SINGAPORE - Structural cracks were found about a month before an uncompleted viaduct near Upper Changi Road collapsed and caused the death of one worker and injuries to 10 others.

On Thursday (Aug 1), the court heard that cracks were first found on June 16, 2017, before more were discovered on June 30.

The Pan-Island Expressway viaduct collapsed on July 14, 2017, resulting in the death of 31-year-old Chinese worker Chen Yinchuan. Ten other workers were hurt - two seriously - during the incident.

The public prosecutor said the cracks were discovered when girders, which form the part of the viaduct which was to be cast, were placed on them.

The cracks were found on corbels - which are support structures - at Pier 41, and later on at Pier 42 as well.

The area between the piers was to have been the longest span of the viaduct.

By early July, it emerged that the cracks, which were assessed to be structural in nature, were the result of inadequate corbel strength defined during the design stage of the construction.

The corbel strength for Pier 41 and 42 was allegedly inadequate for the load the support structures were supposed to bear. The design for corbels at eight other piers was also said to be inadequate, with some at only a quarter of their required strength.

Deputy Public Prosecutor Yang Ziliang said in his opening statement on Thursday that "eight out of the 10 piers with permanent corbels would have developed significant structural cracks leading to sudden brittle failure and collapse when the viaduct was opened to traffic".

The court heard that Robert Arianto Tjandra of subcontractor CPG Consultants became aware of the errors by early July 2017 but he did not inform Or Kim Peow Contractors (OKP), the main construction company behind the project.

He also did not redesign the corbels but attempted instead to take remedial steps on-site, including strengthening the supporting structures - steps which were allegedly illegal and proved futile.

When concrete was poured to cast the span of viaduct between piers 40 and 41 on the early morning of July 14, 2017, a section of the viaduct collapsed.

The hearing continued in the afternoon with engineer Yeung Chun Keung taking the stand. Mr Yeung, who was the technical director of OKP during the incident, told the court that the corbels were “underdesigned”.

Now retired, the prosecution witness compared the design of the viaduct with another on the Tampines Expressway (TPE) which he had worked on.

Although the two viaduct structures were “similar”, the difference in corbel design was very obvious, he said.

For the TPE viaduct, the reinforcement steel bars (rebars) within the corbel were 20mm in diameter and set 150mm apart. But in the PIE viaduct which collapsed, the rebars were 16mm in diameter and set 200mm apart.

This, he said, meant the PIE viaduct was weaker. The corbel was designed to take less than half its intended load, he added, describing the corbel design as not common.

Besides Tjandra, OKP's project director Allen Yee and project engineer Wong Kiew Hai are also on trial over the collapse.

Yee and Wong are charged with not stopping work despite knowledge of the errors, and for obstructing justice by deleting WhatsApp messages and photos relating to the cracks.

Tjandra face five charges in total.

OKP was fined $10,000 on Tuesday for carrying out unauthorised strengthening works on the corbels while accredited checker, Leong Sow Hon, was sentenced to six moths' jail on July 4.

Leong, who was appointed as checker by the Land Transport Authority, is the managing director of Calibre Consulting Singapore.

The group managing director of OKP, Or Toh Wat, was given a discharge not amounting to an acquittal in court on Wednesday for all his three charges in relation to the collpase.