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Possible reasons of Kolkata flyover collapse: A technical analysis
Kolkata, 31st March 2016, Thursday afternoon, an under construction fly over collapses near Ganesh Talkies at Vivekananda road causing 24 deaths and around 80 others injured. The fatality could be more because at the time of collapse normal traffic was under operation just below the under construction bridge.
When there is election time such accident is sure to take political colour. Opposition started blaming Mamata government for this fiasco and even some started accusing that the actual contractor IVRCL gave subcontract to an inexperienced agency, who has close contact with West Bengal chief minister.

However, in this article the focus is on technical analysis of what might have gone wrong in the construction process that lead to its collapse. Is there anybody to be blamed for this and if yes who should be held accountable.

The reason of collapse: The super structure is a composite design. RCC deck is supported over steel girder. Such arrangement is very costly but most safe structure. Thus I don't think the superstructure (deck) failed. There was concreting in the previous day. Sometimes a portion of deck particularly cantilever portion collapses due to failure of temporary support such as brackets etc. But such collapse occurs when concreting work is in progress because wet concrete weighs more than set-concrete. (Wet concrete is 3000 Kg/Cum where as set concrete 2400 kg per cum). Initial setting takes place within 12 to 16 hours depending upon mix design.

From visuals it's clear that the pier cap failed thus bringing down two spans supported over it. Failure of pier has many reasons.

Design aspect: It was known from the beginning that due to space constraint and traffic load, the fly over had to be constructed not restricting the traffic movement. Thus design has taken care of this aspect providing all steel structure (above pile cap all members such as pier, pier-cap and super structure are made of steel member). Steel structure is the safest structure although very expensive. Standard design are checked with STAADPRO and hence it can be concluded that there was no faulty design. Further all other spans were alright proving that this pier/pier cap had some problems.

Execution aspect: Standard Operating Procedure (SOP) of such execution always needs to ensure approved material sourcing, fabrication by expert workforce, pre-inspection and post inspection after assembling, thorough checking of everything in the checklist before any further load is applied. IVRCL is a reputed agency and the concerned government department too is expected to be non-compromising on quality issues particularly when it is being executed while traffic is allowed to move under it.

I believe that there must be some error of omission, which might have happened. After doing successfully most of spans sometimes mid level and junior level engineers becomes bit complacent. Thus inspection might be done casually omitting serious flaws either in joints of pier cap/pier or by mistake some unwanted eccentric loading being done due to piling up construction materials. These are called human errors.

Who should be held accountable: While executing such works, as a senior person I use to check everything personally despite assurance from mid level engineers that they have checked thoroughly. There is nothing wrong if senior and expert people check it once again as even a minor overlook may cause a serious disaster like this. Thus I think the project manager in Kolkata flyover case was perhaps over dependent on his/her mid level engineers skipping his responsibility. Thus he should be held accountable.

The supervising agency (in this case the concerned government department) has the responsibility to cross check everything despite the agency is contract bound for structure and public safety. The concern engineers of supervising department must be held accountable.

Third department to be held accountable is traffic police department. When such work is being executed traffic department has mandatory responsibility of public safety. They may not be engineers but they could take necessary safety provisions as commonsense.

For example when I was constructing a flyover at Cuttack on NH-5 (at present it's NH-16), despite our sound safety plan, the Cuttack traffic department decided not to allow any traffic under the flyover for 72 hours of concreting. They stopped all traffic movement under the bridge through public notice. Some light vehicles took some diversions through village roads but the heavy traffic had to be detained along the NH.

The traffic department was criticized for being over-cautious but imagine how serious they were towards public safety. Had the traffic department in Kolkata taken such bold decision, they might have attracted public anger but such collapse would have been free from fatality. Thus I hold traffic department also accountable.

(The author is a very experienced construction professional with expertise in execution of bridge projects)

Editorial NOTE: This article is categorized under Opinion Section. The views expressed in this article are solely those of the author and do not necessarily represent the views of merinews.com. In case you have a opposing view, please click here to share the same in the comments section.
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