MEXICO CITY – Construction failure led to corn collapse of an overpass in Mexico City’s subway system that killed 26 people and injured several, according to preliminary results of an independent investigation released by the city government on Wednesday.
The report, produced by the Norwegian risk management company DNV, suggests that serious problems with welding and placement of metal pins, screw pins throughout the structure, directly contributed to the collapse.
“We can tentatively determine that the incident was caused by a structural fault,” the report said, referring to “deficiencies in the construction process.”
The results support the results of a study by the New York Times that highlighted shabby construction on the subway line. Some of the bolts that held the structure together appeared to have failed due to poor welds, The Times found, a crucial flaw that likely caused the transition to recede.
Engineers heard by The Times pointed to the presence of ceramic rings or casings left in place after the welding process, and to irregularly placed knobs as evidence of subcontracting – findings confirmed by the DNV survey.
Its report documented a “failure to remove the protective ceramic” around the bolts, which “reduced the adhesive area” with the concrete holding up the tracks. Too few buds were used to fuse the structure together, and their location was inconsistent, something that “contradicts the design of the transition,” the report said, repeating another finding from the Times survey.
Investigators for DNV also noted that different types of concrete had been used to build the transition, possibly because workers had to make adjustments on site during construction. On the steel beam during the transition, the report found poorly planned, problematic welding.
DNV said its report was based on “the field study and laboratory testing of samples from the accident” and that it “only contains DNV’s hypothesis at this time.” The full investigation will be completed later this year, the company said in a statement.
The Mexico City government, which hired DNV to investigate the causes of the crash, is also conducting its own investigation into the accident.
“We promised to provide comprehensive care to the victims and to hire a specialized company to understand with technical professionalism and, based on scientific evidence, the root cause of this terrible tragedy,” said Claudia Sheinbaum, Mayor of Mexico City, during the presentation of the DNV report .
The results of the independent investigation could spell trouble for two of Mexico’s most powerful figures: Foreign Minister Marcelo Ebrard and Carlos Slim, one of the world’s richest businessmen.
Sir. Ebrard, the mayor of Mexico City when the line was built, wanted it completed before leaving office in 2012, according to several people working on the project. He is seen as a strong contender to succeed President Andrés Manuel López Obrador in Mexico’s next presidential election in 2024.
In response to the release of the preliminary report, Ebrard said in a statement that determining the cause of the crash would require both a technical investigation and “an investigation that reviews the entire decision-making process in the design, layout, supervision and maintenance” of the metro line.
Mr. Slim’s conglomerate, Group Carso, built line 12 – the part of the subway that collapsed – to expand the company into the lucrative railway industry.
On Wednesday, Ms. Sheinbaum said she would “contact the companies that were part of the construction consortium that built line 12 to establish a technical dialogue.”
In response to previous questions from The Times, Antonio Gómez García, CEO of Group Carso, suggested that maintenance failures may have been to blame for the metro’s collapse. Sir. Ebrard had previously said it was impossible to know whether his successor had “performed all the maintenance” required after major earthquakes.
However, the preliminary report from DNV showed that the rails and their mechanical components were “under normal conditions” and met with “routine maintenance protocols.” Mexico City metro workers also said they performed “daily preventative maintenance activities,” according to the report. Investigators will continue to analyze whether the structure was subjected to abnormal weight that could have caused the beams to buckle.
Carso is now building a significant portion of Tren Maya, a 950-mile railroad designed to bolster the economy of southern Mexico – one of the country’s poorest regions – and stand as Mr. López Obradors heritage project.
Some engineers and architects working on Tren Maya have complained about problems similar to those when they built the subway: a hasty, disorganized process that has no master plan to manage the construction. And Mr López Obrador has insisted he wants Tren Maya to be completed before leaving office in 2024.