Gravity RCC Dam founded on Drilled Shafts
Gravity RCC Dam founded on Drilled Shafts
(OP)
I am working on a conceptual design for a reservoir dam. The dam will be roughly 1600 meters long and consists of a gated spillway, an RCC section designed for auxiliary overtopping (roughly 460m long), and an earth embankment section (835m) strictly to contain water and not designed to be overtopped. The water table is at 7 meters below existing ground surface and competent rock is at roughly 30 meters below ground excavation. I am proposing to excavate to just above water table and place drilled shafts to competent rock (the dam will be roughly 30 meters in height from water table elevation). I am looking for any insight or supplemental references on drilled shafts foundations supporting gravity dams. If anyone can help, it would be greatly appreciated. Thanks.





RE: Gravity RCC Dam founded on Drilled Shafts
RE: Gravity RCC Dam founded on Drilled Shafts
RE: Gravity RCC Dam founded on Drilled Shafts
RE: Gravity RCC Dam founded on Drilled Shafts
The better method of construction is to either excavate to compentent material to start construction (with the required dewatering and coffer dams) or to construct slowly allowing the materials to consolidate and gain strength. There are probably many additional ways to construct a dam at this location but those are the one that come to mind off the top.
RE: Gravity RCC Dam founded on Drilled Shafts
A couple of thoughts:
You wouldn't be able to grout the alluvium, so you would probably need some form of cutoff wall, such as plastic concrete placed under slurry, depth depending on materials in the fndn - $$. (A fully penetrating c/o is, of course, preferable to partially penetrating c/o, in general.)
You would need a pretty massive structural connection between the piers and the RCC in order to transfer the weight. The clay would carry practically none of it. Again, $$.
You would need to prepare for large differential settlements where the conventionally constructed embankment on soft clay abuts the RCC on piers.
Overall, if it's not considered feasible to exc clear to bedrock, you may be better off with embankment all the way across, with some other means of passing the water, such as a fuse-plug auxiliary spillway, overtopping protection on embankment, etc. Allow for consolidation settlements by either staged construction or just overbuilding it if fndn conditions allow w/o concern for stability during construction.
Let us know what you decide on.
RE: Gravity RCC Dam founded on Drilled Shafts