Thread by @Lidsville

Now that serious geotechnical problems have materialized in #SiteC's foundations, as many experts predicted they would, my engineer friend has some questions about dam design given the unstable geology. I think his Qs may help us see why fixing these problems is unlikely. #bcpoli

..With the photos in two #SiteC articles today & a diagram from an article by the dam's own engineers, our engineer's Qs are easy to illustrate now:
1. @TheTyee:
thetyee.ca/Analysis/2020/…
2. @VancouverSun: vancouversun.com/business/site-…
3. Canadian Dam Assn nxtbook.com/naylor/CDAQ/CD… #bcpoli

@TheTyee @VancouverSun ..I'll preface the engineer's Qs with some background. The part of #SiteC that's in serious stability trouble, acc. to BC Hydro's own (tardy) July 31 reports, is the only part they've actually built so far: the short end of the L that houses the most critical parts of the dam..

@TheTyee @VancouverSun ..And recall that #SiteC's unusual L-shaped dam design has never been tried with an earthfill dam (the most dangerous kind) before, let alone an earthfill dam on the worst foundation conditions that experts like Harvey Elwin have ever seen:

https://twitter.com/Lidsville/status/1297211818029408257?s=20

#bcpoli

..Now, the area of #SiteC currently having unspecified foundation trouble (we must assume it's movement of the whole structure, with cracks being the most typical symptom of that) is where the spillways, generating station & turbines are, which require zero move't to function..

..After Gordon Campbell resurrected #SiteC from the trash bin that experts had relegated it to, BC Hydro hired corporate engineers who saw that the S. bank (aka right bank) of the Peace was too unstable to attach a dam to, & designed the L-shape to avoid that bank in 2010-2011..

..My old friend Vern Ruskin, an original BC hydroengineer who led teams building BC's great dams on the Columbia and Peace Rivers, back in the era when BC Hydro actually had institutional knowledge of how to build dams, didn't think much of this L-shaped design or the site..

..Now recall another engineer friend's descriptions of the unique shale at #SiteC, which is 1000s of feet deep. It's not "rock" as we'd understand it. It's also weaker than most other shales. Deceptively hard when dry, when wet it swells & falls apart..

https://twitter.com/Lidsville/status/1223339234351710208

..Now for my engineer's Qs & a note: "The material shown as "bedrock" or "rock" on drawings & descriptions & supporting all the concrete weight on the S bank, is not real rock but a soft clay that behaves like rock when dry, but loses its compression (bearing) strength in water."

BC Hydro talks of "foundation enhancements" but engineer says they're "simply added into this clay which is still unacceptable material, as competent foundation rock like carbonate rock found in the mountains, or granite, does not exist this far east along the Peace River."

..Let's get into the engineering nitty gritty now. Here's the diagram of #SiteC's South bank buttress for the spillways/generating stations/spillways. This is the short end of the L, where Hydro poured well over 1m cubic m of roller-compacted concrete that now seems to have slid.

..Recall this diagram from the 2016 paper written by #SiteC's own engineers. Our engineer points to that grey diagonal - that's the roller-compacted concrete buttress in the paper's title. You see that sort of shallow wedge at the bottom of it? nxtbook.com/naylor/CDAQ/CD…

..That curved bump at the bottom of the buttress is a kind of "shear key." Recall BC Hydro's sheepish July 31 reports which admit foundation problems under the whole south bank edifice, & talk about possibly fixing them with anchors, extra drainage, &...shear keys. What is that?

..A "shear key" is more or less something wedged into the ground to stop a structure from sliding. Simple diagrams below will give you an idea. Q: how can BC Hydro possibly add such a thing to an immense, already-poured structure weighing millions of tons, & into weak substrate?

..So the buttress design for #SiteC's powerhouse/spillways had a kind of rounded shear key of its own, but to no avail? Seems water has weakened shale under whole buttress: is the shear key now sliding through it to the river, or is shale swelling & uplifting under fdn, or both?

..Those diagrams show diff parts of the South bank buttress. More Qs from engineer: how is the slanted buttress itself not a kind of dam, since the shale behind will fill w/ water & thus exert powerful hydrostatic pressure against it? May also be how water seeped under dam fdn.

.."Water seeping thru the shale & behind the buttress can make the buttress a dam. When/if filled, the 26m deep water in the approach channel will raise the height of water behind the buttress & powerhouse up to full reservoir height, adding further load on buttress from behind."

..This is why in BC Hydro's #SiteC reports there was talk of trying to add extra drainage - would we be hearing such talk if there weren't water buildup exerting enormous pressure on the structures? & How do you build drainage once a concrete structure of this size is in place?

..As for the 3rd solution, "anchors" - how do you anchor something weighing millions of tons when it sits entirely on unstable ground that melts when wet, no bedrock anywhere? What do you anchor it to? Engineer's earlier joke: to skyhooks. #scifi #Sitec

https://twitter.com/Lidsville/status/1291793090261315584?s=20

..This is too long so I'll stop here. But I think you get the idea. Please ask questions. We can go into much more detail.

My final remark: this is not fixable. No more billions poured into pointless attempts to salvage this. Scrap it now. #SiteC

Oops, said "spillways" twice. Second one was meant to be "turbines" which are part of the generating station, sometimes called the powerhouse

..PS Engineer's summary: "All the weight on the buttress incl the buttress' own weight is being transferred to the shear key & from there into the soft clay by compression (ie pushing on the clay). But the soft clay is weak in compression so how does it support all this weight?"

..It would be nice if BC Hydro or any of its engineers would answer these questions and give us much more detail than the vague but alarming info supplied to us in their reports. We are paying for #SiteC. It's our money and our risk. #bcpoli sitecproject.com/sites/default/…

..What's really crazy: John Nunn, the original head #SiteC engineer, has a degree in soil mechanics & ought to know this shale. But he is on both the BC Hydro board AND the shadowy "project assurance board" overseeing #SiteC, so he's checking his own work. That's sketchy.

..A response to this thread from an energy expert who can't comment publicly on this #SiteC mess. (Twitter: where unlike journalism, you can quote the anonymous). I agree captured provinces are the problem, but restoring energy regulators to full independence would help. #bcpoli