The cost of the Sevoke-Rangpo railway line's construction is expected to cross Rs 12,500 crore, which is a three-fold increase from the 2020 estimate and more than 10 times the expenditure projected in the 2008-09 budget.

B.K. Gupta, the chairman-cum-managing director of Ircon International Limited, said there had been an escalation in the project cost.

“The revised estimate is under the process of sanction. It will (touch) Rs 12,500 crore," said Gupta.

Ircon International is a government of India undertaking.

The 44.96km-long railway line had been included in the budget of 2008-09 with a project estimate of Rs 1,339.48 crore.

Major construction activities started only in 2018 because of the delay in obtaining environmental clearance.

In 2020, the ministry of railways in a statement through the Public Information Bureau (PIB) had projected a project cost of Rs 4,085 crore.

An official said stations and ancillary infrastructure would be of high quality and that, too, had led to the escalation in the cost.

Gupta was at Rangpo in Sikkim on Monday to oversee the completion of the final concrete lining in tunnel No 14 of the route. “Essentially, this is the first tunnel where all kinds of civil work have been completed. Later on, the tracks will be laid,” explained an official of the construction agency Abir Infrastructure Pvt Ltd.

Tunnel No 14 is about 1,977-metre-long.

The entire project consists of 14 tunnels, 22 bridges and five stations, one of which will be under the ground at Teesta Bazar. Over 38km of the route passes through tunnels, accounting for about 86 per cent of the entire alignment.

Gupta said the “project was relatively difficult”. “Work is difficult in tunnels 8 and 10 as we are encountering soft rock and it is difficult to mine,” said Gupta, who is also an additional member, civil engineering, Railway Board.

The railway official, however, said he was confident of completing the project by December 2024.

Sources said about 76 per cent of tunnelling work had been completed and they included mining activities in six of the tunnels.

With the completion of the rail line from Sevoke in Bengal to Rangpo in Sikkim, the Himalayan state will be on the railway map of the country. Plans are afoot to extend the route to Nathu-la along the China border.

“Sanction has been granted for the survey. It is likely to start soon,” said Gupta.

Two surveys — one for the route from Rangpo to Gangtok and the other from Gangtok to Nathu-la — will take place.