The HCMC Management Authority for Urban Railways (MAUR), investor of the first metro line, said EB1 and EB4, two Elastomeric Laminated Bearings pads on the metro line’s elevated section, weigh 117 kilos, nine kilos lighter than the design approved five years ago.

MAUR has pointed out the difference in a statement sent to Shigeki Ihara, project manager for Japan’s Sumitomo Corporation.

A consortium comprising Vietnam’s Civil Engineering Construction Corporation No. 6 (Cienco 6) and Sumitomo Corporation is the main contractor for the line that will run 19.7 km from Ben Thanh Market in District 1 to Suoi Tien theme park in District 9.

The investor’s statement follows investigation of cracks detected on the elevated section of the line in Thu Duc District on October 30.

The contractor is yet to make any official statement on the cracks, only saying it has fixed the issue. There has been no explanation forthcoming on how the cracks happened and their implications for the safety and longevity of the project.

Shigeki Ihara, project manager for the Sumitomo Corporation, said last month that the incident was just a "single case" on one beam.

The lack of explanation from the contractor has prevented MAUR, the project’s main investor, from preparing a report on the incident for submission to higher authorities.

What the contractor has said so far "is not convincing," and paves the way for the contractor to "disclaim responsibility," MAUR has said.

The investor has demanded that the contractor hands over evidence of its own investigations and submit an official report on the issue no later than December 12, but nothing has happened more than a week after the deadline.

Carrying out its own investigation, the investor found that after the pad between the two beams of the metro line’s elevated section fell off, cracks had appeared on the beam and the rail lost its connection with the supporting system below.

MAUR and the project’s consulting unit, NJPT, a consortium led by Japan’s Nippon Koei, have recently agreed that the contractor opens up the track pads where the cracks appeared to check and find out why this happened.

What they found is that the two pads of EB1 and EB4 in the area are lighter than designed.

Now MAUR has told the contractor that it has all the reasons to "question the qualities of all pads that have already set up on the project."

It has requested the contractor to submit results proving that all pads in use so far meet the specified technical requirement.

The Elastomeric Laminated Bearings pads, which are made from high purity elastomers that encapsulate layered internal steel reinforcing plates, are designed for use in bridge and building constructions as a beam support.

Work on the much-delayed HCMC , which began in August 2012, is more than 78 percent complete now. The city hopes to advance this to 85 percent this year and begin commercial operations by the end of next year.

The metro route No.1 will have 14 stations – 11 on elevated sections and three underground.

Its construction is expected to cost VND43.7 trillion ($1.89 billion).

In all, HCMC plans to build eight metro lines running a total of 220 km.