After 16 days of intense efforts by multiple agencies, all 41 workers trapped inside Uttarakhand's Silkyara tunnel in Uttarkashi have safely been evacuated on Tuesday evening.
Following is a timeline of the disaster and the rescue efforts:
November 12: The labourers get trapped as portions of the Silkyara-Dandalgaon under-construction tunnel on the Brahmkhal-Yamunotri highway collapse following a landslide at around 5.30 am on the day of Diwali.
Arrangements made to supply oxygen, electricity and eatables to the trapped labourers through air-compressed pipes as multiple agencies, including the NDRF, SDRF, BRO, project executing agency NHIDCL and ITBP, begin rescue efforts.
November 13: Contact is established with the trapped workers through a pipe meant to supply oxygen to them and they are reported to be safe. Fresh rubble keeps falling from above due to which the debris accumulated in an area of around 30 metres spreads to 60 metres.
November 14: Steel pipes of 800- and 900-millimetre diameter are brought to the tunnel site to be inserted through the rubble with the help of an auger machine for horizontal digging.
However, when more rubble falls from the cavity created by the cave-in, two labourers sustain minor injuries.
November 15: Dissatisfied with the first drilling machine, the NHIDCL asks for a state-of-the-art auger machine, which is airlifted from Delhi to speed up the operation.
November 16: The drilling machine is assembled and installed. It starts working past midnight.
November 17: The machine drills about 24 metres through the 57-metre rubble stretch by the afternoon and four MS pipes are inserted. The process comes to a halt when the fifth pipe hits an obstacle.
Another high-performance auger machine is flown down for the rescue efforts.
In the evening, during the positioning of the fifth pipe, a big cracking sound is heard in the tunnel. Fearing the possibility of further collapse in the vicinity, the operation is suspended immediately.
November 18: Drilling does not resume on Saturday as experts feel that the vibrations created by the diesel-driven 1,750-horse power American auger inside the tunnel might cause more debris to collapse, posing a risk to the lives of the rescue personnel.
Alternative options are explored by a team of officials from the PMO and experts who decide to work on five evacuation plans simultaneously, including vertical drilling through the top of the tunnel to rescue the trapped labourers.
November 19: Drilling remains suspended while Union minister Nitin Gadkari who reviews the rescue operation says boring horizontally with the huge auger machine appeared to be the best bet.
November 20: PM Narendra Modi speaks to CM Pushkar Dhami over phone to take stock of the operations.
However, the team is yet to resume the horizontal drilling that got suspended after a boulder appeared to block the progress of the auger machine.
November 21: Rescuers release the first video of the labourers trapped. The workers, wearing yellow and white helmets, are seen receiving food items sent to them through a pipeline and talking to each other.
Two blasts are set off at the Balkot-end of the tunnel, beginning the process of drilling another tunnel - an alternative to the Silkyara-end option. But experts said the approach could take up to 40 days.
The NHIDCL resumes overnight the horizontal boring operation from the Silkyara end that involved an auger machine.
November 22: Horizontal drilling of 800 mm diameter steel pipes reaches about 45 metres with only 12 metres remaining of the around 57-metre debris stretch. Ambulances are kept on standby.
However, in a late evening development, the drilling hits a hurdle when some iron rods come in the way of the auger machine.
November 23: The iron obstruction that had caused a delay of six hours in the drilling is removed. Officials say the 48-metre point has been reached by the drill. But boring through the rubble is put on hold again apparently after cracks appeared in the platform on which the drilling machine rests.
November 24: The 25-tonne machine is restarted and drilling is resumed. However, in a fresh hurdle, the drill hits a metal girder halting the operation again.
November 25: The blades of the auger machine drilling through the rubble is stuck in the debris, forcing officials to consider switching to options that could drag on the rescue by several days, even weeks.
Officials now consider two alternatives: manual drilling through the remaining 10-12 metres of the rubble or drilling down 86 metres from above.
November 26: Vertical drilling of 19.2 metres is done to create an alternative escape route. As the drilling progressed, 700-mm wide pipes are being inserted to create an escape passage.
November 27: Rat-hole mining experts are called in to help with rescuers requiring to dig through horizontally around 10 metres of rubble. Simultaneously, vertical drilling from above the tunnel has reached a depth of 36 metres.
November 28: Rescue workers break through the last stretch of the rubble at about 7 pm.
NDRF and SDRF men enter the steel chute to reach the trapped workers and start bringing them out on wheeled-stretchers one by one.
All 41 labourers have been evacuated.
