Uttarkashi. Rescuers on Monday pushed through a six-inch-wide pipeline through the rubble of the collapsed Silkyara tunnel, a breakthrough that will help them supply larger quantities of food and possibly allow live visuals of the 41 workers trapped inside for eight days.

Earlier, a four-inch existing tube was being used to supply oxygen and items like dry fruit and medicines into the section of the tunnel beyond the rubble of the collapsed portion of the under-construction tunnel on the Char Dham route in Uttarakhand.

National Highways and Infrastructure Development Corporation Limited (NHIDCL) director Anshu Manish Khalkho called it the "first breakthrough" at the site. "We have sent the pipe 53 metres to the other side of the rubble and the trapped workers can hear and experience us," he said.

Drones and robots from the Defence Research and Development Organisation (DRDO) have also been brought to the site to look into the possibility of other escape routes for the trapped men.

But rescue workers were yet to resume the horizontal drilling through the debris after a boulder appeared to block the progress of the heavy-duty auger machine earlier this week.

Rescuers are also preparing to exercise the option of drilling more than 80 metres down into the hill to reach the workers. A road has been laid for heavy drilling machinery used by the Oil and Natural Gas Corporation (ONGC) to get to the top.

International tunnelling expert Arnold Dix also reached the disaster site to review rescue efforts. He heads the Geneva-based International Tunnelling and Underground Space Association.

The pipeline development comes on the day Prime Minister Narendra Modi called up Uttarakhand Chief Minister Pushkar Singh Dhami to take stock of the rescue operation. According to a statement, the PM said it was necessary to keep up the morale of the trapped workers.

Col Deepak Patil, who is also involved in the relief operations, told reporters that food items like dalia (porridge), khichdi, and sliced apples and bananas can now be sent into the new pipeline.

They will be packed in plastic bottles with wide mouths, he said. Also mobile phones and chargers could be sent to the workers, or a telephone line inserted, he said.

He said the rescuers will try to establish a link for live streaming visuals from inside.

The rescuers and those inside the tunnel have been communicating with each other even now, and relatives allowed to talk with the workers. But the six-inch pipe will be a significant upgrade. The existing four-inch pipe was good enough to send only food items like dry fruit and roasted chickpeas.

The NHIDCL director said the next step is to remove the drill bit from the pipe. “Once that is done food, medicines and other essentials will start being sent to the trapped workers," Khalkho said.

He had told reporters earlier in the day that “endoscopy-like” camera equipment was soon to arrive from Delhi and be sent through the lifeline pipe. The rescuers and the trapped men will them be able to see each other.

He said they will study whether the robots bought to the site can negotiate the slippery and uneven surface inside the tunnel. Pictures captured by the drones so far are not clear as there is a lot of dust inside.

PM Modi’s conversation with Dhami was the third since the disaster struck.

According to a statement issued by the Chief Minister’s Office, the prime minister said necessary equipment and resources are being provided by the Centre and the trapped workers will be safely evacuated through mutual coordination.

Tunnelling expert Dix expressed satisfaction at the efforts so far.

“I have just been down in the tunnel. Enormous amount of work has been done there in preparation, and we are just coming up here at the top of the mountain to consider other options as well," Dix told reporters.

"I only arrived yesterday but the work I have seen even between yesterday and today is extraordinary... The plan for today is working out the best thing to do to get the men out," he said.

Dix did not spell out a timeline.

Medical teams are stationed at the site. A team from the Prime Minister's Office is also keeping an eye on the operations after visiting the tunnel for an on-the-spot review, a state government statement added.

The Uttarakhand government said it will bear the travel, food and lodging expenses of relatives of the trapped workers, CM Dhami said Monday.

Psychiatrists have been roped in to maintain the morale of the trapped workers and their families, he said.

Leader of Opposition in Uttarakhand Assembly Yashpal Arya visited the site but was not allowed inside the tunnel. However, he spoke with the officials and was briefed about the rescue operations.

He demanded a CBI inquiry monitored by the Chief Justice of the Uttarakhand High Court to find out if the execution of the project was given to an inexperienced firm and if that led to the disaster.