SINGAPORE — The concrete support structures for a Pan-Island Expressway (PIE) viaduct were so inadequate, they would not support more than half of the total load that they were intended to carry.

This was revealed in court on Monday (June 24), as an engineering consultancy boss pleaded guilty to not checking detailed structural plans and design calculations of the viaduct. The 1.8km bridge links the PIE to Tampines Expressway and Upper Changi Road East.

A collapse was inevitable based on the structural design that was used, the court heard on Monday.

Deputy Public Prosecutor (DPP) Yang Ziliang said: "If the viaduct collapsed after it had been constructed and opened to traffic, the casualties caused would be unimaginable." 

On July 14, 2017, an uncompleted section of the viaduct collapsed, killing Chinese national Chen Yinchuan, 31, and injuring 10 others.

DPP Yang added that investigations found that five of the viaduct’s 10 permanent corbels — concrete support structures — would not be able to take the self-weight of the girder and the deck during construction in the first place, “much less the weight of hundreds of cars that were meant to be driving on the road above them”.

“A collapse of the viaduct would have been inevitable,” he said.

It was the responsibility of Land Transport Authority-appointed accredited checker Leong Sow Hon, 61, to check the 10 permanent corbels.

Leong, a Singaporean and managing director of Calibre Consulting, was supposed to perform original calculations to determine the adequacy of the viaduct’s key structural elements.

But he did not and his crime was discovered after the collapse.

On July 26, 2017, while the Building and Construction Authority was still investigating the cause of the collapse, Leong had initially claimed that he had performed the calculations, checked the adequacy of the corbels and found them to be adequate.

But in Sept 2017, he admitted that he made no calculations at all, after one of his engineers verified from records and found that the calculations were not made.

The company’s engineers had also made their own calculations and found the corbels inadequate.

Investigations later concluded that corbels at eight out of 10 piers with permanent corbels were inadequately designed.

Five of these piers were unable to support their intended weight during the construction stage and would have collapsed during the casting of the slab at the construction stage.

The remaining three piers might continue to support weight during the construction stage, but significant structural cracks would show once it is open to full traffic load, DPP Yang said.

This would lead to “sudden brittle failure”, leading to its collapse, he added.

The prosecution is seeking a jail sentence of at least nine months for Leong, while defence lawyer Tai Chean Ming argued that a custodial sentence is not justified as paralysing a checker to perform his profession “does not increase deterrence”.

Pointing out that no accredited checker has had to serve a custodial sentence, Mr Tai, who is asking for a S$25,000 fine instead, said that a custodial term can deter an accredited checker from “taking (up) their obligations”.

The defence added that the 2017 viaduct accident had been caused by the failure of temporary corbels, not the permanent corbels, and checking the temporary corbels was not part of Leong's duties.

The prosecutor conceded that Leong "played no part" in the checks of the temporary corbels.

After hearing submissions from both parties, District Judge Hamidah Ibrahim adjourned Leong’s sentencing till July 5. 

Leong had pleaded guilty to one charge of failing to check the detailed structural plans and design calculations of the building works in accordance to regulations. One other charge of falsely certifying that he had carried out the required checks will be taken into consideration during sentencing.

Other five parties who have been charged in connection with the 2017 viaduct collapse are expected to claim trial, which is expected to begin on Aug 1.

The accused include:

• OKP Contractors, which had won the contract bid for the viaduct with the lowest tender price. The firm, which was just fined a few days before the 2017 collapse for another lapse in 2015 which had resulted in the death of another worker, faces a fine of up to S$1 million if convicted.

• OKP group managing director, Or Toh Wat, 51, who was allegedly aware of cracks in the corbels but was said to have failed to do proper risk assessments of the affected corbels and take measures to ensure the safety and health of employees.

• OKP’s project director Allen Yee Chee Keong, 49, and project engineer Wong Kiew Hai, 31, who allegedly failed to call for works to be stopped upon discovering cracks, and deleted a WhatsApp conversation between the duo which allegedly contained photographs and information potentially relevant to criminal investigations.

• CPG Consultants’ professional engineer Robert Arianto Tjandra, 45, who approved the design and supervision of the construction works.