Eight years after the Purple Line of Namma Metro became functional, one of the pillars has developed cracks and a slider which is holding the bridge together has got dislocated.
While Bangalore Metro Rail Corporation Limited's (BMRCL) director Ajay Seth says that the honeycomb formation in the concrete is nothing to worry about, he also admits that this is not the first time that cracks have been detected in the same pillar.
In 2012, just a year after the Baiyappanahalli to MG Road train began plying, BMRCL had found an issue with the same pillar and had narrowed it down to honeycomb formation.
“Back then, we were unable to determine the exact cause but had narrowed it down to honeycomb formation. It was repaired and there were no problems until recently,” Ajay Seth said.
Sources in the BMRCL say that the flaws in the pillar may have arisen due to negligence during construction.
“Firstly, the concreting of pillars must be done in a controlled environment where strain and deflection tests can be conducted to determine whether the pillar is sturdy enough to handle the weight and vibrations. Back then, instead of casting it in a factory and then assembling it near the bridge, the concrete was poured on the pillars at the construction site,” a BMRCL official said.
The BMRCL officer further stated that during the construction process, the relevant tests were not conducted at all and even during regular inspection, non-destructive equipment was not used to determine the sturdiness of the pillars.
“To understand the life and the immunity of the beam which is carrying the load, there are numerous tests which are conducted. The oscillations and vibrations can be measured and recorded. It is just not visible to the eye. If these tests were not conducted prior to the concreting, then there would be no way to know whether the pressure from the trains leads to the formation of cracks. During the process, if anything goes wrong, then the concrete will not sit properly. Besides, the iron rods which are rusted could also be a contributing factor for the cracks,” the official said.
A special team has been formed to investigate and measure how over a period of time, the vibrations will increase or decrease the sturdiness of the pillar. “They are looking to see whether there was negligence during construction or whether the quality of materials was substandard. But there have been so many protocols which were not followed and it would be difficult to find out,” the official added.
According to Ajay Seth, an inspection team on Sunday night detected a honeycomb formation in a diaphragm wall of pillar 155 near Trinity Station.
“We immediately provided temporary supports as a precaution but this does not mean that the structure is unsafe. We have also reduced the speed of trains near Trinity Station as an additional precautionary measure. We are operating trains at a speed of 10kmph on a 260m stretch between the MG Road and Trinity Metro stations.”
BMRCL is also consulting with experts to solve the problem. “Since 2012, the BMRCL has been sitting on the fact that something is wrong with the pillar. When they found out that pouring concrete on the beams at the site instead of in the factories can lead to problems, BMRCL changed its policy and now all beams are made in the factories and then assembled at the site,” the official added.
Meanwhile, Bengaluru Development Minister Dr G Parameshwara went on a ride in the purple line from Vidhana soudha to Trinity Metro Station, to check whether passengers are being incovenienced.
The BJP MP PC Mohan has also decided to inspect the pillar near Trinity Metro Station on Saturday evening.