India’s economy is said to be one of the fastest growing economies in the world. This is reflected in the need for infrastructure and energy, to keep up with the economical growth. Infrastructure is required to open up underdeveloped areas of the country and to improve the traffic situation in and between India’s major cities. And in the meantime, the increased industrial activity and growing wealth demands more and more energy to support these activities.

Although India holds significant coal reserves, it also has an almost unlimited amount of natural energy: hydropower. Due to its geological location, as the Indian subcontinent collides with the Asian subcontinent, the Himalayas are a vast source of hydropower which is yet to be utilized. Over the past few years India has started an impressive program to develop a number of hydro-electric power plants in the Northern part of the country.

One of the largest of these projects is the Lower Subansiri Hydro Electric project by the National Hydroelectric Power Corporation of India. This site in the state of Assam, bordering Arunanchal Pradesh, has started construction works and will yield 2000MW. Further projects in that area will be developed to increase the power supply with more than 10000MW.


The project features the construction of a gravity dam 116m high from the river bed level, eight head race tunnels, pressure shafts and a power house to accommodate eight turbines of 250MW each.

Part of the construction of this type of project includes the excavation of tunnels, i.e the headrace tunnels and river diversion tunnels. At Subansiri, SOMA Enterprise has won the order for the latter. To increase the production progress of these tunnels, SOMA has purchased three WIRTH Roadheaders, which have been commissioned successfully. The machines are one former Paurat T2.10 (E134) and two WIRTH T3.20 (E242) roadheaders. The T3.20 is a largest of WIRTH fleet with a weight of 120 tons and an installed cutting power of 300 kW.

The roadheaders will excavate the tunnels with a cross-section of approx. 8.5m high and 11m wide. This will be excavated in two steps, i.e. by benching. The rock is a abrasive sandstone with an average UCS of 30MPa. However the rock is very homogeneous and compact, without cracks or fissures, requiring every cubic meter to be excavated by the picks on the cutterhead. Once the rock has been cut it disintegrates quite easily, especially when it comes into contact with water. This type of rock seems to be typical for the pre-mountainous area adjacent to the Himalayas. It is one of the youngest sandstone formations, which has not had the time and pressure to develop higher compressive strength.


A further challenge is the remote location. The project site is located in the middle of virgin rain forest and every part or support has to be brought to site. The nearest airport is in Guwahati, a days’ driving over a single lane road, through rural area. Certainly an interesting experience, but logistically it requires adequate planning of spares and services to be available on site. To accommodate and cater all personnel for this project, a separate camp with the size of a village, has been set up.

Once the roadheaders have finished their job, the project still has a long way to go before it can start generating energy. Under the current planning, it is expected that all works will be completed by the end of 2010. In the meantime, the roadheaders most certainly will have found another tunnelling job, either for hydropower or other infrastructure.