Deep excavation retaining wall failure in Istanbul, causes building collapse 1

[TehMightyEngineer]

Best video I can find of the collapse of the retaining wall:

https://www.reddit.com/r/Catastroph...oncrete_retaining_wall_failure_allows_a_hill/

Never done a soil nailed retaining wall of this magnitude personally but this looks very haphazardly constructed, not surprised it came down. Geotech's out there, I would love to hear your thoughts.

The excavation wall failure led to the eventual collapse of the structure that was partially supported on the remaining soil:

https://www.reddit.com/r/Catastroph...lding_rolls_down_after_foundations_have_been/

https://www.9news.com.au/world/2018...-apartment-building-crumbles-after-heavy-rain

https://www.dailysabah.com/istanbul...-landslide-collapses-in-istanbul-neighborhood

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[JAE]

The articles mentioned lots of recent rain in the area.

The first thing to fail appears to be the upper horizontal strut - it appears that it released from the wall, as though it is pulled away by its far side attachment (not in the video) and simply drops away as it loses contact with the wall surface. Then the tie-backs start popping and the plates start falling.

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[MacGyverS2000]

And here's the house at the top of the hill collapsing...

https://www.youtube.com/watch?v=MmzjfD1POQw

Dan - Owner

http://www.Hi-TecDesigns.com

 

[EireChch]

@ JAE - the horizontal strut doesnt seem to be adequately fixed to the wall?

Also - the lower portion seems to be missing some shotcrete from excavation level to maybe 10 ft. I dont think it is the cause of the problem but it wouldnt help the situation though

 

[dik]

From the water seeping through the wall, there was a very high hydraulic head.

Dik

 

[bimr]

Thanks for posting this. The pipe breaking like a matchstick at approximately 26 seconds was interesting.

I would be interested to know if this project owner had taken out a building permit and was inspected.

Probably not the case as it appears construction projects are particularly prone to corruption, and bribes are often demanded.

www.business-anti-corruption.com

 

[JAE]

bimr - to me it looked like the pipe didn't break - just fell off the wall. Watch it again and see if you agree with me.

My thought was that the bottom of the retention wall was sliding down and inward, possibly rotating the top part of the wall away from the pipe.
With loss of compression, the pipe just fell away downward.

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[bimr]

JAE (Structural)

Yes, at approximately 25 seconds, the anchorage at the retaining wall loosened causing the horizontal strut (pipe) to fall.

However, on the way down, the end of the horizontal strut (pipe) hit the wall anchors and at 26 seconds, the horizontal strut (pipe) broke in half. It appears that the pipe pieces were connected with splice plates although it is observe clearly on the video.

The apartment building’s owner Emin Ertürk said he had warned authorities about the construction of a hotel in the adjacent plot. Locals told several newspapers that they have warned construction officials of cracks in their buildings.

Beyoğlu Mayor Ahmet Misbah Demircan said the collapsed apartment building, which was built in 1994, did not have required permits. The exposed foundation of the apartment building doesn't look adequate for a building of that size or for the soil conditions.

 

[Agent666]

I guess bad things happen when you excavate below the base of the retaining wall, who would have thought?

the way I see it effectively without any reaction at the base due to the over excavation, the wall cantilevers upwards to the anchors which probably are not designed for that, and it all starts to unzip progressively.

Whenever I've designed smaller tied back walls, the wall extends quite some distance beyond the bottom of the final excavated level into the ground, both to cutoff any potential water flows to limit settlement and to simply provide stability and resist the bottom horizontal reaction.

Building that fell in didn't appear to be reinforced, walls exploded into 1000's of pieces, if reinforced you would expect it to hold together a bit better than it did and slide into the hole.

 

[ornerynorsk]

Reminds me of saying that a machinery tech that I used to work with used as an explanation for myriad mishaps - "gravity works, never forget that".

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Compositepro]

It appears that the pipe strut fell because the bottom of the wall pushed out and the wall above the rows of ground anchors pushed into the soil and released pressure on the strut. This is not surprising after the fact, but not something I would have predicted before seeing the video.

 

[hokie66]

When I was in Turkey a few years ago, I talked to several educated engineers. But they were selling hats, belts, etc. For what it's worth...

 

[JAE]

hokie66 - I think that wall needed a few more belts and suspenders.


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[Brian Malone]

It must have been quite unnerving for the crew on-site to hear all the creaks and groans leading up to the zipper-line of pings of the tie backs snapping. Good thing no one was down in the pit - the excavator is just money.