Sha Tin-Central link scandal: engineers express concern over MTR Corp plans to strengthen Hong Kong’s beleaguered Hung Hom station

Two veteran engineers have expressed concern over the updated design of a scandal-hit station on Hong Kong’s most expensive rail link. Fears about the safety of Hung Hom station were first raised last year, when it was claimed some of the steel couplers embedded in platforms were faulty. This led to a commission of inquiry that concluded Leighton Contractors (Asia), the main firm on the project, deviated from the agreed design when building new platforms under the station. The MTR Corporation based its reinforcement work on the projection that one-third of the couplers and steel bars could not support the platforms or other areas of the station, which formed part of the HK$99.1 billion (US$12.6 billion) Sha Tin-Central rail link, the engineers said. Albert Lai Kwong-tak, convenor at the Hong Kong-based think tank Professional Commons, said that was based on a belief the faulty couplers were randomly distributed in the structures. Lai said it was risky for the rail operator to map out the planned modifications by working on the basis that around one-third of the couplers and steel bars could not support the buildings. “Maybe some areas have two-thirds of couplers and steel bars not working right and that creates a weaker link,” he said. “A structure can collapse when it has a weak link.” On Thursday, the MTR Corp announced a plan to partially open a section of the line from Tai Wai to Hung Hom by the end of 2021, after it submitted two separate reports over construction issues on the platforms and missing safety documents covering three locations at the station. It estimated that up to 36.6 per cent of couplers at the east-west line slab were improperly installed, and the north-south line slab could have at most 33.2 per cent of such substandard couplers, after examining around 200 samples in the two areas. MTR to strengthen Hung Hom station, but repairs could take 18 months Among the 48 defective samples, eight were found to have reinforcement bars not connected to the couplers, and five with bars that appeared to have been cut. The assessments also identified 31 gaps between the east-west line slab and other supporting structures such as a wall and column, probably caused by poor workmanship, which was not identified during supervision of the building project. On Thursday, Roger Bayliss, the MTR Corp’s projects director, said the structures were safe enough for construction to continue. “We need to take comfort from the fact the station has been there for between two and four years, and there are no signs of distress at all,” he said. To rectify the substandard work and other flaws outlined in the reports, the rail giant suggested installing steel supporting structures and steel columns, as well as thickening concrete slabs. The work was expected to take up to 18 months. Lai said he could not assess how serious the safety risk would be after the fixes had been completed. “This is the biggest problem because the MTR Corp only conducted a random check,” he said. “Many places have not been assessed … this cannot be confirmed by a simple statistical projection.” Structural engineer Ngai Hok-yan said the sampling size was not big enough, and said the rail operator should assume there were more faulty steel bars and couplers than suggested by the average projection figure, to avoid risks. He believed the corporation might argue some substandard bars could still support the structures to a certain extent after they were screwed into the couplers. “We don’t know whether the steel bars are installed properly, how much stress will be concentrated on certain points, causing a shortened lifespan of the structure, or even negative structural phenomena, for example, cracks,” he said. Section of Sha Tin-Central link could open by 2020 – but at a price In the reports, honeycombed concrete and shear link irregularities at 18 locations of the east-west line slab were also identified. Request for inspection and survey check forms over rebar fixing and pre-concrete pour were missing at three locations in the station. Only 28 per cent were available at the north approach tunnels, 58 per cent at the south approach tunnels, and 50 per cent at the stabling sidings. An MTR Corp spokeswoman said the two reports had been submitted to the government, which had carefully reviewed and accepted the conclusions of the reports. She said the rail operator had no further comment.