China plans the world's longest undersea tunnel
* China is planning another engineering marvel: a tunnel more than twice the length of the Channel Tunnel underneath Bohai Bay
* The new tunnel will knock 800 miles off the current route between Dalian and Yantai
At more than twice the length of the Channel Tunnel, China's latest mega project is not short of ambition.
A 76-mile-long tunnel will run between the northern city of Dalian with Yantai, on the east coast.
"Work could begin as early as 2015 or 2016," said Wang Mengshu, an expert at the Chinese academy of Engineering, to the China Daily.
He added that the new tunnel will knock 800 miles off the current route between the two cities.
It will also form a vital link in a high-speed rail line from China's frozen north to the tropical island of Hainan, in the south.
China has a history of epic engineering projects stretching back to the Great Wall. More recently it has built the world's largest high-speed railway network, longest bridges, and several of its tallest skyscrapers.
Even so, the new £22 billion sea tunnel will present several challenges. Engineers will attempt to bore three tunnels - one for cars, one for trains and one for maintenance - through the hard rock, 100ft below the sea bed.
Vertical shafts will be dug on islands along the route to provide ventilation.
But the area is prone to earthquakes and the tunnel will traverse two major fault lines. In 1976, a 7.5 magnitude earthquake in the nearby city of Tangshan killed hundreds of thousands.
Experts warned that excavation work through an active fault needs special attention.
"The government is being cautious about the project," said a leading researcher on the tunnel at East Shandong University, who asked not to be named.
"We proposed this idea of a tunnel 20 years ago and many research teams have been looking at it since.
"We set up a special group to study the Channel Tunnel. In fact, every undersea tunnel engineer in the world has learned from the Channel Tunnel because it is the best example in the world. We learned some construction techniques and also some ways of financing our tunnel."
The Channel Tunnel, dug between 1987 and 1991 showed that bores could excavate undersea at high pressure. But technology has improved to such an extent that much more ambitious projects are possible.
Longest transport tunnels in the world*
1. Gotthard Base Tunnel, Switzerland – land railway tunnel beneath Alps connecting Uri and Ticino, opens 2016 – 35.5 miles
2. Seikan Tunnel, Japan – undersea railway tunnel connecting islands of Honshu and Hokkaido, opened 1988 – 33.5 miles
3. Channel Tunnel, UK/France – undersea railway tunnel connecting Folkestone and Coquelles, opened 1994 – 31.4 miles
4. Lötschberg Base Tunnel, Switzerland – land railway tunnel beneath Alps connecting Berne and Valais, opened 2007 – 21.5 miles
5. New Guanjiao Tunnel, China – land railway tunnel beneath Guanjiao Mountains connecting Xining and Golmud, opens 2014 – 20.3 miles
* excludes urban metro tunnels