Occurrences of ‘adverse geology’ at several sites are a cause of some concern

Hydropower: Officials of Punatsangchhu hydropower project authority (PHPA) II are keeping their fingers crossed, hoping that the ‘adverse geology’ it has encountered at several sites doesn’t delay the project.

The project has two years left for its commission and, while the geological problem of loose soil could delay the project, officials said, the problems are under control as of now.

PHPA II managing director, RN Khazanchi, said it had encountered some geological problems, especially on the left bank, the headrace tunnel (HRT) and the tailrace tunnel (TRT).

“The underground tunneling and caverns too have encountered adverse geology,” the managing director said.

Of the 8.6km HRT, 5.6km has been completed. “But the rest is a question mark and we still have our fingers crossed,” he said.

The tailrace tunnel has also encountered similar problems.  Of the 3km, the project has reached 1.6km, while the remaining area is poor geology and not hard rock.

Contractors have dug additional entry points to expedite works on the TRT, while they could not make similar entry points in the HRT, because of the highway running near it.

For TRT, the project opened an additional entry point, and another one will be opened for the surge shaft gallery.

“It’s under control, but takes extra time, for which some innovative measures have to be taken to expedite the remaining works,” the managing director said.

“To prevent the problem from getting worse, we had to open some additional entry points for the tunneling, both for the caverns as well as the tailrace tunnel,” he said.

As of today, the managing director said that they had everything under control and the project would be completed on schedule in December 2017.

Gammon India is working on the main tunneling of the HRT stretching 6.6km, while JaiPrakash is doing the rest and the TRT.  The HRT is the largest of its kind in the sub-continent with a diameter of 11m.

The tunneling works started in June 2011.

The excavations of four de-silting chambers and four power intake tunnels, each measuring 6.4m in diameter and 2km in length, are completed, besides the cofferdam.

The initial sanctioned cost of the project was Nu 37.78B on March 2009 price level with installed capacity of 1020MW.  It is a government of India funded project, on 70 percent loan at 10 percent interest per annum, while 30 percent is grant.

The project is located on the right bank of Punatsangchu along the Wangdue-Tsirang highway between 22km and 35km downstream of Wangdue bridge.


By Tshering Palden