With proper checks Namma Metro accident could have been prevented, says Professor Chandra Kishen

Against the backdrop of the incident, Prof Kishen spoke to The Indian Express and tried to decode the reasons for the collapse of the reinforcement cage and what could be done to mitigate such accidents in the future.

At the outset, what are your initial observations about the collapse of the reinforcement cage?

Prof Kishen: The investigation is still under way and I will be visiting the spot this evening to take some measurements of the structure. Prima facie, I think the reinforcement cage lacked enough supporting structure. I believe any supporting structures (in this case the wires) should have a proper geometry. The angle at which it is supported and the height at which it is supported – this geometry dictates the stability. What I feel is this geometry was improper may be because of space constraints. However, it was not properly designed. I will have to work out whether the diameter of the supporting cables was sufficient. The geometry, the diameter and the height at which it is supporting the reinforcement cage is very important. So these dictate the stability of the reinforcement cage. Along with the self-weight of the bar, the wind factor should also be taken into account to find out the reason for the collapse. The wind is a major force that can cause instability and the cables which are supporting the cage should be designed to resist the wind forces.

You have also conducted other studies in connection with BMRCL infrastructure. For example, the Trinity pillar had developed cracks. How do these case studies differ from each other?

Prof Kishen: The case study of the Trinity metro station pillar and the current incident is totally different. The former was that of a completed and in-service structure and the latter is the failure of a temporary structure that was under construction.

What do you think of other reinforcement cages which are under construction? Are the supporting structures for other cages also under question?

Prof Kishen: The health of other reinforcement cages is dependent on the height of the pillar and the duration it has been supported, among other factors. After the investigation, we will give the BMRCL the specifics and the criteria of the geometry for the supporting structures.

What will be your recommendations to the BMRCL after this incident?

Prof Kishen: We will be giving a checklist to the BMRCL that will detail what all they need to check before they start concreting work. The checklist mandates that the engineers check the geometry of the temporary structure. Technically, the improper geometry of the supporting structure is what might have led to the collapse. However, it boils down to some kind of negligence. This incident could have been prevented. We are also suggesting the BMRCL to go ahead with 2-stage casting of reinforcements so that the height is restricted. Once they do the concreting for the first 8-9 metres, the reinforcement will be supported by the concrete. In that case, we do not require any supporting structure. It is also good to do concreting immediately after the cage is done and not give so much time for accidents to happen. Although BMRCL is carrying out safety measures, I believe more importance should be given to temporary structures during construction. Practices like wearing helmets, using the harness etc must be enforced more strictly.

Earlier in 2018, the professor of civil engineering also inspected the cracks and the repair work that was undertaken at one of the metro pillars near Trinity station. In fact, Kishen monitored the pillar for nearly 30 days to ensure that the structure will remain safe as per the global standards.