THE CATASTROPHIC Singapore cut and cover tunnel collapse that killed four workers in April was caused by design, construction and supervision failings that are endemic in the construction industry.
This is the damning verdict of the investigating committee, contained in an interim report published in Singapore last week.
The committee has been so alarmed by its findings that it has taken the unusual step of publishing the interim report in a bid to change industry practises before another calamity occurs.
Blame for the collapse will only be apportioned when the inquiry concludes in about a month's time. But the report makes clear its concerns by setting out 29 recommendations for change.
The giant collapse occurred on 20 April on a section of cut and cover tunnel being excavated under contract C824 for Singapore Metro's new Circle Line (NCE 29 April).
Main design and build contractor for the work was Nishimatsu-Lum Chang joint venture.
Excavation of the 15m to 20m wide trench had reached 30m below ground level when retaining walls gave way, caving in over a 110m length.
In a letter to Singapore's Minister for Manpower Dr Ng Eng Hen, chairman of the committee of inquiry Richard Magnus said he had 'seen glaring and critical shortcomings in the execution of C824'.
He added that 'these appear to be common in the [Singapore] construction industry. Some of these deficiencies have contributed directly to the collapse of the retaining wall system in C824'.
He continued: 'We are concerned that these shortcomings do not adversely affect the execution of subsisting contracts which involve deep excavation not dissimilar to C824. There are 18 such ongoing projects.'
The report urges: 'There should be a comprehensive engineering review of the design and safety measures of all ongoing projects, particularly where deep excavations are being carried out.'
So far the committee of inquiry has heard evidence mainly from eyewitnesses. Evidence from technical experts is now being presented.
Evidence gathered to date has revealed some frightening headline concerns, including:
lLack of continuity between design and construction lFailure to apply the same safety factors to temporary works as to permanent works lInadequate communication with and supervision of the contractors by the client and of subcontractors by the main contractor lSub-standard workmanship was left unchecked and unremedied.
The report also slams the project for its lax safety culture.
Engineers failed to address properly the risks of low probability, high magnitude accidents because they had not seen them occur before, it says.
'Major hazards are manifested in construction works that have a low probability of occurrence.
The potentiality of these hazards is sufficiently infrequent that their occurrences tend to be easily overlooked 'The fact that accidents have not happened in previous works does not mean that major accidents will not take place. . .
When these hazards take place there is usually a high risk to persons and properties.'
A full report of the inquiry is due next month.