Why the Mexico City Metro Collapsed

[cteno4]

This is sickening to read.

https://www.nytimes.com/interactive/2021/06/12/world/americas/mexico-city-train-crash.html?referringSource=articleShare

 

jeff

[katoftw]

Paywalled content.  Can you give us the general info please.

[cteno4]

I think they allow a few free per month but have to register.

 

litany of horrid construction disasters to get the project done for political reasons, including buying cars built to euro track standards to get them sooner for a North American standard track system that ended up hammering the shoddy track system. Not seen a report this detailed yet in the media.
 

jeff

[Szdfan]

It’s disgusting how many corners were cut and how badly this was built in order to rush completion before an election. 

[bill937ca]

I think at the time I head there were people who didn't like the way the job was done.

 

[cteno4]

It had issues before it opened and ever since with repeated reports, but mostly ignored. Real litany of things like no master plans and only using as built plans by a company that was not a railroad construction company. Switching out rail car providers to one who could get work done faster but wheels to European standards not NA standards along with shorter cars than the elevated track was designed for. Structural parts left out and the main bolt ties between the metal support structure and the concrete base slab being the only attachment between the two and really poorly executed. Numerous times issues were brought up in reports but ignored. All this built in a very earthquake prone zone. Built by one of Mexico’s wealthiest and completely rushed for opening to be mayor’s kick off for a presidential run. It’s like how could you build this to fail. Just sad.

 

jeff

[bill937ca]

And this is also a rubber tired train.

[cteno4]

From what I could find lime 12 is Steel wheels on steel rail using FE-10 rolling stock. From the issue of euro spec cars on NA spec rail I read as probably small differences I  rail and wheel profiles were causing all the hammering that was warping rail. None of the photos of the wreck I could find showed the wheels.

 

jeff

[JR 500系]

Certainly a sad story... Were building regulations not in place during construction whereby there had to be layers and layers of checks by qualified persons before it is deemed completed safely? The studs were poorly welded hence the clean shearing off... Shouldnt there be another fail safe stud to prevent absolute failure? 

 

There didnt seemed to have a factor of safety being calculated during the design phrase.... Which is cost saving yes but can cause undesirable failures.... 

 

All in all poor planning, rushed construction and failure of checks that resulted in this tragic event.... May those who had lost their lives rest in peace..... 

 

on a side note, the case study was easy to read with animated graphics which was really nice! 

[cteno4]

Studs should not have sheared if properly welded and placed but looks like both were not done right. Yeah usually engineering on things like this have a bit of a failsafe backup for the really bad scenarios that will at least prevent things from completely falling apart. Here it looks like bolt shearing and constant pounding along with port supports between the metal beams (they even were outright missing in some places) to stabilize them along with weakly designed beams and inferior metals (all documented thru construction and afterwards) caused the main support beams to bow in and crumple, and thus catastrophic collapse.

 

planning was so rushed they never generated any master plans for construction before they began construction, they just drew things up as they built it but the company that did not have experience doing railways. Put on top of that the intense pressure to meet an opening date and it’s a recipe to do everything the wrong way.

 

sounded like folks spoke up but of course not listened to as they were rushing to get it opened before the mayor’s run for presidency. Whistleblowers in those situations are usually stepped on like bugs. After opening it’s finger pointing and there is not the money to really fix it as it’s going to cost a lot to get it to decent specs now. Even now they are trying to say it was probably a maintenance issue, not a totally flawed design and constructions due to tons of really bad decisions. Last round of fixes sounded like only spot fixes where there was visible damage, not retrofitting for systemic design and construction flaws.

 

the more I read on it elsewhere the sadder it got.

 

jeff

[disturbman]

19 hours ago, bill937ca said:

And this is also a rubber tired train.

i think you are confusing these with some of the other lines that were built by the RATP. The NYT’s infographics also looked like it was rubber tired but the picture doesn’t match that. Seeing the issues described, it wouldn’t have made a difference.

