Construction deficiencies behind deadly Mexico City subway collapse, report finds

Construction flaws led to the collapse of a Mexico City subway line that killed 26 people and left dozens injured last month, according to the preliminary findings of an independent probe released by the city government on Wednesday.

The investigation, carried out by Norwegian risk management firm DNV, suggests that deficient welding of metal studs, which apparently were not well connected to steel beams supporting a concrete slab and the elevated train rails, was among a number of issues that contributed to the May 4 incident. The report said missing metal studs in some sections of the structure, different kinds of concrete used for the slab and unfinished or badly welded joints were some of the other factors that caused the raised railway to buckle, sending two subway carriages plummeting to the streets below.