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RE: journalist query - factors of safety[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: journalist query - factors of safety
- From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
- Date: Fri, 4 Nov 2005 15:37:37 -0500
US Army Corps of Engineer's publication EM 1110-2-1913, Design and Construction of Levees, does in act show a minimum 1.3 factor of safety for slope stability at "end of construction" (Table 6-1b), and even permits factors of safety of 1.0 to 1.2 for rapid drawdown conditions (lower probability conditions). For earth dams, EM 1110-2-1902, Slope Stability, also has a minimum required factor of safety of 1.3 for slope stability at "end of construction", and 1.1 to 1.3 for rapid drawdown. Dams are required to have some "freeboard" above flood level, whereas levees are only required to account for long-term settlement (without added freeboard).
For concrete floodwalls, EM 1110-2-2502, Retaining and Flood Walls, requires a sliding factor of safety of 1.5 for the design flood condition and a reduced factor of safety of 1.33 for water to the top of wall (assuming some freeboard is provided).
EM 1110-2-2200, Gravity Dam Design (for concrete dams), requires a sliding factor of safety of 1.7 for Unusual Load Conditions, including the Standard Project Flood.
I can't explain the reasons for the differences - just reporting the facts.
William C. Sherman, PE
CDM, Denver, CO
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