The collapse of a metro overpass in Mexico City last month, in which 26 people died, was caused by six construction faults, according to an interim report commissioned by the municipal government.
The report was prepared by Det Norske Veritas, or DNV, an Oslo-based risk management and quality assurance consultant. This found evidence of missing or faulty welding on girders, and missing or badly welded bolts.
It also found that different types of concrete were used.
Jesus Esteva, head of Mexico City’s public works department, told a press conference last week that the report showed "on a preliminary basis, that the incident was sparked by a structural fault". He said this had led some girders to deform and others to slide out of position.
He added that laboratory tests would be carried out to determine whether any incorrect or defective materials were used.
Mayor Claudia Sheinbaum said at the conference that officials would continue to investigate and follow up "not only because of our legal obligation but because of our ethical, human and moral commitment".
Line 12 of the Mexico City metro, known as the Golden Line, started operating in October 2012. The section including the site of the collapse was shut down some 15 months later, in March 2014, for nearly nine months to address structural and technical problems.
The then director of the Metro, Jorge Gaviño, said the line "was born with endemic problems that would never be solved in its life".
Mexico’s foreign minister, Marcelo Ebrard, who was the city’s mayor when the Golden Line was built, last week defended his management of the project and reiterated his willingness to work with the authorities.
He said: "I support the carrying out of the necessary expert and technical investigations to determine the causes of the accident and define the responsibilities that may arise."
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Image: Mexico City mayor Claudia Sheinbaum visiting the site of the collapse yesterday with engineers, the secretary of works and services, the director of the construction safety institute, and the director of the Metro (From the Twitter account of Claudia Sheinbaum)
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