Inspection and rectification of the Tala power plant’s head race tunnel (HRT) has started with dewatering.
As of the morning of January 18, about 13.2km of HRT has been dewatered from the total of the 23km.
The dewatering of the HRT is scheduled for completion by January 29, 2022.
Druk Green Power Corporation Limited (DGPCL) managing director Dasho Chhewang Rinzin said that to expedite the rectification work, daily inspections of the dewatered section of the HRT have already been initiated.
The MD said that power supply and communication arrangements are being made in the dewatered section of the HRT and are being extended each day. The logging of damage, if any, is being done on a daily basis and preparations are underway to initiate rectification as soon as possible.
Construction materials and equipment are almost fully mobilised at the site together with some 200 engineers, technicians, and workers.
The whole exercise of dewatering, repairing, and refilling the HRT is being taken up “on a war footing” to ensure that the power plant is available for generation by the end of March 2022.
The MD said that for dewatering and inspection of the HRT to be followed by the repair of any damage encountered in the tunnel, DGPC is availing the services of an international expert and soliciting technical advice from NHPC India.
“A committee of senior Indian and Bhutanese experts from the Punatshangchhu projects and DGPC have been formed to inspect and evaluate the HRT site conditions and advise on the repairs,” the MD said.
The MD also said that Jaiprakash Associates Ltd. has come forward to support the rectification efforts. Other than two applicators for specialised chemical treatment work being brought in from India, all repairs will be carried out by Bhutanese engineers, technicians, and workers.
The MD also mentioned that for the inspection and rectification of the Tala power plant’s HRT, some 185 engineers, technicians, and workers have been mobilised to the site.
“While most of them are from the Tala power plant, DGPC has supplemented the number with personnel from some of its other power plants. The Punatshangchhu, Mangdechhu, and Nikachhu projects have also provided some personnel. BPC and Bhutan Telecom are also providing support,” the MD said.
They are fully engaged, working in three shifts around the clock conducting inspections and preparation for the repair work, with some already engaged inside the dewatered section of the HRT.
The HRT has been charged with water for the last 15 years, since its commissioning in 2006-2007.
“The dewatering of any HRT is to be avoided as far as possible, in order to avoid any inadvertent cave-ins and/or damage to the tunnel.” the MD said.
The MD also said that dewatering should be carefully managed. While there are international standards for dewatering of tunnels, if required, the dewatering tends to be site specific and could depend on the geological conditions through which the tunnel was built and the technical specifications adopted during construction. The refilling of the tunnel also has to be done slowly.
“The bigger problem after dewatering is the actual repair. The Tala tunnel can be accessed from only two locations which are quite restrictive in size,” MD said.
“The construction equipment had to be specifically ordered so that they could be maneuvered through the small access. Inside the tunnel, there are problems with the maneuverability of the construction equipment, materials, and manpower.”
“In a 23km stretch of tunnel, providing a power supply, communication, and ensuring ventilation are challenges that have to be dealt with. Standard Operating Procedures have been in place for smooth execution of the work,” the MD said.
The regular annual maintenance for Tala plant was also started as per the schedule.
MD said that generating Unit 1 has been completed. Units 2 and 3 are currently under annual maintenance. The maintenance of the remaining three units are also being scheduled so that the maintenance of all six units can be completed by May 2022 at the latest before the onset of the monsoons.
Maintenance of the generating units at Tala are an annual feature, as with the other generating units supplied by BHEL India for Chhukha and Kurichhu power plants.