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MEXICO CITY A preliminary expert report on the collapse of an elevated subway line in Mexico City that killed 26 people attributed much of the blame on Wednesday to poor stud welds that connected the steel support beams to a concrete layer supporting the track.
The city government hired the Norwegian certification company DNV to investigate the possible causes of the accident on May 3, in which a span of the elevated line collapsed to the ground, dragging two metro cars.
The report also stated that there were apparently not enough studs and that the concrete poured over them may have been defective; the welds between the sections of steel beams also appear to have been poorly made.
The studs showed flaws in the welding process, the report said.
The existence of construction defects during the construction of the line between 2010 and 2012 could be a blow to the political career of the top Mexican diplomat, who was then mayor, and to the richest man in Mexico, whose company built part of the metro line.
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The report centered on photos and a physical inspection which showed that the metal studs welded to the top of the steel support beams had either broken or come off cleanly, suggesting the welds were faulty.
The beams alone could not support the weight of the platform. The uprights protruding from the beams were covered with a poured concrete slab to help support the weight.
But the studs still had ceramic rings that covered the welds. Used as a method of safety and control to contain molten steel, the rings were supposed to have been removed after welding so that inspectors could see the welds themselves. The fact that they were left in place may suggest that the welds were not properly inspected.
This would be in line with reports that the project was rushed to completion so that the number 12 metro line could be inaugurated by the current Foreign Relations Secretary Marcelo Ebrard before he stepped down as mayor in 2012.
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The section was built by a company owned by telecommunications and construction magnate Carlos Slim, currently the richest man in Mexico and once the richest in the world. Slim is an engineer by training and his companies are currently involved in the construction of parts of the controversial Maya train project, which will circle the Yucatan Peninsula.
Any suggestion that his company did shoddy work on the subway would deal a serious blow to his reputation as an aged statesman in the Mexican business community.
The $ 1.3 billion number 12 line, the most recent section of an extensive metro system opened in 1969, was miserable from the start. The so-called Gold Line cost half as much as expected, suffered repeated construction delays, and was plagued with allegations of design flaws, corruption and conflicts of interest.
A senior executive from one of the companies that built it was the brother of the man who oversaw the project for the government.
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The scandal of the costly new line being forced to close in 2014, just 17 months after its inauguration, essentially forced Ebrard into political exile. He was rescued by his boss, the new president Andrs Manuel Lpez Obrador, who had helped his mayoral nomination in 2006 and resuscitated him by appointing him foreign relations secretary in 2018.
Despite the metro scandal, Ebrard was tasked with Mexico’s efforts to obtain coronavirus vaccines and was seen as one of the main candidates to succeed Lpez Obrador in 2024.
Ebrard said hell would cooperate with investigations into last month’s crash.
Earlier reports from engineering companies have revealed that the city government of Ebrards made a series of surprisingly bad choices when designing and building the metro line.
Experts said the route’s unusually sharp curves exacerbated problems with the design of the steel tracks, which looks more like the New York subway than the European-style rubber tires used on the rest of the system.
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The Gold Line chatted, banged and screamed. The rails began to take on a wavy pattern. Drivers had to slow trains down to 5 km / h (3 mph) on some sections.
In 2014, the Gold Line had to be closed for months to have the tracks replaced or reshaped.
Ballast was added between the train tracks during these repairs, and some say additional weight and possible poor maintenance could have been potential factors in the collapse.
A 2017 official investigation into damage from a deadly 7.1 magnitude earthquake showed indications of construction faults. Authorities decided on quick fixes, welding accessories under the arched beams and reopening service.
Ebrard argued that subsequent investigations showed the line was found to be up to standard when it was built. He wrote that the supervision and maintenance that fell to the administration that succeeded mine remains largely an unknown.
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As a result of previous design and corruption investigations, more than 38 government employees have faced fines or other penalties for improperly contracting work on the train, as well as certain criminal charges.
Since the accident in May, much of the line has been closed. The elevated portion of the lanes rises approximately 16 feet (5 meters) above a middle strip and causeway in the poor South Tlahuac neighborhood. The thin reinforced concrete columns are topped by horizontal steel beams, which in turn support prefabricated concrete track beds on which are laid gravel, railway ties and tracks.
Mexico City’s metro, which serves 4.6 million riders every day, never had the one thing it needed most: money. With ticket prices stuck at 25 cents per trip, one of the lowest rates in the world, the system has never come close to paying its own costs and is dependent on massive government subsidies.
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