Nearly a year after a construction failure which killed one worker and injured 10 others, the Land Transport Authority (LTA) has decided to demolish all crossheads on uncompleted sections of the Upper Changi Pan-Island Expressway viaduct.

A crosshead is the horizontal beam on top of a pillar which supports an elevated structure such as a road.

LTA said more of the viaduct structure may be pulled down if it is deemed unsafe. But it could not say when the demolition will start, nor how many crossheads were affected.

In a statement soon after the main contractor - Or Kim Peow (OKP) Contractors - and five people were charged in court yesterday morning for their role in the fatal collapse in July last year, the regulator said the decision to demolish the crossheads was "a safety precaution following the discovery of cracks on corbels at the incident site earlier".

A corbel is part of the crosshead, which supports the weight of precast beams between two sections.

LTA would not say why the structures were deemed unsafe, but it has since emerged that cracks on several parts of the viaduct were discovered well before the collapse in the early hours of July 14, 2017.

In its statement, LTA said it has appointed an independent professional engineer "to assess the structural integrity of the viaduct under construction". It added: "Any other sections, which are assessed to be unsafe... will be demolished."

With the ongoing court case raising questions over the safety levels of the viaduct, observers said a decision may be taken to redo the entire project. LTA said it is "studying its options carefully and reviewing the viaduct project with OKP".

In a follow-up statement last night, LTA said propping was extended to the parts of the viaduct where cracks were discovered at the corbel area to ensure that there would be no safety risks. It added there has been a stop-work order on the viaduct since the accident.

"The demolition works will commence after the necessary approvals to proceed with the works have been obtained from the relevant authorities," said LTA.

It was unable to say if the demolition would affect the columns on which the crossheads sit.

OKP won the contract to build the congestion-relieving viaduct with a bid that was the lowest in price and lowest in quality.

But because of the 70:30 price-quality weightage LTA assigned to the project, OKP's bid had the highest price-to-quality ratio.

Mr Kirindeep Singh, a senior partner of law firm Dentons Rodyk with experience in construction cases, said equal weight should be given to both factors to minimise the risk of firms compromising on quality.

Elsewhere, cracks had earlier been found on crossheads along the Sengkang-Punggol LRT line.

While LTA had said these "do not compromise the load-bearing capacity of the crossheads and pose no safety risk to commuters", it intends to rectify the cracks as a precautionary measure. These strengthening works - which will include replacing viaduct bearings - will be completed by 2020.