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Western Dam Engineering <br /> Technical Note <br /> <br /> August 2016 <br /> <br />19 <br />to as “suffosion.” Suffosion can lead to settlement or <br />instability and eventual collapse or significant <br />deformation of the embankment. <br /> <br />Figure 9. (a) Suffusion and (b) Suffosion Processes <br />Internal Erosion Potential Failure <br />Modes <br />The potential internal erosion failure mode by which a <br />dam may fail depends on the mechanism that occurs <br />and its location. Table 1 summarizes the mechanisms <br />that are often applicable to specific potential failure <br />modes. The table highlights the most common <br />mechanism(s) for each failure mode. <br /> <br />Table 1 - Internal Erosion Mechanisms <br />by Failure Mode <br /> <br /> <br />Failure Mode <br />Pathways <br /> <br /> <br /> <br />Internal Erosion <br />Mechanisms Th <br />r <br />o <br />u <br />g <br />h <br /> <br />E <br />m <br />b <br />a <br />n <br />k <br />m <br />e <br />n <br />t <br /> <br />Th <br />r <br />o <br />u <br />g <br />h <br /> <br />F <br />o <br />u <br />n <br />d <br />a <br />t <br />i <br />o <br />n <br /> <br />In <br />t <br />o <br /> <br />F <br />o <br />u <br />n <br />d <br />a <br />t <br />i <br />o <br />n <br /> <br />o <br />r <br /> <br />A <br />b <br />u <br />t <br />m <br />e <br />n <br />t <br /> <br />Al <br />o <br />n <br />g <br />/ <br />I <br />n <br />t <br />o <br /> <br />C <br />o <br />n <br />d <br />u <br />i <br />t <br /> <br />BEP X X X X <br />Concentrated Leak X X X X <br />Contact X X <br />Suffusion/Suffosion X X <br />Bolded Xs represent the most common mechanism(s) for each <br />failure mode. <br /> <br />All four mechanisms can occur within internal erosion <br />through the embankment and internal erosion through <br />the foundation. For internal erosion of the <br />embankment into the foundation or abutment, BEP <br />and concentrated leak erosion can occur. For internal <br />erosion along/into conduits or pipes, concentrated <br />leak erosion is often the primary mechanism unless the <br />material along the conduit is low-plasticity or <br />otherwise erodible for the full pathway. <br />Internal Erosion through Embankment <br />When BEP leads to internal erosion through the <br />embankment, it generally exits near the downstream <br />toe of the embankment where, the phreatic line is <br />close to the ground surface and exit gradients are <br />highest. Signs that BEP may be occurring within the <br />embankment include localized deformation, collapse, <br />and sedimentation on the slope or toe. <br /> <br />Concentrated leak erosion through a crack in the <br />embankment can occur due to differential settlement <br />from unfavorable geometry, hydraulic fracturing, <br />desiccation cracking, earthquake induced cracking, low <br />stress or compaction zones, arching at concrete <br />penetrations or abutment walls, construction defects <br />or voids from roots or animal burrows. Signs of <br />concentrated leak erosion through the embankment <br />include sediment deposition on the downstream slope <br />or toe, enlargement or multiplication of surface cracks, <br />and downstream slope bulging. <br /> <br /> <br /> <br /> Figure 10. Internal Erosion through the Embankment by <br />Concentrated Leak Erosion [2] <br />collapse <br />(a) (b)