Manali: A geological surprise in the form of a rivulet has sprung up during work on a tunnel below the 3,978-metre Rohtang Pass in Himachal Pradesh.
Engineers involved in the digging of Rohtang tunnel Monday spoke of a torrential inflow, like that of a rivulet, into the tunnel.
The 8.8-km tunnel, an engineering marvel and a strategic project, will ensure all-weather connectivity to Keylong in Lahaul and Spiti district of Himachal Pradesh.
The work is being undertaken by the Border Roads Organisation (BRO) in collaboration with Strabag-Afcons, a joint venture between India’s Afcons Infrastructure and Strabag SE of Austria.
‘A flow of 30 litres per second of the Seri rivulet is entering the tunnel and its volume can increase to 200 litres per second,’ said BRO Chief Engineer P.K. Mahajan.
The Seri is a tributary of the Beas river and flows down the mountain.
‘The tunnel alignment is crossing beneath the rivulet. High water seepage may be encountered as we move further,’ he added.
Mahajan said the engineers were taking various measures like rock grouting and bolting and using special chemicals to counter and pump out the flow, and that more geological surprises could be in store.
‘Since the area has geothermal energy history, we expect to encounter hot water springs or emission of toxic gases as we move further,’ he said.
Over 350 BRO personnel and 24 experts from Germany and Austria have been working round the clock to meet the February 2015 deadline.
Of the 8.8-km horseshoe shaped tunnel, 2,700 meters from the south portal and 800 meters from the north portal have been excavated since work began in June 2010.
The tunnel is located at altitudes ranging above 3,000 meters and lies beneath the snow covered Rohtang Pass. About 70 percent of the pass’ top remains under snow even during summer.
The average minimum temperature at the tunnel portal, while it is peak summer in the plains, ranges from five to seven degrees Celsius. The maximum is 17-18 degrees.
The tunnel is projected to cost Rs.1,495-crore ($290 million).