By Daryll Nanayakara
*Shown above: Dr Graham Brown (right) and Prof David Ewins, foreign technical experts on the panel, spoke yesterday.
Defective materials used in the rail network could have contributed to train-service disruptions on Dec 15.
They are part of the structures holding up the third rail, which supplies power to trains.
This was a scenario presented by a panel of foreign technical experts yesterday during the Committee of Inquiry hearing over two major service breakdowns which affected 220,000 commuters last December.
Represented by Professor David Ewins from London's Imperial College's Department of Mechanical Engineering, the panel also identified a possible link between the Dec 15 and Dec 17 disruptions.
Prof Ewins explained that a defective fastener and two insulators used to support the third rail had been weakened due to manufacturing flaws.
He did not think that "the system was made weak" by the defective materials used, but said that the "weakness made the system more vulnerable".
Another panel member, Dr Graham Brown from engineering firm Sinclair Knight Merz, said a "confluence of factors" resulted in the breakdowns.
The experts also said that the trains involved in the Dec 15 breakdown could have had a role in the Dec 17 disruptions.
The trains in the Dec 15 breakdown had their collector shoes, which draw power from the third rail, damaged.
But, as they continued running the day after, impact from their defective shoes hitting the third rail could have resulted in vibrations that eventually dislodged two adjacent rail claws.
Without the claws, the third rail sagged excessively and could have led to the Dec 17 breakdown, as the trains could not draw power from it.
While the panel said SMRT's maintenance regime was "commendable and of extremely high standard", the experts added that the rail operator could further tighten its maintenance regime.
They also suggested that SMRT and the Land Transport Authority develop a more robust third-rail assembly structure to reduce the occurrence of dropped claws.
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