Missing bolts and poor welding contributed to Mexico City subway collapse, auditor says

A train carriage is seen at the site where an overpass for a subway partially collapsed with train carriages on it at Olivos station in Mexico City, Mexico May 4, 2021. REUTERS/Henry Romero/File Photo

MEXICO CITY, Sept 7 (Reuters) – A deadly Mexico City subway collapse in May was caused in part by missing bolts in the girders of an overpass that was already showing gaps before a major earthquake, the report said. independent auditor published Tuesday by the city. government.

The 180-page analysis by Norway’s DNV was the latest installment of its technical advice on the May 3 collapse – Mexico’s biggest rail crash in years – which killed 26 people when an overpass and railcar train on metro line 12 suddenly fell on a stream of cars near Olivos station in the southeast of the city.

In phase two of DNV’s findings shared by city officials, the company said deficiencies, including the lack of functional bolts over a significant extent, led to the north and south beams buckling.

The flaws left the structure functioning as two independent beams that took on a weight it was not designed to support.

“This created conditions that led to the distortion of the central cross-sectional frame and the initiation and propagation of fatigue cracks that further reduced the structure’s ability to carry the load,” the report states.

Sections of the collapsed viaduct were in a “compromised state” before a major earthquake in 2017 damaged parts of the metro, the report said. Poor welding practices were also noted by the auditor.

The city government has already started work on rehabilitating the line, and the report’s findings will be shared with a technical advisory committee, said Jesus Esteva, head of Mexico City’s public works department.

“In the next few days we will sign the agreements with the companies. They are the ones who will do the work,” Esteva said, without adding further details.

The metro was built by a consortium made up of Mexican ICA (ICA.MX), Grupo Carso, a company controlled by the family of Mexican tycoon Carlos Slim, and French builder Alstom SA (ALSO.PA).

Grupo Carso had no immediate comment on the report. A spokesperson for ICA did not immediately respond to a request for comment and a representative for Alstom could not immediately be reached.

The collapse put pressure on close allies of President Andres Manuel Lopez Obrador, as well as Slim, Latin America’s richest man, whose construction company was responsible for building part of the collapsed line.

Carso would repair the line at no cost to the government so it could reopen in a year, Lopez Obrador said in June. Read more

DNV was due to submit its follow-up report on August 23, but requested a two-week extension to complete its investigation.

DNV’s initial report found “six deficiencies in the construction process” that contributed to the accident and noted inadequate bolts and warped structural supports. Read more

The company is still expected to deliver a third phase of its findings on the metro collapse.

Reporting by Cassandra Garrison and Raul Cortes; Editing by Bill Berkrot

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