Drilling through the rubble of the collapsed Silkyara tunnel was put on hold again Thursday after the platform on which the equipment is mounted developed some cracks, in yet another setback to the effort to rescue the 41 workers trapped inside.

The rescue workers will “stabilise” the platform on which the 25-tonne auger machine is mounted before drilling is resumed, officials said.

Sections of steel pipes were being inserted through the rubble of the collapsed portion for the workers, trapped for 11 days, to be brought out.

Earlier on Thursday, international expert Arnold Dix had said that the auger machine drilling through the rubble of the collapsed Silkyara tunnel in Uttarakhand is experiencing “some difficulties” again.

The remark from the Australian had come just hours after drilling to evacuate 41 trapped workers resumed, following a six-hour setback Wednesday night as the American machine encountered an iron girdle.

It was cut by experts, working in a confined environment, before drilling resumed Thursday.

Earlier, drilling was put on hold from Friday afternoon to Tuesday night when the machine encountered a hurdle.

“Right now the auger machine is experiencing some difficulties, for the third time,” Dix to PTI. “We have seen this happen before,” he reminded.

He did not elaborate on the nature of “difficulties” this time, and it was not immediately clear that this will lead to any major delay in the rescue operation that has entered its 12th day.

However, he remained optimistic about the success of the rescue effort. He said the work was going on in a cautious manner, as it should.

Dix also warned against rushing as it might "complicate" things.

"Since the trapped workers on the other side of the rubble are safe and fit, not rushing has enormous value because if we rush in a situation like this we might create problems we cannot imagine," he said.

Dix, who heads an international consortium of experts in tunnelling, is in Silkyara to offer advice.