Failure to use crane caused metro accident in Bengaluru: IISc report

Inadequate support mechanisms, specifically the failure to use a crane that could hold the reinforcement cage, caused the metro accident that killed a techie and her son in Bengaluru earlier this month, according to an inquiry report by the Indian Institute of Science (IISc).

The reinforcement cage (rebar) of pier number 218 of the KR Puram-Airport metro line collapsed on a motorcycle in HBR Layout on January 10, killing a woman techie and her toddler son. These were the first public fatalities since construction on the Bengaluru metro began in 2007.

While the police launched a criminal investigation, Bangalore Metro Rail Corporation Ltd (BMRCL) requested the IISc to investigate the reasons for the fall of the 12-tonne, 18-m rebar.

Prof J M Chandra Kishen of the civil engineering department, who conducted the inquiry, inspected the accident site twice. He also spoke to three junior engineers, an executive engineer and a chief engineer.

However, the IISc team could not access the six labourers who were working on the scaffolding and tying four guy-wires around the rebar when it buckled.

The labourers had jumped down to save their lives. They were employed by Nagarjuna Construction Company, the contractor, which has been named in the FIR.

“The safety of temporary structures was overlooked,” a well-placed source told DH, citing the contents of the report, which will be submitted to BMRCL on Monday. “There was a lapse in supporting the rebar. Someone has to take responsibility.”

According to the source, the supporting mechanism for the rebar was critical because it was composed of TMT bars that were lapped in between. A TMT bar is usually 12 metres tall, of which two metres go into the foundation while the remaining 10 metres are erected upright. As the rebar was 18m high, two 12m bars had to be joined together. “The spot where the bars meet becomes a weak region. The rebar won’t stand on its own and tends to bend. This is where an adequate support system becomes crucial,” the source said.

As the workers got busy removing the scaffolding, the guy-wires that supported the rebar took on a lot of weight and bent. “This could have been prevented by using a crane, which holds the top with a hook and prevents the rebar from tilting. It’s a mystery why they didn’t use it,” the source said.

The source also expressed surprise that the use of cranes as a supporting mechanism was not detailed in the method statement, which outlines how each task should be handled.