PI completion could take five more years

January 1 | Kuensel
By Tashi Dema

Looking down from the Wangdue-Tsirang highway, men in hard helmets and heavy earth moving machines look tiny as they excavate earth on the right bank of the diverted Punatsangchhu.

They are digging for the foundation of the dam of the Punatsangchhu I hydroelectric project (PI). Engineers, explaining the status of the construction, said a solution has been found to the sliding that delayed works. Engineers at the site said works are going well and that the dam construction progress is 69 percent complete.

Executive engineer at the dam construction, Pema Tenzin said they have done restoration and strengthening works at the site by grouting the slid rock mass, installed 100 MT capacity pre-stressed cable anchors, 325mm diametre Micro piles and implemented 2,000mm dia reinforced cement concrete (RCC) piles.

“We are widening a stretch of the Wangdue-Tsirang highway, which is above the dam, to remove a portion of the local slide,” the engineer said. He said consolidated grouting with more than 543,648 bags of cement was done and 554 cable anchors were put in different levels in the area.

However, those following the development of the project closely are sceptical that no solution has been found yet.

The construction that started in November 2008 and scheduled to complete by November 2016 got delayed after the right bank of the dam site slid by more than five metres. They encountered another local sliding at the area in 2016.

Some engineers working for the project told Kuensel all is not well, reasoning that a third party expert the management hired, the Norwegian Geological Institute (NGI) did not provide a concrete solution. They confided that when the first major slide occurred, the consultant, Water and Power Consultancy Services (WAPCOS) had assured that they handled more severe problems and they would resolve it.

“But there is nothing much we could do, as we have to depend on external agencies for the remedies,” an engineer said.

PI’s managing director, NC Bansal, acknowledged that addressing the slide continues to pose a challenge, but said the management, in association with its consultants (WAPCOS, CWC, GSI) has analysed the cause of the slide through detailed subsurface investigations based on which a number of stabilization measures have been implemented or are under implementation in a phased manner over a wide reach of dam area. He added that NGI has been appointed to analyse and suggest additional protection measures required in this case.

“To monitor the slide in real time, an IBIS Radar has been installed at the project site in July 2018 and the data is being continuously analysed by CWC, NGI and PHPA-I based on which further protection measures are being taken.”

The managing director assured that the stabilization and protection measures already implemented or under implementation shall enable PI to complete the excavation of the dam area up to a depth of 80ms from the original riverbed, which was at an elevation of EL 1,155ms at dam axis.

“We have already completed the required excavation of the dam at the left bank and as of now, nearly 98 percent of the excavation has been completed,” he said.

N.C. Bansal said that on the advice of consultants, they have taken up the offloading of August 2016 slide after extending of the highway by around 15ms so that the traffic in the area remains unaffected. The offloading of the 2016 slide is expected to take around six to seven months including the support measures required to stabilize the hill slopes.

“After the completion of excavation, concreting of the dam shall be taken up, which shall stabilize the right bank and hence the feasibility of the project shall not be an issue,” he said.

Meanwhile, most of the components of the project like headrace tunnel and desilting chambers are almost complete and the civil works of the powerhouse are on the verge of completion.

In the powerhouse, of the six units, two were installed and other four are being assembled. An assistant engineer, Ugyen Tshewang, said 90 percent of the civil works are complete and the shear zone problem they encountered took about a year to treat. “But everything is on track now,” he said.

Of the 21 transformers, 10 were installed. The surge shaft and pressure shaft, engineers claim, are also complete. “Erection of electro-mechanical components is progressing on schedule,” the managing director said.

He said that the leftover excavation work on the right bank is in progress, which shall be followed by concreting. “After the start of concreting, the project will be completed in a span of three and a half to four years.”

While there are observers who claim that with all the cost escalation and delay, the electricity produced by PI would not be economical and that the production cost and price would be too high and not consumer friendly, which would affect the electricity trade negotiations, NC Bansal said there is a number of hydro projects over the world that faced such problems but the electricity produced by these projects have become economical with the passage of time as the useful life of the project is of the order of 50 years or more after its completion.

He said that the delays from now would not be too long, as they have nearly addressed most of the uncertainties of the project.

The managing director also said the management and consultants are committed to complete the project at the earliest with quality and durability so that both the people of Bhutan and India shall reap the intended benefits of the project in times to come.

http://www.kuenselonline.com/pi-completion-could-take-five-more-years/

Workers at the dam site
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