PIE viaduct collapse: Accredited checker admits not performing checks for support structures

SINGAPORE: The accredited checker for a viaduct project in Upper Changi admitted on Monday (Jun 24) that he had failed to check the designs or perform calculations for the corbels, or support structures.

The incomplete Pan-Island Expressway (PIE) viaduct collapsed in the early hours of Jul 14, 2017, with 11 workers on top of it, injuring 10 of them and claiming the life of 31-year-old Chinese national Chen Yinchuan.

Singaporean Leong Sow Hon, 61, pleaded guilty to one charge of failing to check the detailed structural plans and design calculations of the viaduct building works in accordance with regulations.

He admitted to not evaluating, analysing or reviewing the structural design in the plans and failing to perform original calculations for all permanent corbels. These are key structural elements supporting the ends of the flyovers that made up the 1.8km-long viaduct.

Another charge of falsely certifying that he had carried out the required checks was taken into consideration.

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The 1.8km-long viaduct consists of eight flyovers, with permanent corbels located at expansion joints, the prosecution said. 

Permanent corbels are short reinforced concrete projections via which vehicular loads on a flyover are transferred to columns, and are key structural elements essential for the support and overall structural stability of the viaduct.

The court heard that Leong was an engineer and the managing director of Calibre Consulting, who was appointed as an accredited checker by the Land Transport Authority (LTA) for the viaduct works.

His role, which was created after the 1986 collapse of Hotel New World, was to act as the final checking mechanism to check the structural design apart from the designer, said Deputy Public Prosecutor Yang Ziliang.

The court heard that Leong initially claimed that he had indeed performed the original calculations for the corbels and found them to be adequate. However, he was unable to produce evidence of such calculations.

He admitted that this was false only after engineer Shivananni Yalagunda Siddalingaiah verified from records and documentation that there were no such calculations.

Shivannani in September 2017 admitted that no calculations were performed for all corbels, permanent and temporary, during the submissions stage of building works.

CORBELS WERE INADEQUATE, COLLAPSE "INEVITABLE"

After the incident, calculations found the permanent corbels to be inadequate.

Investigations found that eight of the 10 piers with permanent corbels were inadequately designed, with five piers unable to support the intended weight during the construction stage.

"Therefore, the five permanent corbels would have collapsed during the casting of the slab at the construction stage," said the prosecutor. 

He added that although the remaining three piers might support the weight during the construction stage, the corbels would show significant structural cracks with a full traffic load, followed by "sudden brittle failure leading to collapse".

Because of the incident, the estimated completion date of the viaduct construction has been pushed back by at least two years from the first quarter of next year to the first half of 2022.

Leong is the first person involved in the case to plead guilty. The rest - including the qualified person who designed the building works and the builder Or Kim Peow Contractors - are set to claim trial.

The prosecution asked for at least nine months' jail, saying there was "complete inadequacy" in checking the corbels. 

They added that "the collapse of the viaduct would have been inevitable", and many people would have been harmed either during the construction stage or after the viaduct was open to traffic.

Leong's defence lawyer Lim Lian Kee asked instead for a S$25,000 fine, saying that the viaduct accident had been caused by the failure of temporary corbels, not the permanent corbels.

Checking the temporary corbels was not part of his duties, said the lawyer. The prosecutor conceded that Leong "played no part" in the checks of the temporary corbels.

The lawyer said the design and checking process was carried out by the qualified person, Robert Arianto Tjandra, and his client, who was the secondary person.

If Arianto had been doing his job, there was "very low likelihood" that potential harm would have occurred, said the defence.

District Judge Hamidah Ibrahim adjourned sentencing to Jul 5.

This story has been updated to reflect Leong Sow Hon's nationality.