[cteno4]

Yeah I think they looked at the whole system and saw most of the lines were rubber tire. But 12 appears to be metal wheels and the reason lots of stress being put on track and roadbed and potentially leading to the final collapse. AFAICT it’s metal wheels on the FE-10.

 

jeff

[gavino200]

11 hours ago, JR 500系 said:

Certainly a sad story... Were building regulations not in place during construction whereby there had to be layers and layers of checks by qualified persons before it is deemed completed safely? The studs were poorly welded hence the clean shearing off... Shouldnt there be another fail safe stud to prevent absolute failure? 

 

There didnt seemed to have a factor of safety being calculated during the design phrase.... Which is cost saving yes but can cause undesirable failures.... 

 

All in all poor planning, rushed construction and failure of checks that resulted in this tragic event.... May those who had lost their lives rest in peace..... 

 

None of this is unusual in Mexico. Ask any Mexican and I bet they'll tell you this doesn't surprise them at all. I've already had the conversation with a few friends from CDMX. Political corruption and cynicism in MX are at a truly shocking level. It's tragic, as it's a beautiful country with a wonderful culture. I still hope it can change. 

 

 

Quote

 

on a side note, the case study was easy to read with animated graphics which was really nice! 

 

Agree. It was a bit like being on a jury. Or in a classroom? 

Edited June 15, 2021 by gavino200

[Nick_Burman]

22 hours ago, cteno4 said:

Yeah I think they looked at the whole system and saw most of the lines were rubber tire. But 12 appears to be metal wheels and the reason lots of stress being put on track and roadbed and potentially leading to the final collapse. AFAICT it’s metal wheels on the FE-10.

 

jeff

 

The Mexico City metro was built as a rubber-tired metro in part due to availability of French finance and in part due to CDMX's fickle geology, what with most of the city being built over a filled-in lake, the Lago de Chalco.  However two lines - A and 12 - were built as steel wheel/rail lines because they were outside the former lake area and also because rubber tire construction has become very expensive. 

 

 

Cheers NB

[disturbman]

Beside the cost difference, isn't it also because the technology has lost its few performance advantages in acceleration and breaking distance/precision and become irrelevant? The new automated subway lines around Paris are being built as normal steel-wheeled lines, and not as rubber-tired.

[gavino200]

3 hours ago, disturbman said:

Beside the cost difference, isn't it also because the technology has lost its few performance advantages in acceleration and breaking distance/precision and become irrelevant? The new automated subway lines around Paris are being built as normal steel-wheeled lines, and not as rubber-tired.

 

Interesting. How did it lose it's advantage?

[Nick_Burman]

21 hours ago, gavino200 said:

 

Interesting. How did it lose it's advantage?

 

Lighter construction, new developments in traction technology (especially 3-phase AC transmissions) and braking (rail equivalent of ABS, for example).

 

 

Cheers Nicholas

 

[disturbman]

Thanks @Nick_Burman, I haven't had time to expand.

It's to the point that, in the early 10s, or late 00s, the RATP seriously studied the possibility of "depneumatizing" Paris subway line 11 as part of the 6km northward extension of the line. As a reminder for our non-French/Parisian posters, the line was historically the first line to adopt the technology and served to prove it in commercial service, leading the path to the "pneumatizing" of line 4, 1 and 6 in the 1960s and 70s

This proposal of abandoning the rubber-tyre technology was quite a shock at the time, since this technology and the pilotage automatique, or "auto-pilot", an almost fully automatized technology, requiring only drivers input when leaving the stations, were developed simultaneously in the 1950s. Before equipping all lines bare one starting the end of the 1960s. The PA and rubber-tyre technology led to the development of fully automatic subways technologies in France, like the Val or line 14.

 

In the end, iirc, the reversal was abandoned because of costs; and perhaps also of the love of the RATP for its own technologies. I'm certain there will be studies and debates about "depneumatizing" all rubber-tyre lines in the 2050-60, when the renewal of the rolling-stock of line 1 and 14 will come up.