Dyraaba dam, construction of which was completed in January.
The powerhouse where construction is now in its final stages.
Iranian contractor Farab has purchased extra high-tech machinery to speed up the construction of the multi-million dollar Uma Oya hydro-power and irrigation project, now more than 80 percent complete.
“The main equipment and machinery used in the construction of the Uma Oya project were all purchased from internationally known companies to better ensure the quality of the work,” said Farab. “We recently purchased some new equipment to speed up tackling the unexpected challenges we faced.”
One of the biggest development and construction schemes in Sri Lanka, Uma Oya aims to provide water for drinking, industry and irrigation in the southeastern dry zone of the South Asian island and generate much-needed hydro-electric power.
The project consists of a hydro-electric power plant, 23 km of tunnels, and the Puhulpola and Dyraaba dams, which regulate the two main tributaries of the Uma Oya River. When operational, the power plant will add 120 MW to Sri Lanka’s electricity generating capacity.
Construction work on the Dyraaba dam was finished in January and work on the other dam is 60 percent complete. According to Farab the construction of the power plant is also in its final stages.
When operational, the project will boost living standards in underprivileged districts in the southeast. Mainly dependent on agriculture, many people there do not have access to enough water.
According to the Ministry of Mahawali Development and Environment, there are more than 30,000 hectares of agricultural land in the area that cannot be fully utilised due to water shortages and the lack of irrigation facilities. However, through the Uma Oya project these lands can be more fully utilised and another 5,000 hectares of new land can be cultivated.
The Sri Lankan government is also aiming to develop industry in the area after the completion of the project.
Although more than 80 percent of Uma Oya scheme is already complete, some serious “unexpected challenges” delayed the construction of a 15-km tunnel. The tunnel, which will connect the Dyraaba dam to the power plant, will be the longest tunnel in Sri Lanka. It marks the first-ever use of a tunnel-boring machine on the island.
Earlier this year, underground water seeped into the tunnel for the second time since tunnel construction began. Some local residents complained their wells had dried up and their houses and crops had been damaged. The issue grabbed headlines and fuelled environmental concerns.
Experts say that when it comes to large-scale underground projects, Sri Lanka’s complex geology makes it difficult to foresee all potential hazards. Even some small-scale projects in Sri Lanka have faced large water ingress during construction. That had a negative impact on the environment and local people who rely on underground water for domestic and agricultural use.
The Samanalawewa hydro-electric project financed by Japan and Britain for example, has been subject to large leaks. Though remedial work was carried out to control the leakage, the measures have proven largely ineffective.
“Doing underground construction, you can never know exactly what you will meet once underground,” said Knut F. Garshol, an internationally renowned grouting expert who is advising Farab on carrying out the sealing work. “Pre-investigations cannot provide you with detailed information on the exact geology and hazards ahead of time.”
When water first leaked into the tunnel in December 2014, Farab hired an expert team to assist in grouting the cracks.
“The machinery used in sealing the leak remained on-site after the issue was tackled,” said Farab. “We did not expect to face the same problem with such magnitude again but decided to have the equipment to ensure all necessary precautions. In addition to this equipment, we have purchased new machines to speed up the grouting work.”
The company also said some improvements are being made to the tunnel-boring machine by its German manufacturer, Herrenknecht, to improve its pre-excavation grouting capacity.
Farab said due to the importance of the project and the complex geology of the area, it had always sought the best advice from other prominent construction companies. Switzerland’s Amberg, a leading company in underground construction techniques with tunnel-boring machines, is one of the companies which advises Farab on tunnel construction.
“The construction work of the other two tunnels of the project, each over 3.5 km in length, is finished successfully and 10 out of 15 km of the last water conveyance tunnel has been excavated,” said David Lees, Amberg’s chief site supervisor on the project.
From the two tunnels completed, one was excavated by TBM and one by conventional drill and blast method.
“All possible measures were taken during the tunnel excavation to minimise the impact on the surface. However, some unexpected hazards associated with underground construction cannot be easily avoided,” Lees said.
Farab said it had suspended excavation work to concentrate on tackling the water ingress.
Sri Lanka’s government and Farab have taken steps to compensate those who were affected by the construction work. Farab has been providing water in affected areas since the first leakage occurred in 2014. More than 95 million litres of water were distributed in affected areas in June 2017 alone. Both Farab and the government are working to relieve the hardship of the residents of the areas.