Results of tests into strength of bars underneath scandal-hit station’s platform untrustworthy, engineering experts tell inquiry
- Pair from University of Hong Kong raise doubts about tests on couplers at Hung Hom
- Response comes during heated debate on what is acceptable level of safety
Two engineering experts have told an investigation into Hong Kong’s costliest rail project claims a lower safety standard is still acceptable for the structural safety of the station at the centre of the scandal are wrong.
The pair said the results of the supporting test by the supplier of the steel bar connectors placed underneath the new platforms at Hung Hom station were untrustworthy.
Testifying on Tuesday before the commission of inquiry into the shoddy building work that has plagued the HK$97.1 billion (US$12.4 billion) Sha Tin-Central rail link, the comments by professor Francis Au Tat-kwong, and Dr Albert Yeung Tak-cheong, came during a heated debate over whether 60 per cent of the construction performance was an acceptable indicator of platform safety.
Leighton Contractors (Asia), the main contractor for the project, is embroiled in allegations that steel reinforcement bars were cut short to fake proper installation into couplers on a platform at the station, and that supporting diaphragm walls were changed without authorisation.
According to the couplers’ supplier, BOSA Technology, the correct installation was to have 10 threads fully engaged into the coupler, or a minimum embedded length of 40mm.
However, the firm later said its couplers were designed with a much stronger yield strength. It conducted a test in November last year on five coupler samples, one of which showed that a 60 per cent of engagement length, about 26mm into the couplers, would produce a tensile strength of 705 MPa, well above the 625 MPa statutory requirement.
But, Au, department head of civil engineering at the University of Hong Kong, criticised the test results and the small sample size.
“The results are really untrustworthy,” he said. “Should we only partially engage all the couplers by 60 per cent?”
In particular, Au pointed out a case of 100 per cent engagement which recorded a strength of only 663 MPa, lower than the 60 per cent engagement.
“I don’t accept 60 per cent as the engagement criteria,” he said. “The problem is I don’t think this is the standard testing procedure because this is something which is unusual … We can’t accept the test results.
“How can we tell people that we shouldn’t tighten all couplers in full length and just tighten 60 per cent of the length? It doesn’t make sense.”
Yeung, associate professor of the university’s department of civil engineering, agreed, and questioned if the source of the samples and the testing methodology were reliable.
He said a minimum of 40mm embedded length should be adopted to ensure station safety, citing in his report to transport minister Frank Chan Fan’s remarks that the government needed to guarantee 100 per cent safety for rail projects.
“But what has Frank Chan got to do with civil engineering? … What if he said in a metaphorical way that he wanted 200 per cent safety?” asked Paul Shieh Wing-tai SC, for Leighton.
Philip Boulding QC, for the MTR Corporation, responded: “Your contention that it ought to be 40mm engagement is simply nonsense.”
Yeung also addressed the latest findings of the inspection of the coupler connections at the station platforms, and said some defective samples without any exposed threads might suggest the bars had been shortened.
“For the threaded section shorter than the design without any exposed threads, there may be a possibility that it has been cut,” he said
So far, 31 of the 77 steel bars checked have been found to be faulty at the two platforms, accounting for a substandard rate of 40 per cent.
The hearing continues.