Sliding Stability

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Learn from the failure of Bayless Dam due to instability at DamFailures.org

"A proper stability analysis cannot be performed without knowing the potential planes of weakness beneath the structure, the strength of the materials along potential planes of weakness, uplift forces that occur on the structure or on planes of weakness, the strength of backfill materials, and all loads and load conditions to which the structure may be subjected. Knowledge of geologic formation beneath the structure is also important in defining seepage conditions and uplift pressures. Without adequate foundation explorations and testing, the safety factors provided to assess stability of the structure are meaningless. Preliminary stability analyses are useful to identify design parameters, which require special attention. In some rock foundations there may be many faults, shear zones, and discontinuities that make it impossible to do little more than predict average shear and cohesive strengths of the materials that make up the foundation. Use of lower bound values for foundation shear strength or upper bound values for loads is only acceptable when it can be demonstrated that the added costs to improve the accuracy of the strength and loading data will not lead to significant savings for the structure or foundation."

"Stability must be assessed on selected surfaces within the structure... Sliding safety must also be assessed at/or near the foundation-structure interface. This surface may be either level or sloping. Generally, it may by assumed that a surface that slopes upward (in the direction of possible sliding) will have a beneficial effect, while one that slopes downward will increase the possibility for sliding... Where a shallow weak seam exists below a structure's contact with the foundation, or a structure is imbedded below the top of the foundation, two possible failure modes are present. One mode involves slippage along the weak plane directly under the structure plus slippage along a plane through the foundation above the weak seam (crossbed shear for rock or passive resistance for soil). When the weak seam extends a large distance past the toe of the structure without daylighting, the second mode will usually be critical."

Examples

Learn from the failure of Bayless Dam due to instability (DamFailures.org)

Best Practices Resources

Stability Analysis of Concrete Structures (EM 1110-2-2100) (U.S. Army Corps of Engineers)

Sliding Stability for Concrete Structures (ETL 1110-2-256) (U.S. Army Corps of Engineers)

Gravity Dam Design (EM 1110-2-2200), USACE, 1995

Design of Small Dams, USBR, 1987

Trainings

On-Demand Webinar: Stability Evaluations of Concrete Dams

On-Demand Webinar: Introduction to Concrete Gravity Dams

Citations:

Revision ID: 4478
Revision Date: 11/18/2022