The measures to prevent another P I slide

2026-02-20 - 07:45

And also maintain the electromechanical equipment In the first week of February 2026, the Punatsangchu Hydroelectric Project Authority (PHPA) held its authority meeting in Delhi, where one of the key agenda items was the stabilisation measures for the weak right bank. However, given the major slides at the 1,200 MW Punatsangchu I (P I) site in July 2013, August 2016 and January 2019, despite billions spent on rectification measures in the intervening years, which significantly delayed the project and escalated costs, it is reasonable to ask what will be different this time to prevent another slide, further delays, and additional cost overruns. P I Dam Site In the longer term, the more critical question is what measures are in place to prevent the right bank from collapsing and endangering the dam, and the entire project. On the issue of strengthening the right bank, and after several rounds of discussions, the Bhutanese side had three main asks. The main one is removing as much of the overburden or the slope above the Wangdue-Tsirang national highway above the dam, as possible, covering a stretch of 450 meters. The volume of soil and rock to be removed is estimated at an astronomical 5 million cubic metres. A standard tipper truck can carry between 10 and 16 cubic metres, and it would require approximately 500,000 to 312,500 truckloads. The Indian side initially proposed a lesser removal at a 30-degree slope, which would be cheaper. However, the Bhutanese side pushed for a 26-degree slope, citing concerns over long-term stability. This was the main disagreement that stalled discussions for a long time, and was resolved only after Bhutan agreed to bear the additional Nu 4 billion cost for the extra 4-degree slope reduction. An official explained that removing the overburden, which will even affect part of the PHPA colony, is intended to reduce overall weight and pressure on the right bank. Another reason for removing the overburden is to allow reinforced concrete piles and cable anchors to be driven deeper into the mountain, effectively pinning and stitching the right bank into the firm rock below. The piles are two-metre diameter reinforced concrete pillars, extending 80 to 130 metres deep, to be inserted vertically to stabilize and hold the slope together. These will be complemented by cable anchors, groups of long steel rods drilled 80 to 120 metres into the mountainside. Each anchor will have the capacity to hold 100 to 120 metric tons or more and will be secured with a concrete base cap at the outlet. Although final numbers are yet to be confirmed, more than 300 piles and around 800 cable anchors are expected to be installed to pin and stich the right bank. The second ask is building deep drainage wells inside the right bank to collect water inside the mountain and pump it out using specialized pumps. This is particularly important during the operational phase when the reservoir is filled. By chance, due to the fractured nature of the right bank, if any dam water seeps through the right flooded hill side to the right bank in front of the dam through any cracks or fractures, it can easily be collected and removed instead of water up building inside the right bank and weakening it. Along with the deep wells there will be extensive grouting done with concrete to improve internal stability. The third ask, which has been agreed upon, involves strengthening one of the two diversion tunnels currently used to divert water from the dam site and installing a gate over it. An official explained that the main reason is that such a diversion tunnel can be used in the winter months to divert the water away from the stretch in front of the dam, allowing repairs to the stilling basin, which is the concrete basin area in front of the dam which absorbs the water force. This basin prevents erosion in front of the dam. Additionally, in the event of a massive flood, the tunnel could serve as an additional gate alongside the five proposed sluice gates on the dam. In terms of stabilization activities, one of the first tasks will be to address the January 2019 slide and remove it first. Around 26 reinforced cement concrete (RCC) piles, each 120 to 130 metres deep, will be inserted vertically at road level into the hillside to stabilize that section. Work will then begin to cautiously remove the old slide material below the road. This will be followed by further strengthening measures, including additional piles and cable anchors. At the same time, starting from around March 2026 the dam construction is expected to be started by Larsen and Toubro (L&T), the original contractor. Even the right bank stabilization measures will be done by L&T which will tender out and hire experts for the implementation too. L&T was given the works as they company agreed to not seek any liquidated damages for the delay in dam construction. In the meantime, the scope and schedule of the right bank stabilization measures are being designed by the Central Water Commission (CWC) who is the civil works consultant for the P I project. The designs are expected to come soon after which it will be looked at by the project and while no hiccups are expected, if there are still issues then the Technical Coordination Committee (TCC), which is a technical body with members from both countries, can come together and discuss further. Before dam construction begins, a formal agreement is expected to be signed between L&T and PHPA. Currently, minor works such as access road development are underway. Another issue that has to be resolved is the dam design and this will also be done by the CWC. In the past, after the 2019 slide, the CWC presented the idea that the dam on the right bank side be constructed over 288 concrete piles driven into the ground to avoid excavating the shear zone below the right bank side. However, the Bhutanese side was not in favor of this idea as it was not done in any part of the world. The National Hydroelectric Power Corporation (NHPC), acting as a third-party assessor, also expressed reservations about building part of the dam on piles. It remains to be seen how the final CWC design will address this concern. An official said that tests have been done on rocks, soil and other features at the dam site and CWC will incorporate these findings into its design. The lower right bank is proposed to be built as benches of 15 meters height at a time with a 5 meter width and strengthened. This would also allow vehicle access in case of issues in the future. Basically, a lot of time taken over agreeing to and designing the stabilization measures on the right bank was due to the fact that while the Indian side sought quicker and lower-cost solutions due to implications for overall project cost and tariff, the Bhutanese side wanted to ensure a safe and stable right bank and dam that would last for a long time and not lead to any major disaster. 6 turbines in P I lying unused for almost a decade Electromechanical equipment While the right bank and dam issue is getting resolved, another major shadow that hangs over the project is the electro-mechanical equipment, and specifically the 6 turbines which were supplied from 2016-17 and fully erected by 2023. These huge machines were never designed to remain idle for such an extended period, and the same applies to other electrical components in the power house. Here, the project is working with the supplier BHEL which is expected to supply a plan and costs within a month on what are the things that are to be done to maintain and preserve the electromechanical equipment. An official said the project does not want to undertake independent maintenance work, as BHEL could later raise objections. Any maintenance or repair work, including activities such as replacing heating oil, will therefore be carried out jointly. Apart from the six main generating units, several switches and components in the control panels may need replacement due to ageing. The earlier P I control system was manual but DGPC has been in the process of putting in an automated control system with major works here already done. The transmission part of the P I will come under test soon as the P II power is expected to be connected to a P I Port Yard and Transformer which can be used by the P I project, and at the same time evacuate the P II power. Currently, P II power must travel to Jigmeling before distribution to the rest of the country. Once connected to the P I infrastructure, this longer transmission route can be avoided.