Earth Dam Core Inclination

[moe333]

Dave (and others),
The DSOD "likes" clay cores inclined at least 0.5:1 (H:V) to reduce the potential for horizontal cracking resulting from larger core settlement vs. shell settlement. Is this just a DSOD issue or do other agencies "like" this as well. I am looking at a design that has a vertical downstream clay core face.

Thanks

 

[BigH]

How high is the core?

 

[moe333]

120 feet

 

[dgillette]

If you are limited by available borrow to a thin core, my instinct says to prefer it sloped, but I haven't seen clear evidence that it matters much if the materials are all properly compacted. I honestly do not know whether the arching/horizontal cracking issue is real or theoretical with good compaction. With a thick core, sloped upstream and vertical downstream, it seems pretty unlikely to be a problem unless there are very large differential settlements between core and the adjacent downstream zones (which might argue for 98% instead of 95% on a high embankment). That's my hunch, not based on detailed analysis. How easily could you put a slope on the downstream side?

Of the last three large dams we've built, one has an inclined core, one has a central core sloped 0.5:1 both ways, and one is 1:1 upstream and vertical downstream. (Disclaimer - I wasn't the designer on any of them.) I think that material went in dry of optimum on all three, rolled to 98% or more (standard) with 825s or modified 825s with more sheeplike feet, so there shouldn't be a whole lot of consolidation from dissipation of construction pore-water pressure. There is more potential for that with 95% compaction placed wet of optimum.