A heavy drilling machine was airlifted from Delhi Wednesday to replace the "failed" equipment which was being used earlier to create a passage for 40 workers trapped in an under-construction tunnel that collapsed three days back, officials said.

The new machine, that landed at the Chinyalisaur helipad, over 30 kilometres from the tunnel on the Chardham route, is being put into service, amid apprehension by workers at the site on the progress of the multi-agency rescue operations.

Workers chanted slogans at the mouth of the tunnel on the Brahmakhal-Yamunotri National Highway, protesting over the "slow" pace of the operation to rescue their colleagues trapped inside for over 72 hours now.

The plan was to use an 'auger machine' to drill through the rubble of the tunnel's collapsed portion and insert 800-mm and 900-mm diameter sections of mild steel pipes -- one after the other. Once this happens, the workers trapped on the other side of the rubble can crawl out to safety.

But the first drilling machine turned out to be too slow and technical issues developed, the officials said. Also, falling debris inside the tunnel damaged the equipment and injured two rescue workers on Tuesday.

The replacement machine came in two parts on an Indian Air Force Hercules aircraft to Chinyalisaur on Wednesday afternoon and was being transported by road to the tunnel, about two hours away, Uttarkashi Superintendent of Police Arpan Yaduvanshi said.

"We will start installing it as soon as it arrives and in four-hours hours it will begin the drilling operation. With a capacity to penetrate 4-5 metres of rubble per hour, we can expect it to penetrate 50 metres through the rubble in 10 hours," NHIDCL Director Anshu Manish Khalkho said here.

A portion of the tunnel, part of the ambitious Chardham All-Weather Road project, collapsed on Sunday. The 30-metre collapsed section is 270 metres from the mouth of the tunnel from the Silkyara side. Officials said the labourers were safe, and oxygen, electricity, medicines, food items and water were being supplied to them through pipes.

Khalkho, however, said it was not possible to specify a definite timeframe for the evacuation of the trapped labourers but effort was on to make a headway at the earliest and rescue them all safely. Constant communication is being maintained, he added.

According to a list of the trapped workers issued by the emergency operation centre, 15 are from Jharkhand, eight from Uttar Pradesh, five from Odisha, four from Bihar, three from West Bengal, two each from Uttarakhand and Assam, and one from Himachal Pradesh.

Tuesday's landslide and slow performance of the drilling machine deployed earlier hampered efforts to insert steel pipes through the tunnel's debris to create the passage, the NHIDCL director added.

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