Thread by @Lidsville

It's been 1 week since Horgan's #SiteC announcement. Unsurprisingly it's also been 1 week of hearing from engineers & construction experts about the proposed geotechnical "fix" at Site C (what little the BC govt released). This could be a long thread. Apologies to non-nerds..

NOTE: because #SiteC is shrouded in secrecy & full info is never released, engineers & construction experts can only go by the scant info that's available. If BC Hydro/BCH engineers want to argue that other engineers don't know the details, we invite them to release those now.

Having said that, we already had a little technical information on #SiteC, which is now combined with the Geotechnical Safety Overview Report that the NDP govt released on Friday, so we have a fair amount to go on. See:
news.gov.bc.ca/files/Site_C_G…
and also
news.gov.bc.ca/files/2-26-21_…

Even though the NDP gov't is withholding over 100 engineering reports from the public, as @BenParfittCCPA has reported here: policynote.ca/minding-the-sh…
and we have a great deal of information on the hazards at #SiteC from its design engineers themselves:

https://twitter.com/Lidsville/status/1297975972633837568?s=20

@BenParfittCCPA In the diagram above, the bulge at the bottom end of the grey sloped concrete "buttress" is a "shear key" or wedge-like brake to stop the buttress from sliding/moving on shale. Unsurprisingly it didn't work; the engineers failed. There are several of these buttresses...

@BenParfittCCPA ...The buttresses sit on the short end of this experimental, L-shaped dam. They are the foundation for #SiteC's key working parts: spillways & turbines/generating station. Turbines don't tolerate any significant movement. What solution has been proposed to stabilize buttresses?

Oh first, the engineers verge on boasting about their L-shaped dam design & buttresses in this paper they delivered to the Canadian Dam Assn in 2016, which by the way reveals just how weak the "bedding planes" are beneath the dam: nxtbook.com/naylor/CDAQ/CD… #SiteC

A diagram of the new "fix" at #SiteC can be found on P.7 (was on P. 16 with a more informative diagram that's now gone; did anyone get a screenshot?)
See the blue vertical lines? The fix involves these massive piles or pilings acc to the report. news.gov.bc.ca/files/Site_C_G…

Ah, correction. The other drawing was in the Milburn summary which is here, P. 16. Note the dotted red line here - that's the bedding plane that failed to support the buttresses; now they have to try to support this dam on much deeper material. #SiteC news.gov.bc.ca/files/Milburn_…

These reports persist in calling the material below these dam structures "bedrock" but it's not what we'd call solid bedrock. What these concrete structures & the dam will actually be sitting on is a soft clay shale with engineering properties that change with exposure to water..

The proposed #SiteC fix is installing up to 125 piles (blue verticals) 2.5 metres in diameter & 25 metres deep, supposedly down to more stable layers. As you can see, these piles attach to the concrete spur extending beyond the shear key toward the river. This raises concerns.

For more information go to P. 6 of the Geotech Safety Report news.gov.bc.ca/files/Site_C_G…

Every engineer & construction expert who contacted me flagged these piles as an unstable solution for #SiteC that they themselves would avoid. Selected remarks: "Adding these "anchor piles" is a very risky proposal. If it doesn't work as planned, there is no way to recover..."

First, to drill those piles you are putting ~125 x 8.2' wide holes into the RCC (roller compacted concrete, weaker than poured) foundation, which may further weaken it. But the engineer here highlights other dangers in this fix: #SiteC

I'll elaborate on the engineer's concerns re: the weakness of this #SiteC "fix," but first a point from a former BC Hydro Senior Construction Manager for the Peace Region on the seismic vulnerability of this design. Note: he thinks these piles may actually be caissons (google it)

Engineer continues: "We don't know how they plan to attach these pipes to the existing concrete but any connection will be under an extremely large rotating force or torque (called a "moment") that would likely crack the concrete, and then the pipe won't support anything..."

..Engineer: "I have no idea how much it will cost to install these pipes and I think it's a waste of money. It won't work to hold the foundation solid with no movement, and may damage the foundation beyond repair if it wants to slide toward the river, which it will." #SiteC

.."The problems with the early straight-line dam design they rejected due to instability are tough, but nothing like this L-shaped design. The original had all its weight sitting spread out on the riverbed. This one has it sitting on a point as it tries to slide down hill" #SiteC

....."It's good the Milburn report, in concluding the geotechnical section, mentions potential "instability" of the earthfill dam due to low shear strength, & deals with instability of the heavy concrete installations on the south bank, also due to lack of shear strength...

.."But we can't come up with engineering calculations to safely design these facilities, because this cohesionless shale, with its range of engineering properties depending on whether wet or dry, defies analysis. It's hundreds of feet deep at #SiteC & there's no competent rock.."

..Engineers & construction experts alike have raised this point: "Those piles/pipes will be sitting in water all the time & water will work its way down the outside of pipes & weaken the shale to where it won't anchor anything."

The recent #SiteC reports don't address this.

Construction manager adds: "At 2.5m (8 feet in diameter) times 125 pipes (caissons) adds up to 312.5m, well over 1000 feet of mud removed & filled with concrete. It will be hard to keep seepage water out, even if they pump it out. This is one costly non-fix solution... #SiteC

Engineer adds some rough calculations:

"These pipes are simply to solve a problem caused by a faulty design & assumption the shale had adequate shear strength, which it doesn't.

I assume France & Hoeg weren't allowed to criticize the L shape design with all the concrete sitting above the river bed ready to slide?"

""Our review services were performed within the limits prescribed by BC Hydro in a manner consistent with the level of care & skill normally exercised in the current standard of professional engineering practice." - experts France & Hoeg

What the hell are they saying here?"

Some other points, in no particular order because there are so many. Engineer: "All the buttresses are independent of each other, so they will move randomly. How can the reservoir behind them ["approach channel"] be contained if anything fails up there from the movement?"

The 2nd #SiteC fix shows that Hydro has recognized the danger of the "approach channel" part of the reservoir that will push on the buttresses in the short end of the L, are already moving even before the reservoir is filled). They plan to beef up the watertightness there..

"They finally recognized the danger of approach channel water getting in behind the buttresses, & will "enhance" the lining to prevent this. Still a v dangerous design, because if water gets in there the buttresses become a dam & no amount of piles in shale will hold it in place"

Oh: to match the construction manager's calculations (earlier in thread), engineer just calculated loss of material from drilling these new pilings:

There is more. A lot more. But I'm going to stop this thread here for now. Please ask questions. I can probably answer them with the material they've given me, or I can ask them to clarify. A big thanks to all of them for being so generous with their time, over several years.

I will just add, for myself, that I am disappointed that international experts with global reputations like France and Hoeg would agree to opine on this project with apparently limited information & constrained terms of reference (their statements subtly refer to this).

If @BCHydro wants to counter any of the above, we'd love to hear from you! While you're at it, please give us access to all reports, including the more than 125 engineering reports Tim Little signed. Hoeg & France aren't responsible for safety; you are.

@bchydro Engineer friend adds: "We would like to know BC Hydro's method of lowering the reservoir to relieve the pressure on the dam and buttresses if a problem starts to materialize." (There isn't one, as far as we can tell.)