Third of Mexico City metro line 12 has flaws to address – civil engineers

Mexico’s college of civil engineers (CICM) presented the first in a series of reports on its inspection of line No. 12 of the Mexico City metro, announcing that 32% of the elevated sections have flaws that must be addressed before reopening.

“Grade B affectations were found on 32%, which does not mean that they are high risk, but rather that they indicate situations where there are vulnerabilities and pathologies that have to be analyzed in greater detail,” said Bernardo Gómez, coordinator of the CICM’s technical committee for structural safety, presenting the report at a press conference on Thursday.  

The engineer’s comments come a day after the independent investigation run by Norwegian firm DNV released its own preliminary report. DNV reported the discovery of six "deficiencies" in the construction process that likely led to the May 3 span collapse that killed 26 people.

Line No. 12 was built by a consortium formed by Grupo Carso’s construction division CICSA, Mexican builder ICA and France’s Alstom.

The findings of both the CICM and DNV reports, as well as the conclusions in an article published on June 12 by The New York Times, all point to failures by the group and CICSA in particular that are thought to have contributed to disaster. 

The CICM report, furthermore, suggests construction flaws exist at multiple points on the line beyond the area of the span collapse, representing structural issues that have to be resolved before operations on the line, which carries around 220,000 passengers a day during regular operations, can resume. 

The initial CICM analysis consisted of a visual inspection carried out by 101 specialists along the entire 14.6km-elevated section of the line, with the exception of the collapsed section. 

Gómez explained that 68% of the line has grade C deficiencies, which are “common situations,” while the grade B deficiencies “require further study.” 

Among these deficiencies, he revealed that there were “questionable” welding practices (as shown in image below), insufficient spacing between beams, cracks in columns and girders (girders), as well as anomalies in the support of the metal structure. 

Source: CICM

He said some of them could have been caused by the powerful 2017 earthquake and, as such, “it’s important not to make a judgment about them, though there must be a more detailed analysis.” 

The head of the CICM’s structural safety committee said the issues that require further study include: welds to the center of the span, insufficient spacing between beams and the lintels, column fissures, fissures in span beams and lintels, problems with neoprene supports, diaphragms positioned poorly or missing and inconsistencies where horizontal link-beam stiffeners are shorter in some areas than in others.

Thursday’s report was the first of three expected from CICM, where the group will also be presenting its findings on elevated sections of lines 4, 9 and B of the metro system. 

Gomez recommended “not to restart the operation of the elevated section of line No. 12” until all reports have been submitted and he called for “a rehabilitation project" to address all the deficiencies. 

The CICM also listed the following recommended actions: 

• A review of the separation between the Periférico (Mexico City beltway) vehicular bridge and the columns of the elevated viaduct of the metro. 
• Repair of cracks in columns. 
• Repair of cracks in pre-stressed tablets where a high level of leaks was observed. 
• Repair of the lintels damaged by the wear from seismic absorption system. 
• An in depth review of previous work carried out near the Nopalera station.