Two steel bar cages used for building diaphragm walls to support the MTR’s new Exhibition Centre station were constructed in the wrong direction in 2016, because of errors relating to engineering terms in the design drawings.
The issue is the fourth engineering problem reported recently at the under-construction HK$97.1 billion Sha Tin to Central Link.
The MTR Corporation confirmed the existence of the problem, but said it had been fixed and approved by the government’s Buildings Department. The error was very serious and could have reduced the structural support capacity of the walls, according to a veteran engineer.
According to internal documents obtained by Apple Daily, the MTRC issued a non-conformance report in June 2016 to the contractor, a joint venture of Leighton Asia and China State Construction, on the diaphragm wall issue.
According to a quality alert notice from Leighton, the shop drawings for the steel bar cages were incorrect owing to a misunderstanding.
The two sides of the cages should be described as “soil” and “excavation” sides – the excavation side should be thicker than the soil side, and faces the station, so that it can withstand pressure from the soil side.
However, they were incorrectly described as “north” and “south” sides in the drawings. As a result, two of the steel cages were installed in an incorrect direction, whereby the two sides had exchanged positions.
The on-site staff member and inspectors did not discover the problem until concrete has been poured into the steel cages. The two walls were not torn down and rebuilt.
To fix the issue, buttress panels were installed to strengthen the walls. The contractor said the remedy was approved by the Buildings Department.
In the “lesson learnt” column of Leighton’s quality alert notice, it said it needed to review internal checking routines and resources, and encourage staff to be vigilant and aware of unusual or incorrect items.
Remedy reviewed and done
MTR Corporation Projects Director Philco Wong said on a Commercial Radio programme on Wednesday that the remedy proposal was reviewed by the MTRC and relevant authorities.
He said the MTRC put safety first and has installed a round-the-clock monitoring system at the site. He said engineering staff would check figures on the site every other day, and geotechnical engineers would make an analysis every fortnight.
So Yiu-kwan, a veteran civil and structural engineer, told Apple Daily that it was a rare and serious mistake. He said that, if the steel cages were installed in the incorrect direction, there may be a risk of collapse.
He questioned why the contractor and the MTRC did not discover the issue earlier: “This should not be difficult to discover. One side was thicker, one side was thinner, the contrast is clear. If there were checks, how did they not find out it was installed in the wrong direction?”
He said the issue could be fixed by strengthening the walls, but the design of the stations must change, and the MTRC management and the government should be notified.
Transport Secretary Frank Chan said the government was disappointed that it only knew of the recent engineering problems after the media revealed them.
“If they told us earlier, we could make remedies earlier so that the public will not be so worried,” Chan said.
Democratic Party lawmaker Lam Cheuk-ting said the Legislative Council should conduct a special meeting over the recent scandals at the Sha Tin to Central Link.
He said Chan was one of four government officials on the MTRC’s board and Chan must share part of the responsibility.