The 1,020MW Punatsangchu II Hydroelectric Project Authority (PII) is likely to be delayed by about eight to nine months from the current completion date, according to the project management.
This would mean that the project might complete by 2021 if everything goes on track. The last date of completion was December 2020.
This, however, is not confirmed, as it was learnt that both the governments (India and Bhutan) have asked the management to frame a realistic completion date, which the management is working on.
PII’s managing director, Amresh Kumar, said the collapse in the downstream surge gallery (DSSG) in March 2016 have a ricochet effect on the entire powerhouse complex together with the impact on the DSSG.
“The project commissioning is likely to be delayed by about eight to nine months. However, best efforts are being made to comply with the December 2020 schedule.”
Engineers say that while the management initially declared December 2020 as the commissioning date and they are trying to complete the civil works by the time frame but the electromechanical work would need a minimum of 18 months, which would delay the completion.
They explained that when the civil works near completion, electromechanical works would start.
“Until the strengthening work is complete and muck is removed, electromechanical works cannot start,” an engineer said.
A superintending engineer, NR Gaur, who officiates the engineer-in-charge, said they completed about seven percent of the electromechanical works. “We installed the butterfly valve chamber. Our progress depends on the civil works.”
Engineers said that of the 314ms length of the DSSG, 140ms is being abandoned because of the collapse and they now have two surge chambers, one in the south, which is 107ms long and one in the north, which is 60ms.
The main hitch, according to the engineers is on the northern side, where there are space constraints to deploy equipment.
They said that in the south surge chamber, there is balance excavation, which poses challenges in taking out the muck.
“When there is space constraint, the approach slope gradients become steep and we are not sure if we need an additional tunnel or not,” an engineer said. “We have not received the final drawings from the designer and they said they need 30 more days.”
He also said they proposed for some fast-tracking of the work through some short approaches to take the work independently. “In the northern side, we are executing the work independently and looking for similar options even in the south.”
According to the engineer-in-charge, Gorab Dorji, restoration and strengthening works are going on in DSSG and strengthening works are being executed in the transformer and machine hall.
He said that the powerhouse complex is 67.30 percent complete and explained that all the excavation works were actually completed but because of the collapse in DSSG, the stability of all other components have been affected.
On either side of the walls, grouting and cable anchoring are done after which the cavity of 91ms, which is half empty and half loose muck would be filled up. “While the empty would be filled up, the loose portion would be grouted,” Gorab Dorji explained.
He also said the transformer has been impacted most and the area was filled with mucks from outside. “Additional strengthening with rock bolt and grouting was done.”
The engineer-in-chief said that in the machine hall, refilling was done in January 2017 and they did additional strengthening after that.
The engineers said that while the disaster occurred, they ensure quality construction of the project.
Gorab Dorji said that they are ensuring the project serves a minimum of its 100 years design life. “As monitoring team, we are putting the best effort to ensure quality construction.”
He said expensive equipment are installed in the machine hall and transformer and if anything happens, all equipment would be damaged and lives would be lost. “The machine hall and transformer is being strengthened to give additional support to ensure long-term stability. We do whatever designers recommend.”
He said the strengthening works are time-consuming but they are ensuring the stability for long-term benefit.
Another engineer, Zeko, said they are using improved methods to ensure proper strengthening measure with design support. “We use FMI rock bolts.”
Meanwhile, the dam construction, according to the management is 76 percent complete and the headrace tunnel is 92.3 percent complete.
Engineers said that four dam blocks of the 12 required special treatment and they came across shear zone during excavation. “The toppling of the cofferdam, which comes out in media often is not an issue,” an engineer, Sonam Zam, said. “It is designed to over topple since cleaning up is economically viable.”
The superintending engineer for the dam, Sonam Tobgay, said the dam is out of any geological surprises or critical areas.
It was learnt that of the Nu 72B approved for the project in 2015, the project spent Nu 53B as of last week of December.