Design or service life for all bridge/flyover structures must be 100 years; if any flyover has to be demolished before 100 years then there is designing error
There are around 20 flyovers and bridges in Guwahati, with work ongoing for four more. As the city transforms into a "city of flyovers," one question arises: How safe are these flyovers, and what is the lifespan, or "design life," of a flyover? Will the flyovers function properly indefinitely, or will they need to be demolished at some point?
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A source in the Union Ministry of Road Transport and Highways (MoRTH), speaking to GPlus, said, “The design or service life for all bridge structures, except ancillary items like bearings, expansion joints, wearing courses, etc., must be 100 years,” adding that for important and strategic bridges, depending on their location, importance, and other parameters, the lifespan may be increased on a case-by-case basis by the state or central government.
The Chief Engineer of the Public Works Department (Roads), Sanjeev Shyam, also speaking to GPlus, said that in Assam, the design life of flyovers and bridges is 100 years, as the same materials are used for construction following the same regulations.
In September 2016, MoRTH issued a notice to all states regarding the design and general features for bridge structures to be constructed on highways. “All new bridges and their components shall be structurally designed strictly according to Indian Road Congress (IRC):112, following the 'Limit State Design Philosophy,' except for those components for which IRC codes and standards based on the limit state are not available. Loading will be considered as per IRC:6, including 385-tonne special vehicles. The latest edition of the code notified/published either at the time of project consideration, conceptualisation, or at least 60 days prior to the last date of bid submission must be considered,” the notice stated. The design discharge for computing the waterway and length of the bridge should be based on the maximum flood discharge, with at least a return period of 100 years, according to the notice.
A source in the National Highways and Infrastructure Development Corporation Limited (NHIDCL) stated that any structure (flyover, road overbridge, or bridge on a river) is designed with a 100-year planning horizon. The flyovers should be earthquake-resistant for 100 years and should not be affected by any loads. Similarly, bridges on rivers are designed in such a way that floods cannot affect them for 100 years, and the course of the river should not change at the location of the bridge. On the other hand, the bitumen layer has a life of five years.
Meanwhile, there are rumours that the Six Mile flyover may be demolished due to frequent repairs. The flyover has once again come under scrutiny as restoration work disrupts the daily life of commuters and residents. Public criticism has been mounting over the perceived inefficiency of the Public Works Department (PWD) in maintaining the structure, which has required multiple repairs despite being a relatively new addition to the city’s infrastructure. Moreover, commuters are increasingly fearful when navigating the flyover.
However, a PWD official ruled out any immediate talk of demolition, while stating that nothing could be said about the future. Speaking to GPlus, the official said, “Reports saying the Six Mile flyover will be demolished are incorrect, as there is no such plan at present,” adding that the repair work will be completed before Advantage Assam 2.0 in late February.
Another PWD source mentioned that the ongoing repair work is a temporary solution, and the engineering expert organisation RITES has been entrusted with the responsibility of studying the flaws in the Six Mile flyover.
The flyover was inaugurated in 2009 and was constructed by M/S Simplex Concrete and Piles (India) Ltd. The original work of the 1.65-km flyover was awarded on October 3, 2005, with a tendered value of ₹40.70 crore and a completion deadline of 18 months. The sub-soil investigation, conducted by the department in September-October 2005, was not accepted by the consultant, who requested a re-investigation. The fresh sub-soil investigation, carried out in February 2006, indicated variations in the quantity of work to be executed, leading to an increase in the estimated cost. As a result, the tender was revised from ₹40.70 crore to ₹58.54 crore. The work was completed in 2009 at an expenditure of ₹56.38 crore.
The PWD source stated that after RITES completes its study of the flaws, a decision will be made, and if necessary, the flyover will be demolished. Questioning whether the design life should be 100 years, the source added that a proper investigation will be conducted, and anyone found guilty will be punished.
The NHIDCL source also mentioned that if the cracks are merely hairline, they can be grouted, but if they are deeper, there may be an issue with the design.
A PWD source indicated that some hairline cracks on a pillar have been observed, and grouting procedures are currently underway to treat the cracks chemically and restore the structure. Grouting is a process of injecting fluid materials, like cement, into soil or rock to fill pores and fissures.
The question remains: Is there a design flaw in the Six Mile flyover, and what about the other flyovers in the city?
