Vertical drilling from above the Silkyara-Barkot tunnel has been done up to 31 metres, former DG of Border Roads Organisation Harpal Singh said on Monday at the site of the rescue operation.

A total of 86 metres have to be drilled vertically to prepare an escape passage for the 41 workers trapped for the last 15 days. Pipes of 1.2 metres in diameter have to be laid vertically through the top of the tunnel by this method adopted as a second option.

Preparations are also underway to start horizontal drilling inside the main tunnel manually, he said. Rescuers need to manually dig 10 to 12 metres through the rubble after the auger machine broke down.

"Frames of 800 mm diameter pipes have been prepared. We will move ahead by half a metre to one metre gradually. If all goes well and no obstacles are encountered a 10-metre stretch can be covered in 24-36 hours," he said.

The auger drill -- a corkscrew-like device with a rotary blade at the front end -- that was drilling into the debris got stuck Friday evening, forcing officials to give up on the 25-tonne machine.

Parts of the auger were left to be removed from an 8.15-metre area on Sunday night. Extracting the shaft and fins of the machine from the rubble completely was necessary to pave the way for manual drilling and pushing of pipes which is in the final stretch with around 12 metres more to go. All parts of the machine have now been removed.