Inspectors have found another 21 cracks in welds or structural steel parts of Line 12 of the Mexico City subway, a section of which collapsed in May and killed 26 people, authorities said Wednesday.

Studies in the section that fell found that the collapse was caused by construction defects, such as poorly made welds and missing bolts that were supposed to join the steel beams to the concrete, as well as a faulty design. The newly discovered cracks are found in other parts of the line that are still standing.

So far only a third of the inspection has been completed, so more such defects could still be found.

External inspectors have been invited as part of the work to reopen and reinforce the line, including some from the Autonomous University of Nuevo León.

Telecommunications and construction mogul Carlos Slim has said that his subsidiary Grupo Carso will cover the cost of rebuilding the section that collapsed and reinforcing other parts of the elevated line, in order to meet stricter standards in a city ​​prone to severe earthquakes.

This year, Mexico City prosecutors announced criminal charges against 10 individuals and companies for defects in construction and design.

In the case of the companies involved, prosecutors have said the goal of the criminal charges is to make them pay for or repair the damage to both the subway train and the victims. The charges are for manslaughter or negligence, damages and injuries.

Inspections of the section that fell detected poorly welded, misplaced or missing bolts. These bolts connect the supporting beams made of steel to a concrete surface over which the track passes.

Prosecutors also cited faulty welds on the steel beams, which did not adhere or broke. The steel braces – metal braces intended to keep the track’s two main steel girders at a uniform distance – were either too short or not properly fixed, and the raised line was not designed with a sufficient margin of safety.

In the past, some companies that were involved in the construction of the line more than a decade ago have alleged that subsequent repairs put too much weight on the raised section.

Line 12 of the Mexico City metro was built at a cost of 1.3 billion dollars between 2010 and 2012, when the current chancellor Marcelo Ebrard was the head of government of the capital. Ebrard is considered a candidate to succeed President Andrés Manuel López Obrador.

The project was fraught with over-budget costs, as well as alleged design flaws, corruption, and conflicts of interest.

The city was forced to close the line in 2014, just 17 months after its inauguration, so that the tracks could be replaced or repaired. The section that collapsed has been closed since May.

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