soflaac, thanks for that post. I had no idea of the destruction that would come from that dam breaking. That is unreal what could happen to those innocent people. All I can do is send hopes a prayers their way. This is awful. A total shit storm that we are watching

I read a Chinese translated site, claiming it cannot catastrophically fail, because it’s a gravity dam.

Does that make sense?

I have seen small creeks wash 1000#+ boulders down stream

I'm the last thing from a geologist or dam expert, but I believe some who are advised that even more than the dam structure itself failing the threat also includes the natural structure the dam is built on.

Once the base begins to be compromised, it can lead to cascading failure of the whole structure.

quote:

I read a Chinese translated site, claiming it cannot catastrophically fail, because it’s a gravity dam.

Does that make sense?

By catastrophically fail, I think what they mean is come crashing down, all at once.
I hope they are right about that, but that dam is definitely compromised.

China admits Three Gorges Dam 'deformed' by flood
China says 2nd major flood caused 'displacement, seepage, deformation' of Three Gorges Dam
https://www.taiwannews.com.tw/en/news/3972343

Yes, the twitter video shows the whole dam just falling down at once and the water proceeding. I didn't find that all that illustrative.

quote:

Originally posted by ChuckFinley:
Yes, the twitter video shows the whole dam just falling down at once and the water proceeding. I didn't find that all that illustrative.

I'm kinda doubting the dam breaking apart at once wasn't really the point of the video.

That article mentions that the dam has deformed but that it is elastic deformation. By definition, elastic deformation means that the material hasn’t yielded and the deformation isn’t permanent. When the load is removed, the material should resume its original shape (or at least part way, since all of the load will never be removed).

I hope the Chinese government officials who reported this are telling the truth, but, with like anything they say, I have my doubts.

Does anyone know how much elasticity there would be in the materials used to construct the dam? I'm trying to avoid having a Rosie O'Donnell moment.

There's another dam on the Yangtze not far downstream of the Three Gorges Dam. I have to wonder how that's holding up also.

I was around 'dam builders' much of my pre-adult life. My dad & his clan were all in various heavy construction trades. They readily offered their opinions of whatever the latest snafu arouse from various projects and the occassional failure of such.

Earth fill vs concrete vs combination designs are all complicated by a wide range of variables. Some are capable of some degree of 'elastic deformation' without immediate structure failure and some aren't.

I haven't seen convincing arguments regarding elasticity & temporary deformation in huge concrete dam components.

Does anyone with engineering experience have a prediction about what will happen at the dam? You would think there would be some serious evacuations if failure was certain, but who knows in China? Hopefully the rain will stop.

quote:

Originally posted by Kuisis:
Does anyone with engineering experience have a prediction about what will happen at the dam?

Read back a few pages. We had a dam inspection expert give his analysis and opinion.

TL;DR: He thought it was probably going to hold. But that was before Yet More Water, the reports of some "non-structural" failures, the admissions of some deformation, and before leaks had been reported, IIRC.

quote:

Originally posted by Kuisis:
Does anyone with engineering experience have a prediction about what will happen at the dam?

Short of skimming all ten pages, some facts which broadened my knowledge come to light on this post and page:

https://sigforum.com/eve/forums...000026274#4000026274

Okay, maybe this was answered already... why don't then just let more water out? Seems to me when you build a damn you would give it a way to let most of the water escape with out it backing up to over flow on the high side... yes, I know it will flood down stream but a flood is better than a big wave.

quote:

Originally posted by Blume9mm:
Okay, maybe this was answered already... why don't then just let more water out? Seems to me when you build a damn you would give it a way to let most of the water escape with out it backing up to over flow on the high side... yes, I know it will flood down stream but a flood is better than a big wave.

short answer is they have been letting out an extremely high 'outflow' of water

flooding downstream has been bad

maybe even close to the 'max' outflow of what they can -- iirc all the floodgates have been opened

the volume of water from the flooding has been extreme

=================================

The reason they are not letting more water out is either because they can't or they don't want to. I know that sounds trite, but that's the deal. We are focusing on the Three Gorges Dam because of its size, but there are many dams in the Yangtze system. It's a balancing act. If you let more water out at Three Gorges, you increase flooding and pressure on the downstream dams, some of which are likely in worse shape structurally than Three Gorges. So they are probably letting out as much as they need to at Three Gorges to keep their safety readings in the green (or maybe yellow in this case), while trying to minimize downstream impacts.

It could also be that they are already at maximum discharge. All of the primary spillway gates are open, based on what I've seen reported. Modern dams, even in China, should have an emergency spillway to pass water in the event that the primary spillway is inoperable or is overwhelmed. It's generally only used as a last resort to prevent a catastrophic failure. See the Oroville Dam crisis from a couple of years ago for how an emergency spillway can save the day. Three Gorges does not have a designated emergency spillway that I can see. My presumption is that the locks and/or ship lift are designated as the emergency spillway. I'd be curious to know if they are using those to pass water right now at the risk of damaging the structures. That would tell us something about their level of concern.

I also note that most of the discussion and concern has been around the primary dam, the massive concrete structure that shows up in all of the pictures. This flooding is also putting pressure on the south saddle dike adjacent to the main dam. You can see it on aerial photographs running perpendicular southwest of the main dam. That is an earthen structure that is likely more susceptible to failure.

Regarding deformation, anytime stress is added to a system beyond what it previously seen, deformation is going to occur. It's the natural stress-strain relationship of materials. If this is indeed elastic deformation, as China has claimed, it's not a big deal. Even it's plastic deformation, meaning permanent, it may not be a big deal. I don't trust any information coming from an official Chinese source, so who knows what the actual numbers are.

Nothing that I've seen makes me think failure is imminent or even likely. However, I'm hesitant to speculate on what will happen without good data, and nothing coming out of China appears to be good data at the moment.

Given the PRC's talent for understatement, if they're admitting to ANY concerns about the dam...

quote:

Nothing that I've seen makes me think failure is imminent or even likely. However, I'm hesitant to speculate on what will happen without good data, and nothing coming out of China appears to be good data at the moment.

Thanks for your informed analysis, jaaron11.
Although I loathe the CCP, I pray for the people.

quote:

Originally posted by DennisM:
Given the PRC's talent for understatement, if they're admitting to ANY concerns about the dam...

Agreed. That’s what gives me the most concern.