"Construction of civil works of the tunnel is in progress, and a progress of about 4.16 km tunnel heading has been achieved," Jaitley informed Lahaul-Spiti legislator Ravi Thakur in a missive last week.

The Defence Minister, replying to Thakur's letter, said the work was in progress from both the north and south portals of the 8.8-km-long tunnel.

"However, certain difficulties such as significant change in rock class was encountered compared to what was initially assumed, and severe tunneling conditions in some portions are being encountered," Jaitley admitted, while replying to the letter about the delay in execution of the horse-shoe-shaped tunnel.

The Rs 1,495-crore tunnel's foundation stone was laid by United Progressive Alliance (UPA) chairperson Sonia Gandhi on June 28, 2010, in the picturesque Solang Valley near here.

The Defence Minister said the Border Roads Organisation (BRO), an organisation under the Defence Ministry, has been directed to take appropriate measures for early completion of the tunnel, being built under the 3,978 metres Rohtang Pass in the Himalayas.

Official sources said that the tunnel might miss its February 2015 deadline and was likely to be completed by 2017.

They further said it will also face a cost overrun of Rs 500-600 crore.

"The project is delayed owing to tough climatic conditions and geological surprises coming one after another," an official, associated with the project said.

He said the project is currently facing high water seepage and loose strata towards Dhundi, 25 km from here.

The project is being built by the BRO in collaboration with Strabag-Afcons, a joint venture between India's Afcons Infrastructure Ltd. and Strabag SE of Austria.

"The reason for the delay cited by officials is inclement weather and heavy snowfall in winter. However, this kind of weather was prevalent in the area when the work was awarded and this would have been taken into account while the target date was fixed," Thakur, vice chairperson of the National Commission for Scheduled Tribes, said in the letter.

In October 2013, the construction work was partially suspended after a portion of the tunnel roof collapsed on the south portal. There was no loss of life.

The Cabinet Committee on Security cleared the tunnel project in September 2009.On completion, the tunnel will be a boon for the cold deserts of Lahaul Valley, where over 20,000 people remain cut off from the rest of the country in winter owing to the closure of the Rohtang Pass.

The tunnel, with a horse-shoe shaped cross-section, will be 11.25 metres wide at road level, providing ample room for two-way traffic, and is designed to cater to a maximum vehicular speed of 80 km per hour. But the Rohtang tunnel alone might not be enough to make the Manali-Keylong-Leh highway an all-weather road.

There are two other major snowbound passes along the way - Baralacha La and Thaglang La.To overcome this, the project envisages constructing a 292-km-long all-weather road, Nimu-Padam-Darcha, via Shinkun La Pass, traversing the remote Zanskar region of Jammu and Kashmir, estimated to cost an additional Rs 286 crore.

BRO Deputy Director General Brigadier VS Kattarya, in a communication to Thakur in February, said the construction of Nimu-Padam-Darcha via Shinkun La Pass has been on at various stretches.

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