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comm#780--Re: sloped retaining walls[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: comm#780--Re: sloped retaining walls
- From: "Michael Hemstad" <hemstad.ml(--nospam--at)tkda.com>
- Date: Thu, 26 Oct 2000 12:45:26 -0500
If the slope of the backfill is made flatter than the angle of repose of the soil, the lateral force it exerts goes to zero. The structure is then called "slope paving", and you just have to toe it in at the bottom of the slope to prevent the paving from sliding. We usually use a vertical foundation wall with no particular design force, a few feet deep (around here, we try to get it below frost). For slopes greater than the angle of repose, you're back to a retaining wall, but with reduced lateral forces. Also, as Stan noted, the wall itself is more effective because its weight is in a better position to reduce overturning. As to determining the lateral forces, go back to first principles, i.e. a sliding wedge. Since the front face of the wedge is reduced, it is lighter and thus exerts less force in sliding. Most soils textbooks explain this adequately; I like Bowles, "Foundation Analysis and Design." We usually batter walls (slope them backwards) perhaps 1:24, then design them as vertical, both because they look nicer, and because the actual forces experienced by the wall are reduced. The slope effect, by the way, doesn't stop at vertical. Around here we see a lot of modular block walls built to cut a parking lot into a slope. Sometimes the basic engineering principles and assumptions (i.e. anchorage and drainage) are pretty much ignored by the builders, and after a few years they start to bulge and shift. If you see such a wall with negative batter (top overhanging the base), and it looks like rain, don't park under it. Michael Hemstad, P.E. phone: 651/292-4468 fax: 651/292-0083 e-mail: hemstad.ml(--nospam--at)tkda.com Toltz, King, Duvall, Anderson & Assoc., Inc 1500 Piper Jaffray Plaza 444 Cedar Street Saint Paul, Minnesota 55101-2140
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