After weeks of delay, the Norwegian company DNV delivered the second of three parts of the opinion on the collapse of the Metro Line 12 viaduct on May 4. It reinforces the theory of the lack of bolts in the construction of the work. However, Fernando Coca, an expert on the subject, assures that the document only generates more doubts than certainties.
MEXICO CITY.- It was the bolts. That says the second opinion that the Norwegian company, hired by the government of Mexico City to discover why a section of Line 12 of the Mexico City Metro collapsed. The finding is not news, as it was reported in July, when the first part was presented, however, this new version leaves more questions than answers.
“For me, this topic comes to be a ratification of what they had already said before, that the damn bolts were not placed, but they do not want to talk about maintenance, they do not want to talk about the operation and the manuals, which are decisive to know why what failed”, says Fernando Coca Meneses, journalist, author of the book La linea Dorada, los lobos al acecho ; as well as a former Metro official.
As it was announced last June 15 and as the New York Times published a few days before through a leak, the construction of the elevated viaduct had flaws from the work, since the beams that supported the concrete slabs on which they ran the Metro trains were loose since some bolts were not placed correctly. This union made the three pieces, the two steel beams and the slabs, act as a unit, however, having been placed, they affected the functioning of the structure, so to speak, they were “dancing”.
This false fastening, as explained at the conference by city authorities together with representatives of the DNV company, caused excessive vibration, causing cracks in the structure, which eventually created cracks and buckling in the beams of the section that collapsed.
“What the opinion lacks is to say why those bolts were not put in. What did Carso’s specialists calculate to not put them? Yes, in the construction log there were elements to say that they did not put the bolts, what must be determined is why. A few weeks ago, when Slim left the National Palace, he said that his calculators had done the best job, however there was some buckling in the structure due to the lack of these”.
A week after delivering the first opinion, Carlos Slim, owner of the Carso company, went to the National Palace to speak with President Andrés Manuel López Obrador about the incident on Line 12, a day later, the president himself assured that the The tycoon’s company would take charge of the rehabilitation of the line at no additional cost.
Hidden flaws that were documented in photos
In this new part of the segment, it is pointed out that the lack of bolts, coupled with the daily use of the railways, generated deformations in the beams, which were first identified in the longitudinal reinforcement of the north beam in January 2017, which indicates that the structure was already in a compromised condition before the 2017 earthquake and not as a consequence of it.
Although it later says: these deformations were not detectable on inspection with the naked eye, the report ensures that these failures manifested themselves in cracks and moisture stains that are even perceptible in photos on Google Maps. Later in the same report it is documented that a drone inspection in December 2019 identified significant “downward deflection” in both beams.
In this regard, Fernando Coca comments: “They tell us that since January 2017 something was also seen there. So why don’t they tell us what maintenance they did when those damages were found. That’s where maintenance must have come in. If something is losing its shape and the beams have that elastic function of cushioning the weight, wow! Well, this deformation is a response to the loads, generated by the operation of the trains. Later they say that the ballast, the tracks and everything else is normal, except for this”.
“Many of the users and neighbors said that they saw how gravel, grit fell, so was it visible or not?”, continues Fernando Coca. “I have insisted on the Metro logs, since the union told us that in December they detected a crack that is one like these that generate the deflection. And? Why didn’t they do anything?
These contradictions seem minimal, they are proof that they want to leave the whole issue on the bolt issue.
“I don’t know if they are going to go after the bolt worker,” says Fernando. “What I want to know is what the calculators and certifiers did. They are the ones who see that if the plan says that you are going to put 50 bolts and there are only two, then the work does not pass. These are international companies that should have realized that the design was poorly done and that it put the viability of the work at risk.”
Victims’ lawyer accuses contempt of authorities
Teófilo Benítez Granados, defense attorney for the victims of Line 12 of the Metro, expressed his disappointment with the results of the ruling by the Danish company DNV. He accused both the federal government and the head of government of Mexico City of prioritizing their political stability over the comprehensive reparation of the victims.
A minor deflection that was not addressed
One day after the company DNV presented the second part of the technical report, the head of government, Claudia Sheinbaum, and the secretary of Works and Services of Mexico City, Jesús Antonio Esteba, presented the reinforcement project so that Line 12 operate again. During the conference and when asked if these damages were known in advance or not, the Secretary of Works replied that, according to the analyzes carried out by the company, the deflection presented by the collapsed section was not sufficient to be considered a risk in the construction.
“DNV determines that it has 7.23 centimeters of deflection in 2019, based on these drone flights that were made, however, the Construction Regulations of the Federal District, for a clear of 30 meters, contemplate that a deflection could arrive, as maximum deflection, up to 13 centimeters; then, within the range of deflections established by the regulations, it would be the one observed by DNV. This is important to mention”, said the secretary. Then he continued:
“Also, the College of Civil Engineers itself, when it inspects the rest of the sections, says that, at a glance, and it is also important to mention, at a glance, no deformations are detected that could imply a Grade A, which It’s already risky. Here, DNV takes advantage of that study, that this study was not made to see deflections in beams, it was made for verticality, and, well, DNV marks it as a finding, but it is not the cause of the collapse; the cause of the collapse has to do with the deficiencies in the construction procedures”.
The reinforcement of Line 12 will consist of the placement of steel beams that will connect the sections of the elevated viaduct with the columns that support it and it is expected that they will be ready within 12 months.
