Deep cracks found in ceiling of Hong Kong high-speed railway terminus
MTR Corporation insists the fissures are the result of 'normal shrinkage effects'; construction experts think the problem may be more serious
Deep cracks have been found in concrete ceilings at the West Kowloon high-speed rail terminus, raising more questions about the already delayed construction project.
The MTR Corporation insisted that the cracks did not affect the structural safety of the HK$67 billion railway project, but construction specialists called for immediate remedies.
The cracks were found in the ceiling of basement level three - the plant room - of the southern section of the terminus.
Beneath the level are rail platforms and above is a car park.
Photographs of the cracks seen by the South China Morning Post show about a dozen long cracks on the concrete slab ceiling of the basement. There are also metal structures erected to support the ceiling.
A person who provided the pictures said water had seeped through the cracks in the one-metre-thick slabs during heavy rain in late May and delayed other essential installations at the level.
"The cracks found in the slabs are obviously a failure in engineering standards," the person said.
He said the contractor could have overlooked some procedures, such as concrete curing, as it rushed the project.
He described the cracks as a "safety issue" that could only be addressed by removing the cracked slabs, but he was worried the problems would be covered up.
In response to inquiries, a spokeswoman for the MTR insisted the cracks were the result of "normal shrinkage effects". She refused to clarify the scale and locations of the cracks. She said only that cracks were discovered in "places" from basement one to two.
"Further investigation concluded that these are shrinkage effects, which are not uncommon in concrete construction and do not affect the structural safety,'' she said.
She said the contractor, a joint venture of Liang O'Rourke, Hsing Chong and Paul Y that was awarded the HK$3.3 billion contract in 2010, had been asked to handle the cracks with injections.
The rail operator's ability to manage the project was called into question in April when it was disclosed that its opening would be delayed by two years to 2017.
The delay is now the subject of an independent investigation initiated by the government.
Chan Chi-ming, head of construction at the Institute of Vocational Education, rejected the MTR's explanation that the cracks were the result of shrinkage.
He said shrinkage would lead only to a web of surface cracks but the cracks in the basement, as shown in the photographs, seemed to have cut vertically across the slabs.
Chan also said the cracks appeared to have a directional pattern, suggesting they might not be sporadic but systematic.
The cracks could leave the building owner a big burden of maintenance in the long term, although they might not pose immediate structural safety threats, he warned.
Chan suspected that the cracks were caused by uneven work site subsidence that created larger-than-expected tension on the concrete. He called on the MTR to release more information about the cracks.
"They should have made some provisions about the cracks but apparently the cracks turned out to be worse than expected. Cracks like this should not appear in a well-managed construction project," he said.
Chan also said the photographs indicated the cracks had been filled with injections.
Shown the pictures of the cracks, veteran structural engineer Greg Wong Chak-yan described the defects as "not good" and called for immediate remedies.
"The cracks are not ignorable defects. Cracks of such width and depth require remedial measures," he said.
Still, he said that, while such cracks were undesirable, they "do occur in a few places" in a project of great size due to defective concrete or a poor pouring process. "As long as the defect does not occur in a significant percentage of the works, it is not alarming," he said.
Wong said if the cracks were found at a similar location in each basement level, the problems could be related to design or structural defects like an insufficient number of steel reinforcing bars.
Another veteran engineer who was an adviser to the express rail project said that while cracks were inevitable in concrete structures, he could not ascertain if these had anything to do with rushing to meet deadlines.
He disagreed that site subsidence could be a cause, as the building was not erected on top of soft soil but on hard granite rock.
He said cracks wider than 0.2 millimetres would require remedies such as injecting chemicals into the concrete to fill the pores inside it.
"Frankly, the construction quality of the railway is not that bad. It sounds like a problem because it receives so much attention," he said.
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