The six-year study, in partnership with Bhutan's Department of Geology and Mines, has identified 10 possible road tunnels that would connect urban centres and key infrastructure. These include a new hydro-electric plant and a proposed new airport in the south of the country, which has a population of 700,000.
The existing road system follows treacherous mountain passes more than 3km high. The passes are often subject to landslides during the monsoon season and closed altogether in the winter because of snow.
In 2000, a huge landslide near Jumja, on the main road connecting India and Bhutan, cut off the chief route into the country and led to severe shortages of food and fuel.
"The government wants to link the country so you can reach any town in Bhutan within a day," NGI project leader on the Bhutan scheme Rajinder Kumar Bhasin told GE. "At the moment it can take several days to travel 200km by road.
The government of Bhutan is expected to "seriously consider" commissioning the tunnels after the general election this month. European tunnelling consultants, working in a joint venture with Indian contractors, are thought to be in the frame to build it. Consortia will be expected to come up with a private finance initiative design and build model.
The tunnels are expected to present complex technical challenges because the rock is fragile and highly sheared, and would have to be heavily supported with rock bolts and shotcrete.
Testing by NGI found a mixture of highly fissured quartzite and augen gneiss with some schists and marble. Bhasin added that the tunnels would be hewn by drilling and blasting. Transporting tunnel boring machines (TBMs) up the mountainous terrain would be too difficult and the rock is not homogenous enough.
"There have been experiences in the Indian Himalayas where TBMs have got stuck," added Bhasin.
The tunnel is expected to be funded through the sale of electricity from the newly completed Tala hydroelectric plant and other hydroelectric plants that are expected to generate 30,000MW of power per year.
The tunnel network would include:
- The 1.2km Jumja Tunnel
- A 9km tunnel along the route
from the capital Thimpu to the
airport at Paro (see map)
- A tunnel up to 3km through
the Thrumsingla Pass along
the east-west highway linking
Wangdue and Thrumsingla
- A 10.6km tunnel from Thimpu