The 1,200 MW Punatsangchu I and 1,020 MW Punatsangchu II is headed for more delay and cost escalations after a report by the Norwegian Geological Institute (NGI) recommended additional measures to strengthen the sliding right bank of P I, and approved the proposed works for the collapsed roof of the surge chamber in P II.
The NGI was hired by the PHPA management as a third party expert from February 2017 after the P I right bank slide kept sliding even after a three phase and ongoing expensive rectification measures, and also after the collapse of the roof of the cavern in the surge chamber in P II.
It has been learnt that the Bhutanese side pushed for the hiring of NGI to ensure that all full proof rectification measures are done and a fully safe project is handed over on completion.
The exact delay and cost escalation will be known after the Central Water Commission (CWC) of India does a presentation of the extent of engineering works to be done and the associated costs based on the NGI report. The CWC is expected to present its report by 14th August to the PHPA.
Even in the best case scenario the delay at the least is expected to be around four to five additional months. This being the time period from February to July when NGI did its study and presented the report.
The PHPA MD R.N Khazanchi conceded that there would be at least up to a four month delay at this point of time. He said there would also be a cost escalation thought it would be nominal compared to the project cost and the loan interest being borne by the project due to delays.
This would mean that the earlier 2021 end to the first quarter of 2022 completion date of P I could well move into mid 2022 and possibly beyond. In the case of P II the September 2019 deadline of P II could move into January 2020 and beyond.
In the case of the P I project a major never development is that the NGI report has asked PHPA to excavate large amounts of soil and rocks from a much higher place of 150 to 200 meters from the current point of excavation and stabilization.
This would lead to less pressure on the slope from above but would also lead to a gentler slope. To achieve this benches of steps will have to be created at around 30 meters height along with cement grouting and 325 mm ‘dia piling’.
Cementing grouting is pumping in cement into cavities and also on the surface to stabilize the slope while dia piling is equivalent to driving in large steel and concrete nails into the mountainside to fix the lose surface slope to a stronger bed rock deeper in the mountain.
However, with the need to clear more soil from the top the NGI report anticipated that around 30 acres of mainly paddy land belonging to around 32 households may have to be acquired. This private land acquisition is also expected to lead to more delays.
In P I a major source of concern and potentially even longer delay is that any work to clear the top would have an impact on the ongoing dam construction excavation at the bottom. This is because of safety concerns that boulder and materials from the top could tumble down to the dam site.
This would mean that work cannot be carried out simultaneously without grave safety risks. Here Khazanchi said that the additional work will be carried out in parallel with the dam excavation. However, on safety related questions by this paper Khazanchi said that the steps will take care of issues but even for safety concerns work can be scheduled at different periods.
P I in July 2013 saw a slide happening on its right bank and since then the CWC has done works to stabilize the slope in three phases with significant cost. The approach has been to do some work and then observe for slides. There was a Nu 3.5 bn price tag attached at the time for the rectification measures. However, even after the third phase of the rectification measures by CWC the machines detected a slide of 5 to 10 mm a month. This was the final push that got the Bhutanese side to recommend NGI for third party advice on the issue.
Given that the project was originally supposed to be completed by November 2016 this would mean around a six year delay. The last approved project cost of the project in July 2015 was around Nu 93.75 bn. The P I project has been plagued by delays and cost escalation on account of its dam relocation and the subsequent right bank slide.
In the case of the P II project the NGI has largely approved the proposal developed by CWC and WAPCOS.
In January 2016 the P II project came across a shear zone or geologically weak zone in its downstream surge chamber in the power house complex which lead to the death of six Indian workers after a the roof of the cavern collapsed.
The collapse has blocked of the North side of the tunnel while the South side is still open. The PHPA is burrowing two access tunnels from the side to reach the area but given the shear zone the work is being done slowly and carefully along with experts from the National Institute of Rock Mechanics from India.
The nature of the task can be understood from the fact that the body of the workers are still buried under the rubble.
The affected area is around 90 meters in height and around 100 meters in length.
It has been understood that the Bhutanese side has proposed a new rock bolting technology used in the Dagachu project in the case of the P II project.
The last approved cost of the P II project in 2016 was Nu 72.90 bn.