April 14: Mining engineer Paul Verrall has burrowed tunnels across continents for the last 25 years, but never like the one being dug under the Hooghly.

Verrall, 56, is the tunnel construction manager of Afcons for the East-West Metro project. He had previously worked on a Metro rail tunnel under a river in Malaysia, but admits that it cannot be compared to the 500-metre wide and over 30-metre deep Hooghly tunnel.

"I was involved in the construction of the rail tunnel under the Klang river in Malaysia in the 1990s. But that was nothing. This one's huge," Verrall told Metro on Thursday, a day before the East-West tunnel ventured past the riverbank.

"This is the biggest underwater tunnel I will be going under, in terms of width," said Verrall, a Briton who lives in South Africa. "The width of the tunnel under the Klang river was 100m from one bank to the other. But under the Hooghly, the width is 500 metres. One has to understand the difference."

The enormity of the task at hand does overwhelm Verrall, but he is confident about crossing the channel without any hassle. "Unless we encounter some unknown geological feature or there is an unforeseen event, we should have no trouble," he said.

By the end of June, Verrall expects both the tunnels to reach the Calcutta side.

"When a tunnel was built under the English Channel, it was the first. There were concerns but it was built successfully. This one is like the Chunnel (the Channel Tunnel)," Verrall said.

According to him, the stiff clay of the riverbed would be of help. There is less chance of water seepage through this type of soil, he said.

For the Chennai Metro, Verrall had overseen five tunnel-boring machines operating simultaneously. It was a task he found challenging because of layers of sandy soil loaded with water above the hard rocks at the bottom.

While his energies are currently focused on the East-West project, Verrall is a man of many parts. He rides motorcycles and goes deep-sea fishing, surfing and diving. Back in South Africa, he owns a fishing boat.

"Here, it's only work. In the city, you can't ride a motorcycle the way I do in South Africa. It's all about speed," he smiled.

In Chennai, he had wanted to go deep-sea fishing but did not get permission.

So, isn't building a tunnel under a river enough excitement? "The biggest infrastructure projects are always boring. Because you have to be careful and follow standard operating procedures," said Verrall's colleague, project manager Virinder Kaul. "The main concern while creating a tunnel under a river is that if something happens, it's difficult to intervene from outside, unlike on land."

Like Verrall, he believes that the stiff clay under the Hooghly would be of help in constructing the tunnel. "But there's always an element of uncertainty. It's like the first day of a Test match. You don't know how the pitch will behave," he quipped.