Long-Term Risk Assessment of Levee Cutoff Walls-Power Point Presentation

Power Point Presentation

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The presentation addresses the long-term risk assessment of seepage cutoff walls in levees, focusing on how aging infrastructure may deteriorate over decades and how that affects levee safety and USACE risk assessments. It notes that while cutoff walls are generally assumed to be stable, there is no widely accepted method to monitor or quantify their long-term condition and functionality.<br /><br />The study identifies potential deterioration mechanisms such as seismic effects, drying-related cracking, chemical reactions with soil or water, vegetation growth, and animal burrows. Possible failure modes include increased seepage through cracks or degraded material, piping, slope instability, failure at joints or edges, underseepage where walls are not tied into impermeable layers, and seismic slope failure.<br /><br />To better understand the issue, the team reviewed expert opinions from USACE levee safety specialists and other subject matter experts, and used a simulation to show how wall conductivity affects exit gradients and seepage performance. The conclusions suggest that cutoff walls are generally durable and effective at reducing seepage, but aging walls in high-risk or high-consequence areas should receive more monitoring and investigation.<br /><br />Recommended future work includes adding cutoff wall attributes to national levee and dam databases, modeling damaged wall performance, and coring older walls to check for increased permeability. The presentation also cites case histories from dams showing that seepage barriers often remain effective long-term, though some localized leakage or increasing seepage can occur.

Keywords

seepage cutoff walls

levee safety

long-term deterioration

USACE risk assessment

aging infrastructure

seepage performance

failure modes

underseepage

wall conductivity

monitoring and investigation