS_Liquefaction) for any amplitude of shaking in each segment; (3) if liquefaction is not triggered in any of these segments, assess the magnitude of shear-induced pore-water pressures due to seismic or vibratory events of any amplitude; (4) assign a liquefied strength to segment(s) that experience seismic liquefaction, i.e., FoS_Liquefaction < 1 or significant pore-water pressure generation, i.e., total pore-water pressure ratio ≥ 0.7; and (5) conduct a post-triggering stability analysis to assess flow failure potential. This procedure is illustrated using the 1971 seismic permanent deformations of Upper San Fernando Dam and 2015 Fundão tailings dam failure.