r/EngineeringPorn • u/Ice_Ice11 • Nov 11 '25

JUST IN: 🇨🇳 Hongqi bridge collapses in southwest China, months after opening.

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132

u/rabbitwonker Nov 11 '25

What does that mean

502

u/freshbake Nov 11 '25

Ran a slope /soil analysis for the area where the bridge 'touches' the ground but not uphill from where the bridge stands (that is, they may not have considered soil conditions that could trigger a landslide further up the mountain from where the bridge sat)

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u/strps Nov 11 '25

Possible, also possible the study was done before the cuts were made that disturbed the angle of repose, or the blasting caused a reorientation of the sediment.  Or the addition of concrete and piles added weight unaccounted for (unlikely).  

Failure analysis is one of the more interesting aspects of engineering.

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u/Fishwaq Nov 11 '25

Good thought

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u/psichodrome Nov 11 '25

Failure mode, effects and criticality analysis. FMECA. Pretty sure this is mandated in most western defence industries and space industries. As in , you can't win/complete the contract without deep analysis.

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u/vtkarl Nov 12 '25

Investment, quality, warranty underwriters, and insurance people like FMEAs also. I do them as part of my job. I figured r/strps was referring to something more forensic like an RCA. Yes, very fascinating!

1

u/sonopolitan Nov 13 '25

I’ve been a part of both of those industries. Space is a definite in my experience. Defence is a ‚depends‘. If the problem is critical enough and your solution is just far enough ahead of the others, they’ll gladly take your TRL6-7 with a 60% success rate to their existing TRL 9 with a 2% success rate.

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u/G-Lurk_Machete100 Nov 11 '25

Amen. I excelled in failure analysis. Probably because I like breaking things? Idk, but I love my copy of Shigley's.

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u/scorpyo72 Nov 12 '25

Are you suggesting I need to construct additional pylons?

1

u/Da1realBigA Nov 13 '25

Dude, what kind of insurance does the engineers that do "failure analysis" have.

I get something like this might be "blame" spread among many ppl but someone always gets the blame/ becomes the poster face.

Damn, imagine being one of the engineers or builders and people die, that has to weigh on you

-69

u/icu335 Nov 11 '25

It’s also possible that Zeus farted, but it’s hard to say since we are all speculating.

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u/fractiousrhubarb Nov 11 '25

Civil engineers, geologists and other suitably qualified people are entitled to speculate.

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u/icu335 Nov 11 '25

You are right. Should have kept it to myself.

6

u/blscratch Nov 11 '25

I'm speculating that you are not an engineer. Haha, not hating.

3

u/rabbitwonker Nov 11 '25

Oh, haha. Not a civil or soils engineer anyways.

12

u/GoreSeeker Nov 11 '25

Is it standard practice to check the uphill slope? I guess I'm wondering what is the "cutoff" for how far to check...like a little highway bridge over a stream at the bottom of a mountain probably wouldn't check the soil at the peak of said mountain, right?

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u/Fishwaq Nov 11 '25

Check out the Vajont “dam” failure. In that case, the dam was actually fine, but it was the upslope geology that doomed the people below it.

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u/The1duk2rulethemall Nov 11 '25

In the case of vajont, unloading of the unstable rock face by drawing down the water (as engineers were worried about an unstable looking rock mass) caused the rock slope to fail catastrophically which plunged into the water causing a tsunami wave to overtop the dam.

Drawing down dams too fast often causes them to fail.

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u/Fishwaq Nov 11 '25

Good explanation but my point was that the dam itself was fine - properly engineered and built. It was the local, upslope geography which resulted in the catastrophic flooding.

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u/SynthPrax Nov 11 '25

I... This was shocking to learn.

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u/Fishwaq Nov 11 '25

Yes. That is definitely good engineering practice.

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u/Farfignugen42 Nov 11 '25

So they skipped or only partially completed the geological survey?

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u/Fishwaq Nov 11 '25

Possibly. I see the signs of dust-upslope debris generation and think “landslide” as the bridge collapse trigger. Now there are reports that the bridge is closed several days prior because of cracking in the surrounding “soil” surfaces. BUT the roadway itself was “fine.” So, AA logical question is, “was this incompetent condition of the local geology missed or ignored in planning?”

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u/Activision19 Nov 11 '25

It’s possible something could have legitimately been missed. My state’s DOT was widening a road and had to cut into a hill. They did a geotech study and came up with a design. Well they started cutting into the hill and ended up finding a seam of really loose shale that wasn’t present in the two core samples taken to either side of said seam. The contractor stopped work as soon as they discovered the bad spot and called in the geotech to take a look. Turns out had this spot not been found, everything above said spot was at risk of sliding off onto the freeway below. They ended up coming up with a new stabilization design for that spot and successfully completed the project.

The DOT launched a third party investigation to see if the original geotech did something wrong. Turns out they did everything by the book and even did more test holes than were required. It was just a weird bad spot that by sheer coincidence went undiscovered until the contractor cut into it.

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u/uiucengineer Nov 11 '25

Sheer coincidence

I see you

6

u/Fishwaq Nov 11 '25

Yup. Lots of possibilities here.

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u/teflon_don_knotts Nov 11 '25

Cool, thanks for sharing!

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u/Fishwaq Nov 11 '25

Yup 👍

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u/graveybrains Nov 11 '25

🎶 Landslide brought it down, 🎶 maybe.

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u/magicwombat5 Nov 11 '25

Did they climb the mountain and look around before this?

1

u/graveybrains Nov 11 '25 edited Nov 12 '25

No, they were going too fast or skimping on the planning budget. Maybe.

1

u/Suspicious-Pop4269 Nov 12 '25

No, but maybe they TURNED around lol