The man tasked with digging out the 33 trapped Chilean miners has told how he and his team of experts pulled off the amazing rescue.

Andre Sougarret, 46, spoke as nearly all the rescued miners left hospital after their 69-day ordeal.

Three days after men were sealed 2,000ft within the San Jose gold mine, the engineer was summoned by Chile's president Sebastian Pinera and told he would be in charge of the rescue.

His mission was unprecedented. No-one had ever drilled so far to reach trapped miners and no-one knew where to find them.

The last miner to reach the surface, shift foreman Luis Urzua, told him: "People like you are worth a lot of money in Chile."

Mr Sougarret's management of the crisis was so successful that nearly all the miners emerged healthy.

He told how he assembled a team of experts and methodically worked on the problem that would become the biggest challenge of his life.

Mr Sougarret, who ran the world's most productive subterranean mine, El Teniente, for Chile's state-owned Codelco copper company, said he tried not to dwell too much on the men he was trying to save.

"I never allowed myself to think about what was happening with them - that's anxiety-causing," he said. "I told myself, 'My objective is to create an access, a connection. Put that in your head'.

"Why they were there and what happened, that's not my responsibility. My responsibility is to get there and get them out."

Mr Sougarret flew to the mine in Chile's northern Atacama desert and encountered a nest of confusion, with rescue workers, firefighters, police, volunteers and relatives desperate for word about the fate of their men down below.

Gently but firmly, he made his first move - ordering out the rescue workers until there was someone to rescue. He asked for any maps of the mine and assembled a team, starting with Rene Aguilar, the 35-year-old risk manager at El Teniente.

In the weeks that followed, the two men built an operation that grew to more than 300 people.

Among their first steps was to ride into the mine in a truck.

"What we found was a block, a tombstone, like when you're in an elevator and the doors open between floors," Mr Sougarret said.

They determined the cave-in started at a depth of about 1,000 feet and brought down the very centre of the mine, some 700,000 tons of rock.

Drilling through would risk provoking another collapse, crushing anything below, so an entirely new shaft would have to be drilled to try to reach the men.

They spoke to the miners who had narrowly escaped being crushed in the August 5 collapse and who knew what was in the lower reaches of the mine: tanks of water, ventilation shafts, a 48-hour food supply in a reinforced refuge far beneath the surface.

The drills would have to seek a path through solid rock to avoid veering off into an open or collapsed space below. But the mine had been so honeycombed over its long history that there were no precise maps.

"We were building an idea about where they might be," Mr Sougarret said.

The miners who surfaced before the cave-in described where the men would have been working: probably near a workshop and reinforced refuge where they normally gathered to be taken to the surface for their lunch break.

"Now with all these elements, one could clearly say there is a hope that they were alive," Mr Sougarret said.

"I clearly thought the men could survive for 30 days, maybe 40 depending on the condition of some of the people, with water and air, without food. ... That was the fact that I kept in my head."

Then, on August 19, came a crisis. The drill reached 700 meters - and nothing. "It passed 710, passed 720, and we got to 770 and didn't find anything," Mr Sougarret said.

The drill had in fact veered off, passing so close to the refuge that the miners could hear and feel it.

"That started a crisis with the families. They were very upset because we hadn't reached them," Mr Sougarret said.

Finally, on August 22, the drill broke through to the shaft about 150 feet from the miners' refuge.

From the surface, the rescue team thought they could hear banging on the drill head. Pulling it up, they found a message tied in a plastic bag and pressed inside the thread of the drill: "We're all OK in the refuge, the 33."

In the days that followed, two more boreholes would break through, providing a lifeline for sending down food, medicine and messages of encouragement.

As soon as the miners were found alive, Mr Sougarret mobilised three much more powerful drills, soon to be known as Plan A, Plan B and Plan C, each with different methods of pounding through the rock.

Every day Mr Sougarret talked with the trapped miners, first on a phone dropped down the hole, and eventually by video conference calls.

With three drills advancing towards the men, it was only a matter of time. While Mr Pinera pledged to bring the miners home by Christmas, Mr Sougarret calculated the potential speed of each drill and bet on three dates - December 1 for Plan A to reach the refuge, October 10 for Plan B to reach the workshop and October 30 for the shaft in between.

At 8.05am on October 9, Plan B broke through. He had been off by a single day.

"This last stage for me was like butter," Mr Sougarret said.

"I always said that if these people are alive and I have contact with them and I can get food to them, they could spend a year (below) and nothing will happen to them. It was a question of time